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Organic-inorganic lead halide perovskite solar cells have high power conversion efficiency; however, their poor environmental stability is still a problem that needs to be solved. In this study, a tetrabutylammonium cation is introduced into mixed-cation lead a mixed-halide Cs 0.05 (FA 0.83 MA 0.17) 0.95 Pb(I 0.83 Br 0.17) 3 perovskite as a sacrificial cation to enhance the stability of the corresponding solar cells. Tetrabutylammonium cations located at grain boundaries are beneficial for the formation of two-dimensional perovskite grains perpendicular to the substrate during heat treatment, which can enhance the stability of solar cells against moisture. By optimizing the content of tetrabutylammonium iodide ions, a maximum power conversion efficiency of 12% is achieved for the solar cell with the structure of FTO/c-TiO 2 /m-TiO 2 /perovskite/carbon. Without encapsulation, the tetrabutylammonium contained perovskite solar cell does not obviously degrade at ambient atmosphere (60% relative humidity and 27 °C) for over 1000 h. Moreover, this solar cell can retain over 80% of its initial efficiency for 500 h at 85 °C and in dry air. Image 1 • Tetrabutylammonium cations formed 2D perovskite at grain boundaries during heating. • The hydrophobic property of tetrabutylammonium cations enhanced humidity stability. • A PCE of 12% was achieved for TBA-contained carbon-based PSCs with high stability. [ABSTRACT FROM AUTHOR]

Lead halide perovskites have emerged as promising photovoltaic (PV) materials owing to their superior optoelectronic properties. However, they suffer from poor stability and potential toxicity. Here, computational screening with experimental synthesis is combined to explore stable, lead‐free, and defect‐tolerant PV materials. Heavy cations with lone‐pair electrons and mixed anions of chalcogens and halogens as a descriptor for simultaneous realization of defect tolerance and high stability are adopted. Together with the criteria of possessing direct band gap and optimal gap value, the inorganic material database is screened and CuBiSCl2 in the post‐perovskite structure is identified with an ideal band gap of 1.37 eV. The electronic structure and defect calculations suggest its defect‐tolerant characteristics. By optical absorption measurement, its band gap is confirmed to be ≈1.44 eV, with strong absorption near the band edge. The material is stable against thermal decomposition up to 300 °C and can survive from 25 days of storage at ambient conditions with 60% relative humidity. Prototype solar cells are fabricated and demonstrate an open circuit voltage of 1.09 V and a power conversion efficiency of 1.00%. With the excellent properties above, CuBiSCl2 is proposed to be a promising candidate for PV application. [ABSTRACT FROM AUTHOR]