Halide Double Perovskites CsPdBrI with Tunable Bandgaps for Solar Cells.

Inorganic lead-free vacancy-ordered double perovskites with the chemical formula ABX are promising candidates to overcome Pb-based organic-inorganic perovskite's toxicity and instability issues. We designed the mixed-halide double perovskites CsPdBrI by halogen anions substitution. The structure, stability, and electronic and photoelectric properties were explored using density functional theory (DFT). The negative value of the formation energy indicated that the CsPdBrI perovskites are thermodynamically stable. These perovskites exhibit tunable bandgap values in the range of 0.77-1.73 eV, which are direct or quasi-direct bandgaps except for CsPdBrI. Their absorption spectrum shows that the absorption range of visible light expands significantly. The theoretical spectral limit maximum efficiency (SLME) of CsPdBrI with 1.3 eV and CsPdBrI with 1.04 eV reached 32 and 30.4%, respectively, which are becoming comparable to or slightly surpassing CHNHPbI, indicating they could be candidates for single-junction solar cells. In addition, the CsPdBrI and the CsPdBrI, with the bandgap of 1.12 and 1.04 eV, respectively, could be the bottom cell to form the homogeneous tandem solar cells with the CsPdBr, which could be the top cell with the bandgap of 1.73 eV.