Preparation of 2D Perovskite Layer by Solution Method to Improve the Stability of FAPbI<sub>3</sub> Perovskite Solar Cells

Organic-inorganic metal halide perovskite solar cells (PSCs) have been widely studied due to their excellent photoelectric conversion performance, but the inherent chemical instability of CH(NH₂)₂PbI₃ (FAPbI₃) has hindered its long-term development. In particular, the surface interface of the membrane has prominent humidity sensitivity due to lower activation energy, the defect of the surface interface has a strong correlation with the film stability, and the treatment result of the defect is one of the key factors to improve the long-term stability. FAPbI₃ suffers phase transition from black perovskite phase to yellow non-perovskite phase at room temperature, and the moisture will accelerate this phase transition. Interface engineering is one of the common methods to improve the stability of perovskite solar cells. In addition to interface engineering, there is also a strategy of stacking a two-dimensional (2D) perovskite layer on the surface for interface passivation. However, the preparation methods of 2D perovskite layer are most limited. In this paper, through the preparation process of the whole solution method and post-treatment mode of annealing were adopted, the hybrid perovskite solar cells of vitamin perovskite were successfully prepared. FAPbI₃ perovskite surface was uniformly spin-coated with butylamine iodide (BAI) solution, and the formation of 2D perovskite was driven on the surface of FAPbI₃ perovskite. Due to the passivation of 2D perovskite layer on the defects at the surface interface, the carrier non-radiative recombination is reduced, so that the carrier lifetime is greatly improved. Due to the hydrophobicity of long chain molecules in 2D perovskite, the long-term stability of the device has been significantly improved. Consequently, the unencapsulated device containing 2D perovskite layer remained above 80% after working nearly 1000 hours of relative humidity (RH) of 60% in ambient air at room temperature. The 2D perovskite layer can significantly improve the long-term stability of the film without affecting the charge carrier transport performance. This method to improve the stability of the device by constructing 2D perovskite layer is in line with the requirements and development trend of high-quality perovskite solar cells, and is a strategy with great development potential.