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Lau, Yin Ping. "Si/CdTe heterojunction fabricated by closed hot wall system." HKBU Institutional Repository, 1995. http://repository.hkbu.edu.hk/etd_ra/44.
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Martin, de Nicolas Silvia. "a-Si : H/c-Si heterojunction solar cells : back side assessment and improvement." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112253/document.
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Parmi les technologies photovoltaïques à base de silicium, les cellules solaires à hétérojonction a-Si:H/c-Si (HJ) ont montré une attention croissante en ce qui concerne leur fort potentiel d’amélioration du rendement et de la réduction de coûts. Dans cette thèse, des investigations sur les cellules solaires à hétérojonction a-Si:H/c-Si de type (n) développées à l'Institut National de l'Énergie Solaire sont présentées. Les aspects technologiques et physiques du dispositif à HJ ont été revus, en mettant l'accent sur la compréhension du rôle joué par la face arrière. À travers le développement et la mise en œuvre des films de a-Si:H intrinsèques et dopés (n) de haute qualité des cellules solaires à HJ, les conditions requises en face arrière des dispositifs ont été établies. Une comparaison entre plusieurs types de champ surface arrière, avec et sans l’introduction d’une couche buffer, est présentée et les caractéristiques des cellules solaires résultants sont discutées. Une discussion autour du contact arrière de cellules solaires à HJ est aussi présentée. Une nouvelle approche d’oxyde transparent conducteur en face arrière basé sur les couches d’oxyde de zinc dopé au bore (ZnO:B) est étudié. Dans le but de développer des couches de ZnO:B de haute qualité bien adaptées à leur utilisation dans des dispositifs à HJ, différents paramètres de dépôt ainsi que des traitements après dépôt comme le post plasma d’hydrogène ou le recuit laser sont étudiés et leur influence sur des cellules solaires est évaluée. Au cours de ce travail il est montré que la face arrière des cellules solaires à HJ joue un rôle important sur l’accomplissement de hauts rendements. Cependant, l'augmentation de la performance globale du dispositif dû à l’optimisation de la face arrière de la cellule est toujours dépendante des phénomènes ayant lieu en face avant des dispositifs. L'utilisation des films optimisés pour la face arrière des HJs développées dans cette thèse, associée à des couches améliorées pour la face avant et une nouvelle approche de métallisation nous a permis d’atteindre un rendement de conversion record de plus de 22%, démontrant ainsi le grand potentiel de cette technologie à HJ de a-Si:H/c-SiAmongst available silicon-based photovoltaic technologies, a-Si:H/c-Si heterojunctions (HJ) have raised growing attention because of their potential for further efficiency improvement and cost reduction. In this thesis, research on n-type a-Si:H/c-Si heterojunction solar cells developed at the Institute National de l’Énergie Solaire is presented. Technological and physical aspects of HJ devices are reviewed, with the focus on the comprehension of the back side role. Then, an extensive work to optimise amorphous layers used at the rear side of our devices as well as back contact films is addressed. Through the development and implementation of high-quality intrinsic and n-doped a-Si:H films on HJ solar cells, the needed requirements at the back side of devices are established. A comparison between different back surface fields (BSF) with and without the inclusion of a buffer layer is presented and resulting solar cell output characteristics are discussed. A discussion on the back contact of HJ solar cells is also presented. A new back TCO approach based on boron-doped zinc oxide (ZnO:B) layers is studied. With the aim of developing high-quality ZnO:B layers well-adapted to their use in HJ devices, different deposition parameters as well as post-deposition treatments such as post-hydrogen plasma or excimer laser annealing are studied, and their influence on solar cells is assessed. Throughout this work it is evidenced that the back side of HJ solar cells plays an important role on the achievement of high efficiencies. However, the enhancement of the overall device performance due to the back side optimisation is always dependent on phenomena taking place at the front side of devices. The use of the optimised back side layers developed in this thesis, together with improved front side layers and a novel metallisation approach have permitted a record conversion efficiency over 22%, thus demonstrating the great potential of this technology
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Meitzner, Karl. "Heterojunction-Assisted Impact Ionization and Other Free Carrier Dynamics in Si, ZnS/Si, and ZnSe/Si." Thesis, University of Oregon, 2015. http://hdl.handle.net/1794/19294.
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With increasing global energy demand and diminishing fossil fuel supplies, the development of clean and affordable renewable energy technology is more important than ever. Photovoltaic devices harvest the sun’s energy to produce electricity and produce very little pollution compared to nonrenewable sources. In order to make these devices affordable, however, technological advances are required.
In this dissertation a novel photovoltaic device architecture that is designed to enhance sunlight-to-electricity conversion efficiency of photovoltaics is proposed and demonstrated. The increase in efficiency arises due to enhancement of the internal quantum efficiency of photoexcitation in the semiconductor absorber. In other words, the probability that the absorption of a single photon will produce two or more electron-hole pairs, instead of just one, is increased. This occurs through the process of impact ionization, by which a highly excited charge carrier (via absorption of a high energy photon) relaxes by excitation of a second electron-hole pair. The result is an increased photocurrent, and efficiency, of the photovoltaic device.
Using thin films of ZnS on Si substrates, we demonstrate that the probability of impact ionization is enhanced at the (unbiased) heterojunction between these layers. The magnitude of enhancement depends on material properties, including crystallinity of the ZnS film as well as concentration of oxygen (impurity) at the interface. Thin films of ZnSe on Si substrates do not exhibit heterojunction-assisted impact ionization, but they do display promising characteristics that make them an intriguing system for future work. The same is true for ZnS/Si materials fabricated by O2-free chemical bath deposition.
For the analysis of plain Si as well as ZnS/Si and ZnSe/Si heterostructures, we employ a novel pump-probe transient transmission and reflection spectroscopy technique. A method is demonstrated for using this technique to quantify internal quantum efficiency as well as interface recombination velocity in each of these materials. In bulk silicon, a free carrier absorption cross section that depends on free carrier concentration (above 1018 cm-3) is observed and the relationship is quantified.
This dissertation includes unpublished and previously published co-authored material.
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Gogolin, Ralf [Verfasser]. "Analysis and optimization of a-Si:H/c-Si heterojunction solar cells / Ralf Gogolin." Hannover : Technische Informationsbibliothek (TIB), 2016. http://d-nb.info/1099098130/34.
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Pehlivan, Ozlem. "Growth And Morphological Characterization Of Intrinsic Hydrogenated Amorphous Silicon Thin Film For A-si:h/c-si Heterojunction Solar Cells." Phd thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615488/index.pdf.
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Passivation of the crystalline silicon (c-Si) wafer surface and decreasing the number of interface defects are basic requirements for development of high efficiency a-Si:H/c-Si heterojunction solar cells. Surface passivation is generally achieved by development of detailed silicon wafer cleaning processes and the optimization of PECVD parameters for the deposition of intrinsic hydrogenated amorphous silicon layer.
a-Si:H layers are grown in UHV-PECVD system. Solar cells were deposited on the p type Cz-silicon substrates in the structure of Al front contact/a-Si:H(n)/a-Si:H(i)/c-Si(p)/Al back contact. Solar cell parameters were determined under standard test conditions namely, using 1000 W/m2, AM 1.5G illumination at 25 oC.
Growth of (i) a-Si:H, films on the clean wafer surface was investigated as a function of substrate temperature, RF power density, gas flow rate, hydrogen dilution ratio and deposition time and was characterized using SEM, HRTEM, AFM, SE, ATR-FTIR and I/V measurements.
Structural properties of the films deposited on silicon wafer surface are directly effective on the solar cell efficiency. Morphological characterization of the grown films on the crystalline surface was found to be very complex depending on the deposition parameters and may even change during the deposition time.
At 225 oC substrate temperature, at the beginning of the deposition, (i) a-Si:H films was found grown in epitaxial structure, followed by a simultaneous growth of crystalline and amorphous structure, and finally transforming to complete amorphous structure. Despite this complex structure, an efficiency of 9.2% for solar cells with total area of 72 cm2 was achieved. In this cell structure, TCO and back surface passivation do not exist.
In the
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Müller, Thomas. "Heterojunction solar cells (a-Si, c-Si) investigations on PECV deposited hydrogenated silicon alloys for use as high quality surface passivation and emitter, BSF." Berlin Logos-Verl, 2009. http://d-nb.info/997563184/04.
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Hussain, Babar. "Development of n-ZnO/p-Si single heterojunction solar cell with and without interfacial layer." Thesis, The University of North Carolina at Charlotte, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10258481.
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The conversion efficiency of conventional silicon (Si) photovoltaic cells has not been improved significantly during last two decades but their cost decreased dramatically during this time. However, the higher price-per-watt of solar cells is still the main bottleneck in their widespread use for power generation. Therefore, new materials need to be explored for the fabrication of solar cells potentially with lower cost and higher efficiency. The n-type zinc oxide (n-ZnO) and p-type Si (p-Si) based single heterojunction solar cell (SHJSC) is one of the several attempts to replace conventional Si single homojunction solar cell technology. There are three inadequacies in the literature related to n-ZnO/p-Si SHJSC: (1) a detailed theoretical analysis to evaluate potential of the solar cell structure, (2) inconsistencies in the reported value of open circuit voltage (VOC) of the solar cell, and (3) lower value of experimentally achieved VOC as compared to theoretical prediction based on band-bending between n-ZnO and p-Si. Furthermore, the scientific community lacks consensus on the optimum growth parameters of ZnO.
In this dissertation, I present simulation and experimental results related to n-ZnO/p-Si SHJSC to fill the gaps mentioned above. Modeling and simulation of the solar cell structure are performed using PC1D and AFORS-HET software taking practical constraints into account to explore the potential of the structure. Also, unnoticed benefits of ZnO in solar cells such as an additional antireflection (AR) effect and low temperature deposition are highlighted. The growth parameters of ZnO using metal organic chemical vapor deposition and sputtering are optimized. The structural, optical, and electrical characterization of ZnO thin films grown on sapphire and Si substrates is performed. Several n-ZnO/p-Si SHJSC devices are fabricated to confirm the repeatability of the VOC. Moreover, the AR effect of ZnO while working as an n-type layer is experimentally verified. The spatial analysis for thickness uniformity and optical quality of ZnO films is carried out. These properties turn out to play a fundamental role in device performance and so far have been overlooked by the research community. Three different materials are used as a quantum buffer layer at the interface of ZnO and Si to suppress the interface states and improve the VOC. The best measured value of VOC of 359 mV is achieved using amorphous-ZnO (a-ZnO) as the buffer layer at the interface. Finally, supplementary simulations are performed to optimize the valence-band and conduction-band offsets by engineering the bandgap and electron affinity of ZnO.
After we published our initial results related to the feasibility of n-ZnO/p-Si SHJSC [Sol. Energ. Mat. Sol. Cells 139 (2015) 95–100], different research groups have fabricated and reported the solar cell performance with the best efficiency of 7.1% demonstrated very recently by Pietruszka et al. [Sol. Energ. Mat. Sol. Cells 147 (2016) 164–170]. We conclude that major challenge in n-ZnO/p-Si SHJSC is to overcome Fermi-level pinning at the hetero-interface. A potential solution is to use the appropriate material as buffer layer which is confirmed by observing an improvement in VOC using a-ZnO at the interface as buffer layer. Once the interface quality is improved and the experimental value of VOC matched the theoretical prediction, the n-ZnO/p-Si SHJSC can potentially have significant contribution in solar cells industry.
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Jakkala, Pratheesh Kumar. "Fabrication of Si/InGaN Heterojunction Solar Cells by RF Sputtering Method: Improved Electrical and Optical Properties of Indium Gallium Nitride (InGaN) Thin Films." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1490714042486824.
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Labrune, Martin. "Silicon surface passivation and epitaxial growth on c-Si by low temperature plasma processes for high efficiency solar cells." Phd thesis, Ecole Polytechnique X, 2011. http://pastel.archives-ouvertes.fr/pastel-00611652.
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This thesis presents a work which has been devoted to the growth of silicon thin films on crystalline silicon for photovoltaic applications by means of RF PECVD. The primary goal of this work was to obtain an amorphous growth on any c-Si surface in order to provide an efficient passivation, as required in heterojunction solar cells. Indeed, we demonstrated that epitaxial or mixed phase growths, easy to obtain on (100) Si, would lead to poor surface passivation. We proved that growing a few nm thin a-Si1-xCx:H alloy film was an efficient, stable and reproducible way to hinder epitaxy while keeping an excellent surface passivation by the subsequent deposition of a-Si:H films. Process optimization mainly based on Spectroscopic Ellipsometry, Effective lifetime measurements (Sinton lifetime tester) and current-voltage characterization led us to demonstrate that it was possible to obtain a-Si:H/c-Si heterojunction solar cells with stable VOC of 710 mV and FF of 76 % on flat (n) c-Si wafers, with solar cells of 25 cm2 whose metallization was realized by screen-printing technology. This work has also demonstrated the viability of a completely dry process where the native oxide is removed by SiF4 plasma etching instead of the wet HF removal. Last but not least, the epitaxial growth of silicon thin films, undoped and n or p-type doped, on (100)-oriented surfaces has been studied by Spectroscopic Ellipsometry and Hall effect measurements. We have been able to fabricate homojunction solar cells with a p-type emitter as well as p-i-n structures with an undoped epitaxial absorber on a heavily-doped (p) c-Si wafers.
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Hertl, Vít. "Studium fotovoltaických nanostruktur mikroskopickými metodami." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-444405.
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V této diplomové práci je nejprve ve zkratce uvedena teorie fyziky solárních článků, kde jsou zmíněny klíčové procesy ovlivňující účinnost konverze slunečního záření na elektrickou energii. Dále je předložena rešerše o fotovoltaických nanostrukturách (nanodráty, nanokrystaly), jejichž implementací je možné účinnost solárních článků zvýšit. V přehledu experimentálních technik ke zkoumání fotovoltaických nanostruktur je důraz kladen zejména na korelativní měření pomocí SEM a AFM, vodivostního AFM, měření EBIC a mikroskopické měření elektroluminiscence. V experimentální části jsou předloženy výsledky měření struktur mikrokrystalického křemíku, vzorku hetero-přechodového Si solárního článku s kontakty na zadní straně (IBC-SHJ z projektu NextBase) a V-pitů vzorku InGaN/GaN kvantových jam. Měření elektroluminiscence bylo provedeno na vzorcích III-V polovodičů (InGaP, GaAs). Byly vypočítány jinak těžko dostupné charakteristiky III-V tandemových solárních článků pomocí elektroluminiscence a srovnání vlastností IBC-SHJ zjištěných pomocí mikroskopického měření elektroluminiscence a EBIC. Provedením experimentů bylo zjištěno, jakým způsobem se dělí proud vybuzený svazkem elektronů mezi hrot AFM a vzorek mikrokrystalického křemíku.
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Favre, Wilfried. "Silicium de type n pour cellules à hétérojonctions : caractérisations et modélisations." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00635222.
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Les cellules à hétérojonctions de silicium fabriquées par croissance de couches minces de silicium amorphe hydrogéné (a-Si :H) à basse température sur des substrats de silicium cristallin (c-Si) peuvent atteindre des rendements de conversion photovoltaïque élevés (η=23 % démontré). Les efforts de recherche ayant principalement été orientés vers le cristallin de type p jusqu'à présent en France, ce travail s'attache à l'étude du type n pour d'une part déterminer les performances auxquelles s'attendre avec cette nouvelle filière et d'autre part les améliorer. Pour cela, nous avons mis en œuvre des techniques de caractérisation des matériaux composant la structure et de l'interface (a-Si :H/c-Si) couplées à des outils de simulations numériques afin mieux comprendre les phénomènes de transport électronique. Nous nous sommes également intéressés aux cellules à hétérojonctions avec substrats de silicium multicristallin de type n, le silicium multicristallin étant le matériau le plus répandu actuellement dans la fabrication des cellules photovoltaïques.
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Yu, Fei. "Graphene-enhanced Polymer Bulk-heterojunction Solar Cells." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439310775.
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Shih, Jeanne-Louise. "Zinc oxide-silicon heterojunction solar cells by sputtering." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112583.
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Heterojunctions of n-ZnO/p-Si solar cells were fabricated by RF sputtering ZnO:Al onto boron-doped (100) silicon (Si) substrates. Zinc Oxide (ZnO) films were also deposited onto soda lime glass for electrical measurements. Sheet resistance measurements were performed with a four-point-probe on the glass samples. Values for samples evacuated for 14 hours prior to deposition increased from 7.9 to 10.17 and 11.5 O/□ for 40 W, 120 and 160 W in RF power respectively. In contrast, those evacuated for 2 hours started with a higher value of 22.5 O/□, and decreased down to 7.6 and 5.8 O/□. Vacuum annealing was performed for both the glass and the Si samples. Current-voltage measurements were performed on the ZnO/Si junctions in the dark and under illumination. Parameters such as open-circuit voltage, Voc; short-circuit current, Isc; fill factor, FF; and efficiency, eta were determined. A maximum efficiency of 0.25% among all samples was produced, with an I sc of 2.16 mA, Voc of 0.31V and a FF of 0.37. This was a sample fabricated at an RF power of 80 W. Efficiency was found to decline with vacuum annealing. Furthermore, interfacial state density calculated based on capacitance-voltage measurements showed an increase in the value with vacuum annealing. The results found suggest that the interface states may be due to an interdiffusion of atoms, possibly those of Zn into the Si surface. The Electron Beam Induced Current (EBIC) method was used to determine diffusion length to be at a value ∼40--80 mum and therefore a minority carrier lifetime calculated of 3 musec. It was also used to determine the surface recombination velocity (SRV) of the fractured surface of the Si bulk from the fabricated solar cells. An SRV of ∼500 cm/sec was determined from the fractured Si surface, at a point located at 30 and 20 mum away from the junction interface.
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Cheung, Kai-yin, and 張啓賢. "Metallopolyyne polymers based bulk heterojunction (BHJ) solar cells." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42841719.
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Cheung, Kai-yin. "Metallopolyyne polymers based bulk heterojunction (BHJ) solar cells." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42841719.
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Brenner, Thomas Johannes Konrad. "Device physics of bulk heterojunction polymer solar cells." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610312.
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Feteha, Mohamed Yousef Mohamed. "Heterojunction AlGaAs-GaAs solar cells for space applications." Thesis, University of Central Lancashire, 1995. http://clok.uclan.ac.uk/18836/.
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Two types of solar cell AlGaAs-GaAs structures which are heteroface and triple heterojunction are investigated in this study. A complete theoretical study including optimisation for the optical properties ( transmission and reflection) of the heteroface Alo.sGao.2As- GaAs space solar cell is presented. The grid shadow and window layer effects, angle of incidence and the effects of the layer design parameters for AR-coating and window layer on the optical properties are considered in the calculations. A new structure for space solar cell which consists of double heterojunction AlGaAsGaAs structure with GaAs/AlGaAs heterojunction back surface field (triple heterojunction(TIIJ))-to enhance the performance of the existed double heterojunction solar cell- is proposed. The analytical model for this TIU cell is presented as a function of all the cell's design parameters ( such as _layers doping, thicknesses, etc). The calculated results for this structure is compared with the experimental results for the previous double heterojunction structure. The effects of the design parameters of all layers including the AR-coating on the cell's output performance and the optimisation conditions are studied as well. The techniques of the light trapping and the photon recycling( which are gocxl for space solar cells) are applied for the THJ thin film AlGaAs-GaAs structure to improve further the efficiency . The change of the optimisation conditions due to the usage of these two techniques is also discussed.
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Muñoz, Cervantes Delfina. "Silicon heterojunction solar cells obtained by Hot-Wire CVD." Doctoral thesis, Universitat Politècnica de Catalunya, 2008. http://hdl.handle.net/10803/6354.
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El elevado coste de producción de los módulos de silicio cristalino (c-Si) dificulta el progreso de la industria fotovoltaica como una alternativa viable para la producción de energía limpia. Por esta razón, los fabricantes de células solares buscan diferentes alternativas para conseguir la deseada reducción de costes. Una opción es reducir el grosor de las obleas (<200 m) para obtener así más obleas por lingote. Sin embargo, al reducir el grosor del sustrato es indispensable reducir también la recombinación superficial ya que ésta es crítica para mantener altas eficiencias en los dispositivos. Aunque la superficie del c-Si puede pasivarse eficientemente mediante una oxidación térmica, las obleas delgadas tiendan a doblarse en estos procesos de alta temperatura (~1000°C). También el silicio multicristalino de bajo coste sufre una fuerte degradación del tiempo de vida en el volumen a alta temperatura. Por este motivo, han ganado un especial interés los métodos alternativos de pasivación a baja temperatura.En concreto, las células solares de heterounión en que se utilizan capas de silicio amorfo (a-Si:H) depositadas a baja temperatura sobre obleas de c-Si han ganado interés en la comunidad fotovoltaica debido a su alta eficiencia y rentabilidad. Sanyo ha conseguido eficiencias de más del 19% en módulos producidos industrialmente con la estructura denominada HIT. La novedad de este dispositivo es la introducción de una capa de silicio amorfo intrínseco muy delgada (5nm) entre el c-Si y la capa dopada para reducir la velocidad de recombinación en la interfaz y conseguir tensiones de circuito abierto mayores que 700mV. La mayoría de grupos, incluido Sanyo, usan el depósito químico en fase vapor asistido por plasma de radiofrecuencia (PECVD) para obtener el silicio amorfo. Recientemente, la técnica de depósito asistida por filamento caliente (HWCVD) ha demostrado un gran potencial para fabricar células de heterounión de alta eficiencia. En la técnica HWCVD, además de algunas ventajas tecnológicas, la ausencia de bombardeo iónico reduce el daño en la superficie del c-Si mejorando así las propiedades en la interfaz.
En este trabajo, hemos concentrado nuestro esfuerzo en la optimización de todos los pasos de fabricación para obtener células solares de heterounión obtenidas por HWCVD en un proceso completamente desarrollado a baja temperatura (200ºC). Primero, hemos optimizado el material obtenido por HWCVD variando los diferentes parámetros de depósito (presión, temperaturas de filamento y sustrato, flujos de hidrógeno y silano, nivel de dopaje) para obtener silicio amorfo y microcristalino de buena calidad. Se han conseguido buenas propiedades estructurales, eléctricas y ópticas tanto para material intrínseco como en capas dopadas.
Posteriormente, hemos optimizado el emisor de heterounión sobre sustratos tipo p de c-Si. En particular, se ha estudiado en profundidad la influencia de la capa intrínseca de a-Si:H así como de diferentes pretratamientos superficiales del c-Si. Se han realizado estudios de microestructura con Espectroscopía por Elipsometría Óptica, y medidas de pasivación mediante Fotoconductancia en Estado Cuasiestacionario. Estos estudios han permitido optimizar los precursores de células solares hasta obtener tensiones implícitas de circuito abierto por encima de 690mV. Luego se ha desarrollado el electrodo frontal atendiendo a los requerimientos ópticos y eléctricos. Se ha optimizado la capa antirreflectante (Oxido de Indio dopado con Estaño) en términos de resistividad (<4×10-4cm) y de reflectancia. Después se ha diseñado el peine metálico frontal intentando obtener un buen compromiso entre resistencia serie y factor de sombra. Finalmente, se han fabricado células solares completas con una eficiencia de conversión de hasta el 15.4% sobre obleas de silicio CZ tipo p. En estos dispositivos se ha utilizado un contacto posterior de aluminio recocido a alta temperatura (Al-BSF).
Por otra parte, hemos investigando la posibilidad de sustituir los contactos posteriores de Al-BSF por contactos depositados a baja temperatura basados en capas de silicio amorfo dopadas con boro obtenidas por HWCVD. Hemos estudiado la influencia de los diferentes parámetros de depósito así como el efecto de intercalar una capa intrínseca delgada. Hasta el momento, las células solares con doble heterounión fabricadas completamente por HWCVD han alcanzado una eficiencia de conversión del 14.5% en un proceso completo a baja temperatura (<200º C). Considerando el carácter preliminar de estos dispositivos, éste es un punto de partida realmente prometedor para células solares de heterounión bifaciales fabricadas por HWCVD.
The cost of high efficiency crystalline silicon (c-Si) modules is hindering the progress of the PV industry as a viable alternative for clean energy production. Therefore, cell manufacturers are searching different approaches that could allow the desired cost reduction. For instance, considering that c-Si wafers represent about 30-50% of the module price, the final cost would be significantly reduced by using very thin c-Si wafers (< 200 μm). However, when decreasing the c-Si thickness the rear surface recombination becomes important. Although thermal oxidation very effectively passivates the c-Si surface, thin wafers tend to warp at the high temperatures (~1000 °C) involved in the process. On the other hand, low cost multicrystalline silicon wafers are not compatible with high temperature steps due to strong lifetime degradation. Therefore, low temperature surface passivation schemes have gained special interest due to their compatibility with both thin and low quality c-Si substrates.
Heterojunction solar cells with thin hydrogenated amorphous silicon (a-Si:H) films deposited at low temperature on c-Si wafers have attracted the interest of the photovoltaic community due to their high-efficiency and cost-effective fabrication process. Sanyo Electric Co. has reported conversion efficiencies (η) over 19% for mass produced solar cells with the so-called Heterojunction with Intrinsic Thin-layer (HIT) structure. In this device a very thin (5 nm) intrinsic a-Si:H buffer reduces interface recombination, which leads to impressing open-circuit voltages (Voc) over 700 mV. Most groups, included Sanyo, use the Plasma-Enhanced CVD technique to grow the a-Si:H films. Recently, the Hot-Wire CVD (HWCVD) technique has also demonstrated its potential to fabricate high-efficiency heterojunction silicon solar cells. In the HWCVD technique, besides some technological advantages, the absence of ion bombardment reduces the damage to the c-Si surface.
In this work, we have concentrated our effort in optimizing all the fabrication steps to obtain heterojuction solar cells by HWCVD in a completely low temperature process (200ºC). First, we have optimized the material deposited by HWCVD varying the different deposition parametres (pressure, filament temperature, Hydrogen and Silane flows, doping level, substrate temperature) in order to obtain good quality a-Si:H and c-Si:H layers. Intrinsic and doped materials with good structural, electrical and transport properties have been obtained. Second, we have concentrated our effort in optimizing the heterojunction emitter on p-type c-Si substrates. In particular, the importance of the thin intrinsic a-Si:H buffer and the influence of hydrogen pre-treatments was deeply studied by means of the Spectroscopic Ellipsometry and Quasy-Steady-State Photoconductance techniques. These studies have allowed to obtain solar cell precursors with implicit open circuit voltages higher than 690 mV. Later on, the optimization of the front contact was performed. On the one hand, the indium-tin-oxide transparent conductive coating was optimized to obtain a very low resistivity (<4×10-4 ·cm) and good antireflection properties. Furthermore, the front metal grid was also optimized in terms of the series resistance and shadowing. Last, complete solar cells with conversion efficiency up to 15.4% have been fabricated on flat p-type (14 Ω·cm) CZ silicon wafers with a high temperature aluminum back-surface-field (Al-BSF) contact.
Finally, we have proceeded to investigate low temperature deposited back contacts based on boron-doped amorphous silicon films obtained by Hot-Wire CVD to replace traditional high temperature Al-BSF contacts. The influence of the deposition parameters and the use of an intrinsic buffer layer have been considered. To date, double-side heterojunction solar cells by HWCVD with conversion efficiencies of 14.5% have been already obtained in a fully low temperature process (<200ºC). Considering the preliminary character of these devices, this is a very promising starting point for a further increase in the conversion efficiency of bifacial Heterojunction Solar cells fabricated by HWCVD.
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Painter, J. D. "Recrystallisation and interdiffusion in CdTe-CdS heterojunction solar cells." Thesis, Cranfield University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508015.
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Abrusci, Agnese. "Bulk heterojunction solar cells based on a polyfluorene copolymer." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611593.
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Ooi, Zi En. "On the Corrected Photocurrent ofOrganic Bulk Heterojunction Solar Cells." Thesis, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490944.
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The measured photocurrent ofa solar cell may be considered the sum ofa photo-generated current due solely to the influx of photons, and a photovoltage-induced current that is injected at the electrodes. Correcting the measured photocurrent for the dark current yields the voltage dependence of the photogenerated current alone. This corrected photocurrent can provide important insight into the processes governing the behaviour of a solar cell, yet is seldom measured or discussed within the community. In this dissertation, an original experimental technique designed specifically for the reliable measurement of the corrected photocurrent is described, with the intent of applying it to the study of solar cells based on thin films ofblended donor and acceptor molecular semiconductor pairs otherwise known as organic bulk-heterojunction solar cells. Solar cells based on a number of donor-acceptor combinations were investigated. Using the experimental technique developed here, corrected photocurrent-voltage responses exhibiting remarkably anti-symmetric profiles were obtained and subsequently rationalised with a simple physical model presented in this thesis. From the perspective of this model, the nature of charge extraction at the electrodes - and how this was affected by thermally annealing the device - was examined. Finally, a new low band gap, small-molecule acceptor material was used in bulkheterojunction solar cells, which showed promising photovoltaic performance. However, these devices exhibited anomalous behaviour that was observed in their current-voltage characteristics, which on closer examination, could be explained by electric field dependence in the photogeneration rate. Throughout this work, particular attention was given to the impact of these findings on how device efficiencies may be improved.
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Chang, Shang-wen. "Cu₂S/ZnCdS thin film heterojunction solar cell studies." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54740.
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Cu₂S/CdS solar cells have been studied extensively for the past two decades due to their potentially high efficiencies per unit cost. The operation and characteristics of Cu₂S/CdS solar cells are fairly well understood. However, the properties of the newer Cu₂S/ZnCdS cell type are not well understood.
The main goals of this thesis were to compare Cu₂S/CdS and Cu₂S/ZnCdS cells using Cu₂S/CdS cells as a reference, and to understand the operation and properties of Cu₂S/ZnCdS cells in order to improve cell performance. Four different measurements were used in this research to achieve these goals. They were; electrical, spectral, capacitance and deep trap measurements.
I-V measurements give important electrical parameters of the cells; cell efficiency, fill factor, short circuit current, open circuit voltage, shunt resistance and series resistance are reported. From a In(ISC) versus VOC measurement, the diode factor, A, was found to be about 1 for Cu₂S/CdS, Cu₂S/Zn0.11Cd0.89S, and about 1.2 for Cu₂S/Zn0.25Cd0.75S cells. The relation between In(Joo) (current density) and ϕ (potential barrier height) is linear for both types of cells. The slope of this linear relationship increases as the content of Zn increases in ZnxCd1-xS. Under air mass 1 (100 mW/cm²) illumination, it was found that VOC decays and capacitance increases for Cu₂S/ZnCdS cells. This is attributed to electron relaxation from deep traps near the junction.
Spectral response with and without bias light were measured for both Cu₂S/CdS and Cu₂S/ZnCdS cells. White and blue bias light enhance the spectral response, while red bias light quenches the response. This is attributed to ionization and filling of deep traps near the junction.
Capacitance measurements on both cell types show that 1/C² versus voltage is quite flat, which indicates the existence of an i-layer (insulation layer) in the CdS or ZnCdS near the junction.
Three methods–photocapacitance, space-charge-limited current, and thermally stimulated. current techniques–were used for deep trap measurements. Photocapacitance measurements indicate one deep donor energy and two deep acceptor energy levels. These trap energies become larger as the content of Zn in ZnCdS increases. Space-charge-limited current measurements give a trap density of the order of 10¹⁶ cm³ for both cell types. The shallow energy trap is found to be 0.26 eV below the conduction band edge of CdS. The occurrence of a current-saturated region for Cu₂S/ZnCdS is attributed to the filling of the interface traps near the junction. Thermally stimulated current measurements give two energy levels below the conduction band of CdS; 0.05 eV and 0.26 eV.
From the above results, several differences between the Cu₂S/CdS and the Cu₂S/ZnCdS cells can be seen. The Cu₂S/ZnCdS cells show stronger red quenching, smaller electron lifetime at the interface near the junction, and deeper traps than the Cu₂S/CdS cells. These differences can account for the decline of ISC and the VOC decay. The smaller ISC for the Cu₂S/ZnCdS cells can also possibly result from smaller electron lifetime at the interface, larger interface recombination velocity, different deep trap levels, and enhanced Zn concentration near the junction. The VOC decay for the Cu₂S/ZnCdS cells is mostly due to long decay of charge. Longer decay could be attributed to deeper traps.Ph. D.
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Al-Dmour, Hmoud. "Solar cells based on the nc-TiOâ‚‚ semiconducting polymer heterojunction." Thesis, Bangor University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445094.
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Gutta, Venkatesh. "INVESTIGATIONS OF CuInTe2 / CdS & CdTe / CdS HETEROJUNCTION SOLAR CELLS." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_theses/654.
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Thin film solar cells of Copper Indium Telluride and Cadmium Sulfide junctions were fabricated on plain ITO glass slides and also on those coated with intrinsic Tin Oxide. CdS was deposited through chemical bath deposition and CIT by electrodeposition. Both compounds were subjected to annealing at temperatures between 350°C and 500°C which produced more uniform film thicknesses and larger grain sizes. The CIT/ CdS junction was characterized after performing XRD and spectral absorption of individual compounds.
Studies were also made on CdS / CdTe solar cells with respect to effect of annealing temperatures on open circuit voltages. NP acid etch, the most important process to make the surface of CdTe tellurium rich, was also studied in terms of open circuit voltages. Thermally evaporated CdS of four different thicknesses was deposited on Tin Oxide coated ITO and inferences were drawn as to what thickness of CdS yields better results.
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Xu, Dong. "Fabrication and optimization of novel structure silicon heterojunction solar cells." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 70 p, 2009. http://proquest.umi.com/pqdweb?did=1654493831&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Han, Tianyan. "Bulk heterojunction solar cells based on solution-processed triazatruxene derivatives." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAD036/document.
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La conception de cellules solaires organiques de type hétérojonction en volume a été proposée pour la première fois en 1990. Ces dispositifs sont composés d’un mélange de polymères conjugués, donneurs d’électrons, et de fullerènes, accepteur d’électrons, et ont pour la première fois permis d’atteindre un rendement de conversion énergétique significatif (de l’ordre de 2%) avec des semi-conducteurs organiques. Dans ce contexte, cette thèse a porté sur l'étude approfondie d’une série de molécules donneurs d’électrons de forme d’haltère, dont le groupement planaire est l’unité triazatruxène (TAT) et le cœur déficient en électrons le thienopyrroledione (TPD). Les molécules de cette série se différencient par la nature des chaînes alkyles, attachées à l’unité centrale et aux unités TAT. Plus précisément, la relation entre la nature des chaînes latérales et les propriétés moléculaires et thermiques de ces molécules en forme d’haltère ont été étudiées en détail. L'impact des chaînes alkyles sur la morphologie en film mince à l’échelle nanométrique a également été étudié. Afin de mieux comprendre l’influence de la microstructure des films minces (constitués soit uniquement des molécules donneuses soit de mélanges molécules/fullerènes), le transport de charge dans le plan du film et perpendiculairement au plan ont été mesurées en fonction de la phase (amorphe, cristalline, …) du matériau. Des cellules solaires BHJ en mélange avec le dérivé de fullerène ont également été réaliséesThe prospective conception of electron-donor/electron-acceptor (D/A) bulk heterojunction solar cells was first reported in 1990s, which blended the semiconducting polymer with fullerene derivatives, enhancing the power conversion efficiency. Since then, interests on this domain has been increasing continuously, and the efficiencies of BHJ solar cells have been increased dramatically. In this context, this thesis focuses on the study of a series of dumbbell-shaped small molecule donors, based on a highly planar unit called triazatruxene. The only difference between those molecules is the side-chains attached to central units and TAT units. As a consequence, the relationship between side chains nature and optoelectronic and structural properties of our TAT-based dumbbell-shaped molecular architecture will be investigated in detail. The impact of the alkyl chains on the molecular and thin film properties was also studied, with a particular emphasis put on microstructure and charge transport aspects. In-plane and out-of-plane charge carrier transport, with pure molecules and blend with fullerene, are measured in different systems. BHJ solar cells in blend with fullerene derivatives were also realized
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Chiou, Ta-Cheng, and 邱大晟. "a-Si:H/c-Si Heterojunction Solar Cells." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/23114112769082968040.
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碩士國立臺灣大學
電子工程學研究所
100
In this thesis, the structure, optical and electrical properties of the hydrogenated amorphous silicon ( a-Si:H ) thin films which is fabricated under 140℃ are investigated first. The hydrogen dilution ratio Xg=0.66 is chosen for proper deposition parameter to fabricate a-Si:H/c-Si heterojunction solar cells. Then (i)a-Si/ (n)a-Si hetrojunction is studied by means of current-voltage characteristics measurement. In order to improve (p)a-Si:H/ (n)c-Si interface, two ways are chosen to achieve this goal. Insert an intrinsic a-Si:H at (p)a-Si:H/ (n)c-Si interface not only reduces the leakage current but also improves fill factor. Besides, implement plasma treatment on c-Si surface also improve a-Si:H/ c-Si interface and the open circuit voltage ( Voc ) is increased to 0.58. Finally, in order to increase short circuit current ( Jsc ), back surface field ( BSF ) structure is introduced by means of adding n+ layer at back side of silicon wafer. The solar cell performance is open circuit voltage ( Voc=0.58V ), short circuit current density ( Jsc=33.2mA/cm2 ), maximum output power ( Pmax=11.45mW/cm2 ), fill factor ( F.F.=0.595 ) and efficiency=11.45%.
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Chen, Li-Siang, and 陳立翔. "The Study of AZO/n-Si Heterojunction Solar Cells." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/98001872180886746914.
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碩士正修科技大學
電子工程研究所
103
In this study, Al doped zinc oxide (AZO) films have been prepared by direct current (DC) magnetron sputtering technique with various substrate temperature in the range of RT ,100℃ ,150℃ ,200℃ ,250℃ on glass and N-Si substrates. The temperature of substrate at 250℃ exhibited the lowest electrical resistivity of 1.92×10-3 Ω-cm, carrier mobility of 9.27 cm2/Vs, highest carrier concentration of 3.51x1020 cm-3, and visible range (400-800 nm) transmittance about 80%. However the cell fabricated at 250℃ didn’t show the highest efficiency. Speculation the temperature made thick oxide layer (SiOx) leads to decreased efficiency, because the silicon dioxide increases the growth rate increases with temperature. Grown AZO thin film vacuum annealing in the sputter to passivation for interface states, indeed improve the efficiency effect 6% to8%.
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Pan, Yen-Chih, and 潘彥志. "Optimized periodic surface texture for heterojunction a-Si/c-Si solar cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/40522688646943529711.
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碩士國立東華大學
光電工程學系
99
Because of the finite deposits of coal, oil and gas in earth, people have to search for a renewable energy. For the reason that solar energy will never run out, solar cell, which can turn light into electricity, is most considerable. The conversion efficiency of solar cell is still low due to the band gap of absorption layer, carrier recombination and surface reflection. As the thickness of a-Si is enough, the incident light waves can be sandwiched in a-Si layer by air and c-Si layer to result in planar waveguide. Light trapping from surface texturing and planar waveguide can prolong the light path in solar cell and enhance the absorption of thin film solar cell. Textured surface also can reduce the reflection of interface for the usage of anti-reflection coating to enhance the efficiency. In this thesis, we changed the shape of grating to find the best short circuit current density, then plotted the contour map as the function of grating parameters such as duty cycle, period and etching depth to find the optimized grating structure of better short circuit density for HIT( heterojunction with intrinsic thin layer) solar cell. H field distribution had also be taken into account for further study. Considering the absorption of ITO and active layer individually is necessary for the absorption at long wavelength of ITO is useless to generate hole-electron pair. At last we neglected the absorption from ITO and ensure the ability of light absorption of active layer after periodic surface texturing.
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Liu, Yi-heng, and 劉以珩. "Design of a Si-Ge interlayer for CuGaSe2/Si heterojunction solar cells." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/8ghv47.
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碩士國立中山大學
材料與光電科學學系研究所
106
Current silicon solar cell is developing towards ultra-thin feature for cost lowering, recombination suppressing and potential flexible applications. In this work, we examine the viability of chalcopyrite materials assisting ultra-thin solar cells performance with simulation software AFORS-HET. P type silicon with n type surface doping is support with CISe for light absorption, between them compositional-variated SiGe buffer layer to lower lattice mis-match (SCH-1 layout). Simulation shows Ge induces narrow bandgap and large energy barrier, witch severely reduce Isc. By replacing buffer layer with InSe passivation layer to resolve band structure issues, p-cSi+InSe+CISe design reaches 30% efficiency while remaining under 10μm, being the most promised design, and provided with utmost fabrication value. N type silicon is matched with CGSe, CIGSe, n-type CISe and SiGe buffer layer forming CGSe(CIGSe) +buffer +n-cSi+buffer+CISe heterojunction cell (SCH-2 design), both SiGe buffer layers form energy barrier and greatly hinder hole transportation. Replacing lower buffer with InSe forms reverse field, thus remove CISe, redesigned CIGSe+buffer+150μm cSi structure also failed to reach 20% due to barrier problems from SiGe buffer. CGSe possesses 1.66eV band gap, forming an even higher energy barrier after contacting with SiGe buffer, cancel out the benefit of CISe. After removing CISe and substitute SiGe with amourphous SiGe to bridge band structure between Si and CGSe, CGSe+a-SiGe +150μm n-cSi structure can reach 24.21% efficiency. However, the lack of CISe and ultra thin CGSe of optimized cell does not differ itself from other silicon-based solar cells.
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陳啟文. "Study of surface treatments on AZO/Si heterojunction solar cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/76309886539122579041.
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碩士國立臺灣師範大學
機電科技研究所
100
In this study, for the purpose of removing silicon dioxide on the p-type Si substrate, three different acids were used, buffered oxide etch solution (BOE), hydrogen peroxide (H2O2), and dilute hydrochloric acid (HCl).Additionally, the DC magnetron sputtering method was utilized under the process temperature of 298 K and 573 K. A layer of 100 nm AZO thin film was first deposited on the Si substrate. During the deposition, a flow of 40 sccm argon was infused. Al was sputtered on the bottom of the Si substrate as the bottom electrode. After the AZO/Si heterojunction solar cells were processed, the samples were analyzed in three ways: Transmission Electron Microscope for structural analysis, TEM-EDS for the regional component analysis, and C-V and I-V measurements for electrical analysis. These three methods explored the structure of AZO/Si heterojunction solar cell and the influence of photoelectric properties under different surface treatments and different deposition temperatures. The experimental results revealed that a better IPCE performance was obtained under H2O2 surface pre-treatment and process temperature of 573 K. Furthermore, the photoelectric conversion rate was about 26.6% and the conversion efficiency of each band was much better than the others. Also, the photocurrent density reached 1.1 × 10- 4 A/cm2.
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Tseng, Kao-Wu, and 曾高吾. "Characteristics of SiGe/Si Heterojunction Solar Cell." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/35022300992060575424.
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碩士國立臺灣大學
電子工程學研究所
95
In recent years, SiGe/Si heterostructure has attracted great attention for its applications in electronic devices and optoelectronic devices. In this thesis, we use the molecular beam epitaxy technology to deposit SiGe alloy on silicon substrate to substitute for the conventional silicon material and to improve the conversion efficiency of solar cells. The influence of the doping concentration and thickness of single-crystal on device characteristics are discussed. Finally, we use simulator of solar energy AM1.5G under the illuminated condition. The four important parameters are conversion efficiency, short-circuit current, open-circuit voltage and fill factor. We measure these parameters to analyze and evaluate the performance of solar cells. Four important factors will determine the overall performance of solar cell.
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Chien, Ming-Hao, and 簡明澔. "Efficiency Improvement in Novel p-NiO/n-Si Heterojunction Solar Cells." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/43539162271434900627.
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碩士正修科技大學
電子工程研究所
102
This study successfully fabricates p-Ni1-xO/n-Si heterojunction solar cell using the RF magnetron sputtering. The experiment is divided into three parts to investigate and the conversion efficiency of cell upgraded from 3.39% to 6.31%. First part is to investigate the influence of the RF sputtering power on the performance of p-Ni1-xO/n-Si solar cells, through the four point probe, UV-Vis, capacitance-voltage (C-V), light and dark current-voltage (I-V) measurements. The results show that the cell fabricated at sputtering power of 100 W has the highest conversion efficiency of 4.30% (Voc：0.390 V、Jsc：18.06 mA/cm2、FF：0.611、Rs：4.41 Ω、Rsh：671.76Ω). However, the conversion efficiency of 4.3% is still enough. Therefore, the second and third parts focus on the improvement of Jsc and FF. In the second part, we confirm that the surface texturation of window layer (Al-Y codoped ZnO) etched by diluted HCl effectively increases conversion efficiency of p-Ni1-xO:Li/n-Si heterojunction solar cells. The results show that the short circuit current density (Jsc) of cell etched at 10 s IV increases ~8.5% compared with unetchd cell, resulting in the increase of conversion efficiency to 4.63%. The third part is to improve the back surface Ohmic contact by inserting an ultra-thin LiF (n-Si/LiF/Al). We found the optimum specific contact resistance (ρc) was 4.75x10-3 Ωcm2 when the thickness of 15 Å of LiF inserted. Also, the insertion of LiF (15 Å) in p-Ni1-xO/n-Si solar cell could get the optimum conversion efficiency of 6.31% (Voc：0.441 V、Jsc：21.33 mA/cm2、FF：0.670、Rs：3.587 Ω、Rsh：1691.070 Ω). The improvement of conversion efficiency was due to the dipole-assisted tunneling effect and back surface passivation. Keywords : RF magnetron sputtering, NiO, heterojunction solar cell, LiF
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Tseng, Wen-Yu, and 曾雯譽. "Characteristics of FZO/Si Heterojunction Solar Cells by RF Magnetron Sputtering." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/95703694872102293976.
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碩士正修科技大學
電子工程研究所
101
In this study, fluorine doped zinc oxide (FZO) films have been prepared by RF reactive magnetron sputtering on glass and p-Si substrates. The effects of substrate temperature (from RT to 300°C) on optical and electrical properties of FZO thin films were first studied. The results show that FZO thin film deposited at substrate temperatures of 150°C has largest grain size of 17.3 nm, the lowest resistivity of 6x10-2 Ω-cm, and visible range(400-800 nm) transmittance about 90%. However the cell fabricated at various substrate temperatures shows very poor conversion efficiency due to the high resistivity of FZO thin films in the range of 9x10-1-6 x10-2 Ω-cm. In the second part, the optimal FZO thin films (as-deposited) will be annealed by rapid thermal annealing (RTA) process (from 300oC to 500oC) to improve the conductivity of films, and its influence on conversion efficiency of FZO/p-Si heterojunction solar cell were also investigated. According to the experimental results, the FZO thin film annealed at 500°C shows the lowest resistivity of 3.76x10-3 Ω-cm, the highest mobility of 35.2cm²/V-s and the lowest carrier concentration 4.71x1019cm-3, corresponding to highest conversion efficiency of 6.45% ( Voc：0.48 V、Jsc：31.03 mA/cm2、FF：0.43). The improvement of conversion efficiency can be mainly attributed to the decrease of resistivity of FZO thin film causes decrease of series resistance (RS) of solar cell, thus improving the efficiency. Finally, the thickness of FZO film will be designed as 70 nm, 150 nm, and 200 nm to act an anti-reflective coating layer. From the results, FZO thin film with thickness of 150 nm has highest efficiency. When the film is too thin (70nm), the smaller grain size of film (limited by the thinner thickness) causes decrease of VOC (0.44V), FF (0.37) and conversion efficiency (6.02%) despite the cell shows the highest JSC (37.05 mA/cm2). If the film too thick (200nm), it will cause increase of RS and also decrease of FF, the conversion efficiency of 3.51%.
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Cheng, Yu-Song, and 鄭育松. "Investigation of silicon base p-NiO/n-Si heterojunction solar cells." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/68835472577227961181.
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碩士正修科技大學
電子工程研究所
101
This study reports the fabrication of p-type Ni1-xO:Li/n-Si heterojunction solar cells (HJSCs) by depositing Li-doped Ni1-xO (p-Ni1-xO:Li) on a n-Si substrate (P+/n) using RF magnetron sputtering. The main investigation in this study will divide two parts. Firstly, films deposited on glass and silicon substrates at various working pressures (partial pressure of argon) and temperatures were first analyzed to estimate the optoelectrical properties of p-Ni1-xO: Li thin films. According to the results of experiments, the Ni1-xO:Li thin films deposited at 6 mTorr and 300℃ showed the best crystallization, the high carrier concentration of 1.28×1018 cm-3, high work function 5.32 eV and refractive index of 2.54. The p-Ni1-xO:Li thin film not only acts an emitter layer, but also acts an antireflective coating thin film. The second parts investigate the influence of conversion efficiency of Ni1-xO:Li/n-Si heterojunction solar cell. The initial efficiency is 1.34% (Voc:0.370 V, Jsc:12.354 mA/cm2, FF:0.294, Rs:22.05 Ω and Rsh:360 Ω). The low efficiency can be attributed to the high resistivity of Ni1-xO:Li thin film (2.7 Ω-cm) and thicker SiOx layer (27.78 Å) at interface. In order to solve the problem, a high conductivity n-AZO thin films has been deposited on the p-Ni1-xO:Li thin film as a front electrode contact layer. Thus, the efficiency of cell elevates to 2.33% (Voc:0.354 V, Jsc:22.084 mA/cm2, FF:0.307, ɳ:2.33%, Rs:10.81 Ω, Rsh:320 Ω). Finally, process parameters will be optimized by varying substrate temperature from 300℃ to RT, results to SiOx thickness reduces. Thus, it is shown the best efficiency of 4.89 % (Voc:0.363 V, Jsc:26.452 mA/cm2, FF:0.508) in this study. The dark IV characteristics exhibit the diode ideal factor and leakage current density is approximately 2.33 and 4x10-7 A/cm2, respectively. This study proposes that reduce interface states and improve the optoelectrical properties of p-NiO are two important issues because they can directly and significantly affect the conversion efficiency of p-Ni1-xO:Li/n-Si HJSC. Keywords: heterojunction, nickel oxide, solar cells, sputtering
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Wu, Jun-chieh, and 吳潤節. "Investigation of ITO Layers for Applications in a-Si/c-Si Heterojunction Solar Cells." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/03396366587993201092.
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碩士國立臺灣科技大學
化學工程系
97
Indium tin oxide (ITO) layers are usually used for a-Si/c-Si heterojunction solar cells, because of their high conductivity and high transparency in the visible region of the spectrum. ITO layers also can be used for antireflecting to reduce the reflectance losses. ITO films were deposited by RF-sputtering in this thesis. In our experiment, the lowest resitivity of ITO layer was 3.34 × 10-4 Ωcm at the thickness of 110 nm. The average transmittance in the visible region can higher than 92% and the figure of merit value was 1.53 × 10-2 Ω-1. We can reduce cost by producing thin silicon wafer, but the thin silicon wafer can not treat by traditional high temperature diffusion process. So we deposit a-Si by PECVD to reduce the temperature of process. For the Si-heterojunction solar cells, We measured the carrier lifetime and implied Voc by mic-PCD (Sinton, WCT-120). The highest implied Voc was 620 mV. In I-V measurement, Voc was reduced to 0.44 V, Jsc was 25 mA/cm2. The efficiency of solar cell was 3.27 %, We can attribute to higher series resistance and lower shunt resistance.
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Hsieh, Wen-Feng, and 謝文烽. "Improved Photovoltaic Characteristics of Amorphous-Si/Crystalline-Si Heterojunction Solar Cells Using Laser Scribing Technology." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/qf63z7.
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碩士國立虎尾科技大學
光電與材料科技研究所
98
In this thesis, the improved photovoltaic characteristics of silicon heterojunction were investigated by mean of the very-high-frequency (VHF, 60 MHz) plasma-enhanced chemical vapour deposition (PECVD) under well-controlled discharge conditions. The modulated parameters, including the H2 plasma treatment, the silane concentration [SC %=[SiH4/(SiH4+H2)]×100 %], as well as doping concentration of n-type a-Si [Yn %= PH3/(SiH4+H2+PH3)×100 %] on the characteristics of the heterojunction solar cell were demonstrated. The deposition rates, the optical energy gaps (Eg), incident photon conversion efficiency (IPCE), scanning electron microscope (SEM), UV-VIS-IR spectroscopy and temperature dependent conductivity, respectively, Were studed, the results suggest that by modulating proper conditions, the heterojunction solar cells with a conversion efficiency of around 5.28 %, Jsc of 21.2 mA/cm2, Voc of 510 mV, and Fill factor (FF) of 49.2 % were demonstrated. Improved photovoltaic characteristics of silicon heterojunction solar cells using micro- and nanostructured surface prepared by laser scribing and wet etching technology were demonstrated in this work. The modulated parameters include the velocity, power density, focus length, and frequency of the laser beam. The results indicate that the reflections of the nanostructured surface fabricated by laser scribing and wet etching technique were lower than 10 % for 400–1000 nm wavelength range. The design of hetero long- junction devices raise the short-circuit current density from 19.4 to 22.9 mA/cm2 and conversion effectivey from 3 % to 3.6%.
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Lin, Tzu-Yin, and 林姿吟. "Si Heterojunction Solar Cells Employing Broadband and Omnidirectional Light-Harvesting Hierarchical Structures." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/93472963580388642211.
Full textAbstract:
碩士國立臺灣大學
光電工程學研究所
101
In this thesis, the broadband and omnidirectional light-trapping scheme employing microscale and nanoscale structures are introduced to Si heterojunction solar cells for boosting the photovoltaic performances, and the optical and carrier recombination characteristics of the devices are discussed in detail. In the first part, hierarchical structures consisting of grooves and pyramids are demonstrated in a-Si/c-Si heterojunction solar cells via isotropic etching followed by anisotropic etching. The structure combines the excellent photo managements and creation of long-lived minority carriers into the solar cells, showing an improved conversion efficiency of 15.2%, an open-circuit voltage of 607 mV, and a short-circuit current density of 36.4 mA/cm2. With the superior omnidirectionality, the enhancement of power generation is up to 92% at high incident angles. Such fabrication approach of hierarchical structures open new avenues for various Si-based solar cells with improved conversion efficiency by effective light harvesting. In the second part, semiconductor-insulator-semiconductor solar cells based on IZO/SiO2/Si can be achieved to the conversion efficiency of 7.01% with a VOC of 430 mV and a JSC of 28 mA/cm2 owing to the optimal SiO 2 layer by 5 minutes hot H2O treatment. In addition, the employment of ZnO Nanorods on IZO/Si heterojunction can improves the Jsc from 28.0 to 30.8 mA/cm2 and the efficiency from 7.01% to 7.51 % due to superior light trapping ability.
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Ferrara, Manuela [Verfasser]. "Electroluminescence of a-Si/c-Si-Heterojunction solar cells after high energy irradiation / von Manuela Ferrara." 2009. http://d-nb.info/995437394/34.
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Huang, Yi-Teng, and 黃奕騰. "Improvement of a-Si:H/c-Si Heterojunction Solar Cells through higher deposition temperature." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/47892819236878299687.
Full textAbstract:
碩士國立臺灣大學
電子工程學研究所
104
In a-Si:H/c-Si heterojunction solar cells, the key factor to the high performance are the a-Si:H/c-Si heterointerface and anti-reflection structure. First, we use the high temperature (250 ℃) to deposit a-Si:H layers to improve the interface passivation due to the films quality is better. By inserting high temperature deposition of intrinsic a-Si:H to be the passivation layer, the open circuit voltage (Voc) is apparently increased. Moreover, we concentrate on the interface treatment of the a-Si:H/c-Si interface. Before depositing the a-Si:H films by PECVD, we use the hydrogen treatment to pre-treat the c-Si surface by a low energy plasma. The hydrogen plasma treatment improve both the open circuit voltage (Voc) and fill factor (F.F.) and thereby increase the conversion efficiency of solar cell due to the good passivation of interface and the increase of build-in potential. Second, the anti-reflection structure is introduced to improve the device performance. We use textured substrate formed by wet chemical etching method. By means of this structure, the short circuit current density (Jsc) can be largely enhanced and the efficiency is improved. Finally, the plasma treatment and BSF structure are used in this textured substrate of HIT solar cell. The conversion efficiency is achieved to 16.38%.
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Chen, Yan-Lung, and 陳彥龍. "Study of In2S3 Nanostructures by Chemical Bath Deposition for p-Si Heterojunction Solar Cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/6xrnct.
Full textAbstract:
碩士國立虎尾科技大學
光電與材料科技研究所
99
The article mainly consists of three items. Part I, we reported the surface morphology and the optical properties of β-In2S3 mircopompons phosphors and nanorods of In2S3 thin films, respectively. Part II, textured structures can improve the antireflection by wet anisotropic etching. Part III, a novel AZO/In2S3/p-Si hetero-junction solar cell was fabricated. Part I : Nanorods of β-In2S3 thin films and micro-pompons of β-In2S3 phosphors were prepared by chemical bath deposition (CBD) technique at lower temperature. In general, the surface morphology of the material can affect the optical and physical properties depend on the different synthesis technology. Mircopompons of β-In2S3 phosphors with TEM indicated the pompon with diameter in the range from 1 to 2 μm. The EDS data indicated that the composition of indium and sulfur with the In/S ratio of 44:56 which had been close to the stoichiometry of In2S3 compound. The lattice image and the diffraction pattern revealed the polycrystalline of In2S3 mircopompons. XRD showed both cubic and tetragonal of novel double-phases of β-In2S3. PL spectra indicated the near-band-edge (NBE) emission at 592 nm. Furthermore, the NBE emission was corresponded to orange luminescence. The band gap of β-In2S3 phosphors indicated at 2.06 eV (600 nm) from spectra (dR/dλ versus λ ) of the reflectance traces. On the other hand, nanorod structures of In2S3 thin films were shown by these SEM images. These In2S3 thin films were characterized by X-ray diffractometer, field-emission scanning electronic microscope (FESEM), atomic force microscopy (AFM), photoluminescence (PL) and UV-Vis spectrometry. Part II : pyramid structures were forms the surface silicon using wet etching. Pyramid structures main function to increase the absorption of light, generate more electron-hole pairs, lead to higher short current density. Good experimental parameters can obtain the most structure. The passivation structure can be changed on other parameters such as the relatively low concentration of solution, the lower temperature. Part III : a novel AZO/In2S3/p-Si hetero-junction solar cell was fabricated. First, the textured structure of single-crystal silicon (100) was formed by the wet-chemical etching in the solution. Sequentially, In2S3 thin film was synthesized on the textured silicon substrate by chemical bath deposition (CBD) at lower temperature. Then, AZO thin film was deposited by RF sputtering deposition. The aluminum paste was prepared by spin-coated on the back surface. Textured silicon substrates can provide high absorption of light and increase short current density.
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Huang, Wan-Yu, and 黃琬瑜. "Using Metal Catalyst to Form Si Antireflection Layer and Its Applications on Heterojunction Solar Cells." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/17851701659878181443.
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Lin, An-Hua, and 林安樺. "Highly Efficient Back-Contact Cross-Finger Type PEDOT:PSS/Si Heterojunction Solar Cell." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/74081702605300287811.
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碩士國立交通大學
應用化學系碩博士班
104
This thesis aims at the improvement of back-junction type PEDOT:PSS/Si hybrid solar cells, which was first proposed and demonstrated by Zieke and coworkers with a decent power conversion efficiency. The limited efficiency of current PEDOT:PSS/Si solar cells were basically due to the facts that the heterojunction was located on the front of the cell, resulting in a parasitic light absorption within the organic material. In addition, the rear surface of those front-junction solar cells was usually poorly passivated. To overcome above difficulties, one must place the PEDOT:PSS on the rear side of the device and the solar cell must be fabricated on a thin Si wafer to reduce carrier recombination. By adapting back contact cross-finger type PEDOT:PSS/Si heterostructures on thin Si wafers, we are able to reduce the shading loss to zero and enhance carrier collection. The absence of the metallization grid on the front side increases the short- circuit current (Jsc) of the cells dramatically. BackPEDOT cells with cross-finger type electrodes of different back emitter shading ratios were fabricated and tested. An optimized efficiency of 15.7% was achieved from cells with a shading ratio of 67%. It indicates that, at this particular shading ratio, diffusion lengths and carrier collection efficiency were optimized for both majority and minority carriers. By further increasing the width of Al electrodes from 200 um to 300 um and reducing the pitch between anode and cathode from 200 um to 150 um, the Fill Factor and efficiency of the BackPEDOT solar cells were further improved from 0.54 to 0.6 and from 15.7 % to 17.6%, respectively. Due to the cross-finger type electrodes employed on the devices, the rear side of the cells is not fully covered by the electrodes, which means that there are still exposed organic-silicon junction areas that can absorb sunlight. An efficiency of 1% was measured when the rear side of the solar cell was under 1.5AM illumination. Therefore, in principle, one can expect a total conversion efficiency of 18.6% when both sides of the cell are illuminated simultaneously.
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Chen, Shih-Yen, and 陳世晏. "The effect of anti-reflection structure on the performance of a-Si:H/c-Si Heterojunction Solar Cells." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/96049430264088863934.
Full textAbstract:
碩士國立臺灣大學
光電工程學研究所
101
In the past few years, the anti-reflection structure was largely used in photovoltaic devices to enhance the light extraction. In order to improve the solar cell conversion efficiency, the anti-reflection structure is studied. The heterojunction solar cell without anti-reflection structure is fabricated for comparison. Besides, inserting intrinsic layer is a way to improve efficiency. The (p) a-Si/ (n) c-Si interface is passivated to reduce leakage current. On the other hand, the properties of textured structure are investigated including optical reflectance and surface morphology. The anti-reflection effect of textured structure is significant. By means of anti-reflection structure, the short circuit current density (Jsc) can be largely enhanced and the efficiency is improved. Next, the improvement of fill factor is facilitated by increasing the deposition temperature of indium tin oxide (ITO). Finally, the effect of back surface field (BSF) structure is studied on solar cell with anti-reflection structure.
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Dai, Wen-Ting, and 戴汶廷. "Study of ZnS and CdS Thin Films by Chemical Bath Deposition for p-Si Heterojunction Solar Cells." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/7hv4kf.
Full textAbstract:
碩士國立虎尾科技大學
光電與材料科技研究所
98
For this study which used low-cost, low-temperature chemical bath deposition(CBD) to grow cadmium sulfide(CdS) and zinc sulfide(ZnS) thin films semiconductor n-type heterojunction application of p-Si solar cells. Preparation of CdS and ZnS thin films, the concentration and annealing conditions play a very important role. Good transmittance, uniformity, crystal structure of CdS/ZnS thin films by field emission scanning electron microscopy(FE-SEM), X-ray diffraction(XRD), energy dispersive spectroscopy(EDS) and UV / visible spectrometer to observe the film thickness, surface and profile morphology, structural characteristics, composition and optical penetration, etc., to understand the basic characteristics of such thin films, suitable for p-si heterojunction solar possibilities. Therefore, the preparation of Al / AZO / n-CdS / p-Si / Al device as the goal, to improve energy conversion efficiency. Stability of zinc sulfide thin film transmittance over 85% more than in the 400nm. Surface film uniformity. However, there are some white spots in the film may be deposited zinc sulfide mixed colloidal particles, these particles may be ZnO or Zn(OH)2. This study found that the impedance change at different concentrations of zinc sulfate, and PH values have a significant impact on transmittance.
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Shen, Tzu-yao, and 沈子堯. "Low-temperature Diffusion of Al into Amorphous Si Layers and its Application in Silicon Heterojunction Solar Cells fabrication." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/c6nqd8.
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碩士國立臺灣科技大學
化學工程系
100
A process to form highly Al-doped crystalline Si layers through low-temperature diffusion of Al into hydrogenated amorphous Si (a-Si:H) layers was examined. We found that the conversion of a-Si:H into p+ crystalline Si for the Al/a-Si:H system is affected by the hydrogen incorporation amount of the a-Si:H layers, the thickness of the Al layers, the diffusion temperature, and the treatment time. A typical film resistivity of 8.45×10-3 Ω-cm was obtained after thermal treatment of Al (20nm)/amorphous Si(30nm) for 30 min under 200 oC. Applying the p+ layer thus prepared as the back surface field for p-type mono-crystalline Si hetero-junction solar cell, we achieved a primary cell efficiency of 12.7% on an untextured Si wafer with an open circuit voltage (Voc) of 590 mV. The low cell Voc is most plausibly due to the poor interface between the crystallized p+ doped layer and the Si surface. An attempt to passivate this interface was now underway.
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Lee, Te-Hao, and 李德浩. "Formation of p-type μc-Si layers Through Low-Temperature Diffusion of Al/a-Si:H and its Application in Si Heterojunction Solar Cells." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/81585311305906682068.
Full textAbstract:
碩士國立臺灣科技大學
化學工程系
101
We have explored a process to form highly Al-doped crystalline Si layers through low-temperature diffusion of Al into hydrogenated amorphous Si (a-Si:H) layers prepared by PECVD. A typical film conductivity of ~185 (S/cm) was obtained after thermal-treating Al/a-Si:H for 1 hr at 200oC. Applying the p+ layer thus prepared as the back surface field for p-type mono-crystalline Si hetero-junction solar cell, we achieved a primary cell efficiency of 12.0 % on an untextured Si wafer with an open circuit voltage (Voc) of 590 mV. In particular, unintentional epitaxial growth was found to occur during an intended Al-doped crystalline process, thereby deteriorating the interfacial passivation because of the poor structural quality of nanocrystalline Si. Then, we investigated the possibility to insert a diffusion barrier layer to prevent the interdiffusion of Al into amorphous Si matrix, by which the implied Voc was improved from 590 mV to 695 mV. Moreover, Interdigitated back contact silicon solar cell was fabricated by applying the present technique, which showed a preliminary cell efficiency of 4.26%.
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Hsieh, Chi-Yu, and 謝奇諭. "Study on the Fabrication and Characteristics of c-Si Solar Cell with Heterojunction Structure." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/58204961380077016467.
Full textAbstract:
碩士國立中興大學
光電工程研究所
99
In this study, we use very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) to deposite intrinsic hydrogenated amorphous silicon thin films (i-a-Si:H) and p-type hydrogenated amorphous silicon thin films (p-a-Si:H). VHF-PECVD can produce a high density and low ion energy plasma to enhance the deposition rate and reduce ion bombardment and destruction. As compared with the ratio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD), VHF-PECVD can achieve better quality of thin films because of higher generation rate of atomic hydrogen. In this experiment, we change the process parameters, including the substrate temperature, process pressure , film thickness, and gas flow rate of methane to investigate the film structure, optical properties, and electrical characteristics of these films. We then fabricate HIT (heterojunction with intrinsic thin layer) solar cell by above process parameters to study the relative photoelectric conversion efficiency, open circuit voltage, short circuit current density, and fill factor. The characteristics of intrinsic hydrogenated amorphous silicon thin films deposited in different substrate temperature was measured by Fourier transformed infrared transmission spectroscopy (FTIR). It shows that when the substrate temperature increases, microstructure parameter (R2080) decreases. Because the molecules get more energy, they can achieve more mobility on the surface of the substrate, which makes it easier to form amorphous type. The effect of different process pressure to the microstructure parameter is that as pressure increases, it becomes worse. That is because the reaction molecules get more when pressure increases, but the RF power remains the same. It can’t break efficiently the bonds of the molecules have, so the Si-H2 and (Si-H2)n bonds increase, which makes the microstructure parameter increases. Then we discuss the effect of the film thickness. When a-Si:H deposites on the wafer, it stars with an epitaxial growth or micro structure growth, then grows with amorphous structure. It can be seen from the microstructure parameter, when the thickness of the a-Si:H increases, the microstructure parameter decreases. P type a-Si:H thin films deposited by different methane gas flow rate are analyzied by UV-VIS. It can be found that the optical band gap increases when the methane gas flow rate increases, which can improve the open circuit voltage of the solar cell. But higher gas flow rate of methane will reduce the electric properties of these films that can be seen from the photo and dark conductivity measurement. In this study, i-a-Si:H film is deposited with the substrate temperature at 180℃, process pressure at 700 mtorr, thickness in 15 nm, and p type a-Si:H film is deposited with the thickness in 15 nm, gas flow rate of methane in 20 sccm to fabricate the HIT solar cell. It can achieve photoelectric conversion efficiency of 6.03 %, open circuit voltage of 0.433 V, short circuit current density of 0.0175 A/cm2, fill factor of 0.605, series resistance of 5.69 Ω-cm2, and shun resistance of 1320 Ω-cm2.
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Chiou, Si Ming, and 邱世明. "Study on the applications of Si thin film in the polysilicon thin-film transistor and heterojunction structure solar cells." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/y9nvdc.
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博士國立中興大學
電機工程學系所
103
In this thesis, an investigation into the behavior of silicon thin films in polysilicon (poly-Si) thin-film transistors and heterojunction structure solar cells was conducted. At the onset, it is appropriate to evaluate and discuss the electrical instabilities associated with low temperature poly-Si thin-film transistors (LTPS-TFTs). Two dominant mechanisms normally cause LTPS-TFT degradation: hot-carrier effects and self-heating effects. For N-type LTPS-TFTs, we find that hot-carrier and self-heating effects occur under conditions of Vg = +3 V and Vd = +15 V; and Vg = +18 V and Vd = +15 V, respectively. By means of this research topic, for N-type LTPS-TFTs, a special phenomenon is deemed at hand; there is a turnaround tendency in the degradation trend at Vg = +18 V and Vd = +9 V. However, under high drain bias voltages, a degradation predominance in the TFT characteristic can be observed, such as renderings of Ion and Gm,max. Degradation phenomena of N-type LTPS-TFTs are observed under AC stress in the off-region, with rectangular pulse signals, and dynamic fluctuations ranging from −18 to 0 V along varied parameters such as rising time, falling time, and frequency, are applied to the gate terminal. A drain is simultaneously biased at +5 V to stress the LTPS-TFTs for examining the subject deterioration. From experimental data, we find that the degradation of poly-Si TFTs increases as frequency increases. The rising time of the gate AC signal dominates the degradation characteristic of N-type poly-Si TFTs which operate in the off-region. Such evaluations were inclusive under complementary AC-gate bias stress and normal-AC drain bias stress scenarios. As gate voltages transitionally change during the rising time, accumulated holes should sweep out and flow into the source terminal, resulting from a drain with a positive bias and the floating body structures of TFTs. By utilizing a related BJT parasitic structure model to demonstrate the subject degradation characteristic, three measuring items were employed: a sampling-current measurement, a C–V measurement, and a forward–reverse I–V measurement. An additional study was implemented examining the reliability of gate-all-around multiple nanowire channel (GAA-MNC) TFTs, under hot-carrier stress and gate-dynamic-bias stress at different frequencies. The performance of GAA-MNC TFTs degraded more severely than planar TFTs. Therefore, various effective channel widths of GAA-MNC TFTs were utilized to carry out hot-carrier-stress scenarios. Subsequently, results demonstrated that sharp corner structures cause larger electric fields in channels near the drain region. For devices that maintain vacuum cavity structures within, the reliability of TFTs can be improved after the induction of hot-carrier stress or dynamic-gate-bias stress. This condition is strongly correlated to the use of a thicker gate insulator which results from the vacuum cavity, and thus effectively reduces both lateral and vertical electric fields in the channel near the drain region. As an additional focus area for independent evaluation, effects of low temperature oxidation on textured silicon for heterojunction solar cells were assessed. Potassium hydroxide (KOH) solution was used to etch a polished silicon wafer, to display pyramid structures due to different etching rates between associated (100) and (111) orientations. Moreover, it was found that the average reflectance decreased from 40 % to 11.9 % (350 nm–800 nm) for the polished wafer and KOH-etched wafer. A very-high-frequency plasma-enhanced-chemical-vapor-deposition (VHF-PECVD; 40.68 MHz) was also utilized for depositing amorphous silicon thin films. In this process, with varying thicknesses and H2 dilution ratios, the intrinsic hydrogenated amorphous silicon (α-Si) film was sequentially deposited on glass substrates, with its optical properties sequentially analyzed by UV–vis spectroscopy and I–V measurement. Heterojunction solar cells were fabricated by depositing the hydrogenated α-Si thin films on the textured Si wafer. It was found that the short-circuit current density of the solar cells increased due to the pyramid structure of the Si wafer, thereby enhancing the trapping of light. However, the open-circuit voltage was found to decrease as a result of the high density of metal ion defects and residues, which resulted from the wet-etching process. In order to remedy this issue, the textured wafers were oxidized or annealed to dryness at an ambient temperature of 400°C. Finally, a very thin SiO2 layer was removed by a diluted HF solution. The electrical parameters of the heterojunction solar cells could achieve a conversion efficiency of 9.85%, with an open-circuit voltage of 0.48 V, a short-circuit current density of 30.8 mA/cm2, a fill-factor of 66.7%, a series resistance of 3.43 Ω cm2, and a shunt resistance of 469 Ω cm2.
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Mao, Hsin-Yuan, and 毛信元. "Hot-Wire Chemical Vapor Deposition of Si-Based Thin Films for Heterojunction Solar Cell Applications." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/48192803861965128807.
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博士國立中興大學
材料科學與工程學系所
100
Hot-wire chemical vapor deposition (HWCVD) is one of the semiconductor fabrication processes to grow thin film materials. The HWCVD system is composed of vacuum system, gas flow controls, and catalytic wires where Tungsten, Tantalum or Iridium are often used. In a typical HWCVD process, the temperature of wire can increase to 1500~2000 by increasing the DC current. The source gases are entered into the vacuum chamber and decomposed (or catalyzed) by the high temperature wires. The substrate is exposed to one or more volatile precursors which react or decompose on the substrate surface to produce the desired deposit. The dissertation introduces the solar cell research evolution and the lately study of Si film. It also overviews the mechanisms of hot-wire chemical vapor deposition (HWCVD) and plasma enhanced chemical vapor deposition (PECVD). The advantages and the disadvantages of these two CVD are presented and compared. The study in the dissertation is using the HWCVD system and depositing Si based films for photovoltaic applications. The results includes four subjects of “Growth and characterization of intrinsic Si film”, “Deposition and characterization of poly-Si thin films using a two-step growth method”, “Deposition and characterization of p-type nanocrystalline Si (p-nc-Si) films for photovoltaic applications” and “Deposition and characterization of p-type nanocrystalline Si (p-nc-SiC)films for photovoltaic applications”. The intrinsic Si film such as amorphous, microcrystalline and polycrystalline have grown by HWCVD. The influence of deposition parameters such as substrate temperature and hydrogen dilution ratio has been presentation. Based on the identification of hydrogen dilution, a two-step growth method with high/low hydrogen dilution ratios was studied. In the two-step growth process, a thin seed layer was first grown on the glass substrate under high hydrogen dilution ratio and then a thick over layer was subsequently deposited upon the seed layer at a lower hydrogen dilution ratio. The amorphous Si incubation layer could be suppressed greatly in the initial growth of poly-Si film with the two-step growth method. In the subsequent poly-Si film thickening, a lower hydrogen dilution ratio value of the reactant gases can be applied to enhance the deposition rate. The electrical properties were also enhanced. The effects of H2 on the characteristics of p-nc-Si and p-nc-SiC films were analyzed. The optimized parameters of p-nc-Si and p-nc-SiC films were applied as emitter layer in the Si HJ solar cells. The 12.5 % and 14.09 % of photovoltaic conversion efficiencies could be obtained, respectively. These are very encouraging results for the industrial fabrication of high efficiency heterojunction solar cells by using HWCVD technique.