Heavy-atom functionalization promotes triplet-assisted charge-transfer exciton transport in organic cocrystals

Charge-transfer (CT) states with long transport distance are highly desirable for boosting the performance of organic optoelectronic devices. Although micron-scale CT transport has been observed in cocrystals, effective strategies for enhancing the diffusivity of CT excitons remain a challenge. Herein, based on heavy atom effect (HAE), we successfully promote CT exciton transport in thermally activated delayed fluorescence (TADF) cocrystals through bromine-atom functionalization. In Br-functionalized cocrystal, the diffusivity of triplet CT excitons is enhanced by an order of magnitude, enabling a long-distance triplet-assisted CT transport exceeding 16 μm. By adjusting the Br content, the CT transport and TADF-related kinetics can be effectively modulated, thereby significantly enhancing the utilization of CT excitons and the photocurrent responses of cocrystals. Our findings provide compelling evidence that heavy-atom functionalization can serve as an effective strategy to promote CT transport, which is of great significance for the performance optimization of organic optoelectronic devices.