Adduct phases induced controlled crystallization for mixed-cation perovskite solar cells with efficiency over 21%

Highlights: • The adduct phases in the mixed-cation perovskite are successfully tuned by solvent engineering. . • The adduct phases can control the nucleation process and affect the quality of perovskite film. • The trap density and charge recombination are greatly reduced in the optimized perovskite film. • A champion power conversion efficiency of 21.2% is achieved for planar-type perovskite solar cells. . -- Abstract: Organic-inorganic perovskite solar cells have attracted extensive attentions due to the advantages such as high power conversion efficiency and easy fabrication over other counterparts. Mixed-cation perovskite is considered as one of the most efficient light absorbers for perovskite solar cells and the device performance has a close connection to the quality of the perovskite thin film. Herein, we systematically investigate the influence of adduct phase in the mixed-cation perovskite precursor film on the crystallization of the perovskite. By tuning the adduct phase through solvent engineering, we successfully optimize the morphology and optoelectronic properties of the perovskite film and the planar-type perovskite solar cells with a power conversion efficiency over 21% can be achieved. Our work provides an effective method to control the growth of the mixed-cation perovskite film and thus boost the device performance with enhanced efficiency and stability.