In this paper, 4,4′-ethylenedianiline as a linker, flexible 2,4,6-tris(4-formylphenoxy)- 1,3,5-triazine (TPT − 3 − CHO) and hexa(4-formyl-phenoxy)cyclotriphosphazene (NOP − 6 − CHO) as knots were selected to construct the new flexible EDAN-based COFs (TEDAN and HEDAN) through Schiff base reactions of aldehyde and amine. The as-prepared flexible EDAN-based COFs have high crystallinity, sizable surface area, and thermal stability. With porous properties, abundant electron-rich heteroatoms as well as large π-conjugated network structures that can provide effective binding sites, TEDAN and HEDAN exhibit good reversible vapor-trapped iodine with the adsorption capacities of 4.64 and 2.25 g g −1 , respectively. The aromatic networks of nitrogen-rich units in TEDAN provide many binding sites with guest iodine molecules than that of HEDAN, resulting in higher equilibrium uptake capacity of iodine for TEDAN. In addition, the flexible EDAN-based COFs show “turn-off” detection of non-radioactive iodine in the dispersion state with quenched constants (K SV ) of 5.59 × 10 4 and 2.35 × 10 4 L mol −1 . The fluorescence quenching of the flexible TEDAN-based COFs can be attributed to both the photo-induced electron transfer mechanism and the energy transfer transfer mechanism. The sensitivity of HEDAN is higher than that of TEDAN.
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.
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