Above 30% External Quantum Efficiency in Green Delayed Fluorescent Organic Light-Emitting Diodes

Abstract

Highly efficient green thermally activated delayed fluorescent organic light-emitting diodes with an external quantum efficiency of 31.2% were investigated by using 3-(3-(carbazole-9-yl)phenyl) pyrido[3',2':4,5]furo[2,3-b]pyridine (3CzPFP) derived from carbazole and pyrido[3',2':4,5]furo[2,3-b]pyridine. The host material showed well-matched photoluminescence emission with absorption of the green dopant material, (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) and harvested all excitons of 4CzIPN. The 3CzPFP:4CzIPN film exhibited high photoluminescence quantum yield of 100%, and the green delayed fluorescence device employing the 3CzPFP host showed high maximum quantum efficiency of 31.2 ± 0.5% at 1% doping after optimization of the device structure.

Recent progress of green thermally activated delayed fluorescent emitters

“…In the case of the blue TADF emitters, the limited availability of high-triplet-energy host materials makes it difficult to fully activate and optimize the TADF emissions of the blue emitters. Therefore, the best EQE of the green TADF OLEDs (31.2%) was much higher than that of the red (17.5%) and blue (25.0%) TADF OLEDs [5][6][7].…”

“…After the demonstration of a high EQE close to 20% using the organic 4CzIPN TADF emitter for the first time, several works optimizing the device structure of the 4CzIPN TADF OLEDs followed and reported an improved EQE surpassing the EQE obtained by Adachi et al Several bipolar host materials with a triplet energy high enough for both the singlet and triplet harvesting of 4CzIPN were proven to be better than the carbazoletype host materials and provided EQEs higher than 20% [8][9][10][11][12][13][14][15][16][17]. In particular, 3-(3-(carbazole-9-yl)phenyl) pyrido [3 ,2 :4,5]furo [2,3-b]pyridine (3CzPFP) was the best host material of 4CzIPN and realized the best EQE of 31.2% in the 4CzIPN devices [6]. A mixed host of holeand electron-transport-type host materials also worked effectively as the host of 4CzIPN [17][18][19][20].…”

Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays

“…5), one can find a plethora of nitrogen-containing heterocycles, 63,64 as well as various benzonitriles. [47][48][49]56,57,59,65,66 A third acceptor-class is sulfones, 31,54,58,60,67,68 which seems to be particularly useful to realize deep-blue TADF emission.…”

“…The same is also true for polymeric TADF emitters, where the HOMO and LUMO are located on different monomers of the polymer strand. 75 Both organic 66,78,79 and metal-organic TADF emitters 77 have been shown to reach the maximum theoretical OLED efficiency, which is in the order of 20% to 25% external quantum efficiency in cases where no light-extraction technology is applied. 13 For clarity, the molecular structures of metal-organic TADF emitters are not discussed here.…”

“…In terms of efficiency, TADF is already directly competing with phosphorescent OLEDs, 66,78,79 even though the first TADF OLED was published only 5 years ago. 63 In terms of stability, there are some promising results.…”