The synergistic effect of non-stoichiometry and Sb-doping on air-stable α-CsPbI₃ for efficient carbon-based perovskite solar cells

α-CsPbI₃ with the most suitable band gap for all-inorganic perovskite solar cell (PSC) application faces an issue of phase instability at low temperature in an air atmosphere. Herein, through stoichiometric investigation, α-CsPbI₃ is successfully obtained with excess CsI at 110 °C in an air atmosphere. By doping α-CsPbI₃ with Sb, phase stability is further enhanced and the film morphology is also improved. Carbon-based perovskite solar cells (C-PSCs) based on CsPb_0.96Sb_0.04I₃ achieve a promising power conversion efficiency (PCE) of 5.18%, a record value for α-CsPbI₃-based PSCs without hole transport materials. Significantly, the CsPb_0.96Sb_0.04I₃ C-PSCs retain 93% of the initial PCE after 37 days of storage in an air atmosphere. Therefore, the synergistic effect of non-stoichiometry and Sb-doping presents a promising strategy to design all-inorganic lead halide PSCs with high performance and stability.