Exceeding 20.2% Efficiency in Pseudo‐Planar Heterojunction Organic Solar Cells Enabled by High‐Crystallinity L8‐BO‐C ₄ ‐Induced Morphology Optimization

ABSTRACT Optimizing the morphology of the active layer via the incorporation of a sui` third component is crucial for enhancing the device performance of organic solar cells (OSCs). In this study, a third component L8‐BO‐C 4 is introduced into the D18/L8‐BO pseudo‐planar heterojunction (P‐PHJ) system to prepare P‐PHJ OSCs. L8‐BO‐C 4 and L8‐BO share akin chemical structures, but L8‐BO‐C 4 exhibits significantly higher crystallinity compared to L8‐BO, which is achieved through precise control of the branching position of the alkyl chain on the thiophene unit. The high crystallinity of L8‐BO‐C 4 enables it to act as a crystallization inducer during layer‐by‐layer deposition. It not only induces long‐range ordered orientation in the acceptor molecules but also guides the re‐nucleation and recrystallization of the donor layer through interfacial permeation. The optimized molecular packing and continuous interpenetrating network structure effectively promote the generation, transport, and collection of charge carriers. The power conversion efficiency of the P‐PHJ OSCs based on D18/L8‐BO as the main system is increased from 19.06% to 20.24%. This study demonstrates that the judicious introduction of a functional third component is an efficient strategy for further boosting the performance of P‐PHJ OSCs.