Multifunctional Benzene-Based Solid Additive for Synergistically Boosting Efficiency and Stability in Layer-by-Layer Organic Photovoltaics

The realization of desirable vertical phase separation, enabled by sequential processing that allows for the separate deposition and targeted regulation of donor and acceptor components to construct a well-defined donor–acceptor (D-A) interface, serves as a pivotal factor governing the performance of layer-by-layer organic photovoltaics (LOPVs). This study explores the utility of 4-trifluoromethyl benzoic anhydride (4-TBA), a multifunctional benzene-based solid additive, in the PM6/L8-BO LOPV system, focusing on its role in regulating the vertical phase separation of donor-PM6 and acceptor-L8-BO components to form a well-structured D-A interface. To this end, 4-TBA is doped into the donor-PM6 layer, acceptor-L8-BO layer, or both layers, and its effects on device performance are systematically characterized. The results show that simultaneous doping of 0.05 wt% 4-TBA in both PM6 and L8-BO layers yields the optimal performance, with the power conversion efficiency reaching 18.49% compared to the pristine device with a PCE of 17.05%, and this is accompanied by a significant increase in short-circuit current density from 24.71 mA/cm2 to 26.65 mA/cm2. Additionally, the optimal devices exhibit better stability, as unencapsulated devices retain 76% of their initial PCE after 175 h under ambient conditions compared to 73% for the devices without 4-TBA doping. Essentially, solid additive 4-TBA modulates molecular packing via its interaction between the donor and acceptor molecules and enhances molecular aggregation and hydrophobicity, thereby suppressing bimolecular and trap-assisted recombination, reducing trap density of states, and forming favorable interpenetrating networks. This work validates 4-TBA, which contains benzene rings and other functional groups, as a versatile additive suitable for the LOPV system and offers a generalizable strategy for optimizing LOPV performance by leveraging multifunctional solid additives.