Volatile Additive-Mediated Crystallization Modulation of CsPbI2Br Perovskite Films for Efficient and Stable Solar Cells

Abstract

All-inorganic CsPbI₂Br perovskite is a promising absorber for efficient solar cells due to its excellent thermal stability and suitable bandgap. However, uncontrolled crystallization during solution processing often leads to high defect densities and severe non-radiative recombination, limiting device performance. Here, we introduce a volatile additive-mediated crystallization modulation strategy, where a low-concentration dimethylammonium iodide (DMAI) or dimethylammonium bromide (DMABr) solution is spin-coated onto the wet CsPbI₂Br film after a low-temperature annealing step (60°C), followed by a second annealing at 250°C. This intermediate-stage treatment promotes heterogeneous nucleation and effectively regulates the crystallization process. The resulting films exhibit enlarged grains, smoother surfaces, and reduced defect densities. Consequently, DMAI- and DMABr-treated CsPbI₂Br perovskite solar cells (PSCs) achieve champion power conversion efficiencies (PCEs) of 18.15% and 17.33%, respectively, significantly outperforming the control device (15.29%). Moreover, the DMAI- and DMABr-treated devices also exhibit excellent stability, maintaining over 96% and ∼80% of their initial PCE, respectively, after continuous aging for 1000 h under environmental conditions (relative humidity < 10%) and in a nitrogen atmosphere at 60°C.