Template-Assisted Epitaxial Growth of (111)-Dominated FAPbI3 for Enhanced Photovoltaic Performance and Stability

Abstract

Mixed cation strategy significantly improves device performance and stability. However, the phase separation during the fabrication and ageing process deteriorates efficiency and stability. For FA based perovskites, the (111)-dominated film shows exceptional stability against thermal stress and moisture. (111)-oriented FAPbI₃ with a single cation (FA⁺) is difficult to prepare directly. In this study, (111)-oriented FAPbI₃ was obtained through ion exchange utilizing a (111)-oriented FA_0.85 MA_0.15 PbI₃ template. The DFT results revealed that the ion exchange mechanism occurs along the (111) facet. This transformation enabled a transition in its conductivity type from ntype to p-type. The (111)-oriented p-FAPbI₃ film and device exhibits low defect density and excellent thermal and humidity stability. The (111)-oriented FAPbI₃ the device retained 95 % of the original PCE after stored in N₂ atmosphere at 85 °C and remained 90 % initial PCE under the ambient conditions of 50 % -60 % RH at room temperature under 30 days.