Mitigation of Morphological Defects in Methylammonium-Free Formamidinium-Based Perovskite Solar Cells

Abstract

Operational stability of perovskite solar cells (PSCs) is essential for commercial viability. In this work, we report our efforts to understand the impact of potassium cations on mitigating the morphological defects in the methylammonium-free formamidinium-based perovskite photoactive layer. The addition of potassium cations is favorable for the stable operation of FA0.85Cs0.1K0.05PbI3-based PSCs through retarding the transformation of the intermediate phases. FA0.85Cs0.1K0.05PbI3-based PSCs can retain 96% of the initial power conversion efficiency (PCE) after a 2 month accelerated aging test, whereas more than 40% drop in PCE is observed in FA0.9Cs0.1PbI3-based PSCs during the same aging test. The use of potassium cations provides a practical solution to mitigate the morphological defects in the perovskite layer and thereby enhances the operational stability of the FA0.85Cs0.1K0.05PbI3-based PSCs.