Single-Crystal Methylammonium-Free Perovskite Solar Cells with Efficiencies Exceeding 24% and High Thermal Stability

Grain-free single-crystal perovskites offer a potential avenue to the stability of advance perovskite solar cells (PSCs) beyond that of polycrystalline films. Recent progress in single-crystal PSCs (SC-PSCs) has come primarily from methylammonium (MA)-containing (e.g., FA0.6MA0.4PbI3) perovskite devices, which have achieved a 23.1% power conversion efficiency (PCE). Yet, such perovskites are intrinsically vulnerable to thermal stresses, given the relative volatility of the MA molecule within the perovskite structure. Herein, we demonstrate MA-free SC-PSCs based on an ∼20-μm-thick Cs0.05FA0.95PbI3 single-crystal absorber layer, which achieves new stability and efficiency benchmarks for SC-PSCs. Our devices exhibit 24.29% PCE and retain 90% of their initial efficiency after 900 h at 53 °C. Accelerated aging tests on the Cs0.05FA0.95PbI3 single crystals show that they endured the damp heat test (85 °C/65% RH) approximately twice as long as polycrystalline films of the same composition. These results indicate that MA-free FAPbI3-based SCs are promising candidates to develop the stability and efficiency of PSCs on the road to commercialization.