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

The alloying behavior between FAPbI(3) and CsSnI3 perovskites is studied carefully for the first time, which has led to the realization of single-phase hybrid perovskites of (FAPbI(3))(1-x)(CsSnI3)(x) (0< x < 1) compositions with anomalous bandgaps. (FAPbI(3))(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 (FAPbI(3))(0.7)(CsSnI3)(0.3)-composition perovskite. Solar cells based on this new perovskite show power conversion efficiency up to 14.6%.