Lead-free Perovskites TlGeCl_xBr_3-x (x=0,1,2,3) as Promising Materials for Solar Cell Application: a DFT Study

Abstract

This study investigates the structural parameters and the electronic properties of cubic TlGeClxBr3-x (x=0,1,2,3) lead-free perovskites to evaluate their potential as absorbers in perovskite solar cell devices. Density Functional Theory (DFT) embedded in the Quantum Espresso code was used to calculate these properties. The results revealed that the compounds have optimized lattice constants of 5.244 Å, 5.336 Å, 5.416 Å, and 5.501 Å, for TlGeCl3, TlGeCl2Br, TlGeClBr2, and TlGeBr3 perovskites, respectively. In addition, the compounds are direct band gap (R→R) semiconductors with energy gap values of 0.847 eV, 0.683 eV, 0.556 eV, and 0.518 eV for the respective materials. It is important to note that the band gap of the perovskites reduces as a Cl− ion, two and three Cl− ions are replaced by a Br− ion, two and three Br− ions, respectively. The analysis of their projected density of states indicated that near the valence band maximum of the perovskites, Cl-3p and Br-4p states contributes the most to their total DOS. In contrast, the Ge-4p orbital is the most dominant state close to the conduction band minimum. Based on these energy gap values, the studied materials are promising candidates for lead-free perovskite solar cell devices, with TlGeBr3 projected to be more promising than the other three materials.

Novel vacancy-ordered RbKGeCl6 and RbKGeBr6 double perovskites for optoelectronic and thermoelectric applications: an ab-initio DFT study

“…Similar trend was also observed for their vacancy ordered counterparts K 2 GeCl 6 and K 2 GeBr 6 [11] as well as Rb 2 GeCl 6 and Rb 2 GeBr 6 [13], where it was demonstrated that the anion substitution tunes the electronic band gap of the compounds. The progressive increase or decrease in the band gap energy as one of the cations of anions is substituted by an isoelectronic atom is characteristic feature observed across a wide range of perovskites [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]. This implies that cation and anion substitution is an effective way to tune the electronic properties of materials, which is very important to realize specific application in optoelectronic devices.…”

Optoelectronic, thermoelectric and 3D-Elastic properties of lead-free inorganic perovskites CsInZrX6 (I, Cl and Br) for optoelectronic and thermoelectric applications

“…The band gap value of CsInZrCl 6 is too large (3.6 eV) for solar cell applications. However, this value can be lowered by I doping since it has been shown that mixing Cl-based perovskites with Br or I led to a reduction in the band gap energy [47][48][49]. In addition, the band gap of the material can also be tuned by a number of approaches including chemical modification through anion exchange reactions [50], biaxial strain [51], structural templating [52], and hydrostatic pressure [53][54][55][56][57][58][59][60] CsInZrBr 6 , and CsInZrI 6 , with significantly higher contributions than the other states.…”