Electron-Induced Exciton-Polaron Quenching and Degradation in Radical-Based Near-Infrared Organic Light-Emitting Diodes.

In this study, we investigated the fundamental degradation mechanism of near-infrared (NIR) radical organic light-emitting diodes by analyzing the charge-carrier dynamics and exciton-polaron quenching (EPQ) phenomena in devices based on 2-methyl-9,10-bis(naphthalen-2-yl)anthracene:(4-triphenylamine-2,6-dichlorophenyl)-bis(2,4,6-trichlorophenyl)-methyl (MADN:TTM-TPA) NIR organic emitters. Electrical characterizations, including transient electroluminescence, revealed that a large lowest unoccupied molecular orbital energy barrier within the emissive layer leads to strong electron trapping and excessive electron accumulation. Bias-dependent photoluminescence measurements using single-carrier devices (hole-only devices and electron-only devices) demonstrated that EPQ, a non-radiative decay phenomenon, was aggravated more significantly upon the accumulation of electrons (negative polarons) than upon the accumulation of holes (positive polarons). Furthermore, spectroelectrochemistry analysis confirmed the disappearance of the charge transfer peak in the negative polaron environment. Consequently, this study reveals that the critical degradation of the radical emitter primarily originates from negative-polaron-induced dechlorination, which abolishes the radical (open-shell) character of TTM-TPA, thereby providing clear guidelines for controlling charge balance and securing electron stability in the design of future high-efficiency and long-lifetime NIR optoelectronic devices.