Intermediate Phase‐Assisted Sequential Deposition Toward 15.24%‐Efficiency Carbon‐Electrode Cspbi2br Perovskite Solar Cells

Abstract

All‐inorganic perovskite CsPbI2Br is emerging as a promising absorber material for perovskite solar cells (PSCs) due to its superior photophysical properties and thermal stability. However, there are still many great challenges to obtaining high‐quality, phase‐stable, thick CsPbI2Br films in ambient air to promote further development of the PSCs. Herein, for the first time, an intermediate phase‐assisted sequential deposition for desired CsPbI2Br films is proposed. It is carried out by sequentially spin‐coating PbBr2 and CsI precursors onto the substrate in ambient air, during which a Ruddlesden–Popper (R–P) perovskite intermediate phase film composed of a Cs‐Pb‐I‐Br complex is produced. After annealing, the intermediate phase film is transformed into a CsPbI2Br film consisting of CsPbI2Br grains and CsBr species through a spinodal decomposition reaction. The as‐obtained CsPbI2Br film holds full coverage, micro‐sized grains, and excellent phase stability. Moreover, the CsBr species located at grain boundaries can effectively passivate the defects. Therefore, a carbon‐electrode PSC with such a desired CsPbI2Br film yields the optimized efficiency of 15.24%, coupled with a remarkable photovoltage of 1.312 V and excellent stability in ambient air with relative humidity of 60–70%. The efficiency achieved herein is among the record efficiencies for carbon‐electrode PSCs based on various all‐inorganic perovskites reported currently.