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

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.

Automated summary

This study proposes a method for preparing high-quality CsPbI2Br films at ambient conditions, which involves an intermediate phase transition and spinodal decomposition reaction to achieve phase stability, full coverage, and micro-sized grains in CsPbI2Br films. The carbon-electrode PSC with the desired CsPbI2Br film exhibits excellent efficiency, photovoltage, and stability.