Antimony Doping of CsBi₃I₁₀ for Tailoring the Film Morphology and Defects toward Efficient Lead-Free Thin-Film Solar Cells

The CsBi3I10 (CBI) semiconductor as a light absorber emerges as a promising alternative to lead-based perovskites owing to its low toxicity, good stability, and satisfying physical properties. However, CBI exhibits an uncontrollable crystallization process, poor film morphology, high defect density, and short carrier lifetime, which lead to inferior optoelectronic properties, limiting its practical application in solar cell devices. Here, the Sb doping strategy is successfully developed for CBI films by a one-step antisolvent-free fabrication method. It is found that Sb incorporation in binary CsBi3–xSbxI10 can modulate the crystallization kinetics and optimize the film quality. As a result, polycrystalline films with high density and few pinholes are obtained to enable the enhancement of light absorbance, reduction of defects, suppression of nonradiative recombination, and increase of surface hydrophobicity. The solar cells based on the CsBi2.7Sb0.3I10 film show a remarkably improved power conversion efficiency of 0.82% compared to that of pristine CBI (0.22%), which is among the highest reported efficiencies for CBI-based thin-film solar cells. Moreover, unencapsulated devices based on Sb-doped CBI exhibit outstanding environmental stability and moisture tolerance. This work not only offers insights into understanding the binary Bi-based materials but also provides a new way to fabricate efficient and stable Bi-based solar cells.