Temperature-assisted crystallization for inorganic CsPbI2Br perovskite solar cells to attain high stabilized efficiency 14.81%

Highlights: • Nucleation step and crystallization rate are highly related to the solubility and solvent evaporation rate, respectively. • By carefully adjusted the crystallization process, thick CsPbI₂Br film with larger crystalline grain size is obtained. • The device shows a stabilized PCE of 14.81%, which is the highest PCE for the CsPbBrI₂ solar cells to data. Due to its super thermal stability, inorganic CsPbI₂Br perovskite has attracted more and more attention in the field of photovoltaic application. However, its device performance, as reported to date, is greatly challenged in preparing CsPbI₂Br films with both sufficient absorbance and high quality. Herein, crystallization engineering is applied in producing solution-processed CsPbI₂Br film to guarantee sufficient light harvesting and effective carrier extraction. Further study proves that the precursor solution temperature would largely affect the crystallization progress: (1) the nucleation step is highly related to the solubility of precursor in a specific solvent or solvents at elevated temperatures; (2) the crystal growth rate is highly related to the solvent evaporation rate. To obtain thick film with larger crystalline grain size, the precursor solution temperature should be carefully adjusted for both suppressing the formation of too many nuclei and increasing the crystallization rate at the same time. Finally, the optimized CsPbI₂Br would be obtained when the precursor solution is maintained at 100 °C, the corresponding device shows a stabilized efficiency as high as 14.81%. As far as we know, this is the highest PCE for the CsPbBrI₂ perovskite based solar cells.