Computational study of structural, thermoelectric, elastic and optoelectronic properties of new halide perovskites CsRbTeX6 (X = I, Br and Cl) for solar cell applications

Recently the lead-free halide perovskites materials have attracted considerable attention due to their nontoxic nature and outstanding performances. In this work, using density-functional theory (DFT), the structural, ther-moelectric, elastic and optoelectronic properties of new series perovskites CsRbTeX6 (X = I, Br, and Cl) have been investigated. The Goldschmidt tolerance factor (& tau;) and octahedral factors (& mu;) results show a high structural stability. The computed bond length Te-X and lattice parameter a0 decrease progressively when the size of the X Halide atoms increases. The elastic constants and their derived parameters reveal a brittle behavior, high me-chanical stability and anisotropy nature of these materials. The low values of the bulk modulus in the three structures indicate that they are relatively soft materials and that they are amenable to being converted into thin films, which is essential for solar cell applications. The computed values of Tm are 582.49 K, 579.36 K and 578.71 K for CsRbTeI6, CsRbTeCl6 and CsRbTeBr6, respectively. Because of their high melting temperature, these materials are more appropriate for high temperature applications. The band structure profile exhibits a semi-conductor behavior with indirect band gap of about 2.81 eV, 2.2 eV and 1.51 eV for CsRbTeCl6, CsRbTeBr6 and CsRbTel6 respectively. With such tunable band gaps, the optical performance of these materials has been examined. The results show a very high light absorption in the order of 106 cm-1, a high power conversion efficiency (n) and a low reflectivity in the order 20% in the visible and UV region. Finally, the transport prop-erties reveal a sufficient figure of merit and a high Seebeck coefficient. According to these results, we suggest that the studied perovskites exhibit outstanding performance for thermoelectric and optoelectronic applications.