Rozprawy doktorskie na temat „Organic-inorganic Hybrid Perovskites”

This thesis details the development of a novel photovoltaic device based on organometal halide perovskites. The initial focus of this thesis begins with the study of lighttrapping strategies in solid-state dye-sensitised solar cells (detailed in chapter 3). While I report enhancement in device performance through the application of near and far-field light-trapping techniques, I find that improvements remain step-wise due to fundamental limitations currently employed in dye-sensitised solar cell technology— notably, the available light-sensitising materials. I found a promising yet under researched family of materials in the methyl ammonium tri-halide plumbate perovskite (detailed in chapter 4). The perovskite light-sensitiser was applied to the traditional mesoscopic sensitised solar cell device architecture as a replacement to conventional dye yielding world-record breaking photo-conversion e!ciencies for solid-state sensitised solar cells as high as 8.5%. The system was further developed leading to the conception of a novel device architecture, termed the mesoporous superstructured solar cell (MSSC), this new architecture replaces the conventional mesoporous titanium dioxide semiconductor with a porous insulating oxide in aluminium oxide, resulting in very low fundamental losses evidenced through high photo-generated open-circuit voltages of over 1.1 V. This development has delivered striking photo-conversion ef- ficiencies of 10.9% (detailed in chapter 6).

The primary focus of this thesis is the study of a novel family of materials known as organicinorganic hybrid Perovskites (OIHP), which have recently demonstrated to possess remarkable photovoltaic efficiency. The fundamental properties of these materials related to photovoltaic (PV) applications are studied to characterise electronic and optical behaviours. An all-electron implementation of the Quasi-particle Self-consistent GW (QSGW) is used to perform first principles calculations. The quasi-particle energy bands are analysed for a number of Perovskites, to identify trends and characteristics within this family of materials, and to understand the dielectric response. The dielectric function and refractive index were studied for 4 OIHP and compared to experimental work carried out collaboratively with Leguy et al. [1]. It is found that the relativistic effects are extremely important in characterisation of these materials. The presence of strong spin-orbit interaction combined with significant internal electric fields yields anomalously large Rashba splitting of both valence and conduction states near the band edges. This significantly perturbs the electronic and optical properties of these materials. Such effects have not been previously investigated in the context of photovoltaic materials. The effect of the Rashba splitting on the radiative recombination lifetime of charge carriers is investigated. A model for reciprocal space trapping mechanism of carriers was developed and implemented within the Questaal package. The slightly indirect gap induced by Rashba splitting results in a strongly suppressed photoluminescence when compared to conventional III-V direct-gap semiconductors with an otherwise approximately similar band structure. Such suppression of the radiative recombination enhances the diffusion length and can significantly increase the power conversion efficiency of a solar cell.

The hybrid organic-inorganic perovskites (HOIPs), e.g. methylammonium and formamidinium lead halide (MA/FAPbX3, X = I, Br or Cl), are a class of materials that has recently achieved remarkable performances in photovoltaic applications. This thesis describes the synthesis, structure and properties of this class of perovskites, with particular focus on their crystal chemistry, mechanical responses and structural diversity. Understanding the unique crystal chemistry of HOIPs is crucial for device design. While MA-based perovskites have been widely studied, there are still many open questions on the crystal chemistry of FA-based perovskites. In this work, FAPbX3 (X= Br or I) was shown to undergo a cubic (Pm3 ̅m) to tetragonal (P4/mbm) transition on cooling. Studies on the high-pressure crystallography of FAPbI3 exhibited a similar trend and further illustrated band gap tuning via external stimuli. In addition, the cubic lattice of FAPbBr3 was found to be more strained than its MA counterpart. The observed intrinsic strain was modelled with anisotropic line broadening and < 100 > was found to be the least strained direction. To explore potential applications in flexible devices, crystals of single (Pb-based) and double (Bi-based) perovskites were probed by nanoindentation and their mechanical properties, such as Young’s moduli (E) (10 – 20 GPa) and hardnesses (H) (0.2 -0.5 GPa), were determined. The mechanical responses of MA- and FA-based hybrid perovskites correlated well with the chemical and structural variations in these analogues, showing a general trend of ECl > EBr > EI and EPb > EBi. By analogy with classical inorganic perovskites, the hybrid phases can crystallise in both three-dimensional (3D) and low dimensional perovskite-like forms. To improve the stability and remove the toxicity in the current prototypical hybrid perovskites, compositional engineering was applied, focusing on non-toxic bismuth (Bi) as a viable alternative to lead (Pb) in future photovoltaic materials. We report a new layered perovskite, (NH4)3Bi2I9, which exhibits a band gap of 2.0 eV, comparable to MAPbBr3 and FAPbBr3. This work contributes to the materials design goal of more stable and eco-friendly perovskite devices.

[ES] Las perovskitas orgánicas-inorgánicas de haluros de metilamonio y plomo y sus mezclas han mostrado propiedades optoelectrónicas óptimas como absorbente ideal para aplicaciones fotovoltaicas. Los dispositivos solares basados en perovskita han evolucionado rápidamente, desde una eficiencia del 3.9% en 2009, al 22.7% en 2017 y con un coste de fabricación más bajo que las células solares de silicio. Una desventaja del uso de absorbentes de perovskita en dispositivos fotovoltaicos es su baja estabilidad. Las células con un alto rendimiento, pierden su eficiencia y se degradan rápidamente. Para poder producir estos materiales industrialmente es necesario realizar estudios en profundidad que mejoren la eficiencia y estabilidad. Una vía de mejora es la ingeniería composicional, estrategia que hemos empleado en la elaboración de esta tesis y que consiste en la investigación y mejora de las propiedades optoelectrónicas y morfológicas, derivadas de la sustitución y/o combinación de cationes y aniones, que constituyen el material de perovskita. Se sintetizaron polvos puros de perovskita de I, Br, Cl, a partir de los cuales se prepararon capas puras y mixtas MAPbX3-xYx, con el objetivo de mejorar sus propiedades optoelectrónicas y estructurales. Los análisis de difracción de rayos X mostraron las propiedades estructurales de los polvos cristalinos y capas puras y mixtas. Los análisis de UV-vis y fotoluminiscencia mostraron que el rango de absorción varía a lo largo del espectro visible en función del contenido del haluro en las capas. Los análisis de fotoluminiscencia y calorimetría diferencial de barrido muestran los cambios de fase de las perovskitas puras a distintas temperaturas, coincidiendo dichos cambios en ambos análisis. El análisis FESEM de las perovskitas puras mostró las diferencias morfológicas entre los polvos y capas. Siguiendo esta línea de investigación, se estudiaron con más detalle las perovskitas mixtas de yodo-bromo, con un contenido de bromo de hasta el 33%, consiguiendo ajustar el bandgap para evitar pérdidas en la absorción y mejorar las propiedades optoelectrónicas, estructurales y morfológicas. A pesar de las buenas propiedades optoelectrónicas de las perovskitas de metilamonio, el catión orgánico disminuye su estabilidad, lo que llevó a investigar otros cationes inorgánicos. Las perovskitas de cesio son una alternativa prometedora, y por esta razón hemos sintetizado capas finas de perovskitas de cesio mixtas, CsPbBr3-xIx, para determinar los efectos que produce la sustitución parcial del yodo en las propiedades físicas y la estabilidad. Se obtuvieron capas con una buena resistencia a la humedad y temperatura, favoreciendo su aplicación en el campo fotovoltaico. Se ha estudiado la sustitución parcial del catión de metilamonio con otros cationes orgánicos, como el guanidinio e imidiazolio. Se demostró que pequeñas cantidades de guanidinio mejoran la estabilidad de las capas y su morfología. Se estableció el límite de solubilidad del guanidinio en el 20%, aproximadamente, y se determinó la estructura cristalina de las mezclas. La intensidad del pico de fotoluminiscencia aumentó para mezclas por debajo del límite de solubilidad. Se obtuvieron resultados similares para la sustitución del metilamonio con pequeñas cantidades de imidazolio. Los análisis de rayos X establecieron el límite de solubilidad en aproximadamente el 10% y una mejora en la cristalinidad. Los resultados de fotoluminiscencia sugieren que pequeñas cantidades de imidazolio reducen significativamente las recombinaciones no radiativas, actuando como un pasivador efectivo. Finalmente, se muestra el proceso de fabricación de dispositivos basados en MAPbI3 y sintetizados en función de las condiciones ambientales y empleando el dietil éter como anti-solvente. Los dispositivos mostraron una eficiencia máxima del 14.73%. Se ha probado que la oxidación del spiro-OMeTAD, bajo condiciones cont
[FR] Les perovskites orgàniques-inorgàniques de halurs de metilamoni i plom i les seues mescles han mostrat propietats optoelectròniques òptimes com a absorbent ideal per a aplicacions fotovoltaiques. Els dispositius solars basats en perovskita han evolucionat ràpidament, passant d'una eficiència del 3.9% en 2009, fins al 22.7% en 2017, i amb un cost de fabricació més baix que les cèl·lules solars de silici. No obstant això, un dels desavantatges de l'ús de absorbents de perovskita és la baixa estabilitat. En general, les cèl·lules que mostren un alt rendiment, perden la seua eficiència i es degraden ràpidament. Per a que aquestos materials puguen ser produits industrialment a gran escala és necessari estudiar-los en profunditat per millorar la eficiència i estabilitat. Una de les vies de millora és l'enginyeria composicional, estratègia que hem emprat en l'elaboració d'aquesta tesi i que consisteix en la investigació i la millora de les propietats optoelectròniques i morfològiques, derivades de la substitució i/o combinació de cations i anions, que constitueixen el material de perovskita. S'han sintetitzat pols purs de perovskita per a I, Br, Cl, a partir d'els quals es van preparar capes pures i mixtes MAPbX3-xYx per a millorar les propietats optoelectròniques i estructurals. Mitjançant anàlisi de difracció de raigs X, s'estudiaren les propietats estructurals del pols cristalins i capes pures i mixtes. Els anàlisis d'UV-vis i fotoluminiscència, mostren que el rang d'absorció varia al llarg de l'espectre visible en funció del contingut de l'halur. Les anàlisis de fotoluminiscència i calorimetria diferencial mostren els canvis de fase de les perovskites pures a diferents temperatures, coincidint aquestos canvis en totes dues anàlisis. L'anàlisi FESEM de les perovskites pures, mostra les diferències morfològiques entre els pols i capes. Seguint aquesta línia d'investigació, s'estudiaren les perovskites mixtes de iode-brom, amb un contingut de brom de fins el 33%, ajustant el bandgap per a evitar pèrdues en l'absorció i millorar les propietats optoelectròniques, estructurals i morfològiques. Malgrat les bones propietats optoelectròniques de les perovskites de metilamoni, el catió orgànic disminueix la estabilitat, la qual cosa ha portat a investigar l'ús d'altres cations inorgànics. Les perovskites de cesi són una alternativa prometedora, i per aquesta raó hem sintetitzat capes fines de perovskites de cesi mixtes, CsPbBr3-xIx, per tal de determinar els efectes de la substitució parcial del iode en les propietats físiques i l'estabilitat. Es van obtenir capes amb una bona resistència a la humitat i a la temperatura, afavorint la seua aplicació en el camp fotovoltaic. S'ha estudiat també la substitució parcial del catió de metilamoni amb altres cations orgànics, com el guanidini i imidiazoli. S'ha demostrat que petites quantitats de guanidini milloren l'estabilitat i la morfologia de les capes. S'ha establert que el límit de solubilitat del guanidini es del 20%, aproximadament, i s'ha determinat l'estructura cristal·lina de les mescles. S'ha observat un augment en la intensitat del pic de fotoluminiscència per a mescles per sota del límit de solubilitat. Es van obtenir resultats similars per a la substitució del metilamoni amb petites quantitats de imidazoli. Les anàlisis de difracció de raigs X van establir el límit de solubilitat en aproximadament el 10% i una millora en la cristalinitat. Els resultats de fotoluminiscència suggereixen que petites quantitats de imidazoli redueixen les recombinacions no radiatives, actuant com un pasivador efectiu. Finalment, es mostra el procés de fabricació de dispositius basats en MAPbI3 i sintetitzats en funció de les condicions ambientals, especialment la humitat relativa i utilitzant el dietil èter com anti-solvent. Els dispositius van mostrar una eficiència màx
[EN] Organic-inorganic methylammonium lead halides perovskites and their mixtures have shown optimal optoelectronic properties as an ideal absorber for photovoltaic applications. In the last decade, solar devices based on perovskite have evolved rapidly, going from an initial efficiency of only 3.9% in 2009, to an efficiency of 22.7% in 2017 and being, at the same time, more cost-effective than silicon solar cells. However, one of the main disadvantages when using perovskite absorbents in photovoltaic devices is their low stability. In general, cells that show high performance lose their efficiency and degrade rapidly. For these materials to be scalable it is necessary to carry out in-depth studies aiming at improved efficiency and stability. One of the main sources to improve stability and efficiency is compositional engineering, a strategy employed in the elaboration of this thesis, consisting of the investigation and improvement of the optoelectronic and morphological properties, derived from the substitution and / or combination of cations and anions, which constitute the perovskite material. Pure powders of perovskite were synthesized, for I, Br, Cl, from which pure and mixed MAPbX3-xYx films were prepared in order to improve their optoelectronic and structural properties. By means of X-ray diffraction analysis, the structural properties of crystalline powders and pure and mixed films were studied. Employing UV-vis and photoluminescence analysis, it was observed that the absorption range varied along the visible spectrum as a function of the halide content in the thin films. Both, photoluminescence and differential scanning calorimetry analysis showed the changes of phase of the pure perovskites at different temperatures. FESEM characterization of the pure perovskites showed the morphological differences between the powders and the films. Following this line of research, mixed perovskites of iodine-bromine with a bromine content of up to 33% were studied in more detail. The bandgap was tuned to avoid significant losses in absorption and improve the optoelectronic, structural and morphological properties. Despite the excellent optoelectronic properties of the methylammonium perovskite, the presence of the organic cation decreases its stability, which prompted research into the use of other inorganic cations. Cesium perovskites, are a very promising alternative, and for this reason we synthesized thin films of mixed cesium perovskites, CsPbBr3-xIx, to determine the effects of the partial substitution of iodine on physical properties and stability. Films with a very good resistance to moisture and temperature were obtained, which will favor the application of this type of perovskites in the photovoltaic field. The partial replacement of the methylammonium cation with other organic cations, such as guanidinium and imidiazolium, was also studied, showing that small amounts of guanidinium significantly improve the stability of the films and their morphology. It was established that the solubility limit of guanidinium is approximately 20%, and the crystalline structure of the mixtures was determined. An increase in the intensity of the photoluminescence peak for mixtures below the solubility limit was observed. Similar results were obtained for the substitution of methylammonium with small amounts of imidazolium. X-ray diffraction analyzes established the solubility limit at approximately 10% and an improvement in crystallinity. Photoluminescence results suggest that small amounts of imidazolium significantly reduce nonradiative recombinations, acting as an effective passivator. Finally, the manufacturing process of devices based on MAPbI3 and synthesized according to environmental conditions, especially relative humidity and using diethyl ether as anti-solvent is shown. The devices presented a maximum efficiency of 14.73%, proving that the oxidation of spiro-OMeTAD, under controlled humidity conditions, can improve efficiency.
Vega Fleitas, E. (2018). Study and Characterization of Hybrid Organic-Inorganic Perovskites for Solar Cells Applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/113402
TESIS

Solar cells involving two different perovskites were manufactured and analyzed. The perovskites were (CH3NH3)PbI3 and (CH3NH3)SnI3. Both perovskites have a shared methyl ammonium group (MA) and are used as both light absorbing material and hole conducting material (HTM) in this project. The preparation procedures for the complete device were according to previous attempts to make stable organic-inorganic hybrid perovskites and involved different layers and procedures. Both perovskites were manufactured by mixing methyl ammonium iodide with either lead iodide or tin iodide in different concentrations. This was then deposited on a 600nm thick mesoporous TiO2 layer. Deposition of the hole-transporting material (HTM) was done by spin-coating 2,2´,7,7´-tetrakis-(N,N-dip-methoxyphenylamine) 9,9´-spirobifluorene, also called spiro-OMeTAD. Lastly thermal evaporation was used to deposit a silver electrode. Different measurements were done on the light absorbing materials. The lead perovskite solar cell device was subjected to illumination with Air Mass 1.5 sunlight (100mW/cm2) which produced an open circuit voltage Voc of 0.645 V, a short circuit photocurrent Jsc of about 7 mA/cm2, and a fill factor FF of 0.445. This resulted in a power conversion efficiency (PCE) of about 2% and an incident photon to current efficiency (IPCE) of up to 60%. The tin perovskite has not been used in solar cells before and the initial results presented here shows low performance using the same device construction as for the lead perovskite. However, the incident photon to electron conversion affirms that there is a current in the visible region, and IPCE of 12.5 % was observed at 375nm. UV-visible NIR measurement was used to analyze the light absorption of the perovskite structures and a broader light absorption was observed for the lead perovskite compared to the tin perovskite. X-ray diffraction (XRD) analyzing was done on both perovskite materials using different concentrations and both with and without nanoporous TiO2 film. Both perovskites demonstrate very similar peaks with some exceptions. Photo-induced absorption (PIA) measurement was used for the purpose of showing the magnitude of charge separation or hole transfer in the light absorbing material, both when using the perovskites as a light absorber and a hole conductor. This is measured by analyzing the hole injection from the excited light absorber into the HTM. Hole transfer was observed for the lead perovskite (when used as light absorber) and tin perovskite (when used as hole conductor).

Developing new materials with desired properties is a vital component of emerging technologies. Functional hybrid compounds make an important class of advanced materials that let us synergistically utilize the key features of the organic and inorganic counterparts in a single composite, providing a very strong tool to develop new materials with ”engineered” properties. The research presented here, summarizes efforts in the development of facile and efficient methods for the fabrication of three- and two-dimensional inorganic-organic hybrids based on layered oxide perovskites. Microwave radiation was exploited to rapidly fabricate and modify new and known materials. Despite the extensive utilization of microwaves in organic syntheses as well as the fabrication of the inorganic solids, the work herein was among the first reported that used microwaves in topochemical modification of the layered oxide perovskites. Our group specifically was the first to perform rapid microwave-assisted reactions in all of the modification steps including proton exchange, grafting, intercalation, and exfoliation, which decreased the duration of multi-step modification procedures from weeks to only a few hours. Microwave-assisted grafting and intercalation reactions with n-alkyl alcohols and n-alkylamines, respectively, were successfully applied on double-layered Dion-Jacobson and Ruddlesden-Popper phases (HLaNb2O7, HPrNb2O7, and H2CaTa2O7), and with somewhat more limited reactivity, applied to triple-layered perovskites (HCa2Nb3O10 and H2La2Ti3O10). Performing neutron diffraction on n-propoxy-LaNb2O7, structure refinement of a layered hybrid oxide perovskite was then tried for the first time. Furthermore, two-dimensional hybrid oxides were efficiently prepared from HLnNb2O7 (Ln = La, Pr), HCa2Nb3O10, HCa2Nb2FeO9, and HLaCaNb2MnO10, employing facile microwave-assisted exfoliation and post-exfoliation surface-modification reactions for the first time. A variety of surface groups, saturated or unsaturated linear and cyclic organics, were successfully anchored onto these oxide nanosheets. Properties of various functionalized metal-oxide nanosheets, as well as the polymerization of some monomer-grafted nanosheets, were then investigated for the two-dimensional hybrid systems.

Über die besonders hohe Effizienz von Halid-Perowskit (HaP)-basierten optoelektronischen Bauteilen wurde bereits in der Literatur berichtet. Um die Entwicklung dieser Bauteile voranzutreiben, ist ein umfassendes und verlässliches Verständnis derer elektronischen Struktur, sowie der Energielevelanordnung (ELA) an HaP Grenzflächen von größter Bedeutung. Demzufolge beschäftigt sich die vorliegende Arbeit mit der Untersuchung i) der Bandstruktur von Perowskit-Einkristallen, um ein solides Fundament für die Darlegung der elektronischen Eigenschaften von polykristallinen Dünnschichten zu erarbeiten, und mit ii) den Einflüssen von Oberflächenzuständen auf die elektronische Struktur der Oberfläche, sowie deren Rolle bei der Kontrolle von ELA an HaP Grenzflächen. Die Charakterisierung erfolgt überwiegend mithilfe von Photoelektronenspektroskopie (PES) und ergänzenden Messmethoden wie Beugung niederenergetischer Elektronen an Oberflächen, UV-VIS-Spektroskopie, Rasterkraftmikroskopie und Kelvin-Sonde. Erstens weist die Banddispersion von zwei prototypischen Perowskit-Einkristallen eine starke Dispersion des jeweiligen oberen Valenzbandes (VB) auf, dessen globales Maximum in beiden Fällen am R-Punkt in der Brillouin-Zone liegt. Dabei wird eine effektive Lochmasse von 0.25 m0 für CH3NH3PbBr3, bzw. von ~0.50 m0 für CH3NH3PbI3 bestimmt. Basierend auf diesen Ergebnissen werden die elektronischen Spektren von polykristallinen Dünnschichten konstruiert und es wird dadurch aufgezeigt, dass eine Bestimmung der Valenzbandkantenposition ausgehend von einer logarithmischen Intensitätsskala aufgrund von geringer Zustandsdichte am VB Maximum vorzuziehen ist. Zweitens stellt sich bei der Untersuchung der elektronischen Struktur von frisch präparierten Perowskit-Oberflächen heraus, dass die n-Typ Eigenschaft eine Folge der Bandverbiegung ist, welche durch donatorartige Oberflächenzustände hervorgerufen wird. Des Weiteren weisen die PES-Messungen an Perowskiten mit unterschiedlichen Zusammensetzungen aufgrund von Oberflächenphotospannung eine Anregungslichtintensitätsabhängigkeit der Energieniveaus von bis zu 0.7 eV auf. Darüber hinaus wird die Kontrolle von ELA durch gezielte Variation der Oberflächenzustandsdichte gezeigt, wodurch sich unterschiedliche ELA-Lagen (mit Abweichungen von über 0.5 eV) an den Grenzflächen mit organischen Akzeptormolekülen erklären lassen. Die vorliegenden Ergebnisse verhelfen dazu, die starke Abweichung der in der Literatur berichteten Energieniveaus zu erklären und somit ein verfeinertes Verständnis des Funktionsprinzips von perowskit-basierten Bauteilen zu erlangen.
Optoelectronic devices based on halide perovskites (HaPs) and possessing remarkably high performance have been reported. To push the development of such devices even further, a comprehensive and reliable understanding of their electronic structure, including the energy level alignment (ELA) at HaPs interfaces, is essential but presently not available. In an attempt to get a deep insight into the electronic properties of HaPs and the related interfaces, the work presented in this thesis investigates i) the fundamental band structure of perovskite single crystals, in order to establish solid foundations for a better understanding the electronic properties of polycrystalline thin films and ii) the effects of surface states on the surface electronic structure and their role in controlling the ELA at HaPs interfaces. The characterization is mostly performed using photoelectron spectroscopy, together with complementary techniques including low-energy electron diffraction, UV-vis absorption spectroscopy, atomic force microscopy and Kelvin probe measurements. Firstly, the band structure of two prototypical perovskite single crystals is unraveled, featuring widely dispersing top valence bands (VB) with the global valence band maximum at R point of the Brillouin zone. The hole effective masses there are determined to be ~0.25 m0 for CH3NH3PbBr3 and ~0.50 m0 for CH3NH3PbI3. Based on these results, the energy distribution curves of polycrystalline thin films are constructed, revealing the fact that using a logarithmic intensity scale to determine the VB onset is preferable due to the low density of states at the VB maximum. Secondly, investigations on the surface electronic structure of pristine perovskite surfaces conclude that the n-type behavior is a result of surface band bending due to the presence of donor-type surface states. Furthermore, due to surface photovoltage effect, photoemission measurements on different perovskite compositions exhibit excitation-intensity dependent energy levels with a shift of up to 0.7 eV. Eventually, control over the ELA by manipulating the density of surface states is demonstrated, from which very different ELA situations (variation over 0.5 eV) at interfaces with organic electron acceptor molecules are rationalized. Our findings further help to explain the rather dissimilar reported energy levels at perovskite surfaces and interfaces, refining our understanding of the operational principles in perovskite related devices.

In the last 10 years, the research interest has been drawn towards the hybrid organic-inorganic halide perovskites, an innovative material characterized by remarkable optoelectronic properties and by its simplicity of fabrication; hybrid halide perovskites are currently being employed as active material in solar cells, X-ray photodetectors and light emitting devices. The following thesis presents the characterization of two perovskite-based materials. The first is a methylammonium lead iodide (MAPbI3) thin film solar cell, which has been fabricated and characterized at the University of Konstanz (Germany), with the aim to optimize the deposition procedure. The second material is a methylammonium lead bromide (MAPbBr3) single crystal that have been characterized at the University of Bologna with surface photovoltage and photocurrent spectroscopies, as a function of the deposited dose of X-rays in order to monitor the induced effects of radiation. After the exposure to X-rays, the exciton binding energy, calculated from the surface photovoltage spectra, has been found to increase by 20 meV with respect to the not irradiated sample. A similar result has been found with the photocurrent spectroscopy. The reasons for the increase in binding energy is discussed and attributed to a change in polarizability of the single crystal. The recovery of the crystals has been registered as well and has shown that the material is able to return to the initial condition after just few hours from the last X-ray's deposition.

Solar energy as the most abundant source of energy is clean, non-pollutant, and completely renewable, which provides energy security, independence, and reliability. Organic-inorganic hybrid perovskite solar cells (PSCs) revolutionized the photovoltaics field not only by showing high efficiency of above 22% in just a few years but also by providing cheap and facile fabrication methods. In this dissertation, fabrication of PSCs in both ambient air conditions and environmentally controlled N2-filled glove-box are studied. Several characterization methods such as SEM, XRD, EDS, Profilometry, four-point probe measurement, EQE, and current-voltage measurements were employed to examine the quality of thin films and the performance of the PSCs. A few issues with the use of equipment for the fabrication of thin films are addressed, and the solutions are provided. It is suggested to fabricate PSCs in ambient air conditions entirely, to reduce the production cost. So, in this part, the preparation of the solutions, the fabrication of thin films, and the storage of materials were performed in ambient air conditions regardless of their humidity sensitivity. Thus, for the first part, the fabrication of PSCs in ambient air conditions with relative humidity above ~36% with and without moisture sensitive material, i.e., Li-TFSI are provided. Perovskite materials including MAPbI3 and mixed cation MAyFA(1-y)PbIxBr(1-x) compositions are investigated. Many solution-process parameters such as the spin-coating speed for deposition of the hole transporting layer (HTL), preparation of the HTL solution, impact of air and light on the HTL conductivity, and the effect of repetitive measurement of PSCs are investigated. The results show that the higher spin speed of PbI2 is critical for high-quality PbI2 film formation. The author also found that exposure of samples to air and light are both crucial for fabrication of solar cells with larger current density and better fill factor. The aging characteristics of the PSCs in air and vacuum environments are also investigated. Each performance parameter of air-stored samples shows a drastic change compared with that of the vacuum-stored samples, and both moisture and oxygen in air are found to influence the PSCs performances. These results are essential towards the fabrication of low-cost, high-efficiency PSCs in ambient air conditions. In the second part, the research is focused on the fabrication of high-efficiency PSCs using the glove-box. Both single-step and two-step spin-coating methods with perovskite precursors such as MAyFA(1-y)PbIxBr(1-x) and Cesium-doped mixed cation perovskite with a final formula of Cs0.07MA0.1581FA0.7719Pb1I2.49Br0.51 were considered. The effect of several materials and process parameters on the performance of PSCs are investigated. A new solution which consists of titanium dioxide (TiO2), hydrochloric acid (HCl), and anhydrous ethanol is introduced and optimized for fabrication of quick, pinhole-free, and efficient hole-blocking layer using the spin-coating method. Highly reproducible PSCs with an average power conversion efficiency (PCE) of 15.4% are fabricated using this solution by spin-coating method compared to the conventional solution utilizing both spin-coating with an average PCE of 10.6% and spray pyrolysis with an average PCE of 13.78%. Moreover, a thin layer of silver is introduced as an interlayer between the HTL and the back contact. Interestingly, it improved the current density and, finally the PCEs of devices by improving the adhesion of the back electrode onto the organic HTL and increasing the light reflection in the PSC. Finally, a highly reproducible fabrication procedure for cesium-doped PSCs using the anti-solvent method with an average PCE of 16.5%, and a maximum PCE of ~17.5% is provided.

Efterfrågan på bättre och mer hållbart material ökar. Mer effektivt material kommer att behövas för att möta den ökande, globala efterfrågan. Hybrida organiska-oorganiska material är en typ av material som har varit av stort intresse nyligen, och kan beskrivas som en typ av material som består av både organiska och oorganiska komponenter. Denna avhandling har fokuserat på hybrida organiska-oorganiska material inspirerade av den klassiska perovskitstrukturen ABX3, där komponent A är en organisk katjon, komponent B är en divalent metalkatjon och komponent X är en anjon. Hybrida organiska-oorganiska material som är utgår från den klassiska perovskitstrukturen kan ha olika funktionella egenskaper och en bred variation av tänkbara applikationer. Några exempel på dessa egenskaper och möjliga applikationer inkluderar god fotokonduktivitet för solceller, utmärkt emissionsegenskaper för ljusdioder och justerbara dielektriska egenskaper för elektroniska växlar och sensorer.  De fysiska egenskaperna av det hybrida organiska-oorganiska materialet beror på kristallstrukturen av materialet, som i sig bestäms av valet av komponenter. På grund av de många möjligheter av organiska och oorganiska komponenter så finns det möjlighet att syntetisera helt nya hybrida organiska-oorganiska föreningar som kan ha nya eller förbättrade fysiska egenskaper.  Nuvarande hybrida organiska-oorganiska material som utgår från perovskitstrukturen använder huvudsakligen bly som divalent metalkatjon, och det beror på att den ger den bästa funktionella effekten. Blys toxicitet är dock en stor nackdel för nuvarande blybaserade hybrid oorganiska material. Möjligheten att ersätta bly med en annan divalent metall har undersökts under detta projekt. I denna avhandling så har den organiska katjonen cyclohexylammonium (CHA) varit i fokus som den organiska komponenten. Målet med detta examensarbete var att designa, syntetisera och karakterisera nytt hybrid organisk-oorganiskt material. De hybrida organiska-oorganiska föreningarna CHAZnBr3 och (CHA)2ZnBr4 syntetiserades för den första gången, så vitt författaren vet, och kommer vara i fokus i denna avhandling. De två nya hybrida organiska-oorganiska föreningarna blev strukturellt karakteriserade med X-ray Diffraction (XRD) och termiskt karakteriserade med Thermal Gravimetric Analysis (TGA) och Differential Scanning Calorimetry (DSC).  Den första föreningen, CHAZnBr3, kunde bestämmas att vara ortorombisk vid 298 K. Föreningen bestämdes vara termisk stabil upp till 490 K, och genomgår en fasövergång vid 445 K. Den andra föreningen, (CHA)2ZnBr4, kunde inte bestämmas strukturellt vid varken 100 K eller 298 K. Föreningen bestämdes vara termisk stabil upp till 490 K, och genomgår en fasövergång vid 230 K. Ytterligare karakterisering krävs för att bättre förstå egenskaperna hos dessa föreningar och deras möjliga användningsområden.
The demand for better and more sustainable material is increasing. More efficient materials will be needed to meet the growing global need. Hybrid organic-inorganic materials are one type of materials that have been of great interest recently, which can be described as a class of materials that mix organic and inorganic components. This thesis focused on hybrid organic-inorganic materials inspired by the classical perovskite crystal structure ABX3, where component A is an organic cation, component B is a divalent metal cation and component X is an anion. Hybrid organic-inorganic materials based on the classical perovskite structure may have various functional properties and may have a broad range of potential applications. Some examples of those properties as well as some and possible applications include good photoconductivity and power conversion efficiency for photovoltaic devices, excellent emission properties for light emitting diodes and tunable dielectric properties for electronic switches and sensors.  The physical properties of the hybrid organic-inorganic material are determined by the crystal structure of the material, which in turn will be decided by the choice of components. With the many possible choices for organic and inorganic components, there is an opportunity to synthesize completely new hybrid organic-inorganic compounds that may display new or superior physical properties. Current hybrid organic-inorganic materials based on the perovskite crystal structure mainly use lead as the divalent metal, since it currently gives the best performance. The toxicity of lead is a major drawback for current lead-based hybrid organic-inorganic materials. The possibility to replace lead with another divalent metal has been explored during this project. For this thesis, the organic cation cyclohexylammonium (CHA) has been of focus as the organic component. The aim of this thesis was to design, synthesize and characterize novel hybrid organic-inorganic compounds. The hybrid organic-inorganic compounds CHAZnBr3 and (CHA)2ZnBr4 were synthesized for the first time, to the best of our knowledge, and will be the focus of this thesis. The two new hybrid organic-inorganic compounds were structurally characterized by X-ray Diffraction (XRD) and thermally characterized by Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC).  The first compound, CHAZnBr3, could be determined to be orthorhombic at 298 K. The compound was found to be thermally stable up 490 K, and to undergo a phase transition at 445 K.  The second compound, (CHA)2ZnBr4, could not be fully structurally solved at either 100 K or 298 K. The compound was found to be thermally stable up to 490 K, and to undergo a phase transition at 230 K.  Further characterization will be needed to better understand the properties of these two compounds and their possible applications.

This thesis consists of three main studies: magnetic field effects in thermally activated delayed fluorescent (TADF) organic light emitting diodes (OLEDs), magnetic field effects in bipolar and unipolar polythiophene (P3HT) devices and a study of hybrid organic/inorganic perovskite devices. Spin-dependent transport and recombination processes of spin-pair species have been detected by magnetic field effect (MFE) technique in carbon-based semi- conductor devices. Magneto-electroluminescence (MEL) and magneto-conductivity have been measured as a function of the applied magnetic field, B, in light emitting diodes. TADF materials have been used instead of simple fluorescent materials in OLEDs. We have observed very large magnetic response with TADF materials. The second study is magnetic field effects of regio-regular P3HT based OLED devices. P3HT is a well known semiconducting polymer, and its electrical properties such as magneto-conductance can be affected by an applied magnetic field. P3HT was chosen because it exhibits a sign change in magnetoresistance (MR) as the bias is increased. Unipolar and bipolar devices have been fabricated with different electrode materials to understand which model can be best to explain organic magnetoresistance effect, possibly depending on the operating regime of the device. Transport and luminescence spectroscopies were studied to isolate the different mechanisms and identify their fingerprints. The third study is on hybrid organic-inorganic perovskite devices. With the potential of achieving very high efficiencies and the very low production costs, perovskite solar cells have become commercially attractive. Scanning electron microscopy (SEM) images and absorption spectrum of the films were compared in single-step solution, two-step solution and solution-assisted vapor deposition techniques. Grain size, morphology and thickness parameters of perovskite films were studied within these techniques. Perovskite solar cells were fabricated and their efficiencies were measured.

Der Schwerpunkt der vorliegenden Arbeit liegt in der Charakterisierung der elektronischen Eigenschaften von hybriden organisch-anorganischen Perowskit (HOIP)-Schichten während der Schichtbildung und in verschiedenen Umgebungen mittels Photoelektronenspektroskopie (PES). Insbesondere wird der Methylammonium-Blei-Iodid-Chlorid-Perowskit (MAPbI3-xClx) untersucht. Als erstes werden Änderungen in den elektronischen Eigenschaften, der Zusammensetzung, sowie der Kristallstruktur mittels PES, Flugzeit-Sekundärionenmassenspektrometrie, sowie Röntgendiffraktometrie mit streifendem Einfall analysiert. Die Resultate weisen auf die entscheidende Rolle von Chlor im texturierten Wachstum der Perowskitschicht hin. Die auskristallisierte Perowskitschicht weist eine stärkere n-Typ Eigenschaft auf, welche auf die Änderung der Zusammensetzung während der Schichtbildung zurückgeführt werden kann. Außerdem beweisen die Ergebnisse eindeutig die Ablagerung von Chlor an der Grenzfläche zwischen der Perowskitschicht und dem Substrat. Zweitens werden die separaten Einflüsse von Wasser, Sauerstoff, und Umgebungsluft auf die elektronischen Eigenschaften von MAPbI3-xClx-Schichtoberflächen untersucht. Bereits geringste Wassermengen ähnlich wie im Hochvakuum oder in inerter Umgebung können eine reversible Reduzierung der Austrittsarbeit hervorrufen. Höherer Wasserdampf-Partialdruck führt zu einer Verschiebung des Valenzbandmaximums (VBM) weit vom Fermi-Niveau, sowie zu einer Reduzierung der Austrittsarbeit. Im Gegensatz dazu führt eine Sauerstoffexposition zu einer Verschiebung des VBM in Richtung des Fermi-Niveaus und zu einer Steigerung der Austrittsarbeit. Analog kommt es zu einer Verschiebung von bis zu 0.6 eV bei einer Exposition gegenüber Umgebungsluft, was den vorwiegenden Einfluss von Sauerstoff demonstriert. Die vorliegenden Untersuchungen betonen den kritischen Einfluss der Schichtbildung, der Zusammensetzung, sowie der Umgebungsbedingungen auf die elektronischen Eigenschaften von HOIP.
The present thesis aims at characterizing the electronic properties of solution-processed hybrid organic-inorganic perovskites (HOIPs) in general, and the HOIP methyl ammonium (MA) lead iodide-chloride (MAPbI3-xClx) films, in particular, at different stages, namely from its formation to its degradation, by means of photoelectron spectroscopy (PES). Firstly, the formation of MAPbI3-xClx films upon thermal annealing is monitored by a combination of PES, time-of-flight secondary ion mass spectrometry, and grazing incidence X-ray diffraction for disclosing changes in electronic properties, film composition, and crystal structure, respectively. Overall, the results point to the essential mediating role of chlorine in the formation of a highly textured perovskite film. The film formation is accompanied by a change of composition which leads to the film becoming more n-type. The accumulation of chlorine at the interface between perovskite and the underlying substrate is also unambiguously revealed. Secondly, the separate effects of water and oxygen on the electronic properties of MAPbI3-xClx film surfaces are investigated by PES. Already low water exposure – as encountered in high vacuum or inert conditions – appears to reversibly impact the work function of the film surfaces. Water vapor in the mbar range induces a shift of the valence band maximum (VBM) away from the Fermi level accompanied by a decrease of the work function. In contrast, oxygen leads to a VBM shift towards the Fermi level and a concomitant increase of the work function. The effect of oxygen is found to predominate in ambient air with an associated shift of the energy levels by up to 0.6 eV. Overall, the findings contribute to an improved understanding of the structure-property relationships of HOIPs and emphasize the impact of least variation in the environmental conditions on the reproducibility of the electronic properties of perovskite materials.

Hybrid organic-inorganic solar photovoltaic (PV) cells capable of directly converting sunlight to electricity have attracted much attention in recent years. Despite evident technological advancements in the PV industry, the widespread commercialisation of solar cells is still being mired by their low conversion efficiencies and high cost per Watt. Perovskites are an emerging class of semiconductors providing a low-cost alternative to silicon-based photovoltaic cells, which currently dominate the market. This thesis develops a series of studies on “all-solid state perovskite solar cells” fabricated via vapour deposition which is an industrially-accessible technique, to achieve planar heterojunction architectures and efficient PV devices. Chapter 2 presents a general outlook on the operating principles of solar cells, delving deeper into the specific operational mechanism of perovskite solar cells. It also explores the usual methods employed in the fabrication of perovskite thin films. Chapter 3 describes the experimental procedures followed during the fabrication of the individual components constituting the device from the synthesis of the precursors to the construction of the functioning perovskite PV devices. Chapter 4 demonstrates pioneering work involving the dual-source vapour deposition (DSVD) of planar heterojunction perovskite solar cells which generated remarkable power conversion efficiency values surpassing 15%. These significant results pave the way for the mass-production of perovskite PVs. To further expand the range of feasible vapour deposition techniques, a two-layer sequential vapour deposition (SVD) technique is explored in Chapter 5. This chapter focusses on identifying the factors affecting the fundamental properties of the vapour-deposited films. Findings provide an improved understanding of the effects of precursor compositions and annealing conditions on the films. Chapter 5 concludes with a comparison between SVD and DSVD fabricated films, highlighting the benefits of each vapour deposition technique. Furthermore, hysteretic effects are analysed in Chapter 6 for the perovskite PV devices fabricated based on different structural configurations. An interesting discovery involving the temporary functioning of compact layer-free perovskite PV devices suggests the presence of a built-in-field responsible for the hysteresis of the cells. The observations made in this chapter yield a new understanding of the functionality of individual cell layers. Combining the advantages of the optimum vapour deposition technique established in Chapter 4 and Chapter 5, with the enhanced understanding of perovskite PV cell operational mechanism acquired from Chapter 6, an ongoing study on an “all-perovskite” tandem solar cell is introduced in Chapter 7. This demonstration of the “all-perovskite” tandem devices confirms the versatility of perovskites for a broader range of PV applications.

碩士
國立中山大學
材料與光電科學學系研究所
107
In recent years, there has been a crystalline material - "organic-inorganic hybrid perovskite " structure which has been taken as the potential candidate of future solar cells. These perovskite solar cells have attracted the scientist’s attention due to their easy fabrication process and rapid growth conversion efficiency. Thus, our study is focus on perovskite structure. There are two parts of our work. In the first part, we use inverse temperature crystallization method to grow perovskite single crystals. In the second part, we added Tetrahydrothiophene 1-oxide (THTO) in perovskite precursor solution and use spin-coating method to fabricate thin films. We found that THTO can enhance the prefer orientation for thin films which may be better for device applications. In the first study, we fabricate various types of perovskite single crystals successfully via inverse temperature crystallization such as MAPbBr3, MAPbI3, MA1-xCsxPbI3 and MAPbI3-xClx. The crystal structure has been confirmed by X-ray diffraction analysis and the crystal quality has been analyzed by rocking curve analysis (High- Resolution XRD). We also use SEM, OM to analyze their surface morphology. In our second work, we can observe the films fabricated by adding THTO in solution using X-ray diffraction analysis, was performed prefer orientation on (110) and (220) diffraction angles, and the grain size for adding THTO in the solution is larger than another using SEM images analysis.

碩士
元智大學
化學工程學系
91
Abstract In this study, the organic-inorganic layer perovskite compound (C6H13NH3)2(CH3NH3)m-1PbmBr3m+1 were composed. We can control the inorganic layer thickness by changing the stoichiometry of reactants and reacting environment. They are characterized by use of instrument analysis in order to investigate the relationship between inorganic layers and physical properties and electrical properties. Because of the solubility of this materials we can synthesis polymer nanocompoiste in solution. Then we discuss the effect with different nanodisperse. XRD results showed that the d-spacing increases at constant value with increase the inorganic layers which identified our expectation. The UV-Vis and PL results had red-shift when increase the inorganic layers. The phenomena show that the energy gap can be changed by tunneling the layer structure. By dielectric analysis we understand the dielectric constant is corresponding to the numbers of inorganic layers. Conductivity relaxation time distribution increase when the numbers of inorganic layer increase. We also identified the carrier mobility will increase when the numbers of inorganic layers increase. In polymer nanocompoist, we found different nanodisperse. The UV-Vis and PL spectrum had substantial change when adding polymer and different layer structure. From DEA analysis, we found that different polymer will cause different carrier hoping activity energy and conductivity relaxation conversion temperature.

碩士
明志科技大學
電子工程系碩士班
107
Organic-inorganic hybrid perovskites have been studied intensively due to their high absorption coefficient, high efficiency, long carrier diffusion length, facile fabrication process, and low material cost. Such hybrid perovskites have been applied for various optoelectronic devices including photovoltaic cells, light-emitting diodes, and photodetectors. Organic-inorganic hybrid perovskites exhibit the general formula ABX3, where A is a monovalent organic cation, B is Pb2+ or Sn2+, and X is a halide anion. In this thesis, CH3NH3PbI3 perovskite thin films with different concentrations were prepared using one-step deposition method. Temperature-dependent photoluminescence (PL) were carried out in the temperature range from 10 to 300 K. The carrier emission mechanism, carrier redistribution effect, electron-phonon renormalization and thermal expansion effect on the band-gap are discussed to investigate the thermal behaviors of peak energy, full width at half maximum, and intensity of the PL spectra measured from our samples.

碩士
國立中山大學
材料與光電科學學系研究所
107
The organic-inorganic hybrid perovskite structure is a novel semiconductor, which has the advantages of simple process and excellent photoelectric characteristics, and attracts lots attentions in recent years. Among them, in 2015, Saidaminov, et al. found that in a specific solution, single crystals can be precipitated in perovskite solution in a short time by raising the temperature, called inverse temperature crystallization. This finding provides a fast and efficient way to grow perovskite single crystals. However the mechanism is not fully understood yet. This study aims to investigate the inverse temperature crystallization mechanism of organic-inorganic hybrid perovskite crystals. The issue was approached by the solution measured by UV-Vis absorption spectroscopy. It is found that higher halide coordination number complex of Pb2+ was increased in the solution with higher concentrations of either halide ion or lead ion. Moreover, to raise temperature will also cause higher halide coordination number complex of Pb2+ to be formed. Our results reveal the mechanism for the inverse temperature crystallization: Raising temperature causes the break of the bonding between Pb2+ and the solvent molecule, hence towards higher halide coordination number complex, which favors the formation of MAPbI3 crystals. Moreover, we studies the intermediate compounds constituted of MAI, PbIb2 and the solvent ( DMSO, DMF, or GBL) by thermogravimetric analysis (TGA) and XRD analysis. Our results indicates the three intermediate structures will be decomposed at temperature of ~ 110 C (GBL), 120 C (DMF), and 170 C (DMSO), respectively.

碩士
國立清華大學
光電工程研究所
102
This paper proposed a low temperature, solution process, simple process, a large area of the lead halide perovskite organic/inorganic hybrid solar cell. In this paper, in which the use of lead halide perovskite as the photoactive layer. With the high solubility PbCl2 in DMSO to increase the concentration of the precursor solution, and construct organic / inorganic hybrid solar cell. Our device configuration:Glass/ITO/PEDOT:PSS/Perovskite/PCBM/Al belong to normal structure. Suitably selected the hole and the electron transport layer by spin coating and dried to optimize conditions for the performance of the solar cell of the present paper is better. In this paper, Construction of the solar cell efficiency of up to 7.0 %, short-circuit current of 18.1 mA/cm2 has excellent performance. Lead halide perovskite organic / inorganic hybrid solar cell laden with good efficiency and performance advantages of a large area can be to facilitate the production of large-area components toward future development.

[ITALIANO] In questo lavoro di tesi l’attenzione è stata rivolta allo studio di composti ibridi self-assembled per l’elettronica. Il primo passo è stato la sintesi (dove è stato possibile) e la classificazione strutturale delle polveri policristalline dei composti in esame ovvero alogenuri di metalli (Cu, Sn) intercalati con ammine semplici (formula chimica (CnH2n+1NH3)2CuCl4 e CH3NH3SnX3 con X=Cl, Br, I). In particolare i composti CH3NH3SnX3 risultano avere una struttura cubica mentre quelli (CnH2n+1NH3)2CuCl4 mostrano una struttura ortorombica, un discorso particolare va fatto per il composto (CH3NH3)2CuCl4 la cui struttura è molto discussa, probabilmente monoclina anziché ortorombica. I film sono stati realizzati presso il centro IMEM-CNR di Parma durante la mia permanenza, attraverso una tecnica detta SSTA (Ablazione Termica da Singola Sorgente) in un reattore da alto vuoto partendo dalle polveri come composti precursori. Per i composti dello stagno l’evaporazione è stata effettuata dai sali componenti del composto che volevamo realizzare, anche in questo modo sono stati ottenuti buoni risultati, a testimonianza della buona elasticità della tecnica di deposizione SSTA. La buona qualità dei film è stata valutata attraverso la caratterizzazione morfologico-strutturale e delle proprietà ottiche. La morfologia superficiale dei film è stata analizzata con tecniche microscopiche (microscopio ottico, AFM) che ha mostrato una struttura a grani piccoli dei film mentre con la tecnica di diffrazione da raggi X (radiazione CuK-alfa del rame) è stato realizzato un ampio studio sistematico della struttura reticolare dei composti. L’ottimizzazione del processo di deposizione ci ha portato ad ottenere film monofasici cristallinamente ben strutturati, dall’analisi diffrattometrica infatti si osserva come i composti non presentino fasi spurie e risultino ben orientati asse c. Sui film ottimizzati è stato effettuato uno studio delle proprietà ottiche di assorbimento e fotoemissione al variare della temperatura. Dalle misure di assorbimento è stato possibile osservare le energie delle bande elettroniche in particolare del claster perovskitico CuCl42- con notevole sensibilità a testimonianza delle buone proprietà di ordine strutturale dei film rispetto ai composti bulk. Le misure di fotoluminescenza mostrano invece la presenza di un picco di emissione a circa 380 nm di natura eccitonica. In particolare il composto (C2H5NH3)2CuCl4 per l’elevata stabilità, bassa igroscopicità buona conducibilità ed intensa fotoluminescenza, risulta un candidato ideale per eventuali studi di elettroluminescenza e realizzazioni di dispositivi LED nell’UV. Infine sui film ottimizzati si è proceduto alla caratterizzazione della risposta di trasporto elettrico in continua in funzione della realizzazione di un dispositivo preliminare FET (Field Effect Transistor). Le categorie di film studiati risultano isolanti o semiconduttori, tale caratterizzazione è stata effettuata attraverso misura della resistività in funzione della temperatura. Un dispositivo FET è stato realizzato e misurato utilizzando come elemento attivo (canale) un film del composto semiconduttivo CH3NH3SnBr3. Infine uno studio sulla sensitività all’umidità dei composti proposti è stato effettuato in collaborazione con l’istituto ENEA di portici. I materiali considerati infatti, sono sali igroscopici ed hanno mostrato interessanti caratteristiche per la realizzazione di eventuali sensori di umidità. / [ENGLISH] In this work of thesis study, synthesis, and characterization of two perovskite based hybrid series of compounds was been faced. The search for new materials plays a central role in the framework of new technologies and in sector of consumer electronics. In the last ten years, in fact, an extraordinary growth has been registered (organic electronics) and the increasing business of connection between communication and information technologies and the foreseen possibility of reaching the physical limit of semiconductor technology, have required the search of new ideas to develop cheaper materials and technologies that could generate new applications and form factors to drive the growing needs for pervasive computing and enhanced connectivity. The research in organic-inorganic hybrids in the last years has focused on using the range of interactions found within organic and inorganic worlds in order to create, project and engineering new materials with the desired, innovative or increased functionalities relative to that achievable with organic and inorganic materials alone. The attention in this work is focused on the perovskite based hybrid compounds, proposed by D. B. Mitzi of IBM research center, that result a remarkable example for potentially useful physical properties including enhanced exciton binding energies, nonlinear optical properties, electroluminescence, organic-like mobility, magnetic properties, conductivity and other properties. The advantage of the hybrid compounds is mostly related to the greater thermal stability related to full long-range structural ordering in respect to ordinary organic compounds, without losing flexibility and simple processability that have a principal role in low-cost electronics. Simple processability, in Hybrid organic-inorganic compounds, as the perovskite based hybrids, is in many cases overdrew by self-assembling properties. In the proceeding of this thesis work, the attention will be focused on two series of hybrid compounds: (CnH2n+1NH3)2CuCl4 (where n =1,…,4) (called 2D layered structures) and CH3NH3SnX3 (where X =Cl and Br) (called 3D structures) where alkylammonium chains are the organic components while the constituent unit of the inorganic structure is the octahedral cluster MX64-. The bonding between organic and inorganic components is realized by an ordinary ammine group ( NH3+) that realizes an hydrogen/ionic bond with the halogen atoms. The choice of these two class of compound is related to the interesting electrical, magnetic and optical properties of relative isostructural compounds reported in literature. The possibility to synthesize and study optical properties of transition metal halide compounds is explored, in view of exploiting such a potentiality and to find new materials for UV-LED applications and conductive compounds with organic-like or enhanced mobility. In the framework of the research of enhanced mobilities materials, in fact, hybrid compounds have drive great interest. As for analogues inorganic oxide-based perovskite layered family, metal-semiconductor transition in function of the perovskite layer thickness have been reported in literature in the tin (II) 100 and 110 oriented perovskite families. This first example of conducting layered organic-inorganic halides enable an examination of the electrical transport properties as a function of the dimensionality of the metal halide framework In the development of this thesis it is proposed an introduction on the world of new materials for electronics and a brief overview of hybrid compounds with particular attention on perovskite based ones. Many of the pre-established aims have been reached, in the film deposition, characterizations, and the comprehension of some correlation between the structures of hybrid compounds and their properties. Synthesis problems and the possible techniques in the realization of polycrystalline powders and films of the two series of selected materials are discussed. In fact, many potential applications involving the organic-inorganic hybrids depend on the availability of simple and reliable thin film deposition techniques. In this work a single source evaporative technique (Single Source Thermal Ablation) has been utilized for film deposition. The obtained film were primarily investigated and optimized in respect to the crystallographic quality. The technique used for the investigation of the structural properties of the films realized for SSTA is X-rays diffraction. CH3NH3SnCl3 is the more complex compound to realize in thin film form. Its surface was observed by AFM (Atomic Force Microscope) and SEM (Scanning electron Microscope) analysis. The high flexibility of Single Source Thermal Ablation technique in hybrid films deposition has been demonstrated. The films obtained in the optimized deposition conditions on different substrates (crystalline, amorphous and flexible), results by the different analysis to have good structural, morphological and optical quality. it is analyzed the change in optical properties with the change of one component in the 2D [(CnH2n+1NH3)2CuCl4] and 3D [CH3NH3SnX3] series structure to understand the possible correlations between structure and optical properties. Besides, the 2D layered hybrid structures have attracted the scientists’ interest because these systems act as the artificial multi-quantum well structures. In principle in this type of structure it is possible to obtain excitonic states and so photoluminescence and electroluminescence, by quantum and dielectric confinement effects. Besides, the intrinsic two-dimensional layered structure of some hybrids, added to self-assembling properties, can lead to the possibility to design and synthesize an emitter material with the capability to control electron/hole drain and separation. Analysis of the absorption data was carried out to test the optical quality of SSTA deposited films as well as to determine the predominant optical transition and electronic configuration, while the presence of excitonic states transition have been investigated by photoluminescence measurements performed on the films. All the analyzed 2D layered copper structures realize a photoluminescence emission in the UV. In particular (C2H5NH3)2CuCl4 compound thanks to its high stability, low hygroscopicity, and good conduction properties, results a good candidate to UV-LED applications. Transport properties of perovskite based hybrid materials have been discussed. Resistivity and its temperature behaviour of deposited films of the two series are measured by standard technique while the CH3NH3SnBr3 film mobility was carried out by field effect analysis. A field effect device on SrTiO3 dielectric substrate has been realized and characterized varying gate voltages and temperature. Finally a study on the sensitivity to humidity of the much hygroscopic compounds are reported. In the structure-properties correlations, in the 2D compounds that optical properties don’t depend by changing of alkylammonium molecule and that room temperature resistivity decrease with increase of perovskite sheets coupling have been observed, while in 3D tin(II) structures, energy gap and resistivity increase when cell parameter decrease. By the field effect analysis it has been observed that in the proposed hybrid compounds conduction is due to hole carrier. Preliminary measures on sensitivity to humidity have shown interesting sensitivity properties of this hybrid in particular in 3D ones.

碩士
國立臺灣大學
材料科學與工程學研究所
106
Organic-inorganic hybrid lead halide perovskite solar cells have been developed rapidly because its excellent performance. However, the active material is unstable in ambient air, which limits its practical application. Thermal instability of devices states a more fundamental problem. In this thesis, atomic layer deposited inorganic metal oxides was applied to perovskite solar cells devices in order to solve the problem. We first investigated compatibility of perovskite with a variety of metallic precursors and with oxidants, respectively. We concluded criteria of selecting condition of ALD process and choice of precursors that would not damage perovskite. With optimal parameters, devices with ultra-thin atomic layer deposited Al2O3 or TiO2 direct on top of perovskite showed good performance. However, thermal instability of devices still did not improve due to imperfect coverage of oxides layer resulted from lack of nucleation cite on perovskite surface. To solve this problem, we deposited ALD AZO on organic charge transport layer instead. Device of this architecture reached efficiency of 14.6%, and only dropped to 80% of initial value after 1-day storage in glove box at 85℃. The thermal instability was much improved as efficiency of control devices dropped to less than 50% of initial value.

碩士
國立中山大學
材料與光電科學學系研究所
106
The thesis presents a study of the two-step sequential solution deposition process was studied for the preparation of high quality perovskite absorber layers for film performance analysis and device fabrication. PbI2 thin film was deposited by thermal evaporation and then soaked in the MAI solution to convert into MAPbI3 thin film. Different concentrations of MAI solutions, as well as solutions with different MACl contents were used to study how the crystallinity and coverage of the perovskite films are influenced by the parameters. In the first part, SEM was used for the morphology and crystallinity. In the second part, XRD was used to study the crystalline structure of the films. The third part, UV-vis absorption spectroscopy was used for the absorption spectra. Finally, secondary ion mass spectroscopy (SIMS) was used to probe the contents in the films and their depth profile. Moreover, we apply anti-solvent to form a dense waterproof layer on the surface of the perovskite film to improve the stability under ambient condition. The process prevents water from entering the interior of the perovskite films, hence to retard the decomposition of the perovskite structure. Our results indicate that the method would be essential for the high-efficient and air-stable perovskite solar cells.

碩士
明志科技大學
材料工程系碩士班
107
This study is divided into two parts. Report the growth of perovskite (PVSK) films grains with high average aspect ratio of non-wetting hole transporting materials (HTMS), which increase nucleus spacing by suppressing heterogeneous nucleation and facilitate grain boundary migration in grain growth by imposing less drag force. The reduced grain boundary area and improved crystallinity dramatically reduce the charge recombination in PVSK thin films to the level in PVSK single crystals. In the first part of this study，we synthesized a series of 2,2 and 3,3 substituted thienoisoindigo (TII)-based small molecules (H3−H7) with D-A-D structure and applied them as dopant-free HTMs in PSCs. The photophysical and electrochemical studies on these molecules showed that the HOMO energy levels of H3, H6 and H7 are suitable for hole extraction from perovskites, while the LUMO energy levels of H3−H7 were ideal for electron-blocking from perovskites to ITO electrode. Using p-i-n device structure for perovskite solar cells (PSCs), the best PCE reached 12.1% for H7-based PSC and it is comparable to that of PEDOT:PSS-based PSC, which was 12.0%. The H7-based PSC showed good device stability, its PCE did not decay within 168 hours under argon atmosphere. For the second part of this study，we have synthesized triphenylamine dibenzofulvene–based hole transporting materials featuring different numbers of OMe groups in a facile and cost-effective manner. These hole transporting materials exhibited good hole mobility, thermal stability, and morphological properties and could, therefore, be used as dopant-free hole transporting materials in inverted PSCs. The best cell performance of a device incorporating HTM4 (PCE = 15.78±0.61％) was superior to that of the corresponding PEDOT:PSS–based cell (PCE =12.80±1.31％). Moreover, because the hydrophobicity of HTM4 was greater than that of PEDOT:PSS, it provided a cell with greater long-term stability. We then employed HTM4 for the interfacial modified layer of a NiOx-derived PSC having the structure indium tin oxide/NiOx/HTM4/CH3NH3PbI3 (MAPbI3)/phenyl-C61-butyric acid methyl ester (PC61BM)/ bathocuproine (BCP)/Ag. The presence of HTM4 promoted the growth of micrometer-sized grains of perovskite and induced a lower content of grain boundary defects, both of which improved the carrier extraction. Thereby, compared with conventional NiOx devices, we observed a great increase in the PCE, from 17.16 ± 0.68% to 18.81 ± 0.42%, with a champion cell displaying a PCE of 19.37%. In addition, the PSC based on the bilayer HTM exhibited negligible hysteresis and a stabilized efficiency of approximately 19% after storage in the dark at 25 °C under argon for over 1000 h. This study suggests a new approach for designing interfaces to induce high-performance stable p–i–n PSCs.

碩士
國立臺灣大學
材料科學與工程學研究所
105
This work, we use inorganic nanocrystals of PbS/I- as additive and nucleus to improve thin film morphology and discuss it nucleation mechanism. A small amount of dispersed PbS nanocrystals which were covered with Perovskite precursor molecules of methylammonium iodide (CH3NH3I, MAI) through the ligand-seed like nucleation sites to promote the formation of Perovskite lattice structure. To realize inorganic nanocrystals of PbS/I- as additive in the Perovskite precursor how to transform the Perovskite thin film, we employed an in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) technique for this study. In the precursor without PbS/I-, When the substrate temperature is at 110℃ the Perovskite film is formed in three stage: the first stage increase rapid speed intermediate phase and Perovskite phase appear; the second stage the Perovskite phase growth fast speed; the final stage intermediate phase disappear and Perovskite intensity reach maximum. However, in the precursor with PbS/I-, the first stage Perovskite phase increase rapid speed and intermediate phase intensity very low; the second stage Perovskite phase intensity reach maximum; the final stage the intermediate phase rapid disappear and Perovskite phase remain stable. Moreover, in the 2D-GIWAXS pattern shows that Perovskite phase (110) orientation growth is the vertical direction for the sample deposited with 1wt% MAI capped PbS nanocrystals. And last but not least, without PbS/I- perovskite thin film activation energy is 184KJ/mol; with PbS/I- Perovskite thin film activation energy is 57KJ/mol. The result of this study shows that intermixing PbS nanocrystals in Perovskite precursor solution, such as faster Perovskite crystallization kinetics and lower activation energy, increase crystal domain, enhanced coverage and uniformity. It provides useful technique to improve Perovskite solar cell performance.

碩士
國立交通大學
光電工程研究所
106
Organic-inorganic hybrid perovskites are recognized as a promising candidate for photovoltaic applications. More recently, this emerging type of perovskite materials also becomes highly attractive as active materials for other optoelectronic devices, including lasers, light-emitting diodes (LEDs) and photodetectors. The aim of this thesis is to develop high-performance LEDs based on solution processes. We have found the efficiency of photoluminescence (PL) of CH3NH3PbBr3 thin films can be enhanced after post-deposition surface treatments with bidentate chelating ligands, including 1,10-phenanthroline, 4,4'-bipyridine and 4,7-diphenyl-1,10-phenanthroline (Bphen). The PL intensities of were improved significantly after we spin-coated 1,10-phenanthroline and 4,4'-bipyridine on the thin film surfaces. Meanwhile, the treatments also resulted prolonged PL lifetimes, suggesting the passivation of the defects in the perovskite thin films. The unsaturated or under-coordination Pb ions, which are also Lewis acids, has been considered as one of the origins of the electronic traps in perovskite thin films. Therefore, the chelating ligands, which behaved as Lewis bases, could effectively react with the Lewis acids and passivate the defects. The morphologies of the perovskite films were also examined using X-ray diffraction, atomic force microscopy, and scanning electron microscopy; the results indicated that the surface treatments did not significantly affect the films. Moreover, the lower defect densities, which were deduced from the current-voltage curves of the hole-only devices, after the treatments supported the functions of the above ligands. Finally, perovskite LEDs were fabricated and the device passivated with 1,10-phenanthroline exhibited a nearly doubled quantum efficiency. We anticipate that this approach proposed in this thesis could lead to a general method for improving the PL efficiencies and the device performance.

Defect passivation and surface modification of perovskite semiconductors play a key role in achieving highly efficient and stable perovskite solar cells (PSCs) and light-emitting diodes (LEDs). This dissertation describes three novel strategies for such defect passivation and surface modification. In the first strategy, we demonstrate a facile approach using inorganic perovskite quantum dots (QDs) to supply bulk- and surface-passivation agents to combine high power conversion efficiency (PCE) with high stability in CH3NH3PbI3 (MAPbI3) inverted PSCs. This strategy utilizes inorganic perovskite QDs to distribute elemental dopants uniformly across the MAPbI3 film and attach ligands to the film’s surface. Compared with pristine MAPbI3 films, MAPbI3 films processed with QDs show a reduction in tail states, smaller trap-state density, and an increase in carrier recombination lifetime. The strategy results in reduced voltage losses and an improvement in PCE from 18.3% to 21.5%, which is among the highest efficiencies for MAPbI3 devices. The devices maintain 80% of their initial PCE under 1-sun continuous illumination for 500 h and show improved thermal stability. In the second strategy, we reduce the efficiency gap between the inverted PSCs and regular PSCs using a trace amount of surface-anchoring, long-chain alkylamine ligands (AALs) as grain and interface modifiers. We show that long-chain AALs suppress nonradiative carrier recombination and improve the optoelectronic properties of mixed-cation mixed-halide perovskite films. These translate into a certified stabilized PCE of 22.3% (23.0% PCE for lab-measured champion devices). The devices operate for over 1000 hours at the maximum power point (MPP), under simulated AM1.5 illumination, without loss of efficiency. Finally, we report a strategy to passivate Cl vacancies in mixed halide perovskite (MHP) QDs using non-polar-solvent-soluble organic pseudohalide (n-dodecylammonium thiocyanate (DAT)), enabling blue MHP LEDs with enhanced efficiency. Density-function-theory calculations reveal that the thiocyanate (SCN-) groups fill in the Cl vacancies and remove deep electron traps within the bandgap. DAT-treated CsPb(BrxCl1-x)3 QDs exhibit near unity (~100%) photoluminescence quantum yields; and their blue (~470 nm) LEDs are spectrally stable with an external quantum efficiency (EQE) of 6.3% – a record for perovskite LEDs emitting at the 460-480 nm range relevant to Rec. 2020 display standards.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for degree of Master of Science in Chemistry
The mandate for renewable energy sources to replace the current reliance on fossil fuels as a primary energy source has recently attracted a lot of research interest. The research has also focussed on bringing the technologies that take into consideration the goal of reducing environmental pollution. Consequently, approaches using photovoltaic (PV) technologies have been a promising arena to tackle the problem facing energy sources. Recently, more focus has been placed on improving the power conversion efficiency (PCE) of PV devices, such as organic and/or organic-inorganic hybrid perovskite solar cells. Therefore, in this work two different materials were applied in two independent PV devices, namely organic and/or organic-inorganic hybrid perovskite solar cells. One study employed nitrogen doped broken hollow carbon spheres (N-bHCSs), with an aim of enhancing the electronic properties of the P3HT:PCBM active layer of an organic photovoltaic (OPV) solar cell. N-bHCSs were successfully synthesized using a horizontal chemical vapour deposition method (H-CVD) employing a template-based method and the carbon was doped using in-situ and ex-situ doping techniques. Pyridine, acetonitrile and toluene were used as both carbon and nitrogen precursors. The dispersity of the SiO2 spheres (i.e. templates) was found to play a role on the breakage of the N-bHCSs. Incorporation of the N-bHCSs into the P3HT:PCBM active layer was found to enhance the charge transfer and this led to less recombination of photogenerated charges in the interface between the donor and acceptor. The current-voltage (I-V) characteristics of the ITO/PEPOT:PSS/P3HT:PCBM:N-bHCSs/Al solar cell devices revealed an increased chargetransport distance due to increased electron density by n-type doping from the N-bHCSs. The second study employed the organic-inorganic hybrid perovskite (CH3NH3PbI3) material as a light harvesting layer in an ITO/PEDOT:PSS/CH3NH3PbI3/PC6BM/Al solar cell device. Initially, the device parameters were optimised to obtain the best performing device. These include parameters such as the degradation of the hybrid film as a function of time and air exposure. A rapid degradation was seen on the device after 24 h of air exposure which was accompanied by the decrease in the PV performance of the device. The degradation was visually seen by the formation of crystal grains (i.e. “islands”) on the perovskite film.
GR2019

Crystal growth and characterization of few multifunctional materials with perovskite (ABX3) structure are discussed in this thesis. Efforts were made to modify the magnetic and electric behaviour of these materials by selective tuning of A, B and X components. Structural, magnetic and dielectric characterization are detailed in various chapters for doped (A and B site) rare-earth manganites and organometallic compounds with different (Chloride or formate) anions. The relevant aspects of crystal structure and its relationship with ordered ground states are discussed in the introductory chapter. A detailed review of prominent theories pertaining to magnetic and ferroelectric ordering in the literature is provided. Growth of various inorganic compounds by solid-state reaction and floating zone method as well as use of solvothermal techniques for growing organometallic compounds are discussed. Material preparation, optimization of crystal growth processes and results of characterization are addressed in various chapters. The effect of Yttrium doping on structural, magnetic and dielectric properties of rare-earth manganites (RMnO3 where R = Nd, Pr) has been investigated. Neutron diffraction studies (Pr compounds) confirm A-type antiferromagnetic structure and fall in transition temperature as the Yttrium doping level increases. Diffraction experiments in conjunction with dc magnetization and ac susceptibility studies reveal magnetic frustration in excess Yttrium dopedcompounds. When mutliglass properties of 50% B-site doped Nd2NiMnO6 were investigated, evidence of re-entrant cluster glass phase was seen probably due to presence of anti-site disorder. The relaxor-like dielectric behaviour arises from crossover of relaxation time in grain and grain boundary regions. Multiferroic behaviour of the organometallic compound (C2H5NH3)2CuCl4 as well as the ferroelectric transition were investigated in detail. The role of Hydrogen bond ordering in driving structural transitions is elucidated by low temperature dielectric and Raman studies in (C2H5NH3)2CdCl4. It was found possible to tune the magnetic and ferroelectric properties in metal formate compounds (general formula AB(HCOO)3) by selectively choosing organic cations [(CH3)2NH2+; C(NH3)3+] and transition metal ion [B = Mn, Co and Cu]. The nature of magnetic ordering and transition temperature could be altered by the transition metal ion. The effect of reorientation of organic cations which leads to ferroelectric nature is discussed using dielectric and pyroelectric data. Significant results are summarized in the chapter outlining general conclusions. Future prospects of work based on these observations are also provided. The conclusions are corroborated by detailed analysis of experimental data.

Solarzellen aus organisch-anorganischen hybriden Perowskithalbleitern gelten als mögliche Schlüsseltechnologie zur Erzeugung günstiger und umweltfreundlicher elektrischer Energie und somit als Meilenstein für die Energiewende. Um die weltweit stetig wachsende Nachfrage an elektrischer Energie zu decken, bedarf es Solarzellentechnologien, welche gleichzeitig eine hohe Effizienz nahe dem Shockley-Queisser-Limit als auch eine hinreichend gute Stabilität aufweisen. Während die Effizienz von Solarzellen auf Basis von Perowskithalbleitern in dem letzten Jahrzehnt eine bemerkenswerte Entwicklung erfahren hat, lassen sich die wesentlichen physikalischen Mechanismen dieser Technologie noch nicht vollständig erklären. Die elektronisch-ionische Mischleitfähigkeit ist eine dieser Eigenschaften, welche die Effizienz und besonders die Stabilität der Perowskit-Solarzelle beeinflusst. Zentrales Thema dieser Arbeit ist daher die Untersuchung von mobilen ionischen Defekten und deren Einfluss auf Solarzellenparametern. Es wird gezeigt, dass die Migrationsraten ionischer Defekte in Perowskit breiten Verteilungen unterliegen. Durch die Anwendung eines neu entwickelten Regularisationsalgorithmus für inverse Laplace-Transformationen und verschiedener Messmoden für transiente Störstellenspektroskopie kann somit geklärt werden, warum sich berichtete ionische Defektparameter aus der Literatur für gleiche Defekte stark unterscheiden können. Dieses grundlegende Verständnis kann angewendet werden, um den Einfluss von kleinen stöchiometrischen Variationen auf die Defektlandschaft zu untersuchen und das Zusammenspiel zwischen elektronischen und ionischen Eigenschaften besser zu verstehen. Der Einsatz der Meyer-Neldel Regel ermöglicht ferner eine Kategorisierung ionischer Defekte in Perowskithalbleitern. Im letzten Teil dieser Arbeit wird gezeigt, dass elektrische und optische Methoden wie intensitätsmodulierte Spektroskopie geeignet sind, um Informationen über mobile Ionen in hybriden Perowskiten zu erhalten. Zusätzlich wird das elektronische Rekombinationsverhalten näher untersucht.
Solar cells made of organic–inorganic hybrid perovskite semiconductors are considered as a possible key technology for the conversion of cheap and environmentally friendly electrical energy and thus as a milestone for the turnaround in energy policy. In order to meet the steadily growing global demand for electrical energy, solar cell tech- nologies are required that are both highly efficient, i.e. close to the Shockley–Queisser limit, and sufficiently stable. While the efficiency of solar cells based on perovskite semi- conductors has undergone a remarkable development in the last decade, the essential physical mechanisms of this technology cannot yet be fully explained. The electronic- ionic mixed conductivity is one of these properties, which influences the efficiency and especially the stability of the perovskite solar cell. The central topic of this thesis is therefore the investigation of mobile ionic defects and their influence on solar cell parameters. It is shown that the migration rates of ionic defects in perovskites are attributed to wide distributions. By application of a newly developed regularisation algorithm for inverse Laplace transform and different measurement modes for deep-level transient spectroscopy, it can thus be clarified why reported ionic defect parameters from the literature for the same defects can differ significantly. This basic understanding can be used to study the influence of small stoichiometric variations on the defect landscape and to better understand the interaction between electronic and ionic properties. Us- ing the Meyer–Neldel rule also allows the characterisation of ionic defects in perovskite semiconductors. The last part of this thesis shows that electrical and optical methods such as intensity-modulated spectroscopy are suitable for obtaining information about mobile ions in hybrid perovskites. In addition, the electronic recombination behaviour is examined more closely.