Chemical Composition\nand Phase Evolution in DMAI-Derived\nInorganic Perovskite Solar Cells

Inorganic CsPbI3 is promising to enhance the\nthermal\nstability of perovskite solar cells. The dimethylamine iodide (DMAI)\nderived method is currently the most efficient way to achieve high\nefficiency, but the effect of DMAI has not been fully explained. Herein,\nthe chemical composition and phase evolution of the mixed DMAI/CsPbI3 layer during thermal treatment has been studied. The results\ndemonstrate that, with the common DMAI/CsI/PbI2 recipe\nin DMSO solvent, a mixed perovskite DMA0.15Cs0.85PbI3 is first formed through a solid reaction between\nDMAPbI3 and Cs4PbI6. Further thermal\ntreatment will transform the mixed perovskite phase directly to γ-CsPbI3 and then spontaneously convert to δ-CsPbI3. It has been also demonstrated that the DMA0.15Cs0.85PbI3 phase is thermodynamically stable and shows\na bandgap of 1.67 eV, which is narrower than 1.73 eV of γ-CsPbI3. The device efficiency of the mixed DMA0.15Cs0.85PbI3 perovskite is therefore highly improved\nin comparison with the pure inorganic γ-CsPbI3 perovskite.