Methods for Making Low Bandgap Perovskites

The present disclosure relates to a composition that includes a perovskite having a stoichiometry comprising A.sub.1-xFA.sub.xSn.sub.1-yB.sub.y(I.sub.1-zX.sub.z).sub.3, where A is a first cation, B is a second cation, X is a halide, and 0.5 x 0.9, 0.5 y 0.9, and 0 z 1. In some embodiments of the present disclosure, A may include at least one of cesium, guanidinium, and/or methylammonium. In some embodiments of the present disclosure, X may include at least one of bromide and/or chloride. In some embodiments of the present disclosure, z may be equal to zero.