Method for measuring exciton–exciton annihilation rate constants in thermally activated delayed fluorescent emitters to understand efficiency roll-off in OLEDs

with increasing emitter concentration from 3 to 10 wt%. The rate constant for TTA in the film with 10 wt% of DABNA-2 is four orders of magnitude smaller than that for STA and below the sensitivity limit at lower concentration of DABNA-2. Modelling of the OLED efficiency roll-off with experimentally determined parameters shows that STA is responsible for more than half of the efficiency loss at high luminance in the device with this emitter, whilst TTA can slightly reduce the effect of STA. The combination of these measurements and modelling is a powerful tool that can be employed for selecting the optimal host material for a particular emitter and the emitter concentration to minimize efficiency roll-off.