Detection of Dexter energy transfer process in interface-type OLED via utilizing the characteristic magneto-electroluminescence response of hot exciton reverse intersystem crossing

The maximum external quantum efficiency of the host-guest-type organic light-emitting diodes (OLEDs) with interface exciplex as the host has been over 36%. However, studies about the energy transfer processes occurring from the host to guest remain lacking. Herein, a strategy is proposed to probe the energy transfer processes in interface-type OLEDs by utilizing the characteristic magneto-electroluminescence (MEL) response from the hot exciton reverse intersystem crossing (T_2,Rub → S_1,Rub) of rubrene. Specifically, a donor/spacer/accepter (D/S/A)-type interface exciplex device and a D/spacer:<i>x</i>% Emitter/A (D/S:3% Rubrene/A)-type Rubrene-doped device are fabricated. The Förster resonance energy transfer (FRET) process occurring between the singlet state of the exciplex-host and the singlet state of Rubrene-guest is demonstrated by characterizing the photophysical properties of the donor, accepter, and guest materials. The Dexter energy transfer (DET, T_1,Host → T_2,Rub) process between the triplet state of the host and the triplet state of guest is visualized by the comparative studying of the current- and temperature-dependent MEL response curves of D/S/A and D/S:3% Rubrene/A devices, respectively. More importantly, the occurrence of the DET process greatly promotes the electroluminescence intensity of the D/S:3% Rubrene/A device. Furthermore, we also investigate the differences in the electroluminescence performance of devices at low temperature to demonstrate again the co-existence of FRET and DET process in the D/S:3% Rubrene/A system. Obviously, this work not only provides a promising strategy for probing the DET process in OLEDs, but also paves a new way for designing high-performance “hot exciton” type OLEDs.