Efficient Electron Injection and Transport in Fully Stretchable OLEDs

Fully stretchable electroluminescent devices have garnered significant attention due to their transformative potential in applications ranging from wearable displays to implantable light sources. Among the various approaches, OLEDs based on the thermally activated delayed fluorescence (TADF) mechanism hold much allure because of their unity internal quantum efficiency and environmental-/bio- -compatibility. However, the performance, based on the identical emitter, in stretchable OLEDs falls significantly short of that achieved in traditional rigid devices due to fewer n-type materials available for efferent electron injection and transport. Here we propose innovative solutions to bridge this efficiency gap. First, we develop a stretchable electron transport polymer that simultaneously achieves decent electron mobility, suitable HOMO/LUMO levels, high triplet state, good solution processability, and high stretchability. Secondly, we propose a stretchable cathode design with an extremely low work function that is on par with the conventional rigid cathode, which is unprecedented with previously stretchable cathode based on silver nanowires, carbon nanotubes, conducting polymers, and others. Based on those innovations, we remarkably narrow the efficiency gap and eliminate the turn-on voltage differential between the fully stretchable TADF-OLEDs and their rigid counterparts.