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

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 V_OC of 1.230 V, a J_SC 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.