The growth of high-quality perovskite films is complicated by the fact of uncontrollable crystallization pathways from perovskite precursors. During solution processing, extensive undesired nonperovskite products including residual solvate intermediates are produced due to quick solvent evaporation, which will adversely affect the efficiency and stability of perovskite solar cells (PSCs). Herein, we developed a highly efficient phase-transition pathway using a polydimethylsiloxane (PDMS)-based facial mask (FM) incubation technique, which enables significant reduction of the perovskite crystallization rate and depression of perovskite aggregation behavior. A surprising finding reveals that this technique induces complete phase transition from solvate intermediates to the perovskite phase, thereby obtaining phase-pure perovskite film. Meanwhile, a high-quality perovskite film with a shiny smooth surface, decreased defect states, and alleviated lattice strain is achieved after utilizing the FM strategy. Consequently, the target-inverted PSCs deliver a respectable efficiency of ∼21% and superior stability in both shelf storage (over 3700 h with 90% of initial efficiency) and light soaking (over 1000 h with 80% of initial efficiency) conditions. Our work highlights the importance of eliminating residual solvate intermediates to construct high-quality perovskites with excellent phase purity for ongoing production of high-performance perovskite-based optoelectronic devices.

High-quality defect-free perovskite films exhibiting improved surface morphology are required for constructing highly efficient perovskite solar cells (PSCs). Incorporation of appropriate passivation molecules in perovskite films is a popular strategy to achieve this goal. Herein, the defect passivation effect of a series of photosensitive benzoyl derivatives on the perovskite layer is investigated through the comprehensive analysis of perovskite film and corresponding solar cells. Photosensitive molecules introduced with carbonyl groups considerably diminish the defects of Pb 2+ and MA + by forming either coordinate bonds or hydrogen bonds. The ultraviolet (UV) photoinitiation properties of benzoyl derivatives help sufficiently restrain the photodegradation of perovskites during device operation. In addition, photosensitive molecule-assisted passivation strategy effectively inhibits unwanted defect-assisted recombination, improving the power conversion efficiency (PCE) from 16.94% to 19.64%. Meanwhile, passivated devices exhibit considerably enhanced light stability, with >80% of the initial PCE maintained under continuous 1 sun illumination for 700 h. This approach aids in fabricating defect-free and UV-resistant perovskite-based photoactive layers for highly efficient and stable PSCs.

The intermediate phase adduct plays a crucial role in constructing uniform and compact tin perovskite films, thus providing an important approach for developing high-performance lead-free perovskite solar cells. However, the common intermediate phase adduct of SnI2·3DMSO in tin perovskite leads to phase separation and may lack compatibility with mixed cation tin perovskites composed of formamidinium (FA) and methylamine (MA), impeding the further device stability. Here, a facile and reproducible method is developed to fabricate high-quality FA0.75MA0.25SnI3 films by introducing a new stable intermediate phase adduct (SnI2·DMSO·MAFa) by using ionic liquid methylamine formate (MAFa). The resulting stable adduct suppresses the reaction rate between ammonium salts and SnI2, thereby modulating the tin perovskite crystallization and precluding SnI2 clusters formation, and the presence of the SnI2·DMSO·MAFa adduct in perovskite precursor serves as a protective barrier for Sn2+ ions, guarding them against oxidation caused by the presence of DMSO. Moreover, the amino and carbonyl groups in residual MAFa could repair the iodine vacancy and uncoordinated Sn2+ ion defects. These features result in the formation of highly uniform and pinhole-free FA0.75MA0.25SnI3 films. The optimized devices achieve a power conversion efficiency (PCE) of over 10%, a value of 53% higher than that of the control device (6.6%). Besides, the obtained MAFa-derived devices illustrate significantly enhanced stability in a microaerobic atmosphere, with 78% maintained initial efficiency over 2800 h of storage under N2 containing 50–100 ppm of O2.