Enhanced Charge Carrier Transport and Device Performance Through Dual-Cesium Doping in Mixed-Cation Perovskite Solar Cells with Near Unity Free Carrier Ratios.

PbI-enriched mixed perovskite film [FAMAPb(IBr)] has been widely studied due to its great potential in perovskite solar cell (PSC) applications. Herein, a FAMAPb(IBr) film has been fabricated with the temperature-dependent optical absorption spectra utilized to determine its exciton binding energy. A ∼13 meV exciton binding energy is estimated, and a near-unity fraction of free carriers out of the total photoexcitons has been obtained in the solar cell operating regime at equilibrium state.