Optimizing the Charge Balance of Fluorescent Organic Light‐Emitting Devices to Achieve High External Quantum Efficiency Beyond the Conventional Upper Limit

Abstract

The external quantum efficiencies (EQEs) of fluorescent light emitting devices are drastically improved by optimizing the charge balance. When N,N'-di(naphthalene-1-yl)- N,N'-diphenylbenzidine (NPD) is used as a hole-transporting layer (HTL) and Alq(3) as an electron-transporting layer (ETL) with the green dopant 2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl)quinolizino-[9,9a,1gh]coumarin (C545T), the EQE is observed to be approximately 3%. However, when the HTL and ETL materials are optimized, a 7.5% external quantum efficiency (EQE) in a green-emitting device and an 8.2% EQE in a blue-emitting device are achieved at 100 cd m(-2) .

Analyzing degradation effects of organic light-emitting diodes via transient optical and electrical measurements

“…Thus, g r becomes unity for phosphorescent emitters [25][26][27] and can clearly exceed the spin-statistical limit of 25% (Refs. [28][29][30][31][32][33][34][35][36] in the fluorescent case. The third factor stands for the effective radiative quantum efficiency of the emitting system and depends on its intrinsic value q, which is modified by the Purcell effect taking into account the microcavity-like structure.…”

High efficiency and low roll-off green OLEDs with simple structure by utilizing thermally activated delayed fluorescence material as the universal host

“…Kido et al achieved ~ 7% EQE through the optimizing charge balance, but the EQE Max. ~ EQE 1000 still reached ~ 10% [16], whereas the EQE Max. ~ EQE 1000 of all the Fl-OLEDs in this work are only ~ 1%.…”

Triplet fusion delayed fluorescence materials for OLEDs

“…A sky-blue OLED with 2 as the host material was reported to show an EQE of 8.7% and a luminance efficiency (LE) of 16.2 cd A -1 at 20 mA cm -2 . Through transient EL characterization, Kido et al [34] also attributed the high performance of 2-based OLEDs to the TF contribution. Note that the 2-based blue OLED fabricated by Kido et al not only shows a high efficiency, but also displays a negligible efficiency roll-off (EQE@100 cd m -2 = 8.2%; EQE@1000 cd m -2 = 7.7%).…”