Effect of hydrostatic pressure for tuning the band gap of lead-free perovskites A ₂ TlGaCl ₆ (A = Cs, Rb) aimed at optoelectronic device applications

Lead-free perovskites having double halide structures reveal promising optoelectronic characteristics and have a great interest for future technological demands. In this research, the tuning of the band gap at hydrostatic pressure, as well as the pressure-dependent mechanical, thermal, and optical features of A 2 TlGaCl 6 (A = Cs, Rb), were found through DFT simulation. Calculation of tolerance factor, formation energy with a negative sign, and the phonon curvatures confirm thermodynamic plus dynamic constancy of A 2 TlGaCl 6 (A = Cs, Rb). The mechanical constancy of A 2 TlGaCl 6 (A = Cs, Rb) is ensured by the calculated stiffness constants, as they maintain Born’s stability conditions. We observed that the brittle-to-ductile transition of Cs 2 TlGaCl 6 is at 1 GPa, while Rb 2 TlGaCl 6 strongly dominated the ductile nature under the entire pressure. Low bulk as well as Young’s moduli of 18.638 GPa, 19.294 GPa for Cs 2 TlGaCl 6 , and 28.27 GPa, and 21.719 GPa for Rb 2 TlGaCl 6 at 0 GPa pressure ensure the very soft nature of these materials; however, these materials become harder at high pressure. Rising manner of machinability factor with pressure confirms a more damage-tolerant, low-friction, and flexible nature of A 2 TlGaCl 6 (A = Cs, Rb). At 0 GPa, the materials Cs 2 TlGaCl 6 and Rb 2 TlGaCl 6 showed an indirect band gap semiconducting attitude with band gap values of 2.934 eV and 2.327 eV. However, these wider band gaps are gradually becoming narrower under external pressure, which guarantees us the target compounds are more suitable for optoelectronic device applications, including solar cells, LED, plus infrared radiating diodes. The starting of absorption and conductivity spectra after some energy further authorizes the semiconducting performance of these materials, whereas intense peaks of absorption, reflectivity, and conductivity are observed in the UV energy region. Under the entire pressure, the minimum thermal conductivities, k min remain much lower, indicating the applications of A 2 TlGaCl 6 (A = Cs, Rb) in TBC materials.