Cold- and hot-casting to regulate the morphology and charge carrier dynamics of CsBi3I10 towards efficient and stable thin-film solar cells

Abstract

Inorganic semiconductor CsBi₃I₁₀ (CBI) emerges as one of the most promising candidates for lead-free perovskite solar cells (PSCs) due to its low toxicity, high visible light absorption and excellent humidity tolerance. However, poor film morphology and high crystal defects limit its practical application in photovoltaics. Herein, hot-casting and cold-casting technologies are proposed respectively in the fabrication process of CBI to regulate the film quality and photoelectric properties. Significant differences appear in the crystallization process and film morphology of CBI layers, resulting in distinct device performance. In contrast to the CBI film with low density and high thickness formed via the hot-casting technology, the cold-casting accelerates the crystallization rate of CBI, achieving a dense and smooth film with moderate thickness. Consequently, cold-casting improves the crystallinity, smoothness, conductivity and hydrophobicity of the CBI films, all of which contribute to the promotion of charge separation at the interface and the inhibition of non-radiative recombination in the PSCs. The resulting devices exhibit a 2-fold increase in the power conversion efficiency and enhanced environmental stability compared to the devices with pristine CBI. This work provides new insights into the crystallization mechanism of bismuth-based films and proposes another approach for regulating the morphology of perovskite films.