Lead free A2NaInI6 (A = Cs, Rb, K) double perovskites for optoelectronic and thermoelectric applications

Abstract Alkali metal substitution in double perovskites is an appropriate approach to deliberate tuning of band edges which play a vital role in bandgap engineering of emerging semiconducting materials. Here we tuned the optoelectronic behavior by carefully engineering the band edges in A 2 NaInI 6 (A = Cs, Rb, K) systems and by tuning the alkali atoms at A site using density functional theory based WIEN2K code. First of all, the unit cell is relaxed to find the optimized lattice parameters. The substitution of smaller-sized cation at the A site leads to the reduction in lattice parameter which shifts the absorption edge towards a shorter wavelength and reduces the bandgap energy. The value of bandgap energy is noticed at 1.60 eV for Cs 2 NaInI 6 which increases to 1.65 and 1.70 eV for Rb 2 NaInI 6 and K 2 NaInI 6 respectively. The computation of the elastic constant’s dependent modulus of elasticity and the Pugh and Poisson ratio confirm their brittle nature. Their viability for solar-thermoelectric generators is carried out by computing the temperature-dependent transport parameters using the BoltzTrap code showing the potential of these systems for solar thermoelectric generators.