Efficient Nondoped Pure Red/Near-Infrared TADF OLEDs by Designing and Adjusting Double Quantum Wells Structure

The selection of host materials has a great impact on the performance of doping devices, especially near-infrared (NIR) emitters. In this investigation, four diverse host materials serve as a potential barrier layer (PBL) to confine and balance holes and electrons within the potential well layer (PWL), TPA-DCPP, for fabricating nondoped NIR thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) (NNT-OLEDs) with double quantum wells' (DQWs) structure. The hole-type host (mCP) forms an optimum interface energy barrier (IEB) and disperses carriers and excitons in each well, which helps to widen the recombination interval of carriers and restrain the quenching of excitons. Finally, OLEDs with pure red emission and a maximum external quantum efficiency (EQEmax) of nearly 15% (with 0.5 nm well width), deep-red emission with an EQEmax of 12% (with 1.0 nm well width), and NIR emission with an EQEmax of 3.3% (with 5.5 nm well width) are achieved with tunable emission peaks within the range of 641–700 nm by adjusting well width, which are significantly superior to those of doped devices based on the same emitter. This investigation demonstrates a simple, feasible, and effective design strategy for achieving efficient fluorescent OLEDs with controllable wavelength, which solves the blue shift problem in traditional NIR devices of host–guest structure.