Composition and Interface Engineering of High Performing Perovskite Solar Cells

Perovskite solar cells have been established as a disruptive technology in the domain of photo-voltaics. Their facile, low-temperature processing and high-power conversion efficiency make them stand-out among other mature solar technologies. The performance of perovskite solar cells is pro-foundly tied to an interplay of material properties of singular thin films that are assembled to form the photovoltaic device stack. An understanding of optoelectronic, morphological, and other key charac-teristics of each layer and its interfaces is instrumental in advancing the science of perovskite solar cells. Since their inception after just over a decade, much work on perovskite solar cell has been stag-nant to bring the technology to the market. The long-term stability remains foremostly the main hin-drance to facilitating technology transfer. Therefore, the work presented in this thesis explores multi-ple interface and compositional approaches to promote stability and other photovoltaic parameters of perovskite solar cells.In the second chapter of the thesis, a light-soaking exploration was done on perovskite sam-ples that utilize single (TiO2 and SnO2) and bilayered (TiO2/SnO2) electron transporting materials. The work aims to expand consensus on the optoelectronic and morphological features of light-soaked samples and link them with long-term stability. Upon preliminary testing, maximum power point tracking on each sample reveals efficiency preservation of SnO2 and TiO2/SnO2 samples over the course of 1000 hours while prominent degradation was revealed for the TiO2 sample. On a secondary investigation, light-soaking characterizations were performed where fresh and light-soaked samples were characterized to obtain photoluminescence, microscopic, and crystallographic features. The work reveals the added benefit of employing TiO2/SnO2 transporting bilayers to improve both the stability and power conversion efficiency of a perovskite solar cell. Building on an effort to understand TiO2/SnO2 bilayer behaviors, the third chapter investigates the role of halide passivating elements in SnO2 on the performance of perovskite solar cells. The study utilizes three metalorganic precursors based on acetylacetone complexes with chloride and bromide groups to fabricate SnO2 layers at different annealing temperatures. Upon thermal and elemental in-vestigations, the study clearly links the presence of amorphous halide elements in SnO2 to the power conversion efficiency of perovskite solar cells. More-in-depth, the optimal SnO2 annealing tempera-ture for bromide containing samples 250 C compared with 220 C for chloride containing samples. The higher temperature tolerance tendency was correlated to bromide’s lower sublimation sensitivity. Overall, the study highlights the importance of amorphous passivating elements in SnO2 for high per-forming planar perovskite solar cells. Finally, the fourth chapter involves a novel cation mixing approach for 2D perovskites at the interface of the 3D perovskite and the hole transporting layer. Alkyl ammonium halides have been widely used to form light-stable 2D perovskite films upon interaction with excess PbI2. In this study, different alkyl chain cations (propylammonium iodide and octylammonium iodide) were mixed in one solution to form a novel 2D perovskite crystal lattice. Photoluminescence and x-ray diffraction spec-troscopy investigations reveal a unique crystal lattice and a uniform quasi-2