Nonfullerene Agent Enables Efficient and Stable Tin-Based Perovskite Solar Cells

Tin-based perovskites have emerged as the most promising lead-free perovskite materials due to the characteristics of the environmentally friendly and more suitable bandgap. However, the power conversion efficiency still lags behind the lead perovskite owing to unfavorable defects of the perovskite film and poor interface contact between tin perovskite and electron transporting layers. Herein, an n-type conjugated nonfullerene molecule, termed IO-4Cl, is developed for efficient and stable tin perovskite solar cells (TPSCs). The IO-4Cl possesses electron-donating functional groups that can enlarge grain size and passivate defect states of perovskite films through Lewis acid–base interactions. Besides, the IO-4Cl exhibits an appropriate lowest unoccupied molecular orbital level and interface-modification ability, enabling superior electron extraction and transport ability of TPSCs. More importantly, the hydrophobic characteristic of IO-4Cl prevents the decomposition of perovskite films under moisture conditions, improving the moisture stability of TPSCs. Consequently, the TPSCs with IO-4Cl achieve a champion efficiency of 11.49% with an open-circuit voltage increase of 100 mV, and excellent moisture stability under ambient air condition with 30% relative humidity, without encapsulation. The work provides a new inspiration for the introduction of functional nonfullerene materials to obtain highly efficient and stable TPSCs.