Highly efficient and stable organic light-emitting diodes with a greatly reduced amount of phosphorescent emitter

Abstract

Organic light-emitting diodes (OLEDs) have been intensively studied as a key technology for next-generation displays and lighting. The efficiency of OLEDs has improved markedly in the last 15 years by employing phosphorescent emitters. However, there are two main issues in the practical application of phosphorescent OLEDs (PHOLEDs): the relatively short operational lifetime and the relatively high cost owing to the costly emitter with a concentration of about 10% in the emitting layer. Here, we report on our success in resolving these issues by the utilization of thermally activated delayed fluorescent materials, which have been developed in the past few years, as the host material for the phosphorescent emitter. Our newly developed PHOLED employing only 1 wt% phosphorescent emitter exhibits an external quantum efficiency of over 20% and a long operational lifetime of about 20 times that of an OLED consisting of a conventional host material and 1 wt% phosphorescent emitter.

Emission of dispersed‐type inorganic EL devices with frequency‐variable high‐voltage oscillation circuit

“…In the case of device using organic phosphors, the device structure is the organic light‐emitting diode (OLED) based on multiple evaporated layers of phosphorescent emitting layers and charge transport/blocking layers. Although high performance OLEDs have been reported, the costs of several organic semiconductor materials and the batch fabricating process remain high . On the other hand, alternative printed light source is the much earlier alternating current (AC) powder EL device based on activated and encapsulated inorganic ZnS phosphor powders.…”

Multi-Colored Light-Emitting Electrochemical Cells Based on Thermal Activated Delayed Fluorescence Host

“…Compared to fluorescent host, TADF host also enjoy the following advantages: they show a smaller turn-on voltage due to their small bandgap, and require smaller amount of P.D. 9, 10 .

Figure 1( a ) Schematics for the emission mechanisms in TADF-LECs, ( b ) chemical structure of the TADF host, P.D. molecules, morphology modifier and electrolyte employed in this work.

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

“…At the optimal concentration of 4.0%, the device obtains a maximum current efficiency, power efficiency, and EQE of 64.3 cd/A, 62.4 lm/W, and 18.5%, respectively. Different from the traditional host-guest Ph-OLEDs, the energy transfer process with TADF material as the host is mainly through the long-range Förster energy transfer rather than shortrange Dexter energy transfer or direct carrier trapping recombination by the dopant [12,18]. The triplet excitons produced on the TADF host are more easily up-converted to singlet excited state and achieve the energy transfer by the Förster process owing to the small ΔE S-T of the TADF host.…”

“…TADF materials, which could achieve 100% IQE through the efficient reverse intersystem crossing (RISC) of triplet excitons, had a hugely successful harvest as the emitter due to the small energy difference (ΔE S-T ) between the singlet and triplet excited state [7][8][9][10]. Research on TADF material as the host has also received attention in the past few years [11][12][13]. Qiu et al fabricated highly efficient orange Fl-OLEDs with an EQE as high as 12.2% by utilizing TADF materials of 2,4-diphe-nyl-6-bis (12-phenylindolo) [2,3-a]carbazole-11-yl)-1,3,5-triazine (DIC-TRZ) as the host [11].…”

“…Qiu et al fabricated highly efficient orange Fl-OLEDs with an EQE as high as 12.2% by utilizing TADF materials of 2,4-diphe-nyl-6-bis (12-phenylindolo) [2,3-a]carbazole-11-yl)-1,3,5-triazine (DIC-TRZ) as the host [11]. Fukagawa et al achieved decreased efficiency roll-off with Ph-OLEDs by adopting a TADF material of 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine (PIC-TRZ) as the host [12]. Our group also did some research with TADF material as the host, which achieved white FlOLEDs with a maximum EQE of 7.48% [14].…”