Novel KXBr3 (X = Ca, Sr, Ba) lead-free halide perovskites for optoelectronic applications: A DFT investigation of mechanical and optoelectronic properties

Abstract

The present study proposes novel KXBr3 (X = Ca,Sr,Ba) perovskites as promising materials for applications in various optoelectronic devices. The structural, mechanical and optoelectronic properties of the materials are predicted using first-principle calculations based on the Density Functional Theory (DFT) implemented in the Quantum Espresso code. The structural optimization results in stable lattice constants of 5.71 Ȧ, 5.98 Ȧ, and 6.31 Ȧ, for the respective materials. The results confirmed their chemical and mechanical stability, with KSrBr3 and KBaBr3 also exhibiting dynamical stability. Equally important, the perovskites possess ductile behavior, as indicated by their Poisson and Pugh ratio found to be larger than 0.26 and 1.75, respectively. The ductility is also confirmed by their positive Cauchy pressure. From the electronic band structure, it was found that the materials have indirect band gap (R→Γ) of 3.89 eV, 3.72 eV, and 3.58 eV, for KCaBr3, KSrBr3, and KBaBr3, respectively. SCAN approximation was also implemented to obtain more reliable band gap energy of 4.43 eV, 4.27 eV, and 4.14 eV, for the respective compounds. One of the most remarkable optical properties found was their considerably low reflectivity, with maximum values being less than 19 %. This is further reinforced by their high absorption coefficients, reaching 105 cm−1.