Graded Bandgap CsPbI_2+xBr_1−x Perovskite Solar Cells with a Stabilized Efficiency of 14.4%

Highlights

• CsPbI₂Br film was fabricated with the component cell showing PCE as high as 13.45%

• By optimizing, CsPbI₃ QD-based solar cell with PCE of 10.97% was obtained

• A heterojunction was designed at the interface to achieve proper band-edge bending

• CsPbI₃ layer was optimized in bilayer device to achieve a record PCE of 14.45%

Summary

All-inorganic perovskite shows great potential for photovoltaic applications due to its excellent solar cell performance and atmospheric stability. Here, a CsPbI_2+xBr_1−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)₂CH]⁺ 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.