Synergistic Interfacial Engineering with a C60-SB/PFN-Br Hybrid Layer for Suppressing Photocatalytic Degradation in Organic Solar Cells

초록

Zinc oxide (ZnO) is one of the most widely used electron transport layers (ETLs) in inverted organic photovoltaics (OPVs). However, its strong photocatalytic activity and abundance of surface defects induce the generation of radical intermediates under illumination, leading to rapid degradation of nonfullerene acceptors (NFAs) and severe efficiency loss. Here, we propose a hybrid ETL composed of a fullerene derivative (C-60-SB) modified with a conjugated polyelectro-lyte, poly[(9,9-bis(3'-(N, N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) bromide (PFN-Br), which simultaneously tunes the surface energy and reduces the effective work function (WF) of the ETL. The synergistic C-60-SB/PFN-Br interface forms a molecularly ordered, energetically favorable layer that promotes efficient electron extraction and suppresses photocatalytic radical formation. Devices based on C-60-SB/PFN-Br exhibit initial power conversion effi-ciency (similar to 9%) comparable to ZnO-based devices but retain over 85% of their efficiency after 10 h of continuous illumi-nation, whereas ZnO-based OPVs degrade below 70%. Spectroscopic analyses confirm that PFN-Br effectively prevents oxidative reactions and radical intermediates at the interface. Moreover, this stabilization effect extends across multiple donor-acceptor systems, establishing the C-SB/PFN-Br hybrid ETL as a broadly applicable interfacial design strategy for realizing efficient and photostable OPVs.

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