Thickness‐Tolerant A1–A2 Polyelectrolyte Cathode Interlayers via Direct Arylation Polycondensation for 20.5% Efficiency Organic Solar Cells

Abstract Efficient electron transport and extraction at the cathode interface are vital for achieving high‐performance organic solar cells (OSCs). Herein, a sustainable synthesis of novel A1–A2 type polyelectrolyte cathode interfacial materials (CIMs), PNIBI‐NDIN and PNIBI‐NDINBr, via direct arylation polycondensation is reported. These CIMs are composed of two planar, strongly electron‐deficient building blocks—1,2‐naphthaleneimidebenzimidazole and naphthalene diimide—which induce strong interchain aggregation and high electrical conductivity. When employed as cathode interlayers (CILs), both polymers exhibit remarkable thickness tolerance, maintaining over 17% power conversion efficiency (PCE) even at 50 nm thickness—the highest reported to date under such conditions. Moreover, the A1–A2 copolymerization strategy effectively lowers the LUMO levels of the CIMs, facilitating dual‐channel electron extraction from both donor and acceptor domains, and thereby suppressing non‐radiative recombination. As a result, PM6:L8‐BO‐based binary devices incorporating PNIBI‐NDIN and PNIBI‐NDINBr achieve PCEs of 19.33% and 17.89%, respectively, while their ternary counterparts deliver efficiencies of up to 20.45% and 18.34%. These findings highlight the great potential of direct arylation‐derived polyelectrolytes as scalable and high‐performance CIMs for next‐generation OSCs.