High-efficiency organic light-emitting diodes with exciplex hosts

Abstract

Exciplex forming co-hosts have been applied to fabricate high-efficiency organic light-emitting diodes (OLEDs) due to the merits of bipolarity, 100% exciton harvesting, preferred dipole alignment, and sensitizing effects. We review the discovery and development of the exciplex mechanism framework, from its discovery to successful application as hosts for phosphorescent OLEDs (PhOLEDs), thermally activated delayed fluorescence (TADF) OLEDs, and hyperfluorescent OLEDs, as well as in white OLEDs (WOLEDs). Exciplex forming co-hosts utilize the TADF effect to guarantee high exciton utilization efficiency. The charge-injection-free energy level configuration decreases the driving voltages and brings about improved power efficiency. The increased transitional dipole moment of emitters in exciplex forming co-hosts adds outcoupling efficiency to beat the efficiency limit. Exciplexes with the TADF effect also show sensitizing effects, making high-efficiency fluorescent OLEDs possible. This review introduces the progressive achievements of exciplex forming co-hosts, aimed at forming a summary of the present research on exciplex based OLEDs, and hopefully helping researchers grasp the future developing trend of exciplex forming co-hosts.