Graded Bandgap CsPbI2+xBr1-x Perovskite Solar Cells with a Stabilized Efficiency of 14.4%

All-inorganic perovskite shows great potential for photovoltaic applications due to its excellent solar cell performance and atmospheric stability. Here, a CsPbI2+xBr1-x perovskite solar cell with a graded bandgap is explored using CsPbBrI2 and CsPbI3 quantum dots as component cells. Four strategies were pursued to boost the device performance. First, CsPbI2Br film was fabricated as the main absorber, with the component cell showing remarkable power conversion efficiency (PCE) as high as 13.45%. Second, by Mn2+ substitution, SCN- capping, and [(NH2)(2)CH](+) treatment, stable and high-mobility CsPbI3 quantum dot (QD) film was attained. Third, a halide-ion-profiled heterojunction was designed at the CsPbBrI2/CsPbI3 QD interface to achieve proper band-edge bending as graded bandgap for improved carrier collection. Finally, the CsPbI3 QD layer was optimized in the graded bandgap structure to achieve maximum overall light harvesting. As a result, the device achieved a PCE of 14.45%. This is the highest efficiency ever reported for inorganic perovskite solar cells.