Novel Hole-Transporting Materials with High Triplet Energy for Highly Efficient and Stable Organic Light-Emitting Diodes

Abstract

Demonstration of highly efficient organic light-emitting diodes (OLEDs) is becoming commonplace; however, there have been few reports on hole-transporting materials (HTMs) designed for highly efficient and stable green OLEDs. Here, operationally stable HTMs with high triplet energy were synthesized by incorporating dibenzothiophene and dibenzofuran into hole-transporting amino groups. The triplet energy of the amine derivative with dibenzothiophene was increased from 2.35 to 2.56 eV by introducing o,o′-quaterphenyl without impairing the stability. Since the largest triplet energy of the synthesized HTMs is 2.59 eV, the triplet excitons of green phosphorescent emitters and thermally activated delayed fluorescence (TADF) emitters are confined effectively. The operational stability of the phosphorescent OLED (PHOLED) using the synthesized HTM was about 15 times longer than that of the PHOLED using 2,2′-bis­(3-ditolylaminophenyl)-1,1′-biphenyl. The optimized green PHOLED exhibits EQE of over 20% for a luminance of 10 to 10,000 cd m–2 and an expected half lifetime of over 10,000 h with an initial luminance of 1000 cd m–2. The synthesized HTM is effective for improving the efficiency of OLEDs incorporating a green TADF emitter, as well as green phosphorescent OLEDs.

Understanding coordination reaction for producing stable electrode with various low work functions

“…The correlation between the value of Δ WF derived from the Phen derivatives and the electron-injection efficiency has successfully been observed by evaluating the EIL-dependent characteristics of a cOLED having the device configuration depicted in Fig. 4a , employing various EILs 45 . The emitting host we selected here is a thermally activated delayed fluorescent (TADF) material named 2,4-diphenyl-6-bis(12-phenylindolo)[2,3-a] carbazol-11-yl)-1,3,5-triazine (DIC-TRZ), which is ideal for demonstrating an efficient and operationally stable OLED 46 .…”

A Novel Sterically Bulky Hole Transporter to Remarkably Improve the Lifetime of Thermally Activated Delayed Fluorescent OLEDs at High Brightness

“…There are only a few HTLs that fulfill all the requirements of: 1) commercially available, 2) wide energy‐gap, 3) long‐term stability, and 4) used in OLEDs in the scientific literatures. Among them, N 4, N 4′‐bis(dibenzo[b,d]thiophen‐4‐yl)‐ N 4, N 4′‐diphenylbiphenyl‐4,4′‐diamine ( DBTPB ), which is developed by Fukagawa and co‐workers,, is a commercially available, and has already realized promising operational stability of green phosphorescent OLEDs with high η ext at high brightness of 1000 cd m −2 . Additionally, DBTPB has DBT units, and enables simple comparison.…”

“…To overcome this problem, Lee and co‐workers have used calculations to show that the BDE of the C−N bond in arylamine derivatives is greatly improved by the introduction of dibenzothiophene (DBT) or dibenzofuran (DBF) moieties . In fact, Fukagawa and co‐workers have successfully realized a long operation lifetime phosphorescent OLEDs using DBT‐ or DBF‐containing arylamine derivatives . We note that DBT and DBF moieties can also deepen the I p of the resulting HTLs relative to the phenyl moiety.…”

Molecular Design and Device Design to Improve Stabilities of Organic Light-Emitting Diodes

“…In 2015, a novel amine derivative based on dibenzothiophene was synthesized as a high-tripletenergy HTM for efficient and stable OLEDs [23]. The chemical structure of the synthesized HTM, named 4DBTP3Q, is shown in Fig.…”

“…However, in recent years, the stability of OLEDs has begun to be intensively discussed from two viewpoints: operational stability and air-stability. Since high operational stability is essential for almost all OLEDs used for practical applications, there have been many reports on materials suitable for achieving operationally stable OLEDs [12][13][14][15][16][17][18][19][20][21][22][23]. Some OLEDs employing flexible substrates or simple encapsulation structures have been applied for optoelectronic sensors and biophotonics in recent years [24][25][26].…”