Recent advancements and developments in photovoltaic materials have made significant progress owing to the search for efficient and sustainable energy sources. Although lead halide perovskites have demonstrated impressive performance in solar cell applications, they face challenges such as environmental instability and lead toxicity. This study investigates several physical properties of two lead-free double halide perovskites, \(Rb_{2}CuAsBr_{6}\) and \(Rb_{2}TlAsBr_{6}\) , and evaluates their potential for solar cell applications using density functional theory (DFT) within the Wien2k code and spectroscopic limited maximum efficiency (SLME) approach. The negative formation energy and Born criteria confirm the structural stability of both perovskites in the ideal cubic structure. Optoelectronic analyses reveal that \(Rb_{2}TlAsBr_{6}\) , with a direct band gap of 1.51 eV, exhibits better photovoltaic characteristics compared to \(Rb_{2}CuAsBr_{6}\) , which has an indirect band gap of 0.60 eV. Additionally, the SLME analysis shows that \(Rb_{2}TlAsBr_{6}\) achieves a higher SLME of approximately 31.4 %, compared to \(Rb_{2}CuAsBr_{6}\) which has a SLME of 7.44%. Moreover, the calculated thermoelectric properties show that \(Rb_{2}TlAsBr_{6}\) exhibits enhanced thermoelectric performance compared to \(Rb_{2}CuAsBr_{6}\) . These findings highlight the potential of lead-free perovskites, particularly \(Rb_{2}TlAsBr_{6}\) , for next-generation solar cell applications.
