Dual-site mixed layer-structured FA(x)Cs(3−x)Sb(2)I(6)Cl(3) Pb-free metal halide perovskite solar cells

Structure engineering of trivalent metal halide perovskites (MHPs) such as A(3)Sb(2)X(9) (A = a monovalent cation such as methyl ammonium (MA), cesium (Cs), and formamidinium (FA) and X = a halogen such as I, Br, and Cl) is of great interest because a two dimensional (2D) layer structure with direct bandgap has narrower bandgap energy than a zero dimensional (0D) dimer structure with indirect bandgap. Here, we demonstrated 2D layer structured FACs(2)Sb(2)I(6)Cl(3) MHP by dual-site (A and X site) mixing. Thanks to the lattice-symmetry change by I–Cl mixed halide, the shortest ionic radius of Cs, and the lower solution energy due to dual-site mixing, the FACs(2)Sb(2)I(6)Cl(3) MHP had 2D layer structure and thereby the MHP solar cells exhibited improved short-circuit current density.