Diammonium and Monoammonium Mixed‐Organic‐Cation Perovskites for High Performance Solar Cells with Improved Stability

Remarkable power conversion efficiencies (PCE) of metal–halide perovskite solar cells (PSCs) are overshadowed by concerns about their ultimate stability, which is arguably the prime obstacle to commercialization of this promising technology. Herein, the problem is addressed by introducing ethane‐1,2‐diammonium ( + NH 3 (CH 2 ) 2 NH 3 + , EDA 2+ ) cations into the methyl ammonium (CH 3 NH 3 + , MA + ) lead iodide perovskite, which enables, inter alia, systematic tuning of the morphology, electronic structure, light absorption, and photoluminescence properties of the perovskite films. Incorporation of <5 mol% EDA 2+ induces strain in the perovskite crystal structure with no new phase formed. With 0.8 mol% EDA 2+ , PCE of the MAPbI 3 ‐based PSCs (aperture of 0.16 cm 2 ) improves from 16.7% ± 0.6% to 17.9% ± 0.4% under 1 sun irradiation, and fabrication of larger area devices (aperture 1.04 cm 2 ) with a certified PCE of 15.2% ± 0.5% is demonstrated. Most importantly, EDA 2+ /MA + ‐based solar cells retain 75% of the initial performance after 72 h of continuous operation at 50% relative humidity and 50 °C under 1 sun illumination, whereas the MAPbI 3 devices degrade by approximately 90% within only 15 h. This substantial improvement in stability is attributed to the steric and coulombic interactions of embedded EDA 2+ in the perovskite structure.