Electric Field Induced Surface Nanocrystal Growth in 2D Mixed Halide Perovskites

2D halide perovskites that exhibit layered structures through the use of spacer molecules have various advantages with regard to stability and electronic and optical properties over their 3D counterparts. Their highly anisotropic crystal structure gives rise to the directional conduction of charge carriers and ion migration. Here, we report electric field induced changes in the surface of these materials through the growth of nanoscale crystallites in films with significant iodide composition when an electric field is applied to the film after synthesis. The observed structural changes improve crystallinity and conduction and reduce surface charge inhomogeneity, resulting from the 2D layered grain orientation. The impact of these effects on the optoelectronic properties is discussed.