An Alternative Host Material for Long‐Lifespan Blue Organic Light‐Emitting Diodes Using Thermally Activated Delayed Fluorescence

Abstract

It has been challenging to find stable blue organic light emitting diodes (OLEDs) that rely on thermally activated delayed fluorescence (TADF). Lack of stable host materials well‐fitted to the TADF emitters is one of the critical reasons. The most popular host for blue TADF, bis[2‐(diphenylphosphino)phenyl] ether oxide (DPEPO), leads to unrealistically high maximum external quantum efficiency. DPEPO is however an unstable material and has a poor charge transporting ability, which in turn induces an intrinsic short OLED operating lifespan. Here, an alternative host material is introduced which educes the potential efficiency and device lifespan of given TADF emitters with the appropriateness of replacing the most popular host material, DPEPO, in developing blue TADF emitters. It simultaneously provides much longer device lifespan and higher external quantum efficiency at a practical brightness due to its high material stability and electron‐transport‐type character well‐fitted for hole‐transport‐type TADF emitters.

Marching Toward Highly Efficient, Pure‐Blue, and Stable Thermally Activated Delayed Fluorescent Organic Light‐Emitting Diodes

“…As one of the few articles claiming a reasonable device lifespan when using a blue TADF emitter, there is significant room for additional research aimed at increasing the lifetime and EQE at practical luminance; the efficiency of a device using DDCzTrz in mCBP host was likely less than 2% at the luminance of 500 cd m −2 . Cho et al reported an alkyl‐free 2,3,4,5,6‐penta(9 H ‐carbazol‐9‐yl)benzonitrile (5CzCN) TADF blue emitter that was feasible for both vacuum evaporation and solution spin‐coating techniques and exhibited EQE max values of 19.7% and 18.7%, respectively .…”

“…The lack of stable host materials that are suited to the TADF emitter hinders the prospect of realizing stable blue TADF‐OLEDs. Kim et al reported a novel compound by modifying mCBP into 3′,5‐di(9 H ‐carbazol‐9‐yl)‐[1,1′‐biphenyl]‐3‐carbonitrile (mCBP‐CN) to serve as an alternative host to replace the popular DPEPO ( Figure ). A blue TADF‐OLED developed using this host exhibited an EQE of 8.7% with LT 80 of 21 h at the initial luminance of 500 cd m −2 using 5,8‐bis(4‐(2,6‐diphenylpyrimidin‐4‐yl)phenyl)‐5,8‐dihydroindolo[2,3‐c]carba‐zole (BDpyInCz) as the blue dopant .…”

“…Chemical structures, energy diagram of the device structures, and luminance–time curves of the DPEPO: BDpyInCz and mCBP‐CN: BDpyInCz devices, which exhibited EQE values at 500 cd m −2 of 8.3% and 8.7%, respectively. Reproduced with permission . Copyright 2017, John Wiley & Sons.…”

Rigid Oxygen‐Bridged Boron‐Based Blue Thermally Activated Delayed Fluorescence Emitter for Organic Light‐Emitting Diode: Approach towards Satisfying High Efficiency and Long Lifetime Together

“…To overcome these limitations, fewer studies have been reported on the long operational lifetime of blue TADF‐OLEDs. [ 18–22 ] S. G. Ihn et al reported indolocarbazole and pyrimidine‐based TADF emitter, 5,8‐bis(4‐(2,6‐diphenylpyrimidin‐4‐yl)phenyl)‐5,8‐dihydroindolo[2,3‐c]carbazole (BDpyInCz) with a long‐delayed exciton lifetime of 32 µs. [ 18 ] However, their device exhibited a low external quantum efficiency (EQE) (12%) and device lifetime (LT 80 ) of only 8 h at the initial luminance of 500 cd m −2 with deep‐blue color coordinates of (0.16, 0.20).…”

P‐213: Late‐News Poster: Phenanthroimidazole Based Small Molecule Functioning Both as Blue Emitter and Host for Organic Light Emitting Diodes

“…[8]. Use of improper host may lead to worthless recombination outside the emissive layer, unbalanced charge transport and charge leakage at the interface of electrodes [9][10].…”