京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第24010号 / エネ博第446号 / 新制||エネ||84(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 平藤 哲司, 教授 土井 俊哉, 教授 藤本 仁 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

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This thesis presents a universal transfer printing method to introduce a thin layer of interlayer nanoparticle material in the cathode-organic layer interface in organic device. The use of reverse micelles for making nanoparticles restricts the nanoparticles to be directly synthesized on the organic active layer , therefore a transfer printing method using graphene was derived and a characterization method was needed to detect the transfer of nanoparticles in the whole device system. Raman spectroscopy was found to be the best candidate in studying these organic systems. The oxidation behavior and interaction of CVD graphene on Cu with oxygen plasma and mild annealing was monitored closely by a detailed Raman trilogy studies. Raman results also show evidence of graphene oxide successfully transferred to the target organic layer. Raman spectroscopy was further explored to understand all material in the transferred system including the micelles, type of nanoparticles and the organic layer, which then provides valuable insights to the evolution of the different phases of nanoparticle material formed by the reverse micelles technique. Raman was also used to confirm the first-reported formation of the hot-topic perovskites materials in reverse micelles. An extended Raman technique, the unconventional inverted-TERS, was used to detect a monolayer of micelles which was otherwise impossible for a normal Raman setting. The underlying mechanisms of this technique with high-resolution were also proposed. In order to understand and explore the tunability of reverse micelles on nanoparticle synthesis, a study with the pervovskite material was performed. There were evidence of precursors interacting with the pyridine group in the micelles core, which affects nanoparticle formation. The size of nanoparticles is also found to be tunable by using micelles of different block lengths and different solvents. All these findings contribute to future optimization on the nanoparticles to be transfer printed into devices interlayer and ultimately to benefit on the improvement on organic photovoltaics. / Thesis / Doctor of Philosophy (PhD)

It has been 10 years since the first hybrid halide perovskite photovoltaics was fabricated. Power conversion efficiency increases from the initial 3.8% to the current 25.2%. Fabrication method envolves from spin-coating to printable technology, and we deeply experience the drastic development of hybrid halide perovskite photovoltaics. Although hybrid halide photovoltaics render a variety of advantages over traditional photovoltaics, we still cannot find any practical application of these hybrid halide photovoltaics. There exist a few issues which hinder the commercialization of this type of solar cell. Among these issues, the long-term instability of hybrid halide perovskite is the main concern for the next development. This thesis expands on investigating the instability of hybrid halide perovskites from first principles. In Chapter 1, two computational methods employed in the thesis: density functional theory and Ab initio molecular dynamics are introduced. Theoretical investigations of the instability of CH3NH3PbI3 using density functional theory method are mainly conducted at 0 K. The finite temperature effect on this instability of CH3NH3PbI3 is usually neglected. In Chapter 2 of this thesis, we combined density functional calculations and additional thermodynamic data to explain the intrinsic instability of CH3NH3PbI3 under finite temperature conditions. We also analyzed the stability under humid conditions. It is shown that the aqueous solubilities of reactants play an important role in the products’ stabilities. The Born–Haber cycle of NaCl splits the enthalpy change into several components which will give a better understanding of the origin of the corresponding enthalpy change. In Chapter 3, with the extension of the Born–Haber cycle to the hybrid halide perovskites, the reaction enthalpies which govern the intrinsic instability of ionic compounds were analyzed. We proposed a criterion that helps to filter the hybrid halide perovskites with improved stability aimed for photovoltaics. Since the instability of CH3NH3PbI3 is intrinsic. The long-term instability can be settled by discovering alternative perovskite absorber. In Chapter 4, based on literature research, we propose a three-membered ring cation which has a suitable size to fit into the Pb-I framework, leading to optimal band gap for photovoltaics. Besides, the cation has a good ionization energy which will potentially render better stability. Whereas, a comprehensive study of this cyclic ring based perovskite indicates that the instability of the three-membered ring cation will make it impossible to synthesize this theoretical structure. Moisture degradation mechanisms of CH3NH3PbI3 are investigated intensively. More importantly, for practical photovoltaics, we have to imagine different situations the modules will encounter, e.g. after a couple of years, cracks appearing on the modules are inevitable, at this stage, understanding of the degradation mechanism of CH3NH3PbI3 according to liquid water becomes important. Chapter 6 elaborately describes a comprehensive degradation mechanism of CH3NH3PbI3 under liquid water. We investigate the energy barrier for the first dissolution event of CH3NH3PbI3 in water. Furthermore, thermodynamic analyses of CH3NH3PbI3 dissolution in water clearly explain the spontaneity of CH3NH3PbI3 degradation in water. Besides, different mechanisms of CH3NH3PbI3 and CsPbI3 dissolution in water are discussed. / Dissertation / Doctor of Philosophy (PhD)

Les manganites ont été particulièrement étudiés ces dernières années pour leurs propriétés de magnétorésistance colossale (CMR) et l'effet magnétocalorique. Ces oxydes de formule chimique T1-xDxMnO3, (T: terre-rare, D: alcalino-terreux) de structure pérovskite ABO3, présentent une valence mixte Mn3+/Mn4+. Les facteurs clés qui contrôlent les propriétés physiques sont le rayon moyen du site A (), le désaccord de taille des cations du site A (quantifié par la variance σ2 et la valence mixte du manganèse. Lors de notre étude, nous nous sommes focalisés sur l'effet du désordre gelé crée par la substitution aléatoire dans le site A de la structure pérovskite. Des échantillons poly-cristallins ont été synthétisés à cette fin. Les systèmes étudiés sont La0,8Pb0,1□0,1MnO3 et La0,8Pb0,1Na0,1MnO3 de composé mère La0,8Pb0,2MnO3 et La0,7Pb0,05Na0,25MnO3 de composé mère La0,7Pb0,3MnO3. Pour les deux premiers matériaux, l'étude structurale magnétique et électrique est présentée par ce manuscrit. Cette étude a permis de montrer l'existence des clusters ferromagnétique à haute température dans le contexte de la formation de la phase de Griffiths. De plus, nous avons mis en évidence l'existence des excitations magnétiques des ondes de spin à très basses température. A partir de la variation dans la température de Curie, la variation de la constante de raideur de l'onde de spin et l'évolution de la phase de Griffiths, nous avons pu montrer que le matériau La0,8Pb0,1□0,1MnO3 présente le rayon le plus faible et σ 2 le plus élevé comparé à La0,8Pb0,1Na0,1MnO3. Cette étude à montrer que le désordre est le mécanisme influençant sur les propriétés physiques de ces matériaux. Pour le système La0,7Pb0,05Na0,25MnO3, qui présente une température de Curie élevée (au dessus de l'ambiante) les propriétés magnétique ne montrent pas un effet considérable du désordre il est considéré régi par le mécanisme du double échange. Dans ce travail, nous nous sommes aussi intéressés à l'influence du désordre sur les exposants critiques et à l'effet magnétocalorique. L'analyse montre que les exposants critiques pour La0,8Pb0,1□0,1MnO3 sont proches à ceux du modèle de Heisenberg à dimension 3, alors qu'ils sont proches de ceux de la théorie du champ moyen pour La0,8Pb0,1Na0,1MnO3. Le désordre est quantifié d'être corrélé à court-distance ou non corrélé. Pour La0,7Pb0,05Na0,25MnO3, les exposants critiques appartiennent à la classe d'universalité de Heisenberg, comme prévu théoriquement. L'étude de l'effet magnétocalorique montre des valeurs intéressantes pour la variation d'entropie magnétique et la puissance relative du froid pour La0,7Pb0,05Na0,25MnO3. De plus, le caractère inhomogène de ces trois composés est affirmé par l'étude de l'exposant locale n qui varie avec le champ magnétique pour toute la gamme de température étudié. / Manganites have been extensively studied over the past several years, a result of their displaying a colossal magnetoresistance (CMR) and the magnetocaloric effect (MCE). These materials with a perovskite structure (ABO3) are characterized by the general formula T1- xDxMnO3, (T: rare earth, D: alkaline earth), x being the doping level, the latter causing changes in the valence state of the Mn ions to maintain charge neutrality. The key parameters that control the physical properties of these oxides are the mean radius of the site A (), the size mismatch of cations of the site A (quantified by the variance σ 2) and the mixed valence of manganese. In our study, we focused on the effect of the quenched disorder created by the random substitution in the A site of the perovskite structure. Polycrystalline samples were synthesized for this purpose. The systems studied are La0,8Pb0,1□0,1MnO3 and La0,8Pb0,1Na0,1MnO3 have a parent compound La0,8Pb0,2MnO3 and La0,7Pb0,05Na0,25MnO3 with parent compound La0,7Pb0,3MnO3. For the first two materials, structural, electrical and magnetic studies are presented in this manuscript. These studies reveal the existence of ferromagnetic clusters at high temperature in the context of the formation of the Griffiths phase. In addition, we have demonstrated the existence of magnetic excitations of spin waves at very low temperature. From the variation of the Curie temperature, the variation of the stiffness constant of the spin wave and the evolution of the Griffiths phase, we have shown that the material La0,8Pb0,1□0,1MnO3 has the lowest and highest σ2 compared to La0,8Pb0,1Na0,1MnO3. These studies showed that the disorder is the mechanism influencing the physical properties of these materials. For the system, La0,7Pb0,05Na0,25MnO3, which has a high Curie temperature (above ambient) magnetic properties do not show a significant effect of the disorder, which is considered to be governed by the mechanism of double exchange. In this work, we are also interested in the influence of disorder on the critical exponents and the magnetocaloric effect. The analysis shows that the critical exponents for La0,8Pb0,1□0,1MnO3 are close to those of the Heisenberg model in three dimensions, while they are very close to those of mean field theory La0,8Pb0,1Na0,1MnO3. The disorder is quantified to be correlated with short-range or uncorrelated. For La0,7Pb0,05Na0,25MnO3, the critical exponents belong to the Heisenberg universality class, as expected theoretically. The study of magnetocaloric effect shows interesting values of the magnetic entropy change and the relative cooling power La0,7Pb0,05Na0,25MnO3. In addition, the inhomogeneous nature of these three compounds is confirmed by the study of the local exponent “n” which varies with the magnetic field for the entire temperature range studied.

Solar-thermochemische Redoxzyklen stellen eine vielversprechende Technologieoption zur Nutzung und Umwandlung von erneuerbaren Energiequellen dar. Durch Reduktion von Metalloxiden bei hoher Temperatur und/oder niedrigem Sauerstoffpartialdruck kann ein Material in einen Zustand überführt werden, der dazu geeignet ist, Sauerstoff aus einem Gasstrom zu entfernen oder Wasser bzw. Kohlenstoffdioxid zu spalten. Dadurch ist es möglich, Luft zu zerlegen oder Sauerstoff zu pumpen, sowie sogenannte solare Brennstoffe zu erzeugen. Eine besonders vielversprechende Materialklasse stellen dabei die Perowskite dar. Diese Materialien bilden stabile Phasen mit sehr unterschiedlichen Zusammensetzungen. In dieser Arbeit wird gezeigt, wie diese Perowskit-Oxide in thermochemischen Redoxzyklen verwendet werden können und die Mechanismen hinter diesen Redoxreaktionen werden mit in-situ-Röntgenuntersuchungen aufgeklärt. Es wird auch gezeigt, dass die kinetischen Parameter der Oxidationsreaktion sehr vielversprechend sind. Zudem wird demonstriert, wie feste Lösungen aus Perowskiten in einem weiten Bereich verschiedener Zusammensetzungen hergestellt werden können und wie die Zusammensetzung der Perowskite die Phasenbildung und Stabilität beinflusst. Mit diesem Wissen wird ein Schwerpunkt dieser Arbeit auf die thermodynamischen Eigenschaften dieser Perowskite gelegt. Eine neue Methode der gezielten Materialentwicklung wird demonstriert, welche darauf basiert, den Toleranzfaktor und die thermodynamischen Eigenschaften der Perowskite gezielt einzustellen. Sowohl experimentelle, als auch theoretische Untersuchungen werden durchgeführt, letzere basierend auf Dichtefunktionaltheorie (DFT) im Rahmen von „Materials Project“. Über 240 Perowskit-Brownmillerit-Paare wurden untersucht. Detaillierte Modelle wurden entwickelt, um die thermodynamischen Eigenschaften solcher fester Lösungen aus Perowskiten als eine Funktion der Temperatur, des Sauerstoffpartialdrucks, und der Sauerstoff-Fehlstellenkonzentration 𝛿 zu beschreiben. Mit Hilfe dieser Funktionen wurde ein interaktiver Beitrag im Rahmen von Materials Project entwickelt, mit dem Materialeigenschaften in einem weiten Bereich verschiedener Bedingungen untersucht werden können. Darin ist auch eine Perowskit-Suchmaschine enthalten. Diese verwendet ein vereinfachtes Prozessmodell, um den materialspezifischen Energiebedarf von Redoxzyklen auszuwerten und ermöglicht es so, das effizienteste Material basierend auf den Prozessbedingungen auszuwählen. Es konnten neue Redoxmaterialien zur Anwendung in thermochemischen Kreisprozessen identifiziert werden und es wurde festgestellt, dass Perowskite die Effizienz der solaren Brennstofferzeugung bei vergleichsweise niedrigen Reduktionstemperaturen von 1300-1400 °C erhöhen können. So soll eine höhere Reaktorlebensdauer erreicht werden. Es wird auch diskutiert, welche Faktoren die Prozesseffizienz beeinflussen und es werden Ideen präsentiert, welche Schritte nötig sind, um eine kommerzielle Nutzung zu ermöglichen. Der wichtigste Faktor ist dabei die Wärmerückgewinnungseffizienz zwischen Feststoffen. Durch die Veröffentlichung aller Daten im Rahmen von MPContribs/Materials Project durch das Erstellen von interaktiven Graphen wird eine wertvolle Ressource zur schnelleren und zielgerichteten Materialentwicklung bereitgestellt. / Solar-thermochemical redox cycles are a promising technological option in the framework of utilization and conversion of renewable energy. By reducing metal oxides at high temperature and/or low oxygen partial pressure, one can generate a material in a state which can be used to capture oxygen from a gas stream or split water or carbon dioxide. By this means, air can be separated, oxygen can be pumped, or so-called solar fuels can be generated. One especially attractive materials class for application in such redox cycles is constituted by perovskites. These materials form stable phases over a large compositional range. Within this work, we show how these perovskite oxides can be applied in thermochemical redox cycles and study the mechanisms behind these redox reactions using in-situ X-Ray techniques. We also show that the kinetic properties of the oxidation reaction are very appealing. It is furthermore presented how perovskite solid solutions can be formed over a large compositional range and how phase formation and stability are affected by the perovskite composition. Based on this knowledge, the focus of this work is set on the materials thermodynamics. A new method of rational perovskite materials design is developed by adjusting the tolerance factor of the perovskites and their thermodynamics. Both experimental and theoretical materials development are conducted, the latter based on density functional theory (DFT) within the framework of the online resource “Materials Project”. Over 240 perovsite-brownmillerite pairs are included in the search. Detailed models describing the thermodynamics of such perovskite solid solutions are established which allow describing the perovskite redox properties as a function of the temperature, oxygen partial pressure, and oxygen non-stoichiometry 𝛿. Using these functions, we developed an interactive tool within the framework of Materials Project, which can be used to model materials properties for a large range of conditions and also serves as a perovskite search engine. This search engine uses a simplified process model to evaluate the material-specific energy demand of a thermochemical redox process and allows finding the most efficient materials choice for a large range of different operational parameters. We could identify new redox materials for application in such processes and found that perovskites can lead to more efficient thermochemical fuels production than the state of the art, especially if the reduction temperature is lowered to 1300-1400 °C to reach higher reactor longevity. It is also discussed which factors affect the overall process efficiency to which extent, and suggestions are given which steps are necessary for a commercialization of such redox processes. The most important factor is the solid-solid heat recovery efficiency. By making all this data publicly available in the framework of MPContribs/Materials Project through providing user-controlled interactive graphs, we are providing a valuable resource for accelerating the discovery and use of new redox materials.

[ES] El presente trabajo titulado "Elaboración y caracterización de láminas delgadas híbridas orgánico-inorgánicas de perovskita para células solares fotovoltaicas" es una contribución a la mejora del rendimiento y la capacidad de las láminas delgadas de perovskita para su uso en células solares fotovoltaicas. Este trabajo de investigación de laboratorio se divide en dos partes principales. La primera parte está dedicada a la preparación con éxito de películas finas de perovskita basadas en metilamonio MA, formamidinio FA y cesio Cs utilizando precursores, y también a la fabricación preliminar de polvos MAPbI3, MAPbBr3 y MAPbCl3. Se hizo hincapié en la mezcla de halógenos y el dopado. Estas películas finas se caracterizaron con vistas a su uso en células solares. Los resultados muestran que las láminas delgadas producidas son muy adecuadas para su uso como láminas delgadas absorbentes en células solares fotovoltaicas. Además, se estudiaron las distintas propiedades de las películas finas para evaluar su rendimiento. La segunda parte se ocupa del estudio del envejecimiento de las películas delgadas producidas. Esta parte de la investigación está dirigida a estudiar la estabilidad de las películas delgadas producidas. Las películas procesadas se caracterizan primero en estado fresco y luego se exponen al ambiente. Después de 4 semanas de exposición, se caracterizaron nuevamente. Los resultados de las caracterizaciones de las películas envejecidas comparadas con las de las películas frescas muestran el estado de deterioro de las películas. Dependiendo de sus propiedades, estos resultados comparativos muestran que algunas películas son más resistentes a la intemperie que otras. Las películas producidas se caracterizaron principalmente por XRD, SEM, absorción UV- visible y, para algunas películas se añadió AFM y EDS. / [CA] Aquest treball és una contribució per millorar el rendiment i la capacitat de les pel·lícules primes de perovskita per al seu ús en cèl·lules solars fotovoltaiques. Aquest treball de recerca de laboratori es divideix en dues parts principals. La primera part està dedicada a la fabricació de pols MAPbI3, MAPbBr3 i MAPbCl3 i també a la preparació i caracterització de pel·lícules primes per al seu ús en cèl·lules solars. Els resultats van mostrar que les pel·lícules primes produïdes són molt adequades per al seu ús com a pel·lícules primes absorbents en cèl·lules solars fotovoltaiques. A més, es van estudiar les diverses propietats de les pel·lícules primes per avaluar-ne el rendiment. La segona part s'ocupa de l'estudi de l'envelliment de les pel·lícules primes produïdes. Aquesta part de la investigació està adreçada a estudiar l'estabilitat de les pel·lícules primes produïdes. Les pel·lícules processades es caracteritzen primer en estat fresc i després s'exposen a l'ambient. Després de 4 setmanes d¿exposició, es van caracteritzar novament. Els resultats de les caracteritzacions de les pel·lícules envellides comparades amb les de les pel·lícules fresques mostren l'estat de deteriorament de les pel·lícules. Depenent de les seves propietats, aquests resultats comparatius mostren que algunes pel·lícules són més resistents a la intempèrie que d'altres. Les pellícules produïdes es van caracteritzar principalment per XRD, SEM, absorció UV- visible i, per a algunes pel·lícules es va afegir AFM i EDS. / [EN] The present work is a contribution to enhancing the performance and capacity of perovskite thin films for use in photovoltaic solar cells. This laboratory research work is divided into two main parts. The first part is devoted to the manufacture of MAPbI3, MAPbBr3 and MAPbCl3 powders and also to the successful preparation and characterisation of thin films for use in solar cells. The results showed that the thin films produced are well suited to their use as absorbing thin films in photovoltaic solar cells. In addition, the various properties of the thin films were studied in order to assess their performance. The second part deals with the study of the ageing of the thin films produced. This part of the research is aimed at studying the stability of the thin films produced. The processed films are first characterised fresh and then exposed to the ambient environment. After 4 weeks of exposure, they were characterised again. The results of the characterisations of the aged films compared with those of the fresh films show the state of deterioration of the films. Depending on their properties, these comparative results show that some films are more resistant to the elements than others. The characterisations carried out are mainly XRD, SEM, UV-visible absorption and, for some films, AFM and EDS. Key words: development, characterisation, thin films, stability, MAPbX3, FAPbX3, CsPbX3, powders / Doumbia, Y. (2024). Elaboration et caractérisation des couches minces pérovskites hybrides organiques-inorganiques pour les cellules solaires photovoltaïques [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/202699

La thèse présente une étude dans le cadre de la conception ab initio de nouveaux matériaux, avec des applications aux alliages intermétalliques et semi-conducteurs, aux oxydes transparents conducteurs et aux solides moléculaires. Des simulations avec la méthode Minima Hopping combinée avec la théorie de la fonctionnelle de la densité ont été utilisées pour trouver des nouveaux composés dans les diagrammes de phase des composés binaires de Lithium-Aluminium et Sodium-Or, aussi bien que des géométries de faible symétrie de CuBO2 à plus basses énergies que la structure delafossite qui était considérée comme son état fondamental. Nous avons aussi couplé la méthode Minima Hopping et la recherche de structures avec prototypes pour trouver de nouvelles perovskites de nitrure. Egalement, nous avons trouvé que la molécule H3 peut être stabilisée dans des structures à cages de CI à pressions d'environ 100 GPa. Nous avons aussi étudié les propriétés électroniques des alliages de chalcopyrite Cu(In, Ga)S2. Dans un sujet plus fondamental, nous proposons une fonctionnelle d'échange-corrélation semi-empirique optimisée pour obtenir des énergies de formation plus précises pour les solides / In this work we present an ab initio materials design study of several systems covering intermetallic and semiconducting alloys, transparent conductive oxides and molecular solids. We performed Minima Hopping calculations combined with Density Functional Theory that made possible to unveil several stable compounds in the phase diagrams of lithium-aluminium and sodium-gold binary alloys, as well as low-symmetry geometries of CuBO2, significantly lower in energy than the controversial delafossite structure reported as its ground state. We also found that the H3 molecule can be stabilized inside Cl cages at pressures of around 100 GPa. Additionally, we combined high-throughput techniques and global structure prediction methods to find nitride perovskites structures. In a different line, we studied the change in the absorption properties of the Cu(In,Ga)S2 chalcopyrite alloys as it was unexpectedly observed in experiment that with the change of the In/Ga ratio, the S K-absorption edge shifts, while the absorption edges of the other species is largely independent of the composition. In a more fundamental chapter, we propose a semi empirical exchange correlation functional optimized to yield accurate energies of formation of solids. The manuscript is organized as follows

Lead halide perovskites have shown remarkable device performance in both solar cells and LEDs. Whilst the research efforts so far have been mainly focussed on device optimisation, little is known about the photophysical properties. For example, the nature of the bandgap is still debated and an indirect bandgap due to a Rashba splitting has been suggested. In this thesis, we study the early-time carrier relaxation and its impact on photoluminescence emission. We first study ultrafast carrier thermalization processes using 2D electronic spectroscopy and extract characteristic carrier thermalization times from below 10 fs to 85 fs. We then investigate the early-time photoluminescence emission during carrier cooling. We observe that the luminescence signal shows a rise over 2 picoseconds in CH3NH3PbI3 while carriers cool to the band edge. This shows that luminescence of hot carriers is slower than that of cold carriers, as is found in direct gap semiconductors. We conclude that electrons and holes show strong overlap in momentum space, despite the potential presence of a small band offset arising from a Rashba effect. Recombination and device performance of perovskites are thus better described within a direct bandgap model. We finally study carrier recombination in perovskites and the impact of photon recycling. We show that, for an internal photoluminescence quantum yield of 70%, we measure external yields as low as 15% in planar films, where light out-coupling is inefficient, but observe values as high as 57% in films on textured substrates that enhance out-coupling. We study the photo-excited carrier dynamics and use a rate equation to relate radiative and non-radiative recombination events to measured photoluminescence efficiencies. We conclude that the use of textured active layers has the ability to improve power conversion efficiencies for both LEDs and solar cells.

The perovskite family of materials is extremely large and provides a template for designing materials for different purposes. Among them, hybrid organic-inorganic perovskites (HOIPs) are very interesting and have been recently identified as possible next generation light harvesting materials because they combine low manufacturing cost and relatively high power conversion efficiencies (PCEs). In addition, some other applications like light emitting devices are also highly studied. This thesis starts with an introduction to the solar cell technologies that could use HOIPs. In Chapter 2, previously published results on the structural, electronic, optical and mechanical properties of HOIPs are reviewed in order to understand the background and latest developments in this field. Chapter 3 discusses the computational and experimental methods used in the following chapters. Then Chapter 4 describes the discovery of several hybrid double perovskites, with the formula (MA)$_2$M$^I$M$^{III}$X$_6$ (MA = methylammonium, CH$_3$NH$_3$, M$^I$ = K, Ag and Tl, M$^{III}$ = Bi, Y and Gd, X = Cl and Br). Chapter 5 presents studies on the variable presure and temperature response of formamidinium lead halides FAPbBr$_3$ (FA = formamidinium, CH(NH$_2$)$_2$) as well as the mechanical properties of FAPbBr$_3$ and FAPbI$_3$, followed by a computational study connecting the mechanical properties of halide perovskites ABX$_3$ (A = K, Rb, Cs, Fr and MA, X = Cl, Br and I) to their electronic transport properties. Chapter 6 describes a study on the phase stability, transformation and electronic properties of low-dimensional hybrid perovskites containing the guanidinium cation Gua$_x$PbI$_{x+2}$ (x = 1, 2 and 3, Gua = guanidinium, C(NH$_2$)$_3$). The conclusions and possible future work are summarized in Chapter 7. These results provide theoreticians and experimentalists with insight into the design and synthesis of novel, highly efficient, stable and environmentally friendly materials for solar cell applications as well as for other purposes in the future.