Chemistry of Lead Halide Perovskites: Aspects of Solution-Gelation and Acid-Base Reactions with Aliphatic Amines

Abstract

Metal halide perovskites are an exciting and promising class of materials for optoelectronic device applications. Advancement of perovskite photovoltaic and light emitting diode lab-scale efficiencies have increased to or exceeded the performance of many established semiconductor technologies, but on a much shorter time scale. The rapid evolution of halide perovskite technology owes largely to the knowledge base gained from previous thin film technologies as well as a large amount of empirical improvements in processing and device architecture. However, there exist several barriers to commercialization of halide perovskites, mainly, long-term material stability and device operation. These challenges stem from the strong chemical reactivity of halide perovskite materials. Reactions taking place in solution while processing and in the solid-state during device fabrication/characterization lead to many complications and potentially obfuscate interpretation of results. These unique properties also make perovskites a rich platform by which to study many interesting and novel photo-electrochemical phenomena. In this thesis, we study the chemical properties of halide perovskites elucidating aspects of solution-gelation chemistry, the effect of stoichiometry on nano-scale composition, acid-base reactions with simple additives in solution, and solid-state reduction-oxidation reactions influencing electrochemical stability. Fundamental insight gained from these detailed studies facilitate significant improvements targeting specific applications such as fabricating ultrasmooth, ultrathin perovskite films with high emissivity and exploiting impurity chemistry at optimal concentrations leading to defect passivation. These results demonstrate the benefits of identifying chemical reaction mechanisms relevant to halide perovskites. Understanding and predicting how perovskites will react with other material systems and conditions is paramount for progressing the field and overcoming challenges to commercialization of this technology.