Solar cells based on organic-inorganic metal halide perovskite materials, such as methylammonium lead iodide (CH3NH3PbI3), have been the subject of intense investigation during the past 5 years due to high power conversion efficiencies (>22%) and relatively low manufacturing costs. Never before has the field of photovoltaics (PV) seen such rapid and exciting progress. The results are surprising because various low-temperature, solution-based processing methods have been successful in fabricating high-efficiency devices. Nevertheless, much of the work in this area has focused on device performance optimization and there is a lack of basic understanding of underlying physics and chemistry. Without this understanding, it will be difficult to properly design and process the next generation materials and address the stability drawbacks.
In this talk, I will first introduce the phase transitions and equilibria of halide perovskite materials. A near-equilibrium quasi-binary phase diagram will be proposed to explain the formation of perovskites. I will further discuss the nucleation and growth mechanisms during the solution processing of perovskites and how to use it to control the grain size and morphology of the deposited films. Finally, I will present our recent study on the stability of perovskite solar cells. By using laser beam induced current (LBIC) imaging to spatially resolve the evolution of water induced changes in the device performance, we are able to elucidate the degradation mechanisms on a microscopic level and give insights toward improving the long-term stability of the materials and devices.