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.
Highlights
Organic light-emitting diodes (OLEDs) have been intensively studied as a key technology for next-generation displays and lighting
We fabricated 6-wt%-Ir(mppy)3-doped phosphorescent OLEDs (PHOLEDs) using PIC-TRZ as the thermally activated delayed fluorescence (TADF) material and the conventional host CBP to discuss the effect of reverse intersystem crossing (RISC) on the device characteristics[5]
The OLEDs were composed of multiple layers of indium tin oxide (ITO), Clevios HIL 1.5, 4,49-bis[N-(1-naphthyl)-Nphenylamino]-biphenyl (a-NPD, 20 nm), HTEB-2, 6 wt% Ir(mppy)3:host (25 nm), 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBi, 35 nm), LiF (0.8 nm), and Al (100 nm)
Summary
Organic light-emitting diodes (OLEDs) have been intensively studied as a key technology for next-generation displays and lighting. If the Forster energy transfer from the excited states of the host to the phosphorescent dopant can be utilized effectively, there is a strong possibility of reducing the concentration of the emitter dopant, which is 6–15 wt% in conventional PHOLEDs (Fig. 1c)[6,7,8,9,25,26], to 1–3 wt%, similar to that in fluorescent OLEDs27-29 This will significantly decrease the amount of heavy atoms used, resulting in a lower cost. The TADF host/phosphorescent emitter configuration is found to be more suitable for practical use since the demonstrated PHOLED performances are independent of the emitter concentration from 1 to 6 wt%, eliminating the need for a strictly controlled fabrication process The generality of this emitting layer configuration is confirmed by demonstrating an efficient and stable red PHOLED employing PIC-TRZ as the host and a small amount of a red phosphorescent emitter based on platinum
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