Ion Migration and Redox Reactions in Axial Heterojunction Perovskite CsPb(Br1–xClx)3 Nanowire Devices Revealed by Operando Nanofocused X-ray Photoelectron Spectroscopy

Metal-halide perovskites (MHPs) have gained substantial interest in the energy and optoelectronics field. MHPs in nanostructure forms, such as nanocrystals and nanowires (NWs), have further expanded the horizons for perovskite nanodevices in geometry and properties. A partial anion exchange within the nanostructure, creating axial heterojunctions, has significantly augmented the potential applications. However, surface degradation and halide ion migration are deteriorating device performance. Quantitative analysis of halide metal concentration and mapping of the electrical surface potential along the operating NW device are needed to better understand ion transportation, band structure, and chemical states, which have not been experimentally reported yet. This requires a characterization approach that is capable to provide surface-sensitive chemical and electrical information at the subμm scale. Here, we used operando nanofocused X-ray photoelectron spectroscopy (nano-XPS) to study CsPbBr