Highly efficient and low efficiency roll-off single-emissive-layer white organic light emitting devices by quaternary exciplex

Abstract

The challenge of achieving both highly efficient and low-efficiency roll-off single-emissive-layer (SEL) white organic light-emitting diodes (WOLEDs) are still the balance charge transfer and precise manipulation of singlet and triplet. In this context, a novel quaternary exciplex system is fabricated, with blue thermally activated delayed fluorescence (TADF) materials DMAC-DPS, TPXZPO, and traditional fluorescent material MCP were selected as electron-donating materials, and PO-T2T was selected as the electron-accepting material. Three different exciplexes with dissimilar emission wavelengths are formed in the SEL. The quaternary exciplex can be regarded as MCP:PO-T2T exciplex host dopant DMAC-DPS:PO-T2T exciplex and TPXZPO:PO-T2T exciplex. The effective exciton confinement and multiple reverse intersystem crossing (RISC) channels are achieved by doping high triplet TADF electron-donating material, which reduces energy loss and promotes the utilization of excitons. In comparison to the binary and ternary exciplex devices, the quaternary exciplex device exhibited the highest external quantum efficiency of 16.68% due to higher rate constants of RISC (5.96 × 106 s−1) and photoluminescence quantum yield (PLQY). Especially, the internal exciplex to exciplex stepped energy transfer channels ensure slightly efficient roll-off and concentration-independent color shifts in the EL spectra. The external quantum efficiency remained at 16.60% and 15.74% at a luminance of 1000 cd/m2 and 5000 cd/m2, respectively. Therefore, these results indicate that quaternary exciplex has a promising future in the applications of high-performance SEL all-fluorescence WOLEDs.