Moisture is not always bad: HO accelerates the conversion of DMAPbI intermediate to CsPbI for boosting the efficiency of carbon-based perovskite solar cells to over 16.

Inorganic CsPbI perovskite has exhibited great application potential in perovskite solar cells (PSCs) due to its suitable optical bandgap and high chemical stability. However, the perovskite phases of CsPbI are not stable at room temperature, where they transition to non-perovskite phases. Humidity or water has been thought to be the primary factor inducing this phase transition, which should be avoided throughout the procedure of film and device processing. Surprisingly, the present study indicates that preparing a precursor solution in humid air is beneficial to the growth of high-quality CsPbI perovskite to enhance device performance. It is demonstrated that the incorporation of HO in the precursor solution from humid air or by intentional addition significantly changes the composition of coordination compounds and increases the amount of low iodine coordination complexes. As a result, the crystallization of dimethylammonium lead iodide (DMAPbI) intermediate is suppressed well, which accelerates its subsequent conversion to CsPbI perovskite. Consequently, an oriented CsPbI perovskite film with improved crystallinity and lower defect density is obtained. Most importantly, carbon-based PSCs (C-PSCs) based on the CsPbI perovskite film achieve an efficiency of 16.05%, a new record for inorganic C-PSCs.