Cooperation of Dual Organic Spacer Cations and A Site Cations for High Performance Quasi-two Dimensional Ruddlesden-Popper Perovskite Solar Cells.

Ruddlesden-Popper (RP) quasi-two-dimensional (2D) perovskites exhibit enhanced stability compared to their three-dimensional counterparts due to the incorporation of bulky organic spacer cations. However, their efficiency is relatively low owing to the large exciton binding energy and quantum confinement effects associated with these organic spacer cations. In this work, we developed a diversified cation regulation strategy by adjusting both the spacer cations and A-site cations, leading to 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+ induced 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+ reduced the bandgap of the perovskite, facilitating exciton dissociation and enhancing carrier transport capabilities. Ultimately, Under the synergistic effect, the obvious elevation in the efficiency of NiOx-based (BA0.9F-PEA0.1)2(MA0.8FA0.2)3Pb4I13 n=4 quasi-2D RP perovskite solar cells from 12.51% to 15.68% is achieved. Additionally, the unencapsulated devices retained 80.4% of initial efficiency after 1100 hours of heating at 60°C in ambient air with 40% relative humidity, demonstrating excellent thermal and moisture stability.