Overcoming the Conductivity‐Stability Trade‐Off in PEDOT:PSS via Hydrogen‐Bond Modulation Enables 20.0% Efficient Bilayer Organic Solar Cells

Abstract Poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS, PP) offers desired optical transparency and solution processability for fabricating organic solar cells. However, its performance is constrained by the insulating PSS shell that compromises conductivity and induces interfacial incompatibility. Herein, the study proposes a carboxyl‐functionalized molecular modifier, resorcinol‐O, O'‐diacetic acid (RODA), which optimizes the intrinsic properties of PP and synergistically regulates the aggregation dynamics of the PM6 layer. The carboxylic acid groups (─COOH) in RODA form robust hydrogen bonds with the sulfonic acid groups (─SO 3 H) moieties of PSS, inducing phase segregation that disrupts the core‐shell architecture of PP while lowering its acidity. This structural regulation enhances PP‐RODA conductivity and optimizes energy with the PM6's highest occupied molecular orbital level. Concurrently, the modified PP layer promotes the molecular packing of PM6, inducing J‐aggregation with extended π‐conjugation. The dual optimization of the hole transporting layer's conductivity and active layer ordering enables efficiency of 19.97% with a champion efficiency reaching 20.00%, outperforming those of the control devices (18.37%). This work establishes a paradigm for multifunctional interfacial engineering, providing molecular‐level insights into the design of high‐performance device interfaces.