Conjugated Organic Cations Enable Efficient Self-Healing FASnI₃ Solar Cells

The introduction of large-volume amines (LVAs) in Sn-based perovskite films has been shown to lead to promising power conversion efficiency (PCE) in Pb-free perovskite solar cells (PSCs). However, the LVAs adopted so far (e.g., phenylethylammonium [PEA] and butylammonium [BA]) are insulating and could impede charge extraction within the perovskite film. Herein, a conjugated LVA, 3-phenyl-2-propen-1-amine (PPA), is introduced in formamidinium tin iodide (FASnI₃) perovskite. Our results show that the incorporation of PPA results in enlarged grain sizes, reduced trap density, preferential orientation, efficient charge extraction, and enhanced structural stability of FASnI₃ film. These positive effects help in achieving efficient PSCs with a PCE as high as 9.61% with negligible hysteresis and outstanding stability (remains 92% of its initial PCE value after 1,440 h). Furthermore, the presence of PPA enables a self-healing action of PSCs. Most importantly, we report large-area (1 × 1 cm²) Sn-based PSCs achieving PCE of 7.08%. For ecofriendly concerns, Sn-based PSCs have been extensively studied and made inspiring progress during the past few years. Recently, the introduction of large-volume amines (LVAs) (e.g., phenylethylammonium [PEA] and butylammonium [BA]) have shown their promise in enhancing the performance of FASnI₃-based PSCs. However, the insulating nature of these LVAs sets limitations on the charge extraction of the film. Herein, a conjugated LVA, 3-phenyl-2-propen-1-amine (PPA), is introduced aiming at promoting charge extraction within FASnI₃ film. The presence of PPA is found to enlarge the grain size, passivate the grains, and induce the orientation of the film. These merits of PPA deliver PSCs with PCE of 9.61% on 0.09 cm² and 7.08% on 1 cm². Moreover, PPA-based PSCs exhibit robust stability and self-healing behavior. This work sheds critical lights on improving the quality of perovskite film by molecular design of organic cations and highlights the promise of Pb-free PSCs. A conjugated large-volume cation is adopted as an additive to modify FASnI₃ film with much improved film quality. Lead-free PSC devices with PCE of 9.61% on 0.09 cm² and 7.08% on 1 cm² can be achieved. The PSC devices also show robust stability with self-healing ability. This work addresses the promise of Sn-based PSCs and takes a big step forward in the field of ecofriendly lead-free photovoltaic devices.