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.