Synergistic effects of morphological control and enhanced charge collection enable efficient and stable lead-free CsBi3I10 thin film solar cells

Abstract

Lead (Pb) contamination and intrinsic instability of Pb-based perovskite materials greatly limit their application in a reliable and scalable manner, and the development of efficient and stable Pb-free alternatives is highly desirable. CsBi₃I₁₀ represents a promising light absorber owing to its appropriate bandgap, low material cost and solution processability; however, recent studies reveal that low-quality polycrystalline films and poor power conversion efficiencies (PCEs) significantly hinder the practical application of bismuth-based perovskites. Challenges remain in fundamentally modulating the crystallization kinetics and enhancing the photovoltaic performance. Here, we successfully develop a versatile fabrication technology, namely a gas quenching assisted antisolvent method (GQAS), to fine control crystallization and engineer film microstructures, which enables a compact, pinhole free and uniform thin film. Besides, the introduction of a multifunctional molecular additive 1,3-bis[3,5-bis-(trifluoromethyl)-phenyl]thiourea (FS) in CsBi₃I₁₀ can further induce efficient defect passivation, high film hydrophobicity and remarkable water stability. Significantly, the synergistic effects from GQAS and FS greatly improve the film microstructures and charge collection efficiency, yielding one order of magnitude higher PCEs (>1%) in CsBi₃I₁₀ thin film solar cells, which represents one of the highest reported efficiencies for CsBi₃I₁₀. This work provides new insights into the crystallization mechanism, and the developed strategies are generally applicable towards efficient and stable Pb-free PSCs.