Alternative lead-free mixed-valence double perovskites for high-efficiency photovoltaic applications

Lead-based organic-inorganic hybrid perovskites have exhibited great potential in photovoltaics, achieving power conversion efficiencies (PCEs) exceeding 25%. However, the toxicity of lead and the instability of these materials under moist conditions pose significant barriers to large-scale production. To overcome these limitations, researchers have proposed mixed-valence double perovskites, where Cs2AuIAuIIII6 is a particularly effective absorber due to its suitable band gap and high absorptance efficiency. To further extend the scope of these lead-free materials, we varied the trivalent gold ion and halogen anion in Cs2AuIAuIIII6, resulting in 18 new structures with unique properties. Further, using first-principles calculations and elimination criteria, we identified four materials with ideal band gaps, small effective carrier mass, and strong anisotropic optical properties. According to theoretical modeling, Cs2AuSbCl6, Cs2AuInCl6, and Cs2AuBiCl6 are potential candidates for solar cell absorbers, with a spectroscopic limited maximum efficiency (SLME) of approximately 30% in a 0.25 μm-thick film. These three compounds have not been previously reported, and therefore, our work provides new insights into potential materials for solar energy conversion. We aim for this theoretical exploration of novel perovskites to guide future experiments and accelerate the development of high-performance photovoltaic devices.