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.