Phenolic Additive-Doped Cathode Interlayer for High-Efficiency Organic Photovoltaics

The cathode interlayer (CIL) is crucial for the development of organic photovoltaics (OPVs). However, the widespread use of CILs based on perylene diimide and naphthalene diimide is constrained by their strong intrinsic aggregation tendency. Herein, benzoic acid (BA) and its derivatives bearing different quantities of hydroxyl groups (BA-OH, BA-2OH, and BA-3OH) are used as additives to modify NDI-Ph, a naphthalene diimide-based cathode interlayer. Systematic studies reveal that the dipole moment of additives rises with the increasing number of hydroxyl groups, which further facilitates intermolecular interactions with interfacial materials. Benefiting from the enhanced electrical conductivity, optimized interfacial contact, and suppressed charge recombination, the NDI-Ph modified by BA-3OH delivers a champion efficiency of 19.20% in D18:L8-BO-based devices, exceeding the 18.25% efficiency of the control device. Furthermore, with 2PACz as the hole transport layer, the device achieves a high PCE of 20.09%. This strategy has also been proven effective for PDINN- and PNDIT-F3N-based CILs. This work verifies that modulating the number of hydroxyl groups in benzoic acid derivatives can rationally regulate the performance of CILs and prescribes a facile and effective strategy to develop high-efficiency OPVs.