Abstract

In a nutshell, the talk is about ionic charge carriers in mixed conductors (general case of solids exhibiting ionic and electronic conductivities) with a special eye on the photoactive halide perovskites. The first part of the talk is actually concerned with oxide perovskites (SrTiO 3 as a typical example), the charge carrier chemistry of which is rather well understood and the consideration of which forms an appropriate introduction. Starting out from this angle, many phenomena in the halide perovskites which are treated in the major part become understandable. As far as the halide perovskites are concerned, the following key points are addressed: - Measurement, understanding and tunability of ion and electron transport - Thermodynamic and kinetic stability - Light effects on ion transport; photo-degradation and photo-demixing - Ionic control of space charge effects (nanoionics) In broader terms, the contribution highlights the role of solid state ionics for the field of photovoltaics and, as an outlook, points towards optoionics as a future novel scientific field.