Thickness-Insensitive A-D-A-A' Polymeric Cathode Interlayer for High-Efficiency Organic Solar Cells
Organic solar cells (OSCs) require cathode interlayers (CILs) that combine high charge transport, defect passivation, and thickness insensitivity for scalable manufacturing. Here, we report the synthesis of a novel A-D-A-A'-type polymer, PDPP2F-NDI-N, via the green and efficient direct arylation polymerization (DArP) method. The multiple electron-deficient units in the backbone confer strong electron-withdrawing character, effective work function modulation, enhanced built-in potential, high crystallinity, and ordered molecular packing. PDPP2F-NDI-N exhibits a high electron mobility of 1.01 × 10⁻³ cm² V⁻¹ s⁻¹ and electrical conductivity of 3.13 × 10⁻³ S m⁻¹, facilitating efficient charge extraction and transport. Its interfacial modification capability suppresses interfacial defects and reduces non-radiative recombination losses. In ternary OSCs, PDPP2F-NDI-N achieves a high power conversion efficiency (PCE) of 20.44%, with outstanding thickness insensitivity retaining 92.8% of peak PCE at a 30 nm CIL thickness, and a T80 lifetime exceeding 1700 hours under photo-thermal aging. This work demonstrates that poly(A-D-A-alt-A') backbone design combined with DArP synthesis provides an effective strategy for developing high-performance, thickness-insensitive, and stable polymeric CILs, advancing efficient, stable, and scalable OSC applications.