CuAgBi2I8 of high quality, featuring a resolved cubic close packed crystal structure and a direct bandgap of 1.69 eV, was in situ synthesized by tailoring the distribution of Bi in vapor-phase redox reactions. Employing this novel approach, the efficiency of CuAgBi2I8 solar cells reached 3.21%, which is the highest reported to date.
Abstract
Considering sustainable development factors such as element abundance, cost, environmental friendliness, and stability, the research and development of novel inorganic non-lead perovskites are very significant. Copper-silver-bismuth iodide (CABI) is a promising solar cell material with halide perovskite genes, possessing eco-friendly, element-rich, and cost-effective characteristics. The fabrication of high-quality CABI films with tailored compositions still poses a substantial hurdle. We developed a CuAgBi2I8 material that effectively reduced the bandgap to 1.69 eV by optimizing Bi distribution to create an environment conducive to in-situ redox reactions of Bi with I2, Cu, and Ag via vapor-phase synthesis. This strategy proved highly effective in synthesizing high-quality CuAgBi2I8 compound, accompanied by significant improvements in film quality, including enhanced crystallinity, minimized defects, and reduced non-radiative recombination. The crystal structure of CuAgBi2I8 and mechanisms of elemental reactions and diffusion are discussed. Devices featuring the structure FTO/c-TiO2/m-TiO2/CuAgBi2I8/CuI/Spiro-OMeTAD/carbon achieved a champion efficiency of 3.21%, the highest for CABI solar cells. This work provides a novel idea and approach to governing the gas–solid element diffusion and reaction for high-quality CABI and related halide perovskite films.
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