Rozprawy doktorskie na temat „Cu based cells”

Thin film solar cell technologies are rapidly developing, and chalcopyrite (Cu(In,Ga)Se2) based devices have demonstrated the highest power conversion efficiencies on the laboratory scale. However, in spite of this promise, there are concerns about the mid- to long-term viability of the material because it contains the relatively scarce elements of indium and gallium. This has led to the development of kesterite (Cu2ZnSn(S,Se)4) based photovoltaic technologies, which is particularly promising because of its similarities with the chalcopyrite material. In this material system indium and gallium are replaced by the more earth abundant elements of zinc and tin. Device efficiencies are still lower than Cu(In,Ga)Se2, but further research and development has led to significant increases in performance in the past few years. To date the device structure and processing parameters for kesterite based devices has been mostly copied from chalcopyrite based technologies. The objective of this thesis is to further develop these kesterite based technologies, and it covers some of the basic challenges related to it, including secondary phase formation and identification, and optimization of the front and back contact areas. Particular emphasis is placed on the deposition and thermal processing of this compound, and how these affect secondary phase formation and device properties. It is based on several articles which explore these in depth. This includes detailed characterization by Raman scattering spectroscopy, x-ray diffraction, scanning electron microscopy, and other techniques. Highlights of the thesis work include: development of a selective chemical etch to remove ZnS, a common secondary phase in this system, which leads to significant improvements in device performance; elaboration of a sulfo-selenization method to form Cu2ZnSn(S,Se)4 from metallic precursors; and understanding the influence of thermal processing parameters on phase formation and distribution
En los últimos años ha habido un rápido desarrollo en las tecnologías de celdas solares basadas en capa delgada, siendo hasta el momento los dispositivos basados en calcopiritas (Cu(In,Ga)Se2) los que han mostrado una mayor eficiencia de conversión fotovoltaica a escala de laboratorio. Sin embargo, y a pesar de tan prometedores resultados, existe una preocupación sobre la viabilidad a medio y largo término de estos materiales debido a la presencia en su composición de elementos relativamente escasos en la corteza terrestre, como son el In y el Ga. Esto ha llevado al desarrollo de tecnologías fotovoltaicas basadas en kesterita (Cu2ZnSn(S,Se)4), que es especialmente prometedora dada su gran similitud con la calcopirita. En este compuesto, el indio y el galio son reemplazados por elementos más abundantes como son el cinc y el estaño. Los valores de eficiencia de los dispositivos aún están por debajo de los del Cu(In,Ga)Se2, pero nuevas investigaciones y técnicas de desarrollo han llevado a importantes avances en los últimos años. A día de hoy, tanto los parámetros de fabricación como la estructura de los dispositivos basados en kesterita han seguido un camino prácticamente idéntico al de las tecnologías basadas en calcopiritas. El objetivo de esta tesis es el de profundizar en el desarrollo de las tecnologías basadas en kesterita, lo que cubre algunos de los retos básicos relacionados con ellas, como son la formación e identificación de fases secundarias o la optimización de las áreas de contacto frontal y posterior. Se ha puesto especial énfasis en la deposición y los procesos térmicos implicados en el crecimiento de este compuesto, y en ver cómo afectan a la posible formación de las fases secundarias y las propiedades del dispositivo. La tesis en sí está estructurada a partir de los diversos estudios publicados en revistas científicas. Dichos estudios incluyen una caracterización detallada por espectroscopia de dispersión Raman, difracción de rayos X, microscopia electrónica de barrido, y otras técnicas. Los puntos principales de este trabajo son: el desarrollo de un ataque químico selectivo para la eliminación del ZnS (una fase secundaria comúnmente presente en este sistema), con la consecuente mejora de las características del dispositivo; la elaboración de un método de sulfo-selenización para la formación de Cu2ZnSn(S,Se)4 a partir de precursores metálicos; y la resolución de cómo influyen los parámetros de los diferentes procesos térmicos en la formación y distribución de las fases.

Réduire l’épaisseur de l’absorbeur des dispositifs photovoltaïques à base de couches minces est une voie prometteuse pour améliorer leur compétitivité industrielle, via une économie de matières premières et une cadence de production plus élevée. Cela peut aussi accroître leur efficacité en diminuant le parcours des porteurs de charge photogénérés. Cependant, l’efficacité des cellules solaires à base de Cu(In,Ga)Se ₂ (CIGS) ultramince avec une épaisseur d’absorbeur d’environ 500 nm, soit environ 5 fois inférieure aux cellules conventionnelles, est limitée par deux phénomènes : les recombinaisons non-radiatives de charges au contact arrière et l’absorption incomplète de la lumière solaire incidente. Différentes stratégies ont été étudiées afin de limiter ces pertes. Dans un premier temps, la composition des couches ultraminces de CIGS a été optimisée pour y créer un gradient du minimum de la bande de conduction. Le champ électrique résultant permet de faciliter la séparation des charges et de limiter les recombinaisons au contact arrière. L’incorporation d’argent dans la composition du CIGS a également amélioré significativement les performances des cellules ultraminces, pour aboutir à une efficacité de 14.9% (avec 540 nm d’ACIGS, sans couche antireflet), proche du record actuel de 15.2% (avec couche antireflet et 490 nm de CIGS). En parallèle, l’ajout d’une couche de passivation en alumine à l’interface entre le CIGS (470 nm) et le Mo a été étudiée, et a conduit à une augmentation de la tension de circuit ouvert de 55 mV. Dans un deuxième temps, une nouvelle architecture de contact arrière réfléchissant a été développée. Elle consiste en un miroir d’argent encapsulé dans des couches d’oxydes transparents conducteurs. A l’aide d’observations au microscope électronique en transmission, il a été montré que ce contact arrière est compatible avec la co-évaporation de CIGS à des températures ≥500°C. Grâce à une haute réflectivité et un contact ohmique avec le CIGS, il a mené à une amélioration de l’efficacité de 12.5% à 13.5% et du courant de court-circuit de 26.2 mA/cm² à 28.9 mA/cm² par rapport à un contact arrière standard en molybdène. Cette nouvelle architecture ouvre la voie à une augmentation du rendement photovoltaïque des cellules solaires CIGS ultraminces ainsi qu’à de nouvelles stratégies de piégeage optique
Reducing the absorber thickness of thin-film photovoltaic devices is a promising way to improve their industrial competitiveness, thanks to a lower material usage and an increased throughput. It can also increase their efficiency due to a shorter pathway for the separation of photogenerated charge carriers. Still, the efficiency of ultrathin Cu(In,Ga)Se ₂ -based (CIGS) solar cells , which have an absorber thickness ≤500 nm that is approximately 5 times thinner than standard devices, is limited by two phenomena: the non-radiative recombination of charge carriers at the back contact and the incomplete absorption of the incident light. Several strategies were studied in order to mitigate those losses. First, the composition of ultrathin CIGS layers was optimized to create a grading of the semiconductor’s conduction band minimum. The resulting electric field contributes to a better charge carrier separation and a lower back contact recombination rate. The incorporation of silver in the CIGS composition greatly improved the performances of ultrathin cells, leading to an efficiency of 14.9% (540 nm of ACIGS, without antireflection coating), close to the current record of 15.2% (490 nm of CIGS, with antireflection coating). Besides, the addition of an alumina passivation layer at the interface between CIGS (470 nm) and Mo was also investigated, and resulted in an improvement of the open-circuit voltage of 55 mV. Second, a novel architecture of reflective back contacts was developed. It consists of a silver mirror that is encapsulated with layers of transparent conductive oxides. Based on a transmission electron microscopy study, this back contact was shown to be compatible with the co-evaporation of CIGS at 500°C or more. Thanks to a high reflectivity and an ohmic contact with CIGS, it led to an increase of the efficiency from 12.5% to 13.5% and of the short-circuit current from 26.2 mA/cm² to 28.9 mA/cm² as compared to cells with a standard molybdenum back contact. This reflective back contact paves the way toward higher photovoltaic efficiencies as well as novel strategies for further light trapping

Dans cette thèse nous évaluons le potentiel de cellules solaires micrométriques pour une utilisation sous flux concentré. Le but de l’étude est de mettre au point une technologie photovoltaïque à haut rendement, basée sur des technologies de grandes surfaces pour obtenir de fortes productivités, qui soit en même temps économe en matières premières pour respecter les contraintes imposées par un développement du photovoltaïque à l’échelle du terawatt. La miniaturisation des cellules solaires permet d’obtenir une architecture peu résistive, qui évacue efficacement la chaleur. Les microcellules sont donc adaptées à la concentration lumineuse. Des prototypes sont fabriqués, grâce à des techniques de photolithographie. Leur test permet d’évaluer leur rendement. Un gain absolu de 5% de rendement a été mesuré; un rendement maximum de 21. 3% sur une cellule de 50 µm de diamètre à une concentration de ×475 est atteint. Les caractéristiques du régime de forte illumination sont étudiées pour la première fois sur Cu(In,Ga)Se2. La photoconductivité de cet absorbeur est examinée. L’écrantage du champ électrique de l’hétérojonction Cu(In,Ga)Se2 sous fort flux est simulé numériquement et semble expliquer l’influence de l’intensité lumineuse sur la collecte des porteurs, mise en évidence expérimentalement. La possibilité d’une application industrielle est envisagée grâce à la fabrication de microcellules à absorbeur localisé, qui a permis de déterminer une faible vitesse de recombinaison sur les surfaces latérales des cellules (< 4 103 cm/s). Une technique de dépôt sélective, l’électrodépôt, a permis la synthèse de CuInSe2 sur des microélectrodes
In this thesis we explored the potential of thin film microscale concentrator solar cells. The aim of the study is to develop a highly efficient photovoltaic technology, based on large-area processes for high throughput, and which is raw-material thrifty to meet the constraints of terawatt development. The miniaturization of thin film solar cells leads to a low resistive architecture, with easy thermal management, which is therefore adapted to the concentrating regime. The scale effects are studied from an analytical and numerical point of view. Prototype Cu(In,Ga)Se2 solar cells are fabricated with help of photolithography techniques and tested to evaluate the performance of the microcells. A 5% absolute efficiency increase was measured, which led to a 21. 3% efficiency of a 50 µm diameter microcell at a concentration of ×475. The influence of the incident spectra is highlighted. The specific features of the high illumination regime are studied for the first time on Cu(In,Ga)Se2. The photoconductive behavior of Cu(In,Ga)Se2 is analyzed. The screening of the electric field in the Cu(In,Ga)Se2 heterojunction under high light fluxes is evidenced by simulation and may explain the influence of the illumination level on the collection efficiency observed experimentally. The possibility of an industrial application is tackled via the fabrication of mesa delineated microcells, which proves that the edge surface of the microcells have a low recombination velocity (< 4 103 cm/s). A bottom-up approach is studied via electrodeposition. This selective deposition technique enables the synthesis of CuInSe2 on microelectrodes

En quelques années, l'efficacité des cellules solaires à base de Cu(In,Ga)Se2 (CIGS) est passée de 20% à 22.6%. La rapidité de ce développement montre que le CIGS est un matériaux idéal pour les technologies solaires en couches minces. Pourtant, le coût de production cette technologie doit encore être abaissé pour une meilleure compétitivité. La fabrication d'un module avec une couche CIGS plus fine permettrait d'augmenter la production d'une usine et de réduire sa consommation en métaux. Ce travail de thèse vise à réduire l'épaisseur du CIGS d'un standard de 2.0-2.5 µm à une épaisseur inférieure à 500 nm sans altérer les performances des cellules. Cependant, comme rapporté dans la littérature, nous avons observé une diminution des rendements, ce que nous avons analysé en détail en comparant simulations et caractérisations d'échantillons. Celle-ci est causée à la fois par une faible absorption de la lumière dans la couche de CIGS et par un impact important du contact arrière (fortes recombinaisons et faible réflectivité). Pour dépasser ces limites, nous démontrons à la fois théoriquement et expérimentalement que le contact arrière en molybdène peut être remplacé par un oxyde transparent conducteur couplé à un miroir métallique. Nous obtenons de cette manière de meilleurs rendements de cellules. Pour atteindre ce résultat, une optimisation du dépôt de CIGS a été nécessaire. De plus, nous prouvons qu'une couche d'oxyde perforée, insérée entre le CIGS et le contact arrière, limite les recombinaisons des porteurs de charges et réduit l'influence des courants parallèles. Au final, nous avons fabriqué une cellule avec un rendement de 10.7% sur SnO2:F passivé par Al2O3
In the past three years, record efficiency of Cu(In,Ga)Se2 (CIGS) based solar cells has improved from 20% up to 22.6%. These results show that CIGS absorber is ideal for thin-film solar cells, even if this technology could be more competitive with a lower manufacture cost. The fabrication of devices with thinner CIGS absorbers is a way to increase the throughput of a factory and to reduce material consumption. This PhD thesis aims to develop cells with a CIGS thickness below 500 nm instead of the conventional 2.0-2.5 µm. However, as reported in the literature, we observed a decrease in cell performance. We carefully analyzed this effect by the comparison between simulations and sample characterizations: it is attributed, on one hand, to a lack of light absorption in the CIGS layer and, on the other hand, to an increased impact of the back-contact (high recombination and low reflectivity). To resolve these problems, we demonstrated theoretically and experimentally that the use of an alternative back-contact, other than molybdenum, such as a transparent conducting oxide coupled with a light reflector, improves the cell efficiency. To achieve this result, an optimization of the CIGS deposition was necessary. Moreover, we proved that a porous oxide layer inserted between the CIGS and the back-contact limits the charge-carrier recombination and removes some parasitic resistance. Finally, an efficiency of 10.7% was achieved for a 480-nm-thick CIGS solar cell with a SnO2:F back-contact passivated with a porous Al2O3 layer

Cu(In,Ga)Se2 (CIGS) is one of the most promising semiconductor compounds for large-scale production of efficient, low-cost thin film solar cells, and several research institutes have announced their plans for CIGS production lines. But for the CIGS technology to become a commercial success, a number of issues concerning manufacturability, product definition, and long-term stability require further attention. Several studies indicate that CIGS-based modules are stable over many years in field operation. At the same time, it is shown in the present work that they may have difficulties in passing standard accelerated lifetime test procedures like the IEC 1646 damp heat test. In particular, CIGS modules are sensitive to humidity penetrating through the module encapsulation, which will increase the resistive losses in the front contact and cause severe corrosion of the back contact. It is also shown that cells experience degradation in both voltage and fill factor, and the causes of these effects are addressed. By concentrating the light falling onto a solar cell, the device will deliver a higher power output per illuminated absorber area, which can lower the electricity production costs. For CIGS-based solar cells, low-concentrated illumination could be an economically viable approach. In this work it is shown that the yearly performance of a photovoltaic system with CIGS modules can be significantly improved at a moderate cost by using parabolic aluminum mirrors as concentrating elements. However, in order to avoid detrimental power losses due to high temperatures and current densities, the modules need to be designed for the higher light intensity and to be sufficiently cooled during operation. A design where the front contact of the module is assisted by a metal grid has shown promising results, not only for concentrated illumination but also for normal operation. The benefits are enhanced window processing tolerance and throughput, as well as improved degrees of freedom of the module geometry.

Dissertation (Ph. D.)--University of Akron, Dept. of Chemical Engineering, 2007.
"December, 2007." Title from electronic dissertation title page (viewed 03/12/2008) Advisor, Steven S. C. Chuang; Committee members, Lu-Kwang Ju, Edward Evans, W. B. Arbuckle, Stephen Z. D. Cheng; Department Chair, Lu-Kwang Ju; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Thin-film solar cells based on Cu(In,Ga)Se2 contain a thin buffer layer of CdS in their standard configuration. In order to avoid cadmium in the device for environmental reasons, Cd-free alternatives are investigated. In this thesis, ZnO-based films, containing Mg or S, grown by atomic layer deposition (ALD), are shown to be viable alternatives to CdS. The CdS is an n-type semiconductor, which together with the n-type ZnO top-contact layers form the pn-junction with the p-type Cu(In,Ga)Se2. From device modeling it is known that a buffer layer conduction band (CB) position of 0-0.4 eV above that of the Cu(In,Ga)Se2 layer is consistent with high photovoltaic performance. For the Cu(In,Ga)Se2/ZnO interface this position is measured by photoelectron spectroscopy and optical methods to –0.2 eV, resulting in increased interface recombination. By including sulfur into ZnO, a favorable CB position to Cu(In,Ga)Se2 can be obtained for appropriate sulfur contents, and device efficiencies of up to 16.4% are demonstrated in this work. From theoretical calculations and photoelectron spectroscopy measurements, the shift in the valence and conduction bands of Zn(O,S) are shown to be non-linear with respect to the sulfur content, resulting in a large band gap bowing. ALD is a suitable technique for buffer layer deposition since conformal coverage can be obtained even for very thin films and at low deposition temperatures. However, deposition of Zn(O,S) is shown to deviate from an ideal ALD process with much larger sulfur content in the films than expected from the precursor pulsing ratios and with a clear increase of sulfur towards the Cu(In,Ga)Se2 layer. For (Zn,Mg)O, single-phase ZnO-type films are obtained for Mg/(Zn+Mg) < 0.2. In this region, the band gap increases almost linearly with the Mg content resulting in an improved CB alignment at the heterojunction interface with Cu(In,Ga)Se2 and high device efficiencies of up to 14.1%.

Dans cette thèse, nous avons étudié la conception, le prototypage et la caractérisation de microsystèmes photovoltaïques à concentration à base de cellules solaires Cu(In,Ga)Se2. L'objectif est de réduire l'utilisation de matériaux rares en utilisant la concentration de la lumière, et bénéficier des effets de la miniaturisation, comme la dissipation de la chaleur et des pertes résistives inférieurs. Tout d'abord, la conception optique des systèmes à concentration sur la base des microlentilles sphériques est présentée. À l'aide d'un logiciel de tracés de rayon Zemax OpticStudio, nous avons évalué la meilleure combinaison d'éléments, l'épaisseur et les rayons de courbure des lentilles, ainsi que les tolérances de fabrication et de positionnement du système. Un système optique de 1 mm d'épaisseur avec un rapport géométrique de 100 et une tolérance angulaire de +/- 3,5 ° a été conçu. D'autre part, des procédés de fabrication ont été créés et optimisés pour fabriquer un prototype de 5x5 cm² avec 2500 microcellules. Le meilleur mini-module a montré un facteur de concentration de 72x avec une augmentation en valeur absolue de l'efficacité de + 1,6%. Ensuite, des études numériques et expérimentales ont été réalisées sur des systèmes basés sur des concentrateurs luminescents (LSC) et des concentrateurs paraboliques (CPC). Les LSC ont montré un facteur de concentration faible et souffraient de problèmes de répétabilité tandis que les CPC sont une solution très efficace, mais très difficile à fabriquer à l¿échelle du micron. Enfin, nous avons développé un code MATLAB pour estimer l'énergie produite des systèmes conçus, pour évaluer la pertinence des choix technologiques futurs
In this thesis, we studied the design, prototyping and characterization of micro-concentrated photovoltaic systems based on Cu(In,Ga)Se2 solar cells. The objective is to reduce the use of rare materials using the concentration of light, and benefit from the effect of miniaturization such as heat dissipation and lower resistive losses. First, the optical design of 1D and 2D concentrating systems based on spherical microlenses is presented. Using a ray-tracing software Zemax OpticStudio, we evaluated the best combination of elements, thickness and radii of curvature of the lenses, as well as the tolerances of fabrication and positioning of the system. An optical system of 1 mm thickness with a geometrical ratio of 100 and an angular tolerance of +/- 3.5° has been designed. Second, fabrication processes have been created and optimized to fabricate a 5x5 cm² prototypes with 2500 microcells. The best mini-module showed a concentration factor of 72x with an absolute increase of the efficiency of +1.6%. Third, numerical and experimental studies have been performed on concentrating systems based on Luminescent Solar Concentrators (LSC) and Compound Parabolic Concentrators (CPC). The LSC showed a low concentration factor and suffered from repeatability issues while the CPC is a very efficient solution but its specific geometry makes it difficult to fabricate at the micron scale. Finally, we developed a MATLAB code to estimate the producible energy of the designed systems, in order to evaluate the relevance of future technological choices that will be made

Thin-film solar cells are potentially low-cost devices to convert sunlight into electricity. Improvements in the conversion efficiencies of these cells reduce material utilization cost and make it commercially viable. Solar cells from the Thin-Film Physics Group, ETH Zurich, Switzerland and the Florida Solar Energy Center (FSEC), UCF were characterized for defects and other microstructural features within the thin-film structure and at the interfaces using transmission electron microscopy (TEM). The present thesis aims to provide a feedback to these groups on their deposition processes to understand the correlations between processing, resulting microstructures, and the conversion efficiencies of these devices. Also, an optical equipment measuring photocurrents from a solar cell was developed for the identification of defect-prone regions of a thin-film solar cell. The focused ion beam (FIB) technique was used to prepare TEM samples. Bright-field TEM along with scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) including elemental distribution line scans and maps were extensively used for characterizing the absorber layer and interfaces both above and below the absorber layer. Energy-filtered transmission electron microscopy (EFTEM) was applied in cases where EDS results were inconclusive due to the overlap of X-ray energies of certain elements, especially molybdenum and sulfur. Samples from ETH Zurich were characterized for changes in the CIGS (Cu(In,Ga)Se2) microstructure due to sodium incorporation from soda-lime glass or from a post-deposition treatment with NaF as a function of CIGS deposition temperature. The CIGS-CdS interface becomes smoother and the small columnar CIGS grains close to the Mo back contact disappear with increasing CIGS deposition temperature. At 773 K the two sodium incorporation routes result in large differences in the microstructures with a significantly larger grain size for the samples after post-deposition Na incorporation. Porosity was observed in the absorber layer close to the back contact in the samples from FSEC. The reason for porosity could be materials evaporation in the gallium beam of the FIB or a processing effect. The porosity certainly indicates heterogeneities of the composition of the absorber layer near the back contact. A Mo-Se rich layer (possibly MoSe2) was formed at the interface between CIGS/CIGSS and Mo improving the quality of the junction. Other chemical heterogeneities include un-sulfurized Cu-Ga deposits, residual Se from the selenization/ sulfurization chamber in CIGS2 and the formation of Cu-rich regions which are attributed to decomposition effects in the Ga beam of the FIB. Wavy absorber surfaces were observed for some of the cells with occasional discontinuities in the metal grids. The 50 nm thick CdS layer, however, remained continuous in all the samples under investigation. For a sample with a transparent back contact, a 10 nm Mo layer was deposited on ITO (indium tin oxide) before deposition of the CIGS2 (Cu(In,Ga)S2) layer. EFTEM maps indicate that a MoS2 layer does not form for such a Mo/MoS2-ITO back contact. Instead, absorber layer material diffuses through the thin Mo layer onto the ITO forming two layers of CIGS2 on either side of Mo with different compositions. Furthermore, an optical beam induced current (OBIC) system with micron level resolution was successfully developed and preliminary photocurrent maps were acquired to microscopically identify regions within a thin-film solar cell with undesirable microstructural features. Such a system, when fully operational, will provide the means for the identification of special regions from where samples for TEM analysis can be obtained using the FIB technique to study specifically the defects responsible for local variations in solar cell properties.
M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering

The main objective of this thesis is the development of Raman scattering based methodologies for the analysis of advanced electrodeposition-based CIGS technologies, with the identification and characterization of parameters relevant for the efficiency of the solar cells and modules that can be used for quality control and process monitoring applications. The work aims to propose methodologies and tools that can be implemented for the monitoring of the processes at on-line level, contributing to increase the yield and reliability of the processes involved in the fabrication of these devices. The thesis is structured around five papers that have been published in peer-reviewed journals, according to the requirements for the achievement of the degree of Doctor in the Doctoral Program of Engineering and Advanced Technologies in the University of Barcelona. The thesis is structured in seven chapters. The first chapter is an introduction into Chalcopyrite photovoltaic technologies, including their background, current production strategies and optical characterization by Raman scattering based techniques. The main processes used for the fabrication of the CIGS solar cells and modules are described. Later in the introduction Raman scattering is presented as the main technique used in this work and the approach of this thesis to develop process monitoring techniques to assess parameters for each of the layers in the devices is described. Raman spectra are sensitive to chemico-physical and structural parameters of the layers that determine the device efficiency, as the crystalline quality and presence of defects, the chemical composition, as well as stress and strain effects and presence of secondary phases. The second chapter is dedicated to the disclosure of the Raman experimental set-ups that have been developed and that have been used to obtain the data presented in this work and the experimental conditions chosen to ensure reliability in the measurements. A more detailed description of the application of Raman spectroscopy are disclosed in the following chapters, that address the detection of secondary phases in the absorber layers that are relevant for device performance in high efficiency devices (Chapter 3), the chemical characterization of the surface region of the absorbers (Chapter 4), the assessment of the thickness of the CdS buffer layers (Chapter 5) and the electrical conductivity of the window layers (Chapter 6). The secondary phases studied in Chapter 2 are the OVC ones in Cu(In,Ga)Se2 alloys and CuAu polytypes in CuInS2 based cells; determining and clarifying their impact on the optoelectronic characteristics of the cells. This work reports for the first time in the literature clear experimental evidences of the impact of the presence of the OVC phases on the optoelectronic characteristics of the cells. Although the efficiencies achieved within CuInS2 (CIS) solar cells are lower (12.7% ) than the yielded by CIGS devices, the larger bandgap of the CIS semiconductor (1.55 eV) gives interest to these devices for the increase of the open circuit voltage Voc. In this work, the role of the presence of CuAu polytypic domains in advanced cells made by electrochemical processes is investigated. The fourth chapter addresses the development of methodologies for the quantitative analysis of the chemical composition of the surface region of the absorber layers, including the Ga/(In+Ga) relative content in Cu(In,Ga)Se2 absorbers and the S/(S+Se) relative content in Cu(In,Ga)(S,Se)2 absorbers. These are the parameters that allow suitable control of the value of the band gap in the surface region of the absorbers. Next chapters address the Raman scattering assessment of the CdS buffer and Al-doped ZnO window layers, being the control of the thickness of the buffer and conductivity of the window layer are relevant for the device efficiency. The final chapter summarizes the main conclusions
El principal objetivo de esta tesis es el desarrollo de metodologías basadas en la espectroscopia Raman para el análisis de tecnologías fotovoltaicas Cu(In,Ga)(S,Se)2 avanzadas basadas en procesos electroquímicos, con la identificación y caracterización de parámetros relevantes para la eficiencia de las celdas solares y módulos. El trabajo desarrolla y propone metodologías y herramientas que pueden ser implementadas para aplicaciones de control de calidad y monitorización de procesos a nivel "on-line", contribuyendo a incrementar el rendimiento y la fiabilidad de los procesos involucrados en la fabricación de estos dispositivos. La tesis está estructurada en siete capítulos. El primer capítulo es una introducción a las tecnologías fotovoltaicas de la calcopirita, incluyendo las estrategias actuales de producción y su caracterización óptica por medio de técnicas basadas en espectroscopia Raman; más tarde en el capítulo se presenta la espectroscopia Raman como la técnica principal utilizada en el trabajo y se describe el enfoque abordado en la tesis para el desarrollo de técnicas para la monitorización de los procesos. Los espectros Raman permiten obtener información de parámetros estructurales y químico-físicos de las diferentes capas en la estructura que determinan la eficiencia del dispositivo, como la calidad cristalina y presencia de defectos, composición química, estrés y presencia de fases secundarias. El Segundo capítulo describe los sistemas experimentales que se han desarrollado en el trabajo, y las condiciones experimentales determinadas para garantizar la fiabilidad de las medidas. Una descripción más detallada de la aplicación de la espectroscopia Raman se describe en los siguientes capítulos, que abordan la detección de fases secundarias en la capa del absorbedor que son relevantes para la eficiencia de la celda en dispositivos de alta eficiencia (Capítulo 3), la caracterización química de la región superficial de las capas absorbedoras (Capítulo 4), el espesor de las capa buffer de CdS (capítulo 5) y la conductividad eléctrica de las capas ventana (capítulo 6). El último capítulo de la tesis resume las principales conclusiones del trabajo.

Les cellules solaires en couches minces à base d'absorbeurs de type Cu(In,Ga)Se2 (CIGS) représentent une technologie d'avenir à haut rendement de conversion d'énergie. Plusieurs techniques sont utilisées pour synthétiser le CIGS. La pulvérisation cathodique réactive est une technique de dépôt adaptée aux grandes surfaces offrant la possibilité d'effectuer un scale-up industriel. L'objectif de ce travail est de développer et d'optimiser un procédé alternatif hybride de co-pulvérisation/évaporation pour la synthèse du composé CIGS. Pour répondre à cet objectif, différentes études ont été réalisées afin d'assurer le contrôle des différents paramètres de dépôt. Dans un premier temps, la phase plasma a été étudiée à l'aide de la spectroscopie d'émission optique pour pouvoir établir des corrélations entre la composition des couches déposées et les espèces présentes dans le plasma. Ceci a permis d'établir des courbes d'étalonnage et de suivi in-situ de la composition et l'homogénéité de l'épaisseur des couches déposées, ainsi que de déterminer l'existence de différentes modes de pulvérisation, reliés à la température appliquée pour l'évaporation du sélénium. Dans un deuxième temps, différents absorbeurs de CIGS ont été synthétisés à partir du procédé hybride développé. Ces absorbeurs ont été déposés en une et en trois étapes pour analyser l'influence des gradients de composition sur leurs propriétés morphologiques, structurales et optoélectroniques. Un absorbeur de CIGS avec un rendement de conversion maximum de 10,4 % a été fabriqué à partir d'une séquence de dépôt en une étape. Un rendement de 9,4 % a été obtenu avec une séquence dépôt en trois étapes
Cu(In,Ga)Se2 (CIGS) thin film solar cells are a very promising technology for high efficiency energy conversion. Several techniques are used to synthesize CIGS absorbers. Magnetron reactive sputtering is an attractive deposition technique for depositing CIGS absorbers because of its potential for providing uniform coatings over large areas, thus offering the possibility for more competitive industrial scale-up. The objective of this work is to develop and optimize a hybrid alternative co-sputtering/evaporation CIGS deposition process. To meet this goal, various studies have been conducted to ensure control of the various deposition parameters. Initially, plasma was studied with Optical Emission Spectroscopy in order to establish correlations between plasma species and thin film composition, structure and morphology. This has allowed to establish in-situ calibration curves for monitoring the deposited layers composition and their homogeneity, and to determine the existence of different sputtering modes, linked to the selenium evaporation temperature. Then, different CIGS absorbers were synthesized with the stabilized hybrid process. These absorbers were deposited in one and three stages to analyze the influence of composition gradients on their morphological, structural and optoelectronic properties. A CIGS absorber giving a maximum conversion efficiency of 10.4 % was fabricated with a one step process. A 9.3 % efficiency solar cell was obtained with a three-stage deposition process

Le remplacement du CdS dans les cellules solaires à base de Cu(In,Ga)Se2 est un des défis majeurs de la communauté. À ce jour un des matériaux les plus prometteurs est le Zn(S,O,OH) déposée par voie chimique en solution. En raison de la faible vitesse de dépôt du matériau et des phénomènes de métastabilités présents dans les dispositifs formés, il apparaît nécessaire d’optimiser les conditions expérimentales et les interfaces. La 1ère partie de ces travaux a été consacré à l’optimisation des conditions de dépôt des couches minces de Zn(S,O,OH) grâce à l’introduction d’additifs. Il a été possible de souligner l’effet des additifs sur la composition des couches déposées et sur les vitesses de réaction. La 2ème partie de ces travaux a été consacrée à l’optimisation des conditions de dépôt par pulvérisation cathodique de la fenêtre avant (Zn,Mg)O/ZnO :Al permettant une diminution des phénomènes de métastabilité et une limitation de la migration de sodium jusqu’au Zn(S,O,OH). Ces conditions combinées à une variation de la composition de la surface du CIGSe a permis d’obtenir des rendements de photo-conversion supérieurs à ceux des références à base de CdS
The replacement of CdS-based buffer layer in Cu(In,Ga)Se2 solar cells has been one of the main challenges of the research community for the last decade. Today, one of the most promising alternative material is the chemically bath deposited Zn(S,O,OH). Because of its low deposition rate and of metastable behavior, it becomes necessary to proceed to an optimization of experimental conditions and of the various interfaces. The first part of this work has been dedicated to the optimization of the deposition bath thanks to the introduction of new additives. It has been possible to underline the additive effects on both the deposition rate and on the chemical composition of the deposited layers. The second part of this work has been dedicated to the optimization of the (Zn,Mg)O/ZnO:Al window layer. Thanks to an improvement of the sputtering conditions, it has been possible to reduce metastability of the solar cells, and to limit sodium migration up to the Zn(S,O,OH) layer. These optimized conditions combined to the variation of the CIGSe surface composition have allowed us to outperform CdS-based references solar cells

The term „cancer‟ encompasses a large group of diseases that are characterized by the development of abnormal cells, which divide, grow and spread without control in any part of the organism, spreading through blood or lymph vessels into surrounding tissues. Chemotherapy is a type of cancer treatment that uses drugs to kill cancer cells and is focused on stopping or slowing the growth of cancer cells, which divide abnormally and causes tumors. In most of the cases of chemotherapy prescription and selection of the specific drug, the more effective is a combination of two or more medications that, preferentially, should not interact with each other, either on their mechanism of action and/or their metabolism and elimination. Second and third generations of the existing drugs show increased bioactivity against cancer, but side effects are still a matter of concern. Recent studies show a significant interest in metal-based drugs, with some existing drugs being used already as antitumor agents, with proven effectiveness and fewer side effects, comparing to other drug treatments. Copper(II) as a metal and its complexes with various organic compounds have been reported to show cytotoxic activity at low concentrations. The aim of this work is to examine the effects of newly synthesized copper complexes in human cancer cell lines, both in terms of cytotoxicity and of mechanism of action. In this research work, two copper(II) based compounds were (copper(II)-tropolone and copper(II)-hinokitiol complexes), for their cytotoxic properties and tested in the human mammary breast cancer cell line MCF7 and MDA-MB-231 for their effect on viability, oxidative stress, apoptosis and interaction with DNA. Additionally, as a model for in vivo studies, the 3D model testing on cell viability was conducted and showed a positive result against MCF7 cell line survival. Together with that, the comparative analysis of complexes, its ligands and copper salt was performed. These compounds showed quite promising results in terms of their potential effect as antitumor drugs.
O termo „cancro‟ abrange um largo número de doenças, que são caracterizadas pelo desenvolvimento anormal de células que se dividem, crescem e propagam-se de forma descontrolada por todo o organismo, propagando-se através do sangue ou dos vasos linfáticos para os tecidos vizinhos. A quimioterapia é um tipo de tratamento anticancerígeno, que tem por base o uso de fármacos que atuam por parar ou por diminuir o crescimento de células cancerígenas, células que se dividem anormalmente causando tumores. Na maioria dos casos, ao prescrever um fármaco específico, o uso combinado de dois ou mais fármacos é preferencial, sendo que não deve haver nenhum tipo de interação entre os mesmos, quer no mecanismo de ação e/ou metabolismo, quer na eliminação. A segunda e a terceira geração de fármacos existentes, mostraram um aumento da bioatividade contra o cancro, contudo, os efeitos secundários continuam a ser uma grande preocupação. Estudos recentes têm demonstrado um interesse significativo em fármacos com compostos metálicos, sendo que alguns destes fármacos já são usados como agentes antitumorais, com eficácia e menos efeitos secundários comprovados, comparativamente com outros fármacos. O Cobre (II), tanto como metal, tanto complexado com vários compostos orgânicos, mostrou ter atividade citotóxica a baixas concentrações. O objetivo desde trabalho é analisar, em linhas celulares humanas, os efeitos de complexos de cobre recentemente sintetizados, tanto em termos de citotoxicidade como em termos de mecanismo de ação. Neste trabalho de investigação, dois compostos com base no cobre (II), (cobre(II)-tropolone) e cobra(II)-hinokitiol complexos), foram observados e avaliados quanto às suas propriedade citotóxicas, e testados na linha celular humana de cancro da mama MCF7 e MDA-MB-231, quanto ao seu efeito na viabilidade, no stress oxidativo, na apoptose e na interação com o DNA. Adicionalmente, como modelo para estudos in vivo, foi conduzido um teste modelo 3D quanto à viabilidade, onde foram observados resultados positivos contra a linha celular MCF7 sobrevivente. Simultaneamente, foi realizada uma análise comparativa dos complexos sintetizados, dos seus ligandos e do sal de cobre. Estes compostos mostraram resultados promissores com efeitos potenciais como fármacos antitumorais.

碩士
國立東華大學
電機工程學系
97
The electrodes for the Cu(In,Ga)Se2-based solar cells were deposited on the glass substrates by the direct-current magnetron sputtering method in this thesis. The correlations between the sputtering parameters and properties of the deposited films were studied by characterizing the electrical, optical, crystallinity, morphology, and compositional properties. Aluminum-doped zinc oxide films of the front electrodes for the Cu(In,Ga)Se2-based solar cells were deposited on corning 1737 glass substrates with a ZnO/Al2O3 target (Al2O3 2wt.%). The dependences of the carrier concentration, carrier mobility, transmittance, crystallinity, grain size, film stress, surface morphology, and composition of the films on the working voltage, working pressure, substrate temperature, working power, substrate-bias, film thickness, target-substrate distance, and O2/Ar flow ratio were investigated, respectively. The properties of as-deposited aluminum-doped zinc oxide films were analyzed by using the Hall-effect Measurement, UV-VIS Spectrophotometer, X-ray Diffraction, Field Emission Scanning Electron Microscopy, and Energy Dispersive Spectrometer Spectrophotometry. The optimal transparent conductive aluminum-doped zinc oxide films were prepared with a target-substrate distance of 3.5cm, substrate temperature of 200℃, sputtering power of 300W, working pressure of 3m torr, and Ar flux rate of 50 sccm, resulting in the film thickness of 462.5 nm, optical transmittance up to 91.36% in the visible range, and electrical resistivity of down to 7.05 Ω-cm. The back electrodes of molybdenum films were deposited on the soda-lime glass substrates with a molybdenum target (3N5). Both the low resistivity and good adhesion of as-deposited Mo films were obtained by varying the sputtering parameters. The high-quality aluminum-doped zinc oxide and molybdenum films were achieved for the front and back contacts of Cu(In,Ga)Se2-based solar cells, respectively.

銅銦鎵硒薄膜太陽能電池是一種清潔、環保的發電技術。 最近，銅銦鎵硒太陽能電池實現了20.9%的光電轉換效率，超出了多晶硅太陽能電池所保持的20.4%的薄膜太陽能電池的最高紀錄。 多種技術改進促成了這項薄膜太陽能電池的新紀錄。 其中一種重要改進是將1 到2 微米厚的硫化鎘硫化鋅混合窗口層替換成薄層硫化鎘和摻鋁氧化鋅透明導電層。
基於本實驗室在生長高質量銅銦鎵硒吸收層的先進技術，本工作重點研究了位於吸收層和透明窗口層之間的緩衝層和高阻窗口層。 這兩層的常規結構是由化學水浴法生長的硫化鎘層和本征氧化鋅層組成。 本論文的第一部分是關於這種常規結構的參數優化。 經過優化，本實驗室實現了在小型組件（總面積60 平方釐米）上15.6%的最高轉換效率。
本論文的第二部分關於用化學水浴法生長緩衝層。 我們發展了一種新型生長制備，用於避免氣泡和孔洞在吸收層表面的形成。 表面形貌測試結果顯示，使用此種設備生長的緩衝層能均勻的覆蓋銅銦鎵硒吸收層的表面。 其它硫化鎘的生長參數也根據新設備的特點進行了優化。 優化結果顯示，在空間電荷區的復合對電池轉換效率影響較大，而這種復合損失可以經過調整緩衝層與吸收能之間能帶結構得到減少。 我們研究了另外一種用化學水浴法生長的緩衝層：硫化鋅。 硫化鋅是一種無毒的寬禁帶材料，在短波部分有較少的光吸收。因此，它是一種很好的硫化鎘替代物。 我們研究了在不同生長溫度下的生長動力學機制。 最優的生長溫度是95 攝氏度。 經過生長結束後的退火過程，硫化鋅的禁帶寬度由3.61eV 下降到3.2eV。 再經過在氧氣環境中的退火，禁帶寬度可由3.2eV 繼續下降到2.9eV。 在單結電池中，硫化鋅的最優厚度在43 納米到62 納米之間。 在此厚度範圍中，具有硫化鋅緩衝層的電池實現了相對於具有硫化鎘緩衝層的電池更高的轉換效率。硫化鋅電池實現了與硫化鎘電池相近的開路電壓。 此項改進主要是由於在高溫條件下生長的硫化鋅與銅銦鎵硒層形成了更合適的能帶結構。
本論文的第三部分是關於用共濺射的方法生長鋅鎂氧化物緩衝層。 實驗結果顯示，鋅鎂氧化物的晶體結構和禁帶寬度與鎂含量相關。 當鎂含量小於0.4 時，鋅鎂氧化物具有(002)從優方位的纖鋅礦結構。 晶體質量隨鎂含量的增加而降低，同時，鋅鎂氧化物的禁帶寬度隨鎂含量的增加線性增加。 對於濺射方法生長的緩衝層，吸收層的表面鈍化對提高轉化效率非常重要。
本論文的最後一部分是關於高阻窗口層的研究。 相比於由本征氧化鋅構成的高阻窗口層，由鋅鎂氧化物構成的高阻窗口層能使電池有更優的穩定性。對於單結電池，本層的最優厚度是50 納米。對於小型組件，最優厚度在100 納米左右。 關於鎂的最優組分，結果仍爭議，但可以確定的是由較高濺射功率（大於2.2 瓦每平方釐米）產生的濺射損傷是應當盡量避免的。關於光照產生的亞穩定性的研究表明，亞穩定性強度與濺射環境中的氧氣含量正相關。 相對於無氧氣摻雜的電池，通過將1%的氧氣摻入氬氣濺射環境中，電池效率提高了0.5 個百分點。
Cu(In,Ga)Se2 (CIGS)-based thin film solar cells have been regarded as a promising technology for cheap and environmentally friendly electricity generation. CIGS based solar cell has achieved 20.9% conversion effciency, while the offcial record for multicrystalline Silicon solar cell is 20.4%. A series of improvements have lead to this record for thin film based solar cell. An important improvement originated from the replacement of 1- to 2-um-thick doped (Cd,Zn)S layer by a thin, undoped CdS and a transparent conductive oxide(TCO).
Based on our techniques on growing high quality CIGS absorber layer, this work focuses on further optimization of buffer layer and high resistance window layer located between the CIGS absorber and the TCO window layer. The standard buffer structure includes a chemical-bath-deposited CdS layer and an intrinsic ZnO layer. The first part of this thesis is about optimization of this standard structure carried out in our laboratory. The best conversion effciency achieved on mini-module with total area of 60 cm² is 15.6 %.
The second part is about the fabrication of alternative buffer layers by chemical bath deposition. New deposition equipment has been invented to eliminate stationary bubbles and uncovered pinholes on absorber surface in the deposition of CBD CdS. Surface morphology studies shown that the buffer layer grown by this equipment has uniform coverage on the CIGS surface. Other deposition parameters in the chemical bath deposition of CdS buffer layer have been systematically studied employing this new equipment. Our results suggest that the detrimental effect of recombination in SCR region can be mitigated by proper band alignment in the buffer/absorber interface.
Another buffer layer grown by CBD method is ZnS. Because the wider bandgap and less light absorption in short wavelength range, ZnS is a good candidate to replace the toxic CdS buffer layer. The growth kinetics under different deposition temperature have been studied. The optimal temperature profile has been achieved by setting temperature at 95°C. The results of post annealing after deposition indicate that the bandgap energy of CBD ZnS decreases from 3.61 eV to 3.2 eV by annealing in vacuum. A further decrease from 3.2 eV to 2.9 eV could be caused by annealing with oxygen gas. The optimum thickness of ZnS used in single solar cells is between 43nm and 62nm. In this range, devices with CBD-ZnS buffer layer have achieved higher conversion effciency than CBD-CdS buffer layer solar cell. The open circuit voltage for ZnS-buffer devices has approached the value with CdS-buffer. The improvement is mainly due to proper band alignment of ZnS/CIGS interface achieved under high deposition temperature of CBD process.
The third part of this thesis is to study how to deposit (Zn,Mg)O buffer layers by co-sputtering method. It was found that the crystalline structure and optical bandgap of sputtered (Zn,Mg)O varies with Mg concentration. (Zn,Mg)O thin films with Mg concentration less than 0.4 have preferential orientation with a wurtzite phase (002). The crystal quality decreases with increasing Mg concentration and the band gap of the (Zn,Mg)O films has a linear relationship with the Mg concentration in this range. An interesting finding to emerge from this study is that oxygen passivation of absorber surface is critical to improve device performance with (Zn,Mg)O buffer layer deposited by sputtering method.
The last chapter assesses the effect of replacing high resistance window layer with (Zn,Mg)O in devices with CBD-ZnS buffer layer. Compared to devices with i-ZnO (high-resistance window) HRW layer, better device stability has been confirmed on solar cells with (Zn,Mg)O HRW layer. For single cells, the optimum thickness of HRW layer is about 50 nm, and the optimum thickness for mini-modules is around 100nm. Although no conclusion can be drawn with the optimum Mg concentration, the sputtering damage caused by sputtering power density higher than 2.2 W/cm² should be avoided. It was also shown that the metastability effect activated by illumination has positive correlation with the number of energetic oxygen ions in sputtering process. Compared to devices without oxygen doping, a higher effciency (increase of 0.5 % unit) has been achieved by the oxygen/argon doping ratio of 1 %.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Zhu, Jiakuan = 基於銅銦鎵硒薄膜太陽能電池的緩衝層結構研究 / 朱家寬.
Thesis (Ph.D.) Chinese University of Hong Kong, 2014.
Includes bibliographical references (leaves 121-134).
Abstracts also in Chinese.
Zhu, Jiakuan = Ji yu tong yin jia xi bo mo tai yang neng dian chi de huan chong ceng jie gou yan jiu / Zhu Jiakuan.

In this thesis, we studied the role of the defects on the optoelectronic properties of two semiconductors with high potential for photovoltaic application, Cu2ZnSnS4 (CZTS) and Cu(In, Ga)Se2 (CIGS). Both materials are highly doped and strongly compensated, and their optoelectronic properties are governed by a highly complex electronic energy levels structure. In order to further understand the impact of these complex structures on the performance of the devices, several studies were carried out using mainly the photoluminescence technique, and complemented with other optical, morphological, structural, and electrical analyses. For CZTS based solar cells, three series of samples that include studies on the impact of: i) the time of maximum temperature of the sulphurization; ii) the sulphurization method; and iii) the postdeposition annealing on the optoelectronic properties of the CZTS layer, were studied. For CIGS based solar cells, three major topics were addressed: i) solar cells with conventional architecture, ii) solar cells that explore new architectures; and iii) theoretical and experimental study of the influence of defects on the devices performance. The influence of fluctuating potential was shown, and fully explain CZTS and CIGS characteristic luminescence. The optical studies carried in CZTS based solar cells, reveal several issues related to nonradiative recombination or recombination involving deep defects that were closely linked to a poor performance of the studied devices. For different series of CIGS based solar cells, an overall correlation of the influence of the fluctuating potentials with the performance of the devices were obtained. The CIGS related optical results revealed two main recombination deexcitation channels compatible with a shallow donors cluster and the VCu acceptor defect. From theoretical and experimental analyses of CIGS based solar cells, we obtained a higher degree of correlation of electrostatic fluctuating potentials with the open circuit voltage losses of the devices, in comparison with bandgap fluctuations. Finally, we demonstrate the influence of fluctuating potentials in CIGS technology at room temperature. In this thesis, we showed that the optoelectronic properties of CZTS and CIGS are consistent with the existence of the fluctuating potentials, being its impact as a limitative factor on the studied solar cells performance significantly different in the two studied technologies. CZTS based solar cells present serious recombination issues that are significantly more critical for the performance of the device, then the existence of fluctuating potentials. For CIGS based solar cells, the influence of the fluctuating potentials and the performance of the devices are remarkably correlated.
Nesta tese, foi estudado o papel dos defeitos nas propriedades optoelectrónicas de dois materiais com grande potencial para aplicações fotovoltaicas, Cu2ZnSnS4 (CZTS) e Cu(In, Ga)Se2 (CIGS). Ambos os materiais são fortemente dopados e compensados, sendo que as suas propriedades optoelectrónicas são governadas pelas suas estruturas de níveis eletrónicos complexas. No sentido de melhor compreender o impacto da estrutura eletrónica no desempenho das células solares, diferentes estudos foram realizados utilizando principalmente a técnica de fotoluminescência, complementada com análise morfológica, estrutural e elétrica. Para as células solares baseadas em CZTS, foram estudadas três séries de amostras para as quais o impacto i) do tempo da temperatura máxima de sulfurização, ii) do método de sulfurização, iii) do tratamento térmico após a deposição, foi avaliado nas propriedades optoelectrónicas da camada CZTS. Para o CIGS, três tópicos principais foram abordados, i) células solares com arquitetura convencional, ii) células solares para as quais se exploram novas arquiteturas, iii) influência dos defeitos no desempenho das células solares a partir da comparação de modelos teóricos com resultados experimentais. A influência das flutuações de potencial foi evidenciada, sendo que a luminescência obtida, tanto envolvendo o CZTS como o CIGS, foi completamente explicada a partir de modelos de recombinação que envolvem a presença destas flutuações. Os estudos óticos desenvolvidos no âmbito das células solares de CZTS revelaram um grande impacto de mecanismos não radiativos e de recombinação envolvendo defeitos profundos que se relacionam com um fraco desempenho dos dispositivos estudados. Para diferentes séries de amostras de células solares baseadas em CIGS foi obtida uma correlação entre a influência das flutuações de potencial e desempenho dos dispositivos estudados. Os resultados óticos obtidos para CIGS revelaram dois mecanismos principais de desexcitação dos canais radiativos envolvendo aglomerados de dadores pouco profundos e o defeito aceitador VCu. A partir das análises teórica e experimental de células solares de CIGS, obtevese uma maior correlação entre a influência das flutuações de potencial electroestáticas com as perdas de tensão de circuito aberto, do que aquela observada para as flutuações de hiato. Finalmente, foi demonstrada a influência das flutuações de potencial na tecnologia CIGS à temperatura ambiente. Nesta tese, foi mostrado que as propriedades optoelectrónicas do CZTS e CIGS são consistentes com a existência de flutuações de potencial, sendo que o seu impacto no desempenho das células solares é significativamente diferente em cada uma das tecnologias. Enquanto no CZTS os mecanismos de recombinação aparecem como um problema com um impacto no desempenho das células solares mais significativo que as flutuações de potencial, no CIGS uma correlação entre a influência das flutuações de potencial e o desempenho das células solares é notória.
The author acknowledge the financial support of the project UID/CTM/50025/2019, and IF/00133/2015/CP1325/CT0001 from the FCT.
Programa Doutoral em Física

Thin film copper indium gallium selenide (CIGS) solar cells have exhibited single junction power conversion efficiencies above 20% and have been commercialized. The large scale production of CIGS solar cells, however, is hampered by the relatively high cost and poor stoichiometric control of coevaporating tertiary and quaternary semiconductors in high vacuum. To reduce the overall cost of production, CIGS nanocrystals with predetermined stoichiometry and crystal phase were synthesized in solution. Colloidal nanocrystals of CIGS provide a novel route for production of electronic devices. Colloidal nanocrystals combine the well understood device physics of inorganic crystalline semiconductors with the solution processability of amorphous organic semiconductors. This approach reduces the overall cost of CIGS manufacturing and can be used to fabricate solar cells on flexible and light-weight plastic substrates. As deposited CIGS nanocrystal solar cells were fabricated by ambient spray-deposition. Devices with efficiencies of 3.1% under AM1.5 illumination were fabricated. Examining the external and internal quantum efficiency spectrums of the devices reveal that in nanocrystal devices only the space charge region is actively contributing to the extracted photocurrent. The device efficiency of the as-deposited nanocrystal films is presently limited by the small crystalline grains (≈ 15 nm) in the absorber layer and the relatively large interparticle spacing due to the organic capping ligands on the nanocrystal surfaces. Small grains and large interparticle spacing limits high density extraction of electrons and holes from the nanocrystal film. A Mott-Schottky estimation of the space charge region reveals that only 50 nm depth of the nanocrystalline absorber is effectively contributing to the photogenerated current. One strategy to improve charge collection involves increased space charge region for extraction by vertical stacking of diodes. A much longer absorption path for the photons exists in the space charge region with the stacked devices, increasing the probability that the incident radiation is absorbed and then extracted. This method enables an increase in the collected short circuit current. The overall device efficiency, however, suffers with the increased series resistance and shunt conductance of the device. Growth of nanocrystal grains was deemed necessary to achieve power conversion efficiencies comparable to vapor deposited CIGS films. Simple thermal treatment of the nanocrystal layers did not contribute to the growth of the crystalline grain size. At the same time, because of the loss of selenium and increased trap density in the absorber layer, there was a measurable decrease in device efficiency with thermal processing. For increased grain size, the thermal treatment of the absorber layer took place in presence of compensating amounts of selenium vapor. The process of selenization, as it is called, took place at 500°C in a graphite box and led to an increase of the grain size from 15 nm to several microns in diameter. Devices with the increased grain size yielded efficiencies up to 5.1% under AM1.5 radiation. Mott-Schottky analysis of the selenized films revealed a reduction in doping density and a comparable increase in the space-charge region depth with the increased grain size. The increased collection combined with the much higher carrier mobility in the larger grains led to achieved Jsc values greater than 20 mA/cm2. Light beam induced current microscopy (LBIC) maps of the devices with selenized absorber layers revealed significant heterogeneity in photogenerated current. Distribution of current hotspots in the film corresponded with highly selenized regions of the absorber films. In an effort to improve the overall device efficiency, improvements in the selenization process are necessary. It was determined that the selenization procedure is dependent on the selenization temperature and processing environment. Meanwhile, the reactor geometry and nanocrystal inks composition played important roles in determining selenized film morphology and the resulting device efficiency. Further work is necessary to optimize all the parameters to improve device efficiency even further.
text

Submitted to the Faculty of Science, School of Chemistry at University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 05 June 2017.
The colloidal method has extensively been used to synthesize ternary and quaternary copper sulfides and selenides. Although tellurides form part of the chalcogenides, little has been reported on them particularly the synthesis of these nanostructures. Achieving high-quality nanocrystals through colloidal synthesis requires thorough monitoring of parameters such as time, solvent, precursor as they affect nucleation and growth of the nanocrystals. Herein, we report on the colloidal synthesis of ternary CuInTe2 and quaternary CuIn1-xGaxTe2 nanostructured semiconductor materials. A typical synthesis of CuInTe2 entailed varying reaction temperature. At temperatures below 250 °C, no formation of CuInTe2 was seen. At 250 °C formation of CuInTe2 could be observed with the formation of binary impurities. A change in the sequence in which precursors were added at 250 °C yielded pure CuInTe2. Applying different surfactants aided in achieving differently structured morphologies of CuInTe2 nanocrystals. Morphology varied from rods, cubes, nanosheets etc. Different morphologies resulted in different optical properties with the high optical band gap of 1.22 eV measured for 1D rods. Different precursors were employed in the synthesis of quaternary CuIn1-xGaxTe2. Precursor 2 (entailed the use of Cu (acac)2, In (acac)3 and Ga(acac)3) yielded pure CuIn1-xGaxTe2 phase with no formation of impurities. Variation in reaction time influenced the optical properties of the quaternary CuIn1-xGaxTe2 with high band gap obtained at low reaction time (30 min). A change in Ga and In concentration resulted in reduced lattice parameters a and c with lowest values obtained with the highest Ga concentration. However, achieving the intended concentration proved challenging due to the loss of the material during synthesis. Increasing the Ga concentration resulted in a high optical band gap. Conducting the reaction with Hexadecylamine (HDA) resulted in a relatively high optical band though the formation of impurities was evident. The obtained band gap can be attributed to small sized particles as evident from TEM results. Heterojunction ZnO/CIT and ZnO/CIGT solar cell devices were fabricated through a simple solution approach. The performance of ZnO/CIGT device was superior to that of ZnO/CIT in which efficiency increased from 0.26-0.78%. In the ZnO/CIT device, high Voc of 880 mV was recorded while 573.66 mV was measured for ZnO/CIGT device. Chemical and thermal treatments were performed on the ZnO/CIGT devices. The efficiency increased from 0.78 1.25% when the device was chemically treated with a short-chain EDT ligand. A high conversion efficiency of 2.14% was recorded for devices annealed at 300 °C. High annealing temperatures resulted in poor device performance with the lowest efficiency of 0.089% obtained at annealing temperatures of 500 °C attributed to the leaching out of In and Ga into the ZnO layer.
LG2017

Yang, Shihang = 銅銦鎵硒太陽能電池中白光退火系統的設計 / 楊世航.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2009.
Includes bibliographical references (p. 87-91).
Abstract also in Chinese.
Yang, Shihang = Tong yin jia xi tai yang neng dian chi zhong bai guang tui huo xi tong de she ji / Yang Shihang.
Chapter 1 --- Introduction to Photovoltaics --- p.1
Chapter 1.1 --- "Developments, markets and forecasts" --- p.1
Chapter 1.2 --- The physics of solar cells --- p.2
Chapter 1.2.1 --- Light Absorption --- p.2
Chapter 1.2.2 --- Charge Carrier Separation --- p.6
Chapter 1.2.3 --- Solar Cell I-V Characteristics --- p.7
Chapter 1.3 --- Classifications of Solar Cells --- p.10
Chapter 1.3.1 --- Crystalline silicon solar cell --- p.10
Chapter 1.3.2 --- Thin film solar cells --- p.12
Chapter 1.3.3 --- Organic and polymer solar cells --- p.12
Chapter 1.4 --- "Cu(In,Ga)Se2 Solar Cells" --- p.13
Chapter 1.4.1 --- State of the art --- p.13
Chapter 1.4.2 --- Material properties --- p.14
Chapter 1.4.3 --- Basic processing steps --- p.15
Chapter 2 --- Equipment design --- p.24
Chapter 2.1 --- System design concepts --- p.24
Chapter 2.2 --- Sample transfer chamber --- p.26
Chapter 2.3 --- Co-evaporation chamber --- p.28
Chapter 2.3.1 --- Load-lock chamber --- p.28
Chapter 2.3.2 --- Co-evaporation chamber --- p.31
Chapter 2.4 --- Sputtering chambers --- p.34
Chapter 2.4.1 --- Mo sputtering chamber --- p.34
Chapter 2.4.2 --- Three targets sputtering chamber --- p.36
Chapter 2.5 --- Other chambers --- p.38
Chapter 3 --- Design of Rapid Thermal Processing System --- p.42
Chapter 3.1 --- Introduction to RTP --- p.42
Chapter 3.1.1 --- History and current status of RTP --- p.42
Chapter 3.1.2 --- Advantages of RTP system compared to conventional furnaces --- p.45
Chapter 3.2 --- Computational simulation for RTP system design --- p.47
Chapter 3.2.1 --- Introduction to Ansys Fluent --- p.47
Chapter 3.2.2 --- Model setup steps --- p.54
Chapter 3.2.3 --- Physical principles --- p.57
Chapter 3.2.4 --- Models setup and comparisons --- p.62
Chapter 3.3 --- Rapid thermal processing system --- p.76
Chapter 3.3.1 --- Se deposition chamber --- p.76
Chapter 3.3.2 --- Quartz chamber --- p.78
Chapter 3.3.3 --- Lamp frame --- p.79
Chapter 4 --- Conclusions --- p.83
Chapter 4.1 --- RTP heater design --- p.83
Chapter 4.2 --- Future prospect --- p.83
Bibliography --- p.87

碩士
國立清華大學
材料科學工程學系
99
Cu(In , Ga ) Se2 (CIGS)-based solar cell is one of the most promising candidates for future photo-voltaic application. In this thesis, we developed a one-step sputtering process from a single quaternary target. This straightforward process might be suitable for large-area application in industry. In this work, CIGS thin films were fabricated by sputtering from a single target at elevated temperature without additional selenium supply. Both film properties and device properties were investigated. Two targets with different composition were studied, namely, one copper-poor target and one copper-rich target. In the study concerning copper-poor target, we found that grain boundary passivation was quite critical. Hence, additional efforts were put into sodium incorporation. For the copper-rich target, the efficiency of 6\% was achieved. However, high carrier concentration and high copper concentration might limit the device performance. For the copper-poor target, the conversion efficiency was increased from 0.2\% to over 7.5\% by controlling sodium composition.

This thesis is focused on the development of digestible electronics for healthcare. The vision is the development of an edible pill that performs diagnosis inside the body. Any such edible device needs an energy source made of non-toxic materials. This thesis discusses the development of such an energy source. The main idea is based on using a galvanic cell. This thesis constraints itself in exploring Zn/Cu based cells using lemon extract-pectin blend extracts. Cells based on a solid electrolyte, gel based electrolyte and a liquid electrolyte contained in a hardened shell of isomalt are discussed. The load characterisitcs of the cells show promise to deliver energy to power the device for 100 s. Furthermore, the thesis details how the cells could be used as a sensor to sense the pH. To summarize, the thesis develops the means and methods to develop a compact edible power source.

碩士
國立交通大學
生物科技學系
98
Over the past few decades, increasing attention has been paid to synthesize contrast agent for magnetic resonance imaging (MRI). MRI is a non-invasive and high resolution technique that has become a powerful diagnostic tool in medicine. In this study, we designed and synthesized a tryptophan based contrast agent (4S)-4-indolyl-3,6,10-tri(carboxymethyl) -3,6,10-triazadodecanedioic acid (Try-TTDA) and its Gd(III) chelate ([Gd(Try-TTDA)]2?{) that can recognize Cu2+ ion in the living cells. Moreover, the Gd3+ complex attributes excellent selectivity for Cu2+ over a choice of other metal ions. The interaction between Cu2+ and side chain indole of [Gd(Try-TTDA)]2?{ was quenching of intrinsic tryptophan fluorescence. A gradual increases in the relaxivity and signal enhancement of ex-vitro and in vitro MR imaging upon Cu2+ detection. These results implicate that a new MR based contrast agent can serve as a Cu2+ sensor using fluorescence spectrophotometer and MR imaging.

The growing demand for energy is an important issue for the existence and development of humankind. In order to reduce the impact of conventional energy sources on the environment, attention should be paid to the development of new and renewable energy resources. Solar energy is a major environment friendly, renewable and sustainable energy source. Subsequently, with increasing drying up of the terrestrial fossil fuel, solar energy will potentially become an important part of the future energy structure. Concentrated solar power (CSP) technology is a productive way to make effective utilization of thermal energy from sun. Consequently, exploring high efficiency CSP technology is necessary. This has motivated the development of spectrally selective reflector and absorber materials. Recently, reflectors have attracted considerable attention due to their potential application in CSP system. Reflector failure due to the formation of an oxide layer on metallic surfaces has been widely recognized as a major issue, often leading to CSP plant failure. Bronze (an alloy of copper and tin) mirrors, having lustrous reflective surface, were one of the candidate materials for traditional antique mirrors from ancient times. However, research involving these intermetallic materials for reflector application is still limited. The important drawbacks for these materials include complex processing conditions, brittleness, physical and chemical properties like oxidation, wettability etc. The phase composition, surface properties, free electrons density and hence the plasma frequency plays a critical role in controlling the reflectance of any materials. To this end, the main focus of this work was to develop reflector materials from alloys of Cu-Sn, Cu-Al, Cu-Sn-Zn or Cu-Sn-Al system and to understand the composition dependence reflectance properties of both bulk alloys and thin films of varying thickness. In this perspective, the present dissertation demonstrates how one can adopt an alloy design approach to develop bulk optical reflector materials. Extending this to coatings, the efficacy of electrodeposition and thermal evaporation was also illustrated to show thickness dependent reflectance property. The importance of the development of new reflector materials for CSP technology is highlighted in chapter 1. The necessary theoretical fundamentals i.e., the physics aspect of the reflector functionality together with a review of the existing materials for reflector application are summarized in chapter 2. The general description of various experimental methodologies is made in chapter 3. The first part of the present dissertation involves bulk alloy development and second part describes film fabrication. In a few cases, the scratch resistance and the influence of dust and humidity of the environment were also investigated. Chapter 4 demonstrates our attempt to develop a reflector material in the bulk cast form. This chapter describes the development of bulk Cu-Sn intermetallic for application as a solar reflector and further tuning them with tailored substitution of Zn or Al. A conventional metallurgical route (non-equilibrium processing techniques like vacuum arc melting and chill casting) was adopted. The second part (chapter 5 and 6) deals with thin film synthesis. The studies on intermetallic coatings of Cu-Sn alloys by electrodeposition are presented in chapter 5. Further, Cu-Al thin film deposition by thermal evaporation is explained in chapter 6. Some brief highlights of the major chapters of this dissertation are summarized below. Chapter 4 mainly deals with the development of Cu-Sn intermetallic based solar reflector material, where further all substitution was performed using aluminium or zinc. Zinc was chosen due to its solid solution solubility with copper and aluminium was added because of its high plasma frequency. Chapter 4 essentially reports the rationale of reflector alloy design from a metallurgical and physics perspective. The results obtained with the baseline Cu41Sn11 intermetallic and other alloy compositions have been be analysed to bring out the influence of Al or Zn substitution to the baseline alloy. A detailed analysis of the phase assemblage utilizing Rietveld refinement of the X-ray diffraction (XRD) data and wavelength dispersive spectroscopy (WDS), attached to the electron probe micro analyser (EPMA) has been performed. The physical basis of higher reflectance has been explained on the basis of plasma frequency calculation of these alloy compositions. A good correlation between the phase abundance and plasma frequency was seen and is attributed to the high specular reflectance. Moreover, the Cu- 21.2 at % Al alloy composition, consisting of two phases Cu3Al (ωp = 6.47 x 1015 rad/sec) and Cu0.78Al0.22 (ωp = 19.25 x 1015 rad/sec) phases, exhibited 89.5% specular reflectance and 83% solar reflectance with roughness at nanometre level and a hardness of 2.1 GPa. These results establish the suitability of an alloy design approach to obtain a new class of intermetallic reflector materials with a tailored combination of bulk specular reflectance and hardness. Chapter 5 was focussed on the development of lustrous Cu-Sn coatings from an acidic sulfate based electrolyte containing electro generated metal ions. The deposition of individual metals and co-deposition of metals were carried out. Importantly, it has been demonstrated that lustrous coatings can be galvanostatically electrodeposited from acidic sulfate based electrolyte in the presence of Laprol as an additive. The intricate designing of Cu-Sn codeposition was illustrated by systematic changes in the deposition conditions, such as applied current, bath composition and time of deposition. The quantitative analysis of the phase assemblage as well as compositional analysis of different phases was conducted using SEMEDS and XRD based Rietveld analysis. The coating thickness dependent surface morphology and specular reflectance was established. Essentially, we evaluated the properties such as scratch hardness and scratch adhesion, effect of dust and humidity, in reference to the projected CSP applications. Importantly, the useful combination of ~ 80 % specular reflectance and scratch resistance of Cu41Sn11 film were demonstrated to be highly durable under local environmental conditions. In chapter 6, a facile fabrication of Cu-Al thin films on flex glass substrate was demonstrated by systematically varying the applied current and rate of deposition in a thermal evaporation route. The metallic Cu-Al ingot (obtained from arc melting) was heated in vacuum by applying current, and was thermally evaporated onto a flexible glass substrate to obtain the reflector coatings. In particular, the Cu0.78Al0.22 thin films with a plasma frequency ωp = 19.25 x 1015 rad/sec, were fabricated on flexible glass substrates by resistive thermal evaporation. An attempt was made to analyze the relationship among the phase compositions, surface morphology, thickness, surface coverage and optical properties. Importantly, flexible Cu0.78Al0.22 films with a specular reflectance of ~ 84 % in the solar region and scratch resistance at 900 mN load were obtained. It can be envisioned that with all these promising features, the Cu-Al films promise a great potential for use as highly reflective and flexible material for thin-film reflecting concentrators, solar energy devices and other optical mirrors.

碩士
國立臺北科技大學
製造科技研究所
101
In this research, the tranditional two stage process was utilized to fabricate CIGS absorber.In the two stage process, CIGSe films are prepared by selenization of CuInGa (CIG) metallic percursors that CIG precursors are subjected to get diffused with Se vapor. However, In atoms might migrate toward the surface with higher Se concentration during selenization because of chemical affinity of In-Se and Ga-Se. the result would contribute to the accumulation of Ga atoms, causing detrimental influences such as Ga segregation or CuInSe2 and CuGaSe2 phase separation and further affect PV performance of CIGSe solar cells. In this study, we thus prepared the CIG precursors with various Cu/(In+Ga) ratio by sequential sputtering of In and Cu3Ga targets in DC sputtering system, followed by selenization process. In addition, we also investigated the effect of Ga segregation on the micro-structural and electro-optical characteristics on CIGS thin films. The results indicate that the crystalline size in the morphology observation continue to extend with an increase in Cu/(In+Ga) compositional ratio. Moreover, the single phase chalcopyrite CuIn0.7Ga0.3Se2 is predominant in the XRD and Raman results. The phenomenon of apparently Ga segregation can also be observed. After TEM analysis, the phase on the bottom of films shows CuGaSe2. The observation of Ga segregation and elemental distribution is clarified using EMPA and AES as well. In the section of electro-optical characteristicsof CIGSe thin films, all the CIGSe thin film we prepared reveal P-type conductivity. The carrier contentration would alter from1015-1018 cm-3 with varied Cu/(In+Ga) composition ratio. According to result the by extrapolating the slope of the α2(hν) curve and the abscissa, Band gap (Eg) can enhance with an increase in Ga content. However, the In atoms in chalcopyrite structure can not be substituted by Ga efficiently, the trend of extending Eg would be presented apparently. In this case, we utilized sulfurization process to improve the uniformity and Ga segregation throughout the films. In addition, we investigated the effects of temperature and duration on the characteristics like morphology, structure, and photoelectric property of CIGSeS thin films during sulfurization. The results indicate the influence of S incorporation do exert effect on the homogenization of CIGSeS thin films that can improve uniformity and segregation. The open-circuit voltage (Voc) and Band gap (Eg) would be enhanced, resulting in extending the conversional efficiency.

碩士
國立清華大學
電子工程研究所
89
Cu-III-VI2 ternary compound semiconductor is one of the most promising materials for thin film photovoltalic devices, especially solar cells, due to the suitability of its band gap and its high absorption coefficient. Recently, the National Renewable Energy Laboratory (NREL) has reported that the total-area efficiency of the solar cell based on Cu(In,Ga)(Se,S)2 has reached 18.8% ,growing by 3-stage evaporation method. Martin A. Green indicated in his book that the efficiency of a tandem solar cell with three-layer structures, in which energy gaps are 1.0eV, 1.6eV, and 2,2 eV, respectively, could reach 35%. This could be reached by Cu-III-VI2 material due to its band gap can be varied from 1 to 3.5eV by composition control. Therefore, how to develop a suitable industry technique to produce a large area, uniform, high throughput, and inexpensive Cu-III-VI2- based solar cell is very important in 21th’s century. In order to develop a suitable industry technology to prepare the absorber of Cu-III-IV2-based solar cells, we choose the sputtering method as our experimental method. In our experiments, reactive sputtering method with different CuIn alloy targets was utilized to prepare the CuInS2 films. We prepared CuInS2 thin films under different process conditions such as substrate temperatures, RF power, Ar and H2S flow rates. Generally, Cu-rich films we prepared have good crystalline quality and low resitivity. But, it also limed by it rough surface and the problem resulting from surface secondary phases. In-rich films we prepared have smooth surface morphology, but it also suffer from low carrier mobility and smaller grain size. Near-stoichiometric films could be prepared by utilizing a target with Cu/In=0.95 at atomic percentage. The best process condition occurred at a small H2S flow rate ( <=7.5 sccm) and a temperature of 400 °C. In this condition, the films have good crystal quality without surface secordary phases. To control the composition of the films, futher, we also try to add a negative bias to the Mo-coated glass. Although the details of the bias sputtering are not always clearly understood, there is a little doubt that the weak-bounded species grown on the surface of the films may be resputtered due to a low-energy ion bombardment. Increasing the magnitude of the negative bias results that the Cu/In become smaller than 1 and the surface become more smooth. Besides preparing CuInS2 by the reactive sputtering method, we also developed a new technology, named MO-sputtering process, which added a small amount of metal-organic gas during sputtering process to solve the disadvantages that composition control is difficult in the sputtering process using an alloy target. TMGa has been utilized as our metal organic source to prepare Cu(In,Ga)S2 thin films. We have prove that the mo-sputtering can be developed as a new technique to prepare Cu-III-VI2 solar cells.

碩士
國立交通大學
應用化學系碩博士班
103
In this thesis, coumarin was used as a signal unit for chemosensors AC and PHC. Chemosensor AC indicates the presence of cysteine and homocysteine among other amino acids with high selectivity by a significant blue emission. Chemosensor AC displays good sensitivity in buffer solution at the pH value 6.0 to 9.0. The detection limits of AC for cysteine and homocysteine are 65 and 78 nM, respectively. In addition, chemosensor AC can be used as a fluorescent probe for detecting cysteine and homocysteine in living cells. Chemosensor PHC indicates the presence of copper ions among other amino acids with high selectivity by a significant blue emission. The detection limit of PHC for Cu (II) is 8 nM. In addition, chemosensor PHC can be used as a fluorescent probe for detecting Cu (II) in living cells.

碩士
國立臺灣大學
材料科學與工程學研究所
106
Carbon deposition and catalytic ability of anodes are two important issues when using hydro-carbon fuels for solid oxide fuel cells. Nickel based anode (NiO/YSZ) shows a serious carbon deposition reported in recent research. Therefore, CuO is added to replace the NiO. In this study, three anode powders (100%Ni with 8YSZ, 50%Cu-50%Ni with 8YSZ and 100%Cu with 8YSZ) are prepared by powder mixing in well-dispersed slurry. A new approach to verify the effects of carbon deposition by measuring the permeability of the anodes are used in this study. C50N50Z shows a good catalytic ability and low coking rate for CH4. The conductivity of C50N50Z is 1503 Scm-1 at 650 oC. Another two functions of copper can be combined with this anode. Four copper-based metal and nickel wires (Cu, Cu11Ni, Cu-38Zn, Cu9Ni6Sn, Ni) are tested for their electric conductivity at room to high temperature. Due to a high electric conductivity, Cu is good enough to apply as a material for current collector. Five different thermocouples made from above wires are also aging in air for more than 100 h at 200 oC~650 oC. Because of sensibility and less drift (<5%) of thermopotential at 200 oC to 650 oC, three thermocouples Cu-Cu11Ni, Cu-Cu9Ni6Sn and Cu-Ni are suitable for intermediate-temperature SOFC as temperature sensors. Thus, triple function of Cu-based materials can be applied on anode side of SOFCs.

We have performed fluorescence extended X-ray absorption fine structure (EXAFS) measurements on the Cd K-edge of partial electrolyte (PE) treated Cu(In[subscript 0.7]Ga[subscript 0.3])Se��� (CIGS) thin film samples using synchrotron X-ray radiation. This data was compared to the EXAFS spectra of CdSe and CdO standards. Cd local structure models were constructed and used for the least square analysis of the spectra. The first model employed implantation of a cadmium atom and a single oxygen atom into the CIGS lattice. Specifically, an oxygen atom was introduced in the tetrahedral bonded Cd-Se local structure. Employing FEFF8 with WinXAS software package, experimental data was theoretically fitted to the first shell single-scattering paths of the Cd atom in the (PE) treated Cu(In[subscript 0.7]Ga[subscript 0.3])Se��� thin film samples. The main peak observed in the data represents the Cd-Se bonds and the shoulder corresponds to the Cd-O bond. However, the number of total nearest neighbors is not consistent with this model. A two-phase model that includes both Cd-Se tetrahedron and Cd-O octahedron were then reconstructed. Again, a least-agrees very well with the experimental data, and the total first nearest neighbor number is consistent with the two phase model at NN=4.2. This study indicates the surface of Cd partial electrolyte treated Cu(In[subscript 0.7]Ga[subscript 0.3])Se��� thin films contains both CdSe and CdO.
Graduation date: 2004

In this thesis, thin-film solar cells on the basis of Cu(In,Ga)(S,Se)2 (CIGSSe) were investigated. Until today, most high efficient CIGSSe-based solar cells use a toxic and wetchemical deposited CdS buffer layer, which doesn’t allow a dry inline production. However, a promising and well-performing alternative buffer layer, namely indium sulfide, has been found which doesn’t comprise these disadvantages. In order to shed light on these well-performing devices, the surfaces and in particular the interfaces which play a major role for the charge carrier transport are investigated in the framework of this thesis. Both, the chemical and electronic properties of the solar cells’ interfaces were characterized. In case of the physical vapor deposition of an InxSy-based buffer layer, the cleaning step of the CdS chemical-bath deposition is not present and thus changes of the absorber surface have to be taken into account. Therefore, adsorbate formation, oxidation, and segregation of absorber elements in dependence of the storing temperature and the humidity are investigated in the first part of this thesis. The efficiencies of CIGSSe-based solar cells with an InxSy buffer layer depend on the nominal indium concentration x and display a maximum for x = 42 %. In this thesis, InxSy samples with a nominal indium concentration of 40.2% ≤ x ≤ 43.2% were investigated by surface-sensitive and surface-near bulk-sensitive techniques, namely with photoemission spectroscopy (PES) and x-ray emission spectroscopy (XES). The surfaces of the films were found to be sulfur-poor and indium-rich in comparison with stoichiometric In2S3. Moreover, a direct determination of the band alignment at the InxSy/CISSe interface in dependence of the nominal indium concentration x was conducted with the help of PES and inverse PES (IPES) and a flat band alignment was found for x = 42 %. In order to study the impact of a heat treatment as it occurs during subsequent cell process steps, the indium sulfide-buffered absorbers were annealed for 30 minutes under UHV conditions at 200 °C after the initial data set was taken. Besides a reported enhanced solar cell performance, a significant copper diffusion from the absorber into the buffer layer takes place due to the thermal treatment. Accordingly, the impact of the copper diffusion on the hidden InxSy/CISSe interface was discussed and for x = 40.2% a significant cliff (downwards step in the conduction band) is observed. For increasing x, the alignment in the conduction band turns into a small upwards step (spike) for the region 41% ≤ x ≤ 43.2%. This explains the optimal solar cell performance for this indium contents. In a further step, the sodium-doped indium sulfide buffer which leads to significantly higher efficient solar cells was investigated. It was demonstrated by PES/IPES that the enhanced performance can be ascribed to a significant larger surface band gap in comparison with undoped InxSy. The occurring spike in the Na:InxSy/CISSe band alignment gets reduced due to a Se diffusion induced by the thermal treatment. Furthermore, after the thermal treatment the sodium doped indium sulfide layer experiences a copper diffusion which is reduced by more than a factor of two compared to pure InxSy. Next, the interface between the Na:InxSy buffer layer and the i-ZnO (i = intrinsic, non-deliberately doped), as a part of the transparent front contact was analyzed. The i-ZnO/Na:InxSy interface shows significant interdiffusion, leading to the formation of, e.g., ZnS and hence to a reduction of the nominal cliff in the conduction band alignment. In the last part of this thesis, the well-established surface-sensitive reflective electron energy loss spectroscopy (REELS) was utilized to study the CIGSSe absorber, the InxSy buffer, and annealed InxSy buffer surfaces. By fitting the characteristic inelastic scattering cross sections λK(E) with Drude-Lindhard oscillators the dielectric function was identified. The determined dielectric functions are in good agreement with values from bulk-sensitive optical measurements on indium sulfide layers. In contrast, for the chalcopyrite-based absorber significant differences appear. In particular, a substantial larger surface band gap of the CIGSSe surface of E^Ex_Gap = (1.4±0.2) eV in comparison with bulk values is determined. This provides for the first time an independent verification of earlier PES/IPES results. Finally, the electrons’ inelastic mean free paths l for the three investigated surfaces are compared for different primary energies with theoretical values and the universal curve
Die vorliegende Arbeit untersucht Dünnschichtsolarzellen auf Basis von Cu(In,Ga)(S,Se)2 (CIGSSe). Um hohe Effizienzen bei CIGSSe-basierten Solarzellen zu erreichen, wurde bisher meist eine toxische und schlecht in einen Vakuumprozess integrierbare nasschemische CdS Pufferschicht verwendet. Mit Indiumsulfid konnte stattdessen eine vielversprechende alternative Pufferschicht gefunden werden, die diese nachteiligen Eigenschaften von CdS nicht aufweist und Solarzellen mit diesem Puffermaterial zeigen gute bis sehr gute Wirkungsgrade. Um die Ursachen der guten Leistungen herauszufinden, wurden die in der Solarzelle vorkommenden Oberflächen und Grenzflächen, die für den Ladungstransport eine zentrale Rolle spielen, Schritt für Schritt als Modellsysteme charakterisiert. Für einen InxSy-basierten Puffer, der durch die physikalische Gasphasenabscheidung aufgebracht wird, fehlt der Reinigungsprozess der Absorberoberflächen durch die nasschemische CdS Abscheidetechnik. Deshalb müssen Adsorbatbildung, Oxidation und Segregation von Absorberelementen die innerhalb der ersten Tage nach der Herstellung auftreten (je nach Feuchtigkeitsgehalt und Temperatur der Umgebung) berücksichtigt werden. Im ersten Teil der Arbeit werden solche Einflüsse auf die Oberfläche des Absorbers untersucht. Zellen mit einem Indiumsulfidpuffer zeigen Wirkungsgrade, die von der nominellen Indiumkonzentration x abhängen und bei x = 42% ein Optimum aufweisen. Eine stöchiometrische Analyse der InxSy Oberflächen ergab für 40.2% ≤ x ≤ 43.2% eine schwefelarme bzw. indiumreiche Oberfläche im Vergleich zu stöchiometrischem In2S3 (40% In und 60% S). Allerdings zeigen die untersuchten Proben für verschiedene Indiumkonzentrationen im Rahmen der oberflächensensitiven Photoemission (PES) und volumensensitiven Röntgenemission (XES) keine quantitativen Unterschiede. Mit Hilfe der PES und inversen PES (IPES) wurde der Bandverlauf an der InxSy/CISSe Grenzfläche in Abhängigkeit von der Indiumkonzentration untersucht und für x = 42% konnte ein flacher Bandverlauf ermittelt werden. Um den Einfluss des im Herstellungsprozess vorkommenden Temperaturschritts zu untersuchen, wurden die Proben für 30 Minuten auf 200 °C geheizt. Dabei konnte eine signifikante Diffusion von Kupfer aus dem Absorber in den Puffer beobachtet werden. Der Temperaturschritt führt neben der bereits bekannten Effizienzerhöhung vor allem zu einer Verringerung der Bandlücke des Puffers. Der Einfluss der Kupferdiffusion auf die verborgene InxSy/CISSe Grenzfläche wurde analysiert und für x = 40:2% wurde ein deutlicher "Cliff" (Stufe im Leitungsband nach unten) gefunden. Für Indiumkonzentrationen 41% ≤ x ≤ 43.2% wurde ein kleiner "Spike" (Stufe im Leitungsband nach oben) identifiziert, was dabei im Einklang mit den optimalen Wirkungsgraden ist. In einem weiteren Schritt wurde ein mit Natrium dotierter Indiumsulfidpuffer Na:InxSy, der verbesserte Wirkungsgrade zeigt, untersucht. Diese konnte zum einen auf eine deutlich vergrößerte Oberflächenbandlücke des Puffers zurückgeführt werden. Zum anderen wurde nach dem Temperaturschritt im Vergleich zu dem InxSy Puffer eine um den Faktor zwei verringerte Kupferdiffusion an der Oberfläche festgestellt. Des Weiteren konnte bei dem Temperaturschritt eine Diffusion von Selen festgestellt werden, die den vor dem Temperaturschritt vorhandenen "Spike" im Leitungsbandverlauf verringert. Nach dem Aufbringen der i-ZnO Schicht (i = intrinsisch, nicht absichtlich dotiert) als Teil des Frontkontakts auf den Na:InxSy Puffer, wurden Durchmischungseffekte an der i-ZnO/Na:InxSy Grenzfläche gefunden. Im weiteren Verlauf zeigte sich, dass der nominell auftretende "Cliff" zwischen i-ZnO und Na:InxSy durch die Bildung von ZnS reduziert bzw. vernachlässigt werden kann. Im letzten Teil der Arbeit wurde die etablierte oberflächensensitive reflektive Elektronenenergieverlustspektroskopie auf die Absorber- sowie Indiumsulfidoberflächen angewandt. Die ermittelten inelastisch gestreuten Verlustspektren λK(E) wurden mit dem Drude-Lindhard Modell simuliert und somit die dielektrische Funktion der jeweiligen Oberflächen bestimmt. Ein Vergleich mit volumensensitiven optischen Werten zeigt für die InxSy Schichten eine gute Übereinstimmung. Bei der CIGSSe Oberfläche konnten hingegen signifikante Unterschiede festgestellt werden. Dabei wurde erstmals die Oberflächenbandlücke eines Cu(In,Ga)(S,Se)2 Absorbers unabhängig von PES/IPES zu E^Ex_Gap = (1.4 ±0.2) eV verifiziert. Abschließend wurden die mittleren freien Weglängen der Elektronen l für die drei untersuchten Oberflächen für unterschiedliche Energien mit theoretischen Werten und der universellen Kurve verglichen

abstract: The Programmable Metallization Cell (PMC) is a novel solid-state resistive switching technology. It has a simple metal-insulator-metal “MIM” structure with one metal being electrochemically active (Cu) and the other one being inert (Pt or W), an insulating film (silica) acts as solid electrolyte for ion transport is sandwiched between these two electrodes. PMC’s resistance can be altered by an external electrical stimulus. The change of resistance is attributed to the formation or dissolution of Cu metal filament(s) within the silica layer which is associated with electrochemical redox reactions and ion transportation. In this dissertation, a comprehensive study of microfabrication method and its impacts on performance of PMC device is demonstrated, gamma-ray total ionizing dose (TID) impacts on device reliability is investigated, and the materials properties of doped/undoped silica switching layers are illuminated by impedance spectroscopy (IS). Due to the inherent CMOS compatibility, Cu-silica PMCs have great potential to be adopted in many emerging technologies, such as non-volatile storage cells and selector cells in ultra-dense 3D crosspoint memories, as well as electronic synapses in brain-inspired neuromorphic computing. Cu-silica PMC device performance for these applications is also assessed in this dissertation.
Dissertation/Thesis
Doctoral Dissertation Electrical Engineering 2017

碩士
國立中央大學
物理學系
105
In recent decades, the solar energy techniques grow very quickly. Because solar energy cannot exhaust greenhouse gas that is the main cause of greenhouse effect. Currently, the solar cell cannot be commonly employed since its price is still expensive. Our goal in this study is to greatly reduce the cost but only losing little efficiency. One solution is to replace a portion of silver front side metallization by copper. In our simulation, we change number, height and composition of fingers to simulate solar cell efficiency. First, we obtained the parameters which are independent of fingers, and then used PC1D to calculate cell’s IV-data. Secondly, the single diode model is employed to obtain the short circuit current, the series resistance which are independent fingers, dark current, the ideal factor and the shunt resistances. Finally, once the finger’s electrical and structural parameters are included, the cell’s efficiency can be calculated. For cupper-plated front side metallization, the simulation process is similar but considering electric and structural parameters of copper. We discussed the relations between silver height, copper height and efficiency; and the relation between widening ratio and efficiency. By comparing single layer finger with Cu-plated finger, we successfully reduce about 24.47% of Ag with additional 21.38% of Cu , while, only 0.012% of efficiency is losing. This reveals a promising reduction of cost in Si-based solar cell with Cu-platted front side metallization. Finally, we propose a promising calculation tools, combining the PC1D and circuit model, to simulate the best combination of Si-based solar cell with Cu-platted front side metallization, as long as the real electrical and structural parameters implemented from experimental results.

Il processo di riduzione dell'anidride carbonica (CO2) ha suscitato negli ultimi anni grande attenzione nella comunità scientifica. Lo sviluppo di materiali e sistemi in grado di convertire H2O e CO2 in prodotti ad alto valore utilizzando energia rinnovabile e pulita, rappresenta una sfida particolarmente attraente per il prossimo futuro. In questo contesto, lo scopo del presente lavoro di Dottorato è stato quello di valutare diversi approcci, tra cui quelli foto- ed elettrocatalitici, per convertire la CO2 in sostanze chimiche e combustibili a più alto valore aggiunto. L'attività di ricerca ha riguardato sia la sintesi dei materiali catalitici utilizzati per la preparazione/ assemblaggio degli elettrodi sia la progettazione e ingegnerizzazione dei dispositivi elettrochimici. La maggior parte delle attività sono state svolte presso il laboratorio CASPE/INSTM (Laboratorio di Catalisi per la Produzione Sostenibile e l'Energia) dell'Università degli Studi di Messina. Durante il secondo anno, un mese è stato trascorso presso l'Institut Català d'Investigació Química (ICIQ Tarragona, Spagna) e due mesi presso l'Istituto di Chimica e Bioingegneria (ETH Zurigo, Svizzera) nell'ambito del Progetto H2020 A-LEAF e del Progetto di Ricerca e Mobilità ARCADIA. La tesi è organizzata in sei capitoli, più le conclusioni. Il capitolo 1 si concentra sulle questioni ambientali derivanti dall’accumulo della CO2, le implicazioni generali e le conseguenti opinioni e strategie adottate dalla comunità scientifica a lungo termine per affrontare queste problematiche, con riguardo alle principali strategie da attuare quali la cattura e stoccaggio del carbonio (CCS) e i vari metodi fotochimici, biochimici e foto ed elettrocatalitici. I capitoli 2 e 3 riguardano le basi teoriche dei metodi di riduzione foto ed elettrochimici della CO2, e comprendono lo stato dell'arte dei principali elettrodi foto- ed elettro-catalitici utilizzati fino ad ora e gli aspetti ingegneristici della progettazione del reattore. In particolare vengono discussi i dispositivi fotoelettrochimici e fotovoltaici più promettenti, con particolare attenzione alle strategie avanzate riguardanti l'accoppiamento di questi sistemi con diverse configurazioni e utilizzando diversi materiali avanzati, per ottenere prestazioni catalitiche più elevate. I capitoli 4 e 5 illustrano i risultati sperimentali ottenuti con gli approcci foto- ed elettrocatalitici di riduzione della CO2. Viene presentato lo stato dell’arte per questi due diversi approcci, insieme allo scopo specifico di ogni capitolo, evidenziandone in particolare le differenze ma anche i molti punti comuni in termini di meccanismo di reazione e cinetica. I catalizzatori utilizzati per l'indagine sperimentale sono materiali nanostrutturati a base di CuxO, preparati con diverse tecniche, come metodi di precipitazione, solvo-termali ed elettrodeposizione, che sono stati depositati su substrati metallici, ossidi metallici o a base di carbonio. In particolare, l'elettrodeposizione è un metodo molto versatile che permette una deposizione controllata diretta di Cu2O modulando alcuni parametri durante la sintesi, come il tempo di deposizione, il pH e il tipo di elettrolita. La maggior parte dello studio si è concentrata sul semiconduttore ossido rameoso (Cu2O), per le sue caratteristiche interessanti: si tratta di un materiale terrestre abbondante, non tossico, che possiede un band gap di circa 2.2 eV come materiale in bulk. Viene ampiamente utilizzato per sensibilizzatori di celle solari, sensori (vedi Capitolo 6) e nella fotocatalisi della CO2, in particolare per la formazione di CO e CH4. Il capitolo 4 di questo lavoro mostra che, grazie a un nuovo concetto di reattore foto (elettro) catalitico a flusso di gas, la selettività del processo può essere spostata verso prodotti a base di carbonio più interessanti, con la formazione di legami C-C. Questo nuovo dispositivo costruito nei nostri laboratori utilizza nanomembrane funzionalizzate con il rame, basate su una disposizione di nanotubi allineati di TiO2 (preparati mediante ossidazione anodica controllata) cresciuti su un substrato metallico microforato, che agiscono sia come collettore di elettroni sia come supporto meccanico per fornire la necessaria robustezza; questi poi sono stati funzionalizzati con CuxO mediante elettrodeposizione. Questo concetto è molto diverso dagli approcci fotocatalitici CO2 convenzionali. Per via delle caratteristiche e delle condizioni peculiari del nuovo fotoreattore (che lavora sotto un flusso di vapore saturato con CO2 gassosa che attraversa la nanomembrana fotocatalitica), è possibile evidenziare per la prima volta la conversione altamente selettiva della CO2 ad acidi carbossilici C1-C2 (formico, acetico e ossalico) senza formazione di H2, CO, CH4 o altri idrocarburi. L'ossido di rame introduce una via di reazione aggiuntiva alla formazione degli alcoli C1-C3 (metanolo, etanolo e isopropanolo) o ai prodotti derivati (formiato di metile). Le migliori prestazioni sono state ottenute quando le nanoparticelle di Cu2O (tipo p) sono depositate su nanotubi di TiO2 di tipo n, grazie alla creazione di una eterogiunzione di tipo p-n che migliora la raccolta della luce visibile, fornendo una resa quantica apparente (rapporto tra elettroni reagiti e fotoni assorbiti) con illuminazione solare del 21% circa. L'efficienza faradica su questo fotocatalizzatore è stata di circa il 42% a metanolo e il 44% ad acido acetico. Tra i campioni testati, in generale si osserva un'efficienza faradica fino al 47% a metanolo o fino al 73% ad acido acetico. La rilevanza di questi risultati sul meccanismo della fotoriduzione della CO2 è stata anche discussa nel Capitolo 4. Il capitolo 5 si concentra invece sulla riduzione elettrocatalitica della CO2. In questa parte del lavoro, CuxO è stato impiegato come ossido puro (a diversi stati di ossidazione, I e II) o drogato con altri elementi, come S e In (CuSx e Cu-In), per la progettazione di elettrodi compositi in grado di indirizzare la selettività del processo verso l'acido formico o il monossido di carbonio, rispettivamente, attraverso la modifica dell'energia di legame degli intermedi di reazione con i siti attivi catalitici. Nello specifico, le attività di ricerca hanno riguardato preliminarmente l'ottimizzazione delle condizioni operative in termini di configurazione del reattore, pH catodico, potenziale applicato all'elettrodo di lavoro (nel range indagato da -0.4 V a -1.0 V vs. RHE), flusso di ingresso della CO2 e tipo di membrana (cationica, anionica o bipolare). È stato definito un protocollo preciso per l'esecuzione di ogni test elettrochimico, che va dalla voltammetria ciclica e determinazione della capacità alle fasi di cronoamperometria, quest'ultima comprensiva della determinazione dei prodotti di riduzione della CO2. Il test con CuxO puro depositato su uno strato di gas-diffusion-layer (GDL) in presenza di un elettrolita liquido (soluzione acquosa KHCO3 0,1 M) ha mostrato che i) il carico ottimale del catalizzatore su GDL era 10 mg cm-2; ii) la migliore produttività ed efficienza faradica (FE) per acido formico e monossido di carbonio è stata ottenuta a -0,6 V vs. RHE (12.8 µmol h-1 e 5.5%, rispettivamente); il campione CuO/GDL si è comportato meglio di Cu2O/GDL, con un aumento delle prestazioni catalitiche (FE=12.6%). I comportamenti elettrochimici di entrambi gli elettrocatalizzatori sono stati studiati anche attraverso la spettroscopia di impedenza elettrochimica (EIS), evidenziando una resistenza al trasferimento di carica inferiore per CuO/GDL (6.5 Ω) rispetto a Cu2O/GDL (39.5 Ω). L'attività elettrocatalitica è aumentata notevolmente quando venivano usati elettrodi avanzati come CuSx e Cu-In, fornendo rispettivamente una FE ad acido formico del 58.5% e una FE% al monossido di carbonio del 55.6%. Diverse configurazioni delle celle sono state studiate utilizzando questi catalizzatori, a seconda dei percorsi del flusso di gas all'interno della cella nei tre diversi compartimenti (una camera gassosa, un compartimento liquido per il catolita ed un compartimento liquido per l'anolita). La migliore configurazione in termini di elevata FE e bassa formazione di H2 (mediante riduzione protonica come reazione collaterale) si è ottenuta separando l’evoluzione dei prodotti gassosi da quelli liquidi, ovvero raccogliendo i prodotti gassosi direttamente dall'uscita della camera gassosa, superando così le problematiche legate alla bassa solubilità della CO2 in acqua. Sono stati valutati anche i comportamenti di molte membrane selettive commerciali, cationiche (protoniche), anioniche e bipolari, anche rinforzate con teflon. I risultati hanno mostrato che la membrana protonica rinforzata con Teflon Nafion N324 e la membrana bipolare Fumasep FBM-PK hanno fornito la migliore attività; tuttavia, il Nafion rinforzato ha permesso di minimizzare meglio l'osmosi dell'elettrolita e il cross-over dei prodotti di riduzione, evitandone l'ossidazione sul lato anodico. Infine, il Capitolo 6 si concentra sulle strategie per la rilevazione del glucosio nei processi di biofermentazione e in particolare sui metodi amperometrici basati sull'utilizzo di sensori di glucosio non enzimatici. Il processo di biofermentazione più importante è la fermentazione alcolica, che consiste nella produzione di CO2 ed etanolo a partire da diversi substrati zuccherini come glucosio, saccarosio e fruttosio. Le applicazioni industriali oggi mirano a diminuire la dipendenza del petrolio greggio producendo bioetanolo, che viene miscelato con la benzina. In questo contesto, sono stati sviluppati dei sensori a base di Cu2O a forma di nanocubi, con particelle di dimensioni diverse, depositato su supporti commerciali di tipo “screen-printed carbon electrode” (SPCE). Le prestazioni di questi SPCE modificati con Cu sono state valutate in termini di selettività e sensibilità del glucosio mediante analisi di voltammetria ciclica e cronoamperometria e misure di impedenza. Gli elettrodi sviluppati hanno mostrato una buona sensibilità (1040µA/mM cm-2) e selettività nei confronti del rilevamento del glucosio con una risposta ad alto range lineare, senza interferenze da parte di altri substrati, suggerendo che i SPCE modificati con Cu2O potrebbe essere un modo semplice per fabbricare sensori economici e affidabili per monitorare il glucosio nei processi di biofermentazione.
The process of carbon dioxide (CO2) reduction has attracted a great attention in the scientific community in the last years. The development of materials and systems capable to convert H2O and CO2 into valuable products by using renewable and clean energy represents an attractive challenge for the next future. In this context, the aim of the present PhD work is to explore different routes by photo- and electrocatalytic approaches to convert CO2 into value-added chemicals and fuels. The research activity concerned both the synthesis of the catalytic materials used for the preparation/assembling of the electrodes and the design and engineering of the electrochemical devices. Most of the activities were carried out at the laboratory CASPE/INSTM (Laboratory of Catalysis for Sustainable Production and Energy) of the University of Messina. Moreover, during the second year, one month was spent at the Institut Català d'Investigació Química (ICIQ Tarragona, Spain) and two months at the Institute for Chemical and Bioengineering (ETH Zürich, Switzerland) in the framework of H2020 A-LEAF Project and Research and Mobility ARCADIA Project. The thesis is organized in six chapters, plus the conclusions. Chapter 1 focuses on CO2 environmental issues, general implications and consequent opinions and strategies adopted by the scientific community in a long-term period to address these problems, with regard to the main common carbon capture and storage (CCS) strategies and photochemical, biochemical, photo- and electrocatalytic routes. Chapters 2 and 3 concern the theoretical basis on photo- and electro-chemical CO2 reduction routes, including the state-of-the-art of the main photo- and electro-catalytic electrodes used so far and the engineering aspects of reactor design. In particular, the most promising photo-electro-chemical and photovoltaic devices are discussed, with emphasis on the advanced strategies concerning the coupling of these systems with different configurations and using different advanced materials, to achieve higher catalytic performances. Chapters 4 and 5 refer to the experimental results obtained by photo- and electro-catalytic approaches. The states of the art for these two different approaches are presented, together with the specific scope of each chapter, especially highlighting their differences but also the many common points in terms of reaction mechanism and kinetics. The catalysts used for the experimental investigation were nanostructured CuxO-based materials, prepared by different techniques, such as precipitation, solvothermal and electrodeposition methods, and then deposited on metallic, metal oxides or carbon-based substrates. Particularly, electrodeposition was a very versatile method allowing a direct controlled deposition of Cu2O by modulating some parameters during the synthesis, such as time deposition, pH and type of electrolyte. Most of the study was focused on cuprous oxide (Cu2O) semiconductor, for its interesting characteristics: it is an earth abundant material, non-toxic, showing a band gap of around 2.2 eV as bulk material. It has been widely used for solar cell sensitizers, sensors (see Chapter 6) and in CO2 photocatalysis, especially for the formation of CO and CH4. Chapter 4 of this work shows that, due to a novel concept of gas flow-through photo(electro)catalytic reactor, the process selectivity can be shifted to more interesting carbon products, involving the formation of C-C bonds. This novel homemade device uses copper-functionalized nanomembranes, based on aligned TiO2 nanotube arrays (prepared by controlled anodic oxidation) grown over a microperforated metallic substrate, acting as an electron collector and to provide the necessary robustness, which are then functionalized with CuxO by electrodeposition. This concept is quite different from the conventional CO2 photocatalytic approaches. Due to the peculiar characteristics and conditions in the novel photoreactor (working under a cross-flow of gaseous CO2 saturated with water crossing through the photocatalytic nanomembrane), it is possible to evidence for the first time the highly selective CO2 conversion to C1-C2 carboxylic acids (formic, acetic and oxalic acids) without formation of H2, CO, CH4 or other hydrocarbons. Copper-oxide introduces an additional reaction pathway to C1-C3 alcohols (methanol, ethanol and isopropanol) or derived products (methyl formate). The best performances were obtained when Cu2O nanoparticles (p-type) are deposited over n-type TiO2 nanotubes, due to the creation of a p-n type heterojunction that improves visible light harvesting, giving an apparent quantum yield (ratio between electrons reacted and photons absorbed) with solar illumination of about 21 %. The Faradaic Efficiency on this photocatalyst was about 42 % to methanol and 44 % to acetic acid. Among the tested samples, Faradaic Efficiency up to 47 % to methanol or up to 73 % to acetic acid are observed. The relevance of these results on the mechanism of CO2 photoreduction was also discussed along Chapter 4. Chapter 5 focuses instead on the electrocatalytic reduction of CO2. In this part of the work, Cu2O was employed as pure oxide (at different oxidation states, I and II) or doped with other elements, such as S and In (CuSx and Cu-In), for the design of composite electrodes able to address the process selectivity towards formic acid or carbon monoxide, respectively, through the modification of binding energy of the reaction intermediates with the catalytic active sites. Specifically, the research activities concerned preliminarily the optimization of the operating conditions in terms of reactor configuration, cathodic pH, applied potential at the working electrode (in the investigated range from -0.4 V to -1.0 V vs. RHE), CO2 inlet flow and type of membrane (i.e. cationic, anionic or bipolar). A precise protocol was defined for carrying out each electrochemical test, ranging from cyclic voltammetry and capacitance determination to chronoamperometry steps, the latter including the determination of CO2 reduction products. Testing with pure CuxO deposited on a carbon gas diffusion layer (GDL) in presence of a liquid electrolyte (0.1 M KHCO3 aqueous solution) showed that i) the optimal catalyst loading on GDL was 10 mg cm-2; ii) the best productivity and Faradaic efficiency (FE) to formic acid and carbon monoxide was obtained at -0.6 V vs. RHE (12.8 mol h-1 and 5.5%, respectively); CuO/GDL behaved better than Cu2O/GDL, with an increase of catalytic performance (i.e. FE = 12.6 %). The electrochemical behaviours of both the electrocatalysts were also investigated by Electrochemical Impedance Spectroscopy (EIS), evidencing a lower charge transfer resistance for CuO/GDL (6.5 Ω) with respect to Cu2O/GDL (39.5 Ω). The electrocatalytic activity strongly increased when advanced electrodes like CuSx and Cu-In were used, providing a FE to formic acid of 58.5% and a FE % to carbon monoxide of 55.6%, respectively. Different cell configurations were investigated by using these catalysts, depending on the pathways of gas flow within the cell in three different compartments (a gas chamber, a liquid catholyte compartment, a liquid anolyte compartment). The best configuration in terms of maximum FE and minimization of H2 formation (by proton reduction as side reaction) referred to the separation of gas and liquid products, collecting the gas products directly from the outlet of the gas chamber, thus overcoming issues related to the low solubility of CO2 in aqueous solution. The behaviours of many commercial selective membranes were also evaluated, i.e. cationic (protonic), anionic and bipolar, also reinforced with Teflon. Results showed that Teflon reinforced protonic (Nafion N324) and bipolar (Fumasep FBM-PK) membranes provided the best activity; however, the reinforced Nafion allowed better to minimize osmosis of electrolyte and cross-over of the reduction products, avoiding their oxidation at the anode side. Finally, Chapter 6 focuses on strategies for the glucose detection in biofermentation processes and particularly on the amperometric methods based on the use of non-enzymatic glucose sensors. The most important biofermentation process is the alcoholic fermentation, which consists in the production of CO2 and ethanol starting from several sugar substrates like glucose, sucrose and fructose. Industrial applications today are aimed to decrease the dependence of crude oil producing bioethanol, which is blended with the gasoline. In this context, Cu2O nanocubes deposited on commercial screen printed carbon electrodes (SPCEs) with different particles size were developed as sensors. The performances of these Cu-modified SPCEs were evaluated in terms of glucose selectivity and sensitivity by cyclic voltammetry and chronoamperometry analysis and impedance resistance measurements. The developed electrodes showed a good sensitivity (1040µA/mM cm-2) and selectivity towards the glucose detection with a high linear range response, without interference by other substrates, suggesting that the SPCE modification with Cu2O could be a simple way to fabricate inexpensive and reliable sensors to monitor glucose in bio-fermentation processes.

碩士
國立臺灣大學
材料科學與工程學研究所
103
This study used Cu-based materials as an anode of solid oxide fuel cells (SOFCs) and conducted the following R&D works. Properties of Cu and Cu-Zn alloy were investigated, including electrical conductivity, coefficient of thermal expansion (CTE), hardness and oxidation behavior. The oxidation-resistance of Cu, Ni and Ti-6Al-4V was investigated and compared. Moreover, the microstructure of the oxide layers was observed to verify the results of TGA test. This study also developed cobalt-doped SDC cermet as an electrolyte for intermediate temperature (IT)-SOFC. The Cu-based electrode provided good electronic conductivity and prevented carbon deposition. The SDC was used as catalyst and ionic conductor. The methods to synthesize SDC and sinter a dense SDC electrolyte were also provided in this study. Maximum power density of the Cu-based SOFC was 112 mW cm-2 at 750 oC. On the other hand, due to a low melting point and good formability of Cu-Zn alloy, it was suitably applied on 3D printing (3DP) technique. As a result, a melt-extrusion (ME) module was designed to print Cu-Zn alloy. The ME module could reach 1100 oC to extrude Cu-Zn alloy. Besides, the heat insulation of the module was excellent, which was 51 oC outside the module while the temperature in the nozzle was 1000 oC.

碩士
國立清華大學
先進光源科技學位學程
102
In this study, we investigated the depth-dependent compositions and band structure of Cu(In,Ga)(Se,S)2-based solar cell device. In order to measure the elemental composition distribution and the band structure of the multiple-layered films, we polished the CIGSSe-based solar cell with a gradient along the normal direction of the sample to observe the variations of elemental distributions, chemical bonds and electronic band structure by means of X-ray photoemission spectroscopy (XPS). The structural characteristic at the interfaces of layers were also investigated by using X-ray absorption spectroscopy (XAS). According to the observation of the band offset at the interface between CdS and CIGSSe layers, we can deduce that the conduction band corresponds to the cliff type (Ec= -0.47 eV). Therefore, this type of band structure is possibly increased the recombination probability at the interface and lead to a limitation in the open circuit voltage. The fitting results of B 1s photoelectron spectra reveals that in the bottom of ZnO layer, the concentration of the dopant boron becomes increased with respect to the boron oxide. Because the carrier concentration is increased in the region of ZnO layer near CdS, it would be beneficial to improve the carrier transport. Copper depletion was observed in the whole region of CIGSSe layer, which plays a role of acceptor due to copper vacancies and facilitates the formation of p-type semiconductor. The concentration ratio of In/Ga is decreased from the top to the bottom of the CIGSSe layer. The optimal band-gap distribution could be achieved by controlling the In/Ga ratios. We also found that the Mo(S,Se)2 layer was formed at the interface of CIGSSe and Mo layers, providing an ohmic contact and increasing the open circuit voltage to improve the device performance of the CIGSSe solar cell.

碩士
大同大學
光電工程研究所
102
High-efficiency Cu(In,Ga)(Se,S)2 (CIGSSe) thin-flim solar cells have many advantages, including 1. low cost and flexibility, 2. its higher stability under long-term exposure, 3. higher optoelectric efficiency compared with the other thin-film solar cells, 4. wide absorption spectrum. In this research, we present the depth profile of element composition and electronic structure of ZnO/CdS/CIGSSe/Mo/soda-lime glass using scanning photoelectron microscopy (SPEM).SPEM enables us to directly “observe” the depth-dependent composition of the thickness-gradient ZnO/CdS/CIGSSe/Mo/soda-lime glass due to its high spatial resolution (~200 nm) in photoelectron emission. In the results, we found that the upper region of ZnO layer exhibits the upward shift of valence band maximum, which can be attributed to the lower concentration of B-doped ZnO. The band structure of CdS/CIGSSe reveals a spike type. It is also found that the concentration ratios of Ga/In and Se/S are higher at the bottom of CIGSSe layer, leading to a larger band gap and a higher conduction-band minimum near the CIGSSe/Mo interface. In addition, the oxidization effects on the surface of CIGSSe layer under atmosphere exposure are also studied. The experimental results reveal that the oxidized species of Se and Ga at the surface of CIGSSe layer will be formed after several-hour air exposure. We can realize the surface contamination of CIGSSe absorber layer in the manufacturing process and try to provide a critical method for improving the efficiency of solar cell.