Electronic, optical, and thermoelectric properties of perovskite variants A2BX6: Insight and design via first-principles calculations

Lead halide perovskites are considered as a material of choice for solar cell applications. However, there are challenges: organic cations in halide perovskites are unstable, and lead is toxic. To address these issues, we propose and investigate some potential alternatives to lead in the form of A(2)BX(6) perovskites using the first-principles calculations. Besides simple approximation potentials, we use a highly successful hybrid functional HSE06, to calculate the electronic, optical, and thermoelectric properties of A(2)PdI(6) (A = K, Rb, and Cs). Our calculations show that K2PdI6, Rb2PdI6, and Cs2PdI6, are narrow bandgap semiconductors with bandgap of 0.8, 0.92, and 0.9 eV, respectively. The valence band maximum (VBM) of A(2)PdI(6) is mainly composed of I-5p orbitals while the conduction band minimum (CBM) is formed of Pd-4d and I-5p orbitals. Due to the ideal bandgap and excellent light absorption, Rb2PdI6 stands out as a potential candidate for usability in tandem solar cells. In addition, p-type doping at a carrier concentration of 1 x 10(18) cm(-3) makes these perovskites a material of choice for thermoelectric energy applications.