Investigation of micro-mechanism in thermally activated delayed fluorescence quantum well devices by utilizing organic magnetic effects

Abstract

The quantum well organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence material with reverse intersystem crossing (RISC) characteristics have been fabricated in this paper. Meanwhile, the magneto-efficiency (Mη) was obtained by measuring the magneto-conductance (MC) and magneto-electroluminescence (MEL) of the devices, and we research microscopic process of devices by analyzing the characteristic curves of magnetic field effects. Surprisingly, we found that the MC curves of non-quantum-well device showed typical RISC property and the dissociation of triplet excitons by holes at room temperature, but the MC curves merely exhibited the mechanism of electron scattering by triplet excitons in quantum well device. In addition, although the MEL and Mη curves of non-quantum well device demonstrated intersystem crossing (ISC) and triplet-triplet annihilation (TTA) process, the MEL of quantum well device showed the mechanism of electron scattering by triplet excitons and the Mη only displayed the typical ISC curves. As decreasing the temperature from 300 K to 20 K, the ISC processes of quantum or non-quantum well devices increased, however, the TTA process occurred in quantum well device at 20 K and the TTA process of non-quantum well device gradually vanished at 100 K. We propose that the structure property of quantum or non-quantum well devices, temperature-dependent Forster energy transfer, and the lifetime and concentration of the triplet excitons can explain the experimental phenomena very well. Obviously, the research of magnetic effects in quantum well devices not only provides ideas for designing high efficient light-emitting devices, but also can deepen the understanding of organic magnetic effects.