To Reveal Grain Boundary Induced Thermal Instability of Perovskite Semiconductor Thin Films for Photovoltaic Devices

Thermal instability of hybrid perovskite thin films is one of the important issues that must be overcome on the way to commercialization of perovskite solar cells, and it is also essential to deeply understand the degradation mechanism of perovskite thin films caused by thermal instability. In this paper, we demonstrate that the CH₃NH₃PbI₃ film with larger grain sizes and fewer grain boundaries exhibits a higher thermal stability and the solar cell device exhibits improved photovoltaic performance. The grain size is well controlled by employing isopropanol solvent annealing on CH₃NH₃PbI₃ films, and the highest efficiency of perovskite solar cells increases from 16.87% to 18.56% with the increase in the grain size. The results demonstrate that the reduction of grain boundaries is a feasible strategy to solve the thermal instability issue of perovskite thin films.