Hydrogen‐Bond‐Mediated Solid Additives Enabling Enhanced Bi‐Continuous Interpenetrating Network for 20.29% Efficiency Layer‐by‐Layer Organic Solar Cells

ABSTRACT Layer‐by‐layer (LbL) processing technology offers precise control over vertical phase separation in organic solar cells (OSCs), yet optimizing the underlying donor morphology to facilitate acceptor infiltration remains a critical challenge. Herein, we report two novel solid additives of BQ and BBQ, which feature a D‐A‐D type 2,5‐di(thiophen‐2‐yl)pyrazine conjugated skeleton, to regulate the D18 donor layer in D18/L8‐BO devices. The BQ molecule contains carbamate side chains that form robust intramolecular hydrogen bonds with the pyrazine core, locking the backbone into a planar and pseudo‐pentacyclic structure. This structural feature enhances the crystallinity and face‐on orientation of D18 film, fostering an optimized fibrillar network. This network acts as an ideal scaffold for subsequent deposition of L8‐BO, thus resulting in a pseudo‐bulk heterojunction with expanded interfacial area for exciton dissociation and continuous channels for charge transport. Consequently, the BQ‐processed LbL‐OSCs achieve an impressive efficiency of 20.29%. In contrast, the brominated analogue BBQ exhibited relatively excessive phase separation, which disrupted the active layer homogeneity and hindered optimal molecular packing. This work highlights the efficacy of hydrogen‐bond‐mediated solid additives in fine‐tuning the morphology of the donor layer for high‐performance LbL‐OSCs.