Hypophosphorous Acid Additive Engineering for Efficient Cu₂AgBiI₆ Solar Cells

Abstract Perovskite solar cells have demonstrated significant performance advancements over the past decade, characterized by their low‐cost fabrication and compatibility with both rigid and flexible substrates. Despite their potential, challenges such as long‐term instability and the toxicity of lead in high‐performance devices hinder their commercialization. Recently, the perovskite‐inspired material Cu 2 AgBiI 6 (CABI) is explored as a light absorber due to its promising optoelectronic properties. However, its wide bandgap and difficulties in producing high‐quality films limit its photovoltaic performance. In this study, hypophosphorous acid (H 3 PO 2 ) is introduced to the CABI precursor solution, generating in situ silver nanoparticles that enhance light absorption through localized surface plasmon resonance. The incorporation of H 3 PO 2 improved the crystallinity and surface morphology of CABI films while reducing defect states. Solvent vapor annealing is further employed to optimize the film quality. As a result, the optimal CABI solar cell achieved a power conversion efficiency of 2.22%, a fourfold increase over the pristine film (0.55%). Additionally, the CABI device demonstrated an efficiency of 5.66% under 1000 lux 6000 K indoor illumination, showcasing its potential for powering Internet of Things devices. This strategy is further validated in the CuAgBiI 5 system, offering a pathway to enhance the performance of perovskite‐inspired solar cells.