Electronic properties of metal halide perovskites and their interfaces: the basics.

We have witnessed tremendous progress of metal halide perovskite (MHP)-based optoelectronic devices, especially in the field of photovoltaics. Despite intensive research in the past few years, questions still remain regarding their fundamental optoelectronic properties, among which the electronic properties exhibit an interplay of numerous phenomena that deserve serious scrutiny. In this Focus article, we aim to provide a contemporary understanding of the unique electronic properties that has been resolved by the community. First introducing some of the basic concepts established in semiconductor physics, the intrinsic and extrinsic electronic properties of the MHPs are disentangled and explained. With this, the complex interplay of interface-, dopant-, and surface state-induced electronic states in determining the electrostatic landscape in the material can be comprehended, and the energy level alignment in device architectures more reliably assessed.