Tailoring Vertical Exciton Dissociation Pathways via Hydrogen Bonding for High‐Performance Thick‐Film Organic Solar Cells

Organic solar cells (OSCs) with thick active layers demonstrate significant potential for scalable roll‐to‐roll manufacturing in industrial applications. However, increasing the active layer thickness triggers unfavorable morphological evolution, compromising vertical exciton dissociation pathways. Herein, a hydrogen‐bonding functionalized solid additive strategy, centered on 2,4‐dihydroxybenzoic acid (DBA) with multidentate interaction sites, is developed to regulate the vertical architecture and exciton and charge dynamics in thick‐film OSCs. These hydrogen bonds can function as noncovalent crosslinking sites to reinforce ordered molecular packing, suppress excessive phase separation, and promote favorable vertical component distribution. The precisely engineered vertical phase separation morphology results in charge transfer (CT) state‐mediated exciton dissociation dominating at the bottom of the active layer, whereas intra‐moiety delocalized excitation (i‐DE)‐mediated exciton dissociation prevails throughout the remaining regions of the film thickness. The vertical distribution of two exciton dissociation pathways not only benefits efficient charge separation but also facilitates charge transport, alleviating pronounced charge accumulation and recombination. Accordingly, the DBA‐treated 300 nm‐thick D18:L8‐BO devices deliver a high power conversion efficiency of 19.40%, along with improved photo‐thermal stability (T 80 > 900 h). This work provides a promising solution for enabling efficient exciton and charge utilization in the vertical direction, informing the future design of thickness‐insensitive OSCs.