The toxicity of lead and the instability of lead-based perovskite materials in the air are two key challenges in emerging Pb-based inorganic perovskite solar cells. Thus, the development of lead-free and stabilized inorganic perovskite materials is of great interest. In this work, the structural, ductility, and optoelectronic properties of Se-based double perovskites A2SeX6 (A = Rb, K; X = Cl, Br, I) have been studied for the first time by first-principles calculations to determine their potential use in optoelectronic sectors. Results reveal that these new series of A2SeX6 (A = Rb, K; X = Cl, Br, I) double perovskites are structural and mechanical stability. Their ductility increases as the halogen atom goes from Cl to I. Especially, the K2SeI6 possesses better ductility than other double perovskites. Electronic structure calculations exhibit that these new perovskite compounds are indirect band gap semiconductors. The Rb2SeI6 and K2SeI6 have more suitable bandgaps (1.24 and 1.16 eV) and smaller carrier masses, which are suitable for absorber layers of solar cells, while A2SeCl6 and A2SeBr6 are suitable for fabricating the optoelectronic devices in the ultraviolet region due to the wide gap. Furthermore, all these A2SeX6 compounds exhibit excellent optical properties with light absorption coefficients over 105 cm–1. Especially, the Rb2SeI6 and K2SeI6 have more excellent absorption spectra throughout the whole visible region. These results show that both Rb2SeI6 and K2SeI6 are potential candidates for absorption layer materials of solar cells, and A2SeCl6 and A2SeBr6 are suitable for other optoelectronic devices, such as photodetectors, light-emitting diodes, and so on.

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