Structural, mechanical, optoelectronic and thermoelectric properties of Cs1-xAxPbI3 (A=K, Rb) perovskites: Density functional investigation

The structural, mechanical, thermodynamic, electrical, optical, and thermoelectric properties of Cs1-xAxPbI3 (A = K, Rb) perovskites within GGA approximations have been studied. The calculations are performed using the QUANTUM-ESPRESSO computational package based on the density functional theory (DFT) and the pseudopotential method. The calculated elasticity parameters illustrated that Cs1-xAxPbI3 (A = K, Rb) perovskites have mechanical stability conditions at ambient pressure. The calculation of the elastic modulus shows that KPbI3 and Cs0.75 K0 & sdot;25PbI3 with Young's modulus equal to 16.11 GPa and 17.00 GPa have the lowest and highest hardness respectively. The estimated B/GH ratio values were greater than 1.75 for all perovskites, reflecting the flexibility of the compounds. Calculation of band structure confirmed the semiconductor behavior with a direct band gap in the range of 1.38 eV-1.51 eV. Our investigation of charge carrier mobility revealed that electrons have greater carrier mobility than holes in all Cs1-xAxPbI3 (A = K, Rb) perovskites. The optical absorption peaks of Cs1-xAxPbI3 (A = K, Rb) perovskites are located in the visible area, indicating their effective use in optical and optoelectronic devices. Calculations of the Seebeck coefficient revealed the n-type semiconductor nature of all perovskites. Thermoelectric parameters, including the Seebeck coefficient, electrical conductivity divided by the relaxation time, and thermal conductivity divided by the relaxation time, all increase as temperature increases. The thermoelectric properties of Cs1-xAxPbI3 (A = K, Rb) perovskite were improved by increasing the concentration of potassium and rubidium. The maximum electronic figure of merit of all Cs1-xAxPbI3 (A = K, Rb) perovskites at room temperature was 0.99, which makes them good candidates for application in thermoelectric devices.