Boosting Performance of CsPbI3 Perovskite Solar Cells via the Synergy of Hydroiodic Acid and Deionized Water

It remains challenging to fabricate high‐efficiency all‐inorganic perovskite solar cells (PSCs) at low temperature. Herein, the low‐temperature preparation of high‐efficiency CsPbI 3 PSCs using hydroiodic acid (HI) and deionized water (H 2 O) as additives at synthetic temperature as low as 100 °C is proposed, which is beneficial for constructing even more complicated tandem or flexible solar cells. The additive of HI facilitates CsPbI 3 to form a high‐quality and smooth perovskite film at low temperature. The addition of an optimal amount of H 2 O further induces perovskite growth with larger grains and a smoother surface by the dissolution and recrystallization process in the grain boundary, which can suppress defects‐induced nonradiative recombination. In this scenario, the corresponding device with structure of ITO/PEDOT:PSS/CsPbI 3 /PC 61 BM/Ag exhibits a high power conversion efficiency of 11.41% and the fill factor is increased from 62% to about 69%, compared with device based on CsPbI 3 film without extra H 2 O treatment. The appropriate amount of H 2 O promotes the high‐quality multigrain growth of the CsPbI 3 film and reduces the internal defects, contributing to a significant improved charge collection efficiency. Therefore, this research work has paved a significant way to improving the quality of the all‐inorganic perovskite film for highly efficient solar cells.