Ambient-Stable Cubic-Phase Hybrid Perovskite Reaching the Shockley-Queisser Fill Factor Limit via Inorganic Additive-Assisted Process

Additive-assisted organic-inorganic perovskite materials have attracted substantial attention as photovoltaic light absorbers which lead to outstanding power conversion efficiency. Here we report an easy and effective fabrication of cubic-phase perovskite with an inorganic molecule additive like hydrazinium chloride (N₂H₅Cl, to be denoted as HZCl). We predict that this inorganic cation of N₂H₅⁺, which can substitute for the organic A-site in the perovskite structure, can tune Fröhlich polaron properties by controlling the interaction strength and the number of proton coordinations to halide. This prediction is experimentally demonstrated with an optimized perovskite device with 2% N₂H₅Cl additive, which exhibits an unprecedented 85% fill factor (FF) with the highest value close to the Shockley-Queisser limit. An extra power conversion efficiency (PCE) of 2.3% and a fill factor (FF) efficiency of 14% are boosted. These optimized performances by additive effects lead to a new approach based on the theoretical calculation toward an improved performance of the perovskite solar cell.