Chapter 7: Electronic Properties of Metal Halide Perovskites

This chapter summarizes our current understanding of the electronic properties and related excitations of metal-halide perovskites with particular reference to concept and tools already well deployed in the field of conventional semiconductors and optoelectronics, including the intensive use of group theory. This helps to bring out the most distinctive features that make hybrid, and to a less extend all-inorganic metal-halide perovskites, a new and distinct class of semiconductors. The pseudocubic phase serves as a reference structure and many effects, such as strain, phase transitions, relativistic effects, local distortions due to the organic cations, loss of inversion symmetry, etc., can be considered as perturbations to this reference. Brillouin zone folding is shown to afford a simple yet effective tool to unravel the apparent complexity of electronic properties. The importance of spin–orbit coupling is particularly emphasized as it has a dramatic influence not only through its strength but also by alteration of the symmetry selection rules. Issues related to the nature of electronic excitation and charge carriers, as well as their possible coupling to atomic collective (phonons) or localized (polaron) modes are discussed, as well as non-radiative Auger effects.