Electron Transfer Enhanced by Minimal Energy Offset at Organic Semiconductor Interface

Enhancing electron transfer between excited states and reducing their energy offset is generally in a trade-off relation, which must be overcome to develop efficient optoelectronic devices. In this study, we systematically investigated, through the analysis of 45 combinations, how to facilitate the electron transfer from the charge transfer (CT) state at the donor/acceptor interface to the triplet excited state of the emitter to improve the triplet-triplet annihilation emission in organic light-emitting diodes (OLEDs). Our analysis, based on the experimental device properties, revealed that the electron transfer is enhanced by the strong CT interaction and, more importantly, by the minimal energy offset (<0.1 eV). This relation was found to be explained by semi-classical Marcus theory with a small reorganization energy of below 0.1 eV. Furthermore, our analysis led to the discovery of a novel donor/acceptor combination for OLED, yielding an efficient blue emission with an extremely low turn-on voltage of 1.57 V.