Progress and Opportunities for Cs Incorporated Perovskite Photovoltaics

Efficiencies of perovskite solar cells (PSCs) have risen unprecedentedly from 3.8% to 25.2% in just over a decade as the light absorber material has evolved from the original methylammonium (MA)- to formamidinium (FA)-dominated perovskite. While FA lead iodide (FAPbI3) has a lower bandgap and, therefore, a higher theoretical efficiency limit, it is less phase stable, although this can overcome by incorporating cesium (Cs), MA, bromide (Br), or a combination of these. Cs being a nonvolatile component remains in the perovskite film and therefore it is important to understand the effect of the amount of Cs on film properties and associated PSC performance and stability. Future research opportunities for Cs-containing PSCs including large-area demonstrations are also discussed in this review.