Mixed-halide vacancy-ordered double perovskite for photovoltaic and photocatalysis applications

Here, we report detailed first-principles calculations of the structural stability, optoelectronic properties, and interaction with water for a wide range of mixed-halide compositions of vacancy-ordered double perovskites Cs₂Pt(ClₓI_1-x)₆. Our calculations reveal that lower halide dopant levels subdue phase segregation and enhance the stability. Cs₂Pt(ClₓI_1-x)₆ demonstrate improved defect tolerance as compared to Cs₂PtI₆ due to the covalent nature of the Pt---X bond. The chloride-rich Cs₂Pt(ClₓI_1-x)₆ exhibit notably improved stability against reaction with water, far surpassing Cs₂PtI₆ due to the enhanced Cs---Cl bond strength and lower charge transfer between adsorbed H₂O and surface Cs atoms. The spectroscopic limited maximum photovoltaic efficiency for the optimal composition of Cs₂Pt(Cl0.04I0.96)₆ under 1 sun AM1.5G is determined to be $24$% for a 5-μm-thick film. Our calculations also suggest that the valence-band edge of this material might be positioned more positive than the standard potential of the oxygen-evolution reaction. These two factors combined with the high stability against reaction with water indicate that Cs₂Pt(Cl0.04I0.96)₆ might be of considerable interest as a photovoltaic absorber, and possibly as a component of anodes for the photoelectrocatalytic water oxidation. Meanwhile, Cs₂Pt(Cl0.96I0.04)₆ traverses relevant reduction and oxidation redox potentials, affirming it as a promising candidate for the overall photo(electro)catalyst water-splitting reaction.