Halide Double Perovskites Cs<sub>2</sub>PdBr<sub>6–<i>x</i></sub>I<sub><i>x</i></sub> with Tunable Bandgaps for Solar Cells
Yuhuan Li, Tongxiao Yang, Yaqi She, Beizheng Xu, Yonghui Du, Miao Zhang
Abstract
Inorganic lead-free vacancy-ordered double perovskites with the chemical formula A 2 BX 6 are promising candidates to overcome Pb-based organic–inorganic perovskite’s toxicity and instability issues. We designed the mixed-halide double perovskites Cs 2 PdBr 6– x I x 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 Cs 2 PdBr 6– x I x 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 Cs 2 PdBr 3 I 3 . Their absorption spectrum shows that the absorption range of visible light expands significantly. The theoretical spectral limit maximum efficiency (SLME) of Cs 2 PdBr 5 I with 1.3 eV and Cs 2 PdBr 4 I 2 with 1.04 eV reached 32 and 30.4%, respectively, which are becoming comparable to or slightly surpassing CH 3 NH 3 PbI 3, indicating they could be candidates for single-junction solar cells. In addition, the Cs 2 PdBr 3 I 3 and the Cs 2 PdBr 4 I 2, 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 Cs 2 PdBr 6, which could be the top cell with the bandgap of 1.73 eV.