Pressure induced electronic and optical responses of vacancy-ordered double perovskites Cs2BX6 (B = Zr, Pd, Sn; X = Cl, Br, I)

Due to the toxicity and instability of lead-containing perovskites, high-performance lead-free perovskite attracts considerable attention. Lead-free vacancy-ordered double perovskites (VODP) emerge as environmentally friendly and efficient solutions as lead-containing solar cell substitutes. In this study, electronic properties of vacancy-ordered double perovskites Cs2BX6 (B = Zr, Pd, Sn; X = Cl, Br, I) under high pressure are investigated using first-principles methods. Semiconductors with bandgaps between 1.1 to 1.6 eV are considered for application. Our results show Cs2PdCl6 giving 1.60 and 1.32 eV bandgaps at 5 and 10 GPa, Cs(2)PdBr(6 )yielding 1.22 eV at ambient pressure, Cs2SnBr6 having 1.31 and 1.03 eV bandgap at 5 and 10 GPa, and Cs2ZrI6 showing 1.52 and 1.28 eV bandgap at 15 and 20 GPa. Furthermore, we considered the absorption coefficient and spectrum to ensure the materials' optical performance. Cs2PdCl6, Cs2PdBr6, and Cs2ZrI6 display competent absorbance in the visible light range and proved these vacancy-ordered double perovskites as promising lead-free solar cell materials.