Discovery of Rb-based auric–aurous halide perovskites as promising narrow bandgap semiconductors for energy conversion applications

Inorganic gold halide perovskites, owing to their excellent stability and tunable bandgaps, are poised to serve as environmentally benign alternatives to lead halide perovskites in the field of photovoltaics. In this study, we successfully synthesized two inorganic auric–aurous halide perovskites, Rb2Au2I6 and RbAuCl4, using a straightforward and efficient hydrothermal method, achieving millimeter-sized single crystals. Single-crystal structural analysis revealed that Rb2Au2I6 exhibits a three-dimensional (3D) double perovskite structure, whereas RbAuCl4 shows a two-dimensional (2D) Dion–Jacobson (DJ)-type perovskite structure. We further analyzed their crystallographic information and elucidated the reasons behind the structural differences between them. Moreover, first-principles calculations ascertained their high optical absorption coefficients within the visible light spectrum and indirect bandgap properties. Utilizing theoretical models, we discovered that Rb2Au2I6 and RbAuCl4 exhibit spectroscopic limited maximum efficiency (SLME) of 30.12% and 22.30%, respectively, in films of 500 nm thickness, signifying their potential candidacy as solar cell absorbers. Theoretical calculations related to thermoelectric properties illustrate high ZT (thermoelectric figure of merit) values of about 1.4 and 1.2 at 500 K for Rb2Au2I6 and RbAuCl4, respectively. Based on the significantly shortened synthesis of Rb2Au2I6 and RbAuCl4, our study demonstrated their potential in the field of optoelectronics and thermoelectric materials, which could lay a solid foundation for future applications in energy-conversion devices.