Surface electronic structure and dynamics of lead halide perovskites

A number of studies investigating the electronic structure of well-defined lead halide perovskite surfaces have emerged in the last five years. Surfaces and their interfaces can not only have considerable effects on the performance of devices such as solar cells but also open a window into the intrinsic electronic properties of lead halide perovskites. This is particularly true for angle-resolved photoelectron spectroscopy, which is possibly the technique giving the most direct access to the electronic (band) structure of a material. The pump–probe version of the technique, two-photon photoelectron spectroscopy, gives information about the femtosecond and picosecond electron dynamics following optical excitation. This review summarizes the recent progress made using these surface-sensitive techniques. In addition, differences between the optical and electronic properties between the near-surface (hundreds of nm) and the deep bulk material of single crystals are discussed. We point out critical issues concerning the comparability between individual results arising from the different depths and timescales probed, or from differing environmental conditions such as the temperature or the surrounding atmosphere.