Study on the Stability of Ammonium Iodide-Based Mixed-Dimensional Perovskite Solar Cells under Different Humidity

Recently, perovskite materials are widely applied in the photovoltaic field, whereas its practical application is hindered by the humidity instability. To solve this problem, the authors prepared a [(NH₄)_2.4(FA)₈Pb₉I_28.4]_0.85(MAPbBr₃)_0.15 mixed-dimensional (MD) perovskite with superior humidity stability. Herein, we investigated the aging properties of three-dimensional (3D) and MD perovskite under different humidity levels. Through analyzing the performance changes before and after aging tests, the possible mechanism of high moisture resistance for MD perovskite is speculated and verified. After undergoing cation exchange, the surface NH₄ ⁺ combines with H₂O to form NH₄PbX₃*(H₂O)₂ (X = I or Br), and then the two-dimensional (2D) perovskite protective layers are formed on the surface of perovskite, which prevent H₂O from destroying the 3D perovskite structure. Meanwhile, under continuous illumination, the δ-phase FAPbI₃ produced from inside FA⁺ may change into α-phase FAPbI₃. Therefore, the MD perovskite maintains great 3D perovskite structure and displays outstanding humidity stability under high humidity. The devices retain their starting photoelectric conversion efficiency (PCE) for 4000 h under 40% relative humidity (RH) and 80% of PCE over 2000 h under 70% RH. This finding provides a promising prospect for solving the humidity instability of perovskite materials and will promote the development of PSCs.