Recent Advances in Cs2AgBiBr6-Based Halide Double Perovskites as Lead-Free and Inorganic Light Absorbers for Perovskite Solar Cells

Although lead-based inorganic–organic perovskite solar cells (PSCs) have delivered the highest power conversion efficiency (PCE) to date of 25.2%, the toxic nature of lead and poor stability are the biggest hurdles for the commercialization of PSCs. Lead-free halide double perovskite Cs2AgBiBr6 has received increasing attention as a promising alternative for toxic and unstable organic–inorganic perovskites in PSCs due to its nontoxicity, high structural stability, and unique photoelectric properties. However, the PCEs of Cs2AgBiBr6-based PSCs are strongly restricted by the inherent and extrinsic defects in Cs2AgBiBr6 films. Thus, an in-time review to summarize the research progress of Cs2AgBiBr6-based PSCs to provide strategies for the enhancement of PCEs is critical. In this review, the recent advances in Cs2AgBiBr6 as a light absorber in PSCs are summarized and discussed with an emphasis on the structural, photoelectric, and physical properties of Cs2AgBiBr6. The synthesis and fabrication methods of Cs2AgBiBr6 crystals and films are also reviewed. Importantly, strategies for improving the photovoltaic performance of Cs2AgBiBr6-based PSCs are presented, including band gap engineering, film quality optimization, and interface engineering. Finally, current challenges and perspectives are presented. This review aims to provide useful guidelines for future research in this emerging field.