Discovery of a Resonant High-Level Reverse Intersystem Crossing of Hot Exciton from Conventional TTPA Fluorescent Semiconductor and an Attempt on High-Efficiency TTPA-Based OLEDs

Abstract

Although high-efficiency 9,10-bis[N,N-di-(p-tolyl)-amino]anthracene (TTPA)-based organic light-emitting diodes (OLEDs) are widely reported, their physical origins of excited states in TTPA are still vague. Herein, using the fingerprint magneto-electroluminescence probing tool, a resonant high-level reverse intersystem-crossing (HL-RISC, S_{1, TTPA} ← T_{2, TTPA}) of hot-excitons is discovered from the conventional fluorescent TTPA semiconductor whose triplet exciton states are generally ignored in the previous literature. This fascinating HL-RISC channel is well validated by the optical, electric, and magnetic properties of the undoped TTPA-based OLEDs. For TTPA-doped OLEDs, this channel can efficiently occur when triplet energies of the host and the exciton blocking layer are higher than that of T_{2, TTPA}. More importantly, an external quantum efficiency (EQE) as high as 10.14% is achieved from the simple emission layer without using any phosphorescent sensitizer, i.e., just by doping the TTPA emitter into the DMAC-DPS host with thermally activated delayed fluorescence property. This high EQE is attributed to fully harvesting singlet and triplet excitons of the device via the simultaneous utilization of the newly-found HL-RISC from TTPA guest and the low-level RISC from DMAC-DPS host. Accordingly, this work paves a novel pathway for designing high-performance fully fluorescent OLEDs with inherent device stability and low-cost superiority.