Crystallization and Interfacial Regulation of CsPbI3 Perovskites by Dimethylammonium Chloride for Efficient and Stable Solar Cells.

All-inorganic CsPbI3 perovskite solar cells (PSCs) are attractive for perovskite/silicon tandem solar cells because of their suitable bandgap and intrinsic thermal robustness, yet their power conversion efficiencies (PCEs) and long-term stability remain limited by defective film and interfaces. The existing additives often contain bulky organic components, which may serve as grain-boundary barriers, or even form low-dimensional phases or carrier-transport-blocking layers. Here, dimethylammonium chloride (DMACl) is employed to regulate the crystallization of CsPbI3 films. DMACl treatment enlarges the average grain size and spectroscopic and electrical characterizations consistently reveal reduced defect-assisted recombination. Meanwhile, DMACl-derived species at the film surface or grain boundaries simultaneously passivate surface undercoordinated Pb2+ defects and achieve favorable energy-level alignment with PC61BM, thereby establishing a low-defect interface with a low energy barrier for efficient electron extraction and transport. Consequently, the champion inverted CsPbI3 PSC delivers a PCE of 20.97%, with a VOC of 1.230 V, a JSC of 20.70 mA/cm2, and an FF of 82.37%, compared with 18.99% for the control device. Importantly, DMACl treatment markedly enhances device stability under humidity, thermal, and continuous-illumination conditions. In particular, the T80 lifetime under thermal aging was extended from approximately 310 h for the control device to nearly 500 h for the DMACl-treated device.