Homogenous Alloys of Formamidinium Lead Triiodide and Cesium Tin Triiodide for Efficient Ideal‐Bandgap Perovskite Solar Cells

The alloying behavior between FAPbI3 and CsSnI3 perovskites is studied carefully for the first time, which has led to the realization of single-phase hybrid perovskites of (FAPbI3 )1-x (CsSnI3 )x (03 )1-x (CsSnI3 )x perovskites exhibit stable, homogenous composition/microstructure at the nanoscale, as confirmed by microscopic characterization. The ideal bandgap of 1.3 eV for single-junction solar cell operation is achieved in the rationally-tailored (FAPbI3 )0.7 (CsSnI3 )0.3 -composition perovskite. Solar cells based on this new perovskite show power conversion efficiency up to 14.6 %.