Forming a metal-free oxidatively-coupled agent, bicarbazole, as a defect passivation for HTM and an interfacial layer in a p-i-n perovskite solar cell exhibits nearly 20% efficiency

摘要： In this study we synthesized three simple and inexpensive (34–120 USD/g) 3,3′-bicarbazole–based hole transporting materials (BC-HTMs; NP-BC, NBP-BC and PNP-BC) through a metal-free oxidative coupling, in excellent yields (≥ 95%). These bicarbazoles contain phenylene or biphenylene substituents on the carbazole N atom, with extended π-conjugation achieved through phenylene units at the 6,6′-positions of the bicarbazole. When using NBP-BC as a dopant-free HTM in a p–i–n perovskite solar cell (PSC), we achieved a power conversion efficiency (PCE) of 13.04% under AM 1.5G conditions (100 mW cm–2); this PCE was comparable with that obtained when using PEDOT:PSS as the HTM (12.67%). BC-HTMs showed the large grain size (μm) of perovskite than PEDOT:PSS-based, due to defect passiviation on indium tin oxide (ITO) substrate and good hydrophobicity. Furthermore, we realized highly efficient and stable PSCs when using the p–i–n device structure ITO/NiOx/NP-BC/perovskite/PC61BM/BCP/Ag. The bifacial defect passivation effect of the interfacial layer improved the grain size of the perovskite layer and also enhanced the performance; the best performance of the NiOx/NP-BC device was characterized by a short-circuit current density (Jsc) of 22.38 mA cm–2, an open-circuit voltage (Voc) of 1.09 V, and a fill factor (FF) of 79.9%, corresponding to an overall PCE of almost 20%. This device structure has competitive potential because its performance is comparable with that of the record high efficiency PSCs. Under an Ar atmosphere, the PCE of the NiOx/NP-BC PSC device decayed by only 4.55% after 168 h; it retained 90.80% of its original PCE after 1000 h. A morphological study revealed that the films of the BC-HTMs were indeed smooth and hydrophobic, and that the perovskite films spin-coated upon them were uniform and featured large grains (micrometer scale). Time-resolved photoluminescence (TRPL) spectra of the perovskite films suggested that the hole extraction capabilities of the NiOx/BC-HTMs were better than that of the bare NiOx. The superior film morphologies of the NiOx/BC-HTMs were responsible for the performances of their devices being comparable with those of bare NiOx-based PSCs.