Blue Thermally Activated Delayed Fluorescence Organic Light-emitting Diodes Research Articles

Reverse Intersystem Crossing Boosting Sensitizer for Ultra-High Efficiency Blue Organic Light-Emitting Diode.

In designing thermally activated delayed fluorescence (TADF) emitters, a high reverse intersystem crossing (RISC) rate with a high photoluminescence quantum yield is essential. Herein, two blue TADF molecules, 2',5'-di(9H-carbazol-9-yl)-3',6'-bis(3,6-ditert-butyl-9H-carbazol-9-yl)-[1,1':4',1″-terphenyl]-4,4″-dicarbonitrile (CzTCzPhBN) and 2',5'-bis(3,6-ditert-butyl-9H-carbazol-9-yl)-3',6'-bis(3,6-diphenyl-9H-carbazol-9-yl)-[1,1':4',1″-terphenyl]-4,4″-dicarbonitrile (PhCzTCzPhBN) with a high RISC rate, were developed through donor engineering. CzTCzPhBN and PhCzTCzPhBN showed a high RISC rate of 4.00 × 105 and 16.62 × 105 s-1, respectively, with a high photoluminescence quantum yield of 80.1 and 84.9%, which resulted in high external quantum efficiency of 27.0 and 27.8% with color coordinates (0.148, 0.170) and (0.150, 0.230) in blue TADF organic light-emitting diodes, respectively. The high RISC rate and device efficiency inspired two TADF molecules to be used as sensitizers in hyperfluorescence devices. The hyperfluorescence devices showed ultra-high external quantum efficiency of 30.7 and 36.4% with color coordinates (0.125, 0.164) and (0.127, 0.193), respectively.

Judicious Design of Pyridine‐Based Hosts for Stable, Efficient, and Low‐Driving Thermally Activated Delayed Fluorescence Organic Light‐Emitting Diodes

AbstractAlthough thermally activated delayed fluorescence (TADF) based organic light‐emitting diodes (OLEDs) continue to achieve high efficiencies, their device stability still does not necessarily meet industrial standards. To improve device stability, careful design of a stable host material is crucial. Herein, with reference to a common p‐type host material, 3,3′‐di(9H‐carbazol‐9‐yl)‐1,1′‐biphenyl (mCBP), three novel host materials based on a pyridine unit, mCBP‐1N, CzPyPhCz, and CzPyBF, are systematically designed to improve the stabilities efficiently. The green and blue TADF OLEDs are fabricated with these three new hosts. The maximum external quantum efficiencies (EQEmaxs) of green OLEDs are 20.3 % and 14.0% for CzPyBF and mCBP hosts, respectively. Further, high EQEs of 19.2% and 12.9% are maintained even at 1000 cd m−2. Most importantly, the device lifetime of the CzPyBF host can achieve LT95 of 62.7 h, which is 2.5 times longer than that of mCBP. Also, lower turn‐on voltages are achieved by using CzPyPhCz in blue and green devices. With host engineering, the TADF OLEDs are simultaneously improved with lower turn‐on voltages, higher EQEs, and longer device lifetimes.

Mixed-host engineering of blue thermally activated delayed fluorescence devices for enhanced efficiency and suppressed efficiency roll-off

Abstract Blue thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) with enhanced efficiency and suppressed efficiency roll-offs were fabricated using a mixed host consisting of 3,3-di(9H-carbazol-9-yl)-biphenyl (mCBP) and bis[2-(diphenyl-phosphino)phenyl]ether oxide (DPEPO). Notably, mCBP and DPEPO, which are generally used as hosts in blue TADF OLEDs, exhibit material stability and efficiency as their trade-off characteristics. The mixed-host structure, when applied to 10,10′-(4,4′-sulfonylbis(4,1-phenylene))bis(9,9-dimethyl-9,10-dihydroacridine), which is a blue TADF dopant, facilitated a maximum efficiency of 18.1%. Furthermore, the critical current density (J0), at which the external quantum efficiency decreases by half of its maximum value, was observed to be 3.9 times that of the DPEPO device.

An excited state managing molecular design platform of blue thermally activated delayed fluorescence emitters by π-linker engineering

A molecular design platform of blue thermally activated delayed fluorescence (TADF) emitters to boost the external quantum efficiency and efficiency roll-off of blue TADF organic light-emitting diodes (OLEDs) was developed.