Intermediate-Phase-Mediated Crystallization and A-SiteDoping in CsPbI2Br Perovskite Solar Cells Enabled by DimethylammoniumIodide

Abstract CsPbI2Br perovskites are promising wide-bandgap absorbers for tandem photovoltaics but are limited by unfavorable film crystallization and high defect densities. Herein, dimethylammonium iodide is introduced as a multifunctional agent to simultaneously regulate crystallization dynamics and modulate A-site composition. In-situ photoluminescence spectroscopy reveals the formation of a transient intermediate phase that governs nucleation and growth pathways. By combining with in situ structural and spectroscopic analyses, we demonstrate that a fraction of DMA+ cations is incorporated into the perovskite lattice, forming a Cs1-xDMAxPbI2Br phase. The intermediate-phase-mediated crystallization and A-site doping result in enlarged grain size, reduced trap-state density, and suppressed nonradiative recombination. Consequently, carbon-based CsPbI2Br perovskite solar cells achieve a power conversion efficiency of 14.04% with markedly enhanced stability. This work provides mechanistic insight into synergistic crystallization control and compositional engineering in all-inorganic perovskite photovoltaics.