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

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 (C₆₀-SB) modified with a conjugated polyelectrolyte, 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 C₆₀-SB/PFN-Br interface forms a molecularly ordered, energetically favorable layer that promotes efficient electron extraction and suppresses photocatalytic radical formation. Devices based on C₆₀-SB/PFN-Br exhibit initial power conversion efficiency ( 9