A theoretical exploration of the structural feature, mechanical, and optoelectronic properties of Au-based halide perovskites A2AuIAuIIIX6 (A = Rb, Cs; X = Cl, Br, I)

As a possible alternative to lead halide perovskites, inorganic mixed-valence Au-based halide perovskites have drawn much attention. In the current research, we have conducted comprehensive theoretical calculations to reveal the structural feature, thermodynamic and dynamic stability, mechanical behavior, optoelectronic properties, and photovoltaic performance of Au-based halide perovskites A(2)Au(I)Au(III)X(6) (A = Rb, Cs; X = Cl, Br, I). The structural parameters of these compounds are carefully analyzed. Our calculations indicate that the thermodynamic, dynamic, and mechanical stability of monoclinic (Rb2AuAuX6)-Au-I-X-III and tetragonal (Cs2AuAuX6)-Au-I-X-III are ensured, and they are all ductile. The electronic band structure analysis shows that (Rb2AuAuI6)-Au-I-I-III illustrates a direct-gap feature, while (Rb2AuAuX6)-Au-I-X-III (X = Cl, Br) and (Cs2AuAuX6)-Au-I-X-III (X = Cl, Br, I) are indirect-gap materials. The effect of A-site cation substitution on the optical band gaps of the Au-based halide perovskites is elucidated. Our results further suggest that (Rb2AuAuX6)-Au-I-X-III (X = Br, I) and (Cs2AuAuX6)-Au-I-X-III (X = Cl, Br, I) are more suitable for single-junction solar cells due to their suitable band gaps within 1.1-1.5 eV. Furthermore, four compounds A(2)Au(I)Au(III)X(6) (A = Rb, Cs; X = Br, I) not only have high absorption coefficients in the visible region but also show excellent photovoltaic performance, especially for A(2)Au(I)Au(III)I(6) (A = Rb, Cs), whose efficiency can reach over 29% with a film thickness of 0.5 mu m. Our study suggests that inorganic Au-based halide perovskites are potential alternatives for optoelectronic devices in solar cells.