Demonstration of highly efficient orange EL device and warm white OLED

Abstract

Abstract Exciplex is a well-known charge transfer excited-state complex formed between electron-donor and electron-acceptor molecules. The exciplex studied here is resulted from between the donor mCP and the acceptor PO-T2T, which acts as the host of orange emitting OLEDs. The emitter is orange phosphor Ir(pq)2acac. Our device based on the exciplex host and orange phosphor is very simple, but excellent EL performance was observed. That is, peak current efficiency of 35.3 cd/A, power efficiency of 31.0 lm/W and EQE of 18.7% at a 1.5 wt% orange phosphor, respectively. To date this is the highest orange OLED compared with other orange OLEDs with identical color performance. The better results were ascribed to reasonable device design and contribution from both singlet and triplet of exciplex host as well efficient energy transfer from exciplex host to the orange phosphor. The conclusion is based on the fact that exciplex emission comes from TADF process in which there is small ΔEs-t. This strategy enables to resolve the problem of the lower reverse intersystem crossing (RISC). Besides, warm white OLED was also achieved by lowering the dopant concentration, by which incomplete energy transfer from exciplex host to the orange phosphor could take place.