High-Performance Inverted Organic Solar Cells via the Incorporation of Thickness-Insensitive and Low-Temperature-Annealed Nonconjugated Polymers as Electron Transport Materials

Developing new electron transport layers has been an effective way to fabricate high-performance bulk-heterojunction organic solar cells (OSCs). Resolving the longstanding problems associated with commonly used zinc oxide (ZnO), such as electron traps and light-induced device deterioration, however, is still a great challenge. In this study, glycerol diglycidyl ether (GDE) and 1,4-butanesultone (BS) are blended with polyethyleneimine (PEI) to produce cross-linkable PEI-based materials, PEI-GDE and PEI-GDE-BS, which can function as alternative electron transport layers to replace conventional ZnO cathode-modifying layers in inverted OSCs. PEI-GDE and PEI-GDE-BS are amendable to low-temperature annealing processes to produce cross-linked films. The inverted device structure of ITO/ETL/PM6:BTP-BO-4F:PC₇₁BM/MoO₃/Ag was used to evaluate the effects of incorporating PEI-GDE and PEI-GDE-BS as electron transport materials. Compared with ZnO-based devices, the PEI-GDE- and PEI-GDE-BS-based devices exhibit significant improvements in photovoltaic performances due to smoother surface roughness, higher charge collection and exciton dissociation efficiencies, higher electron mobilities, and stronger π−π interactions. In particular, a PEI-GDE-BS-based device shows an outstanding power conversion efficiency (PCE) of 17.55% with a V_OC of 0.83 V, a J_SC of 27.88 mA/cm², and an FF of 75.96%, which offers great possibilities in the applications of flexible solar cells.