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

Abstract

Thermally activated delayed fluorescence (TADF) materials have emerged as an efficient emitter for achieving high efficiency of blue organic light emitting diodes (OLEDs). However, it is challenging to satisfy both high device efficiency and long operational lifetime together. Here, highly efficient and electrochemically stable blue TADF emitter, 5‐(5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)‐10,15‐diphenyl‐10,15‐dihydro‐5H‐diindolo[3,2‐a:3′,2′‐c]carbazole (DBA‐DI) is designed and synthesized for high efficiency and long lifetime OLED. This emitter exhibits high photoluminescence quantum yield of 95.3%, small single‐triplet energy gap of 0.03 eV, short delayed exciton lifetime of 1.25 µs, and high bond dissociation energy (BDE). Also, phosphine oxide free high triplet energy host systems (single and mixed) and exciton blocking layer materials are analyzed using molecular and optical simulations to find an efficient host system with high BDE and suitable emission zone for high efficiency and stable OLEDs. The fabricated OLED with DBA‐DI and high triplet host exhibited a maximum external quantum efficiency (EQE) of 28.1% with blue CIE color coordinates of (0.16, 0.39) and long operational lifetime (LT50) of 329 h at the initial luminance of 1000 cd m−2. Furthermore, the mixed host‐based TADF device showed a slightly lower EQE of 26.4% and almost two times longer lifetime (LT50: 540 h) than the single host device.

Asymmetric Host Molecule Bearing Pyridine Core for Highly Efficient Blue Thermally Activated Delayed Fluorescence OLEDs

“…For the EML, two compounds synthesized as hosts and the 5-(5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-10,15-diphenyl-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole (DBA-DI) blue emitter were employed to prepare the blend film under vacuum thermal evaporation. [29] As ar esult, the pCzPybCz-based blue TADF-OLED device showedah igh EQE of 22.7 %, which was comparable in performance to a pCzBzbCz-based OLED device with an EQE of 24.0 %. In particular, the pCzPybCz-based devicee xhibitedahigho perational stability overarelatively long lifetimeo f2 4h (LT 90 )a t1 000 cd m À2 .T his could be explained by the CÀNb ond dissociation energy (BDE) in the pCzPybCz structure.I nterestingly,t he mixed-host systems, that is, the pCzBzbCz:DDBFT-a nd pCzPybCz:DDBFT-based devices, showedh ighlyi mproved operational lifetimes of 31 and 41 h at LT 90 at 1000 cd m À2 ,r espectively,b ecause the electron-deficient host DDBFT could prevente lectron injection from the electron transport layer (ETL) into the hosts.…”

“…[18,38] DBA-DI as ab lue dopanth as been reported in our previous studies as am aterial exhibiting high quantum efficiency and long operation lifetime. [29] For this reason,w eu sed it as a dopant in this study to evaluate the function of new hosts. A control device was fabricated using the mCP host to evaluate device performance using two new host materials.…”

A Deep Blue Strong Microcavity Organic Light‐Emitting Diode Optimized by a Low Absorption Semitransparent Cathode and a Narrow Bandwidth Emitter

“…Finally, all devices were encapsulated using glass cover and UV‐curable resin under nitrogen atmosphere. In this work, the 9‐[r‐(10‐phenylanthracene‐9‐yl)‐9H‐carbazole (PhPC), [ 43 ] BPPyA, [ 44 ] and DABNA‐NP‐TB [ 45,46 ] were synthesized using previously reported method. The BPPyA is a pyrene‐based fluorescent dopant and it has spectral peak of 460 nm and FWHM of 35 nm in film state.…”

Recent Advancement in Boron-Based Efficient and Pure Blue Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

“…Also, the TDBA-DI emitter and mCBP-CN host system device showed an operational lifetime (T 50 ) of 55.2 h at the initial luminance of 1,000 cd/m 2 . They also reported DBA-DI emitter by removing tert-butyl from the TDBA-DI to achieve high efficiency and long lifetime (Ahn et al, 2020). The DBA-DI showed slight variations in the photophysical properties compared to the TDBA-DI as shown in Table 4.…”