Favorable morphology and compositional distribution enable efficient and stable quasi-2D Dion–Jacobson perovskite solar cells

Two-dimensional (2D) Dion–Jacobson (DJ) halide perovskites are being intensively investigated owing to their superior stability compared with 2D Ruddlesden–Popper (RP) perovskites. Although various organic cations have been reported to form 2D DJ perovskites, their structure–property relationships are rarely studied. In this work, two novel organic cations MDAN (4,4′-methylenedianilinium) and EDAN (4,4′-ethylenedianilinium) were applied to form quasi-2D DJ perovskites with nominal layer number n = 6. An (EDAN)MA5Pb6I19:0.15MACl based inverted solar cell achieved a power conversion efficiency (PCE) of 13.2%, outperforms the 9.6% PCE achieved by a (MDAN)MA5Pb6I19:0.15MACl based device. The formation of quasi-2D perovskites with high-n values was observed for both compounds, while the superior performance is demonstrated by the (EDAN)MA5Pb6I19:0.15MACl based device, which could be attributed to its better film morphology and lower defect density. Intriguingly, we found that EDAN based quasi-2D perovskites were evenly distributed in the film while MDAN based quasi-2D perovskites concentrated near the film surface, accounting for an unfavorable electronic band alignment of the latter. Both (MDAN/EDAN)MA5Pb6I19:0.15MACl films remained unchanged in air with 50% relative humidity for 20 days. This work not only presents a decent device performance, but also explores understanding of tuning morphology towards high-efficiency quasi-2D Dion–Jacobson perovskite solar cells.