High-efficiency and thermally stable FACsPbI₃ perovskite photovoltaics

Abstract

α-FA_1-xCs_xPbI₃ is a promising absorber material for efficient and stable perovskite solar cells (PSCs)^1,2. However, the most efficient α-FA_1-xCs_xPbI₃ PSCs require the inclusion of methylammonium chloride (MACl) additive^3,4, which generates volatile organic residues (i.e., MA) that limit device stability at elevated temperatures⁵. To date, the highest certified power-conversion efficiency (PCE) of α-FA_1-xCs_xPbI₃ PSCs without MACl was only ~24% (ref.^6,7), and has yet to exhibit any stability advantages. Here, we identify interfacial contact loss caused by the Cs⁺ accumulation for the conventional α-FA_1-xCs_xPbI₃ PSCs, which deteriorates the device performance and stability. Through in-situ GIWAXS analysis and DFT calculations, we demonstrate an intermediate phase-assisted crystallization pathway enabled by acetate surface coordination to fabricate high-quality α-FA_1-xCs_xPbI₃ film, without using MA-additive. We herein report a certified stabilized power output (SPO) efficiency of 25.94% and a reverse-scanning PCE of 26.64% for α-FA_1-xCs_xPbI₃ PSCs, exhibiting negligible contact losses and enhanced operational stability. The devices retain >95% of their initial PCEs after over 2,000 hours operating at maximum power point under 1 sun, 85 °C, and 60% relative humidity (ISOS-L-3).