Suppressing the Defects in CsPbI2Br Perovskite Photovoltaic Films via a Homogeneous Cap-Mediated Annealing Strategy

All-inorganic CsPbI2Br perovskite films offer attractive thermal stability and photophysical properties for high-performance optoelectronic devices. However, due to the rapid evaporation rate of the solvent, there are many defects, heterogeneous compositions, and pinholes in the CsPbI2Br films prepared by the common solution method. Herein, the homogeneous cap-mediated annealing strategy is successfully introduced to slow down the evaporation rate of the residual dimethyl sulfoxide solvent molecules in CsPbI2Br precursor films during thermal annealing. Compared with the conventional annealing method, the CsPbI2Br films prepared by the homogeneous cap-mediated annealing have excellent crystallinity with a pinhole-free surface. As a result, the perovskite solar cells based on the homogeneous cap-mediated annealing CsPbI2Br and carbon top electrode exhibited a power conversion efficiency (PCE) of 11.24%, which is much higher than that (4.36%) of the conventional annealing CsPbI2Br-based solar cells. Moreover, the homogeneous cap-mediated annealing strategy can also be introduced to a two-step annealing method. Because of the synergistic effect, the high-quality CsPbI2Br perovskite films with a low root-mean-square of 19.53 nm, enlarged grain size, and reduced defect density are obtained, and the champion PCE of the solar cells is further increased to 12.82%.