Photoelectron spectroscopic studies on metal halide perovskite materials

Modifications of the surface and interfacial properties of metal halide perovskites (MHPs) have become pivotal strategies in designing high-performance photovoltaics and light-emitting diodes. Particularly, photoelectron spectroscopy (PES) plays a vital role in the advancement of MHP-based optoelectronic devices. Herein, we review the recent studies of PESs for perovskite devices. We first give an overview of the principles of PES and related techniques. Different properties of halide perovskite material unveiled by PES are then discussed, including elemental compositions, chemical states, electronic band structures, interfaces of MHPs and functional layers, ions distribution, and thermal- and moisture-induced degradation mechanism. We also revisit some of the issues when carrying out PES measurements on MHPs, such as irradiation and ambient effects and the uncertainty in determining band edge. Based on these findings, we foresee that PES techniques combined with advanced optical and electron microscopies will become increasingly important to correlate the molecular dynamics with the interfacial and chemical properties of MHP materials and devices.