Cooperation of Dual Organic Spacers and A Site Cations for High-Performance Quasi-2D Ruddlesden-Popper Perovskite Solar Cells.

Abstract

Ruddlesden-Popper (RP) quasi-two-dimensional (2D) perovskites exhibit enhanced stability compared to their three-dimensional (3D) counterparts due to the incorporation of bulky organic spacers. However, their efficiency is relatively low owing to the large exciton binding energy and quantum confinement effects associated with these organic spacers. Herein, a diversified cation regulation strategy is developed by adjusting both the spacers and A-site cations, achieving the fabrication of mixed 4-fluoro-phenethylammonium (F-PEA⁺)/n-butylammonium (BA⁺) and formamidinium (FA⁺)/methylammonium (MA⁺) n = 4 quasi-2D RP perovskite solar cells. Primarily, the introduction of F-PEA⁺ induces an ordered distribution of the film from low-n to high-n phases, resulting in enhanced crystallinity, larger grain size, fewer cracks, and voids as well as high-quality perovskite films with preferred orientation. Furthermore, the incorporation of FA⁺ reduces the bandgap of the perovskite, facilitating exciton dissociation and enhancing carrier transport capabilities. Ultimately, under the cooperation effect, the obvious elevation in the efficiency of NiO_x-based (BA_0.9F-PEA_0.1)₂(MA_0.8FA_0.2)₃Pb₄I₁₃ n = 4 quasi-2D RP perovskite solar cells from 12.51 to 15.68% is achieved. Additionally, the unencapsulated devices retain 80.4% of initial efficiency after 1100 h of heating at 60 °C in ambient air with 40% relative humidity, demonstrating excellent thermal and moisture stability.