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

Comprehensive Summary

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 cm ² ·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.