Construction of Three-Dimensional Charge Transport for Thickness-Insensitive Cathode Interlayers in Efficient Organic Solar Cells^†

Efficient interfacial charge transport is essential for achieving high-performance organic solar cells (OSCs), while conventional cathode interlayers (CILs) often suffer from limited thickness tolerance due to insufficient vertical electron transport. Herein, we develop two hyperbranched CIL molecules, TPA-PDINNBr and BTT-PDINNBr, by integrating quaternized perylene diimide (PDI) units with three-dimensional triphenylamine (TPA) or benzo[1,2-b:3,4-b′:5,6-b″]trithiophene (BTT) cores. The three-dimensional molecular architectures preserve the intrinsic electron-transporting capability of PDI while constructing multidirectional charge-transport pathways and regulating molecular packing. Among them, BTT-PDINNBr exhibits enhanced conductivity (2.03 × 10^–4 S·cm^–1) and electron mobility (3.36 × 10^–3 cm²·V^–1·s^–1), resulting from the optimized balance between molecular ordering and three-dimensional transport. Incorporation of BTT-PDINNBr into PM6:D18:L8-BO OSCs delivers a high power conversion efficiency of 19.68% and maintains ~87% of the optimal efficiency with interlayer thicknesses exceeding 50 nm. This work provides a molecular design strategy for robust CILs by highlighting the importance of three-dimensional conductive networks and controlled solid-state packing for scalable and efficient OSCs. (Figure presented.).