Bandgap engineering and optoelectronic properties of all-inorganic lead-free Pd-based double perovskites

The various physical properties of lead-free double perovskites A₂PdX₆ (A = K, Rb, Cs; X  = Cl, Br, I) are revealed for the first time. The calculated structural parameters of these Pd-based compounds are consistent with the experimental data. It is likely to possess a tetragonal structure for K₂PdI₆ at room temperature. Cs₂PdBr₆ is dynamically stable when the pressure is in the range of 0–6.95 GPa. The mechanical properties are analysed and all the compounds are mechanically stable. The band gap trend of the A₂PdX₆ compound is identified when the A-site cation and halide anion are varied. Three A₂PdBr₆ compounds exhibit suitable band gaps for photovoltaic applications. An optimum band gap can be achieved for Cs₂PdBr₆ when the moderate pressure is applied. In addition, the electron shows better mobility than that of the hole for three A₂PdBr₆ compounds. The optical absorption coefficient of the A₂PdBr₆ compound is improved when the A-site cation changes from Cs to Rb to K. Applying pressure is beneficial to enhance light absorption capacity of Cs₂PdBr₆. The findings of this work can provide guidance for the design of potential A₂PdBr₆ compounds for photovoltaic applications.