Investigation of halide-mixing-induced local strains in halide perovskite semiconductors

Over the last decade, solar cell devices based on halide perovskites have seen a dramatic increase in power conversion efficiency and stability in large part due to compositional mixing of prototypical MAPbI3 and FAPbI3 systems (MA = methylammonium, FA = formamidinium). Indeed, one state-of-the art formulation is (Cs0.05FA0.78MA0.17)Pb(I0.83Br0.17)3. However, mixing components of different sizes is likely to result in local strain fields emanating from the substitution site, which have not yet been adequately characterised. Evidence suggests that strain in halide perovskites adversely affects device efficiency and stability, so understanding the local strains induced upon compositional mixing is of paramount importance. The PDF measurements on APbBrxI1-x, APbBrxCl1-x, APbClxI1-x (A is Cs, MA, or FA) proposed here can uniquely characterise such local strain fields.