Transformation of Polarization Mechanisms by Dimensional Reduction in Lead-Free Silver Bismuth Bromide Double-Perovskite Thin Films

Lead-free halide perovskite materials are discussed as alternative materials to replace lead-containing perovskites and minimize risks to human health and the environment. Dimensional reduction of the octahedral metal halide network by incorporating larger organic cations including phenethylammonium (PEA) represents an attractive opportunity to tailor their properties toward applications. Here, differences in characteristics under an applied constant voltage are detected, which arise from the dimensional reduction of the Cs2AgBiBr6 double-perovskite to (PEA)4AgBiBr8. Thin films consisting of these compounds were spin-coated onto microstructured interdigitated electrode arrays. Current–voltage and Kelvin probe force microscopy measurements were performed to reveal the overall or locally resolved consequences of an applied electric field. Both materials showed a reversible ion displacement in small electric fields. At higher field strengths, however, Cs2AgBiBr6 exhibited a persistent contact modification at the interface of the perovskite and the contact metal due to migrating ions, whereas (PEA)4AgBiBr8 still showed a reversible separation of ions. Insulating interlayers that widely attenuate the current demonstrate that these effects are induced by electric fields only, independent of charge injection. The obtained results provide an explanation of improvements of perovskite contacts by interfacial engineering, in particular, describing how a two-dimensional (2D) perovskite layer reduces the hysteresis and interfacial resistance in contact to a three-dimensional (3D) double-perovskite.