Revealing the underlying crystallization mechanism of perovskite crystals affected by additives with a typical surfactant span 20

The additive engineering of perovskite films has been successfully employed to optimize perovskite solar cells (PSCs) and achieved high power conversion efficiencies (PCE). However, the underlying crystallization mechanism of perovskite crystals affected by additives is not clear, greatly limiting the application of this optimization strategy. Herein, we employed a typical surfactant named span 20 into the perovskite precursor to control the growth of perovskite film and fully investigated its effect on the crystallization kinetics of perovskite crystals. Our results indicate that span 20 could not only hider the nucleation of perovskite crystals but also significantly decrease the crystallization rate of perovskite crystals, finally increasing the crystal size of perovskite crystals. Because of the high-quality perovskite film regulated by span 20, the PCE of PSCs increased from 18.59 % to 21.54 %. Meanwhile, the PSCs show good stability that maintain 86 % of initial efficiency after aging for 3000 hours in a low humidity environment. Our work provides guidance for additives regulating perovskite crystals for efficient perovskite solar cells. [Display omitted] •The crystallization kinetics of perovskite crystals affected by a typical surfactant span 20 has been investigated in detail.•Span 20 could effectively regulate crystallization process of perovskite crystals, finally improving the quality of perovskite film.•The modified-span 20 device achieves a best PCE of 21.54 % and show excellent stability in a low humidity environment.