Facile Molecular Modification for Efficient and Stable Carbon-Based CsPbI₃ Perovskite Solar Cells

Carbon-based inorganic perovskite solar cells (C-IPSCs) with promising efficiency, good thermal stability, and low cost have emerged as important candidates for photovoltaic device commercialization. However, the relatively poor phase stability of CsPbI₃ perovskite in humid conditions and the mismatched energy level at the perovskite/carbon interface hinder the efficiency and stability of CsPbI₃ C-IPSCs. Herein, a facile molecular modification strategy is employed to solve the current issues using a multifunctional molecule, ethyl thioacetate (ES). Post-treatment enhances the hydrophobicity of CsPbI₃ films due to the relatively small polarity of ES molecules. The C═O and C–S groups in ES form Lewis acid–base coordination interactions with uncoordinated Pb²⁺ in perovskite, effectively passivating surface defects in perovskite films. In addition, ES treatment optimizes the energy level arrangement, facilitating hole extraction at the perovskite/carbon interface. Thus, ES post-treatment yields a champion PCE of 17.07% for carbon-based CsPbI₃ solar cells. The ES-treated C-IPSCs also show enhanced stability, which retains 80% of the initial PCE after 1360 h at 20% RH, surpassing the untreated counterparts by 19%.