Computational Insights into the Stability, Mechanical, Optoelectronic, and Thermoelectric Characteristics Investigation on Lead‐Based Double Perovskites of (<i>Cs</i>₂, <i>K</i>₂, <i>Rb</i>₂)<i>PbCl</i>₆: P

Abstract Lead‐based double perovskites are studied in the cubic phase using the generalized gradient approximation and the modified Becke–Johnson (mBJ‐GGA) functionals as implemented in the Wien2K code. Goldschmidt tolerance factor and octahedral factor, formation enthalpy, and formation energy translate the structural, chemical, and thermodynamic stability of double perovskites studied. Phonon band structures and elastic moduli ensure the dynamic and mechanical stability of ( Cs 2 , K 2 , Rb 2 ) PbCl 6 . An intermediate band appears in the conduction band and the fundamental transition takes place between 3p‐Cl state and 6p‐Pb site. The refractive index of double perovskites ( Cs 2 , K 2 , Rb 2 ) PbCl 6 in the visible and ultraviolet light hold a huge advantage for solar cell applications. The wide dielectric constant of double perovskites under study makes them capable for absorbing energy between 1 and 5 eV, and are suitable for solar power applications. ( Cs 2 , K 2 , Rb 2 ) PbCl 6 have positive Seebeck coefficient, which reveals that p‐type charge carriers are dominant for enhancing their performance. Cs 2 PbCl 6 has positive thermal conductivity for both n‐type and p‐type character. ( K 2 , Rb 2 ) PbCl 6 have positive thermal conductivity for n‐type character. The complete analysis reveals that they are potentially significant candidates for future solar cells and energy harvesting devices.