Caesium for perovskite solar cells: an overview

Perovskite solar cells have the potential to revolutionize the world of photovoltaics, and their efficiency close to 23% on a lab‐scale recently certified this novel technology as the one with the most rapidly raising performance per year in the whole story of solar cells. With the aim of improving stability, reproducibility and spectral properties of the devices, in the last three years the scientific community strongly focused on Cs‐doping for hybrid (typically, organolead) perovskites. In parallel, in order to further contrast hygroscopicity and reach thermal stability, research has also been carried out to achieve the development of all‐inorganic perovskites based on caesium, the performances of which are actually rapidly increasing. The potential of caesium is further strengthened when it is used as a modifying agent of charges carrier layers in solar cells, but also for the preparation of perovskites with peculiar optoelectronic properties for unconventional applications (e.g., in LEDs, photodetectors, sensors, etc.). This manuscript offers a 360‐degree overview on how caesium can strongly tune the properties and performance of perovskites and relative perovskite‐based devices.