Optimizing the Intralayer and Interlayer Compatibility for High-Efficiency Blue Thermally Activated Delayed Fluorescence Diodes

Abstract

A series of phosphine oxide hosts, 4,6-bis(diphenylphosphoryl) dibenzothiophene (DBTDPO) and 4- diphenylphosphoryldibenzothiophene (DBTSPO), and electron transporting materials (ETM), 2-(diphenylphosphoryl)dibenzothiophene sulfone (2DBSOSPO), 3-(diphenylphosphoryl)dibenzothiophene sulfone (3DBSOSPO) and 4-(diphenylphosphoryl)dibenzothiophene sulfone (4DBSOSPO) were developed to support blue thermally activated delayed fluorescence (TADF) devices with high performance through optimizing intralayer and interlayer compatibility of emissive layers. On the basis of the triplet energy of ~3.0 eV for the hosts and ETMs, excitons can be effectively confined on DMAC-DPS. Compared to DBTSPO, DBTDPO can support the excellent distribution uniformity to blue TADF dye bis[4-(9,9-dimethyl–9,10-dihydroacridine) phenyl] sulfone (DMAC-DPS), owing to their configuration similarity; while 3DBSOSPO and 4DBSOSPO are superior in compatibility with the hosts due to the similar molecular polarity or configuration. Through adjusting the molecular configuration, the electrical performance of ETMs can be feasibly tuned, including the excellent electron mobility (μe) by the order of 10−3 cm2 V−1 s−1. As the result, DBTDPO and 4DBSOSPO endowed their four-layer blue TADF devices with the maximum current efficiency of 33.5 cd A−1 and the maximum external quantum efficiency more than 17%, which are impressive among the best blue TADF devices. It is showed that intralayer compatibility determines the maximum efficiencies, while interlayer compatibility influences efficiency stability.

Molecular Design Strategy of Organic Thermally Activated Delayed Fluorescence Emitters

“…Similarly, a modified version of diphenylsulfone, DMTDAc , could also reduce the fwhm of deep blue TADF emitters . A well-known TADF emitter with a diphenylsulfone acceptor, DMAC-DPS , was a high efficiency deep blue emitter providing high EQE above 20%, but the EL spectrum of the DMAC-DPS device was rather broad. − In order to reduce the fwhm of DMAC-DPS while preserving the high EQE performance, the diphenylsulfone acceptor was tied by a dimethylcarbon linker because the fused structure would disallow molecular motion between sulfone and phenyl unit. Although this design method was not as effective as the whole molecular motion suppressing design method, the fwhm was improved to 65 nm compared to 72 nm of DMAC-DPS .…”

Recent Progress in High‐Efficiency Blue‐Light‐Emitting Materials for Organic Light‐Emitting Diodes

“…Diphenylsulfone acceptor‐derived materials were investigated as high‐EQE blue TADF emitters by linking the acceptor with a strong donor such as acridine due to the weak acceptor strength of diphenylsulfone. In fact, only acridine functioned well as the donor of diphenylsulfone‐based emitters . Carbazole‐type donors were ineffective in diphenylsulfone compounds, which limited the development of diphenylsulfone‐type TADF emitters because acridine reduces the lifetime of the device.…”

Manipulating Charge‐Transfer Excitons by Exciplex Matrix: Toward Thermally Activated Delayed Fluorescence Diodes with Power Efficiency beyond 110 lm W−1

“…Due to the lateral steric hindrance of 3‐DPPO, μ h of CDBP:3DBSOSPO as 5.55 × 10 −4 cm 2 V −1 s −1 is sixfolds larger than its μ e of 7.88 × 10 −5 cm 2 V −1 s −1 . Despite their μ h and μ e , respectively, lower than CDBP and m DBSOSPO, [ 20 ] the carrier transportation balance in CDBP:2DBSOSPO and CDBP:3DBSOSPO are remarkably improved and significantly stronger than the conventional single‐molecular ambipolar hosts, establishing the basis of fast and long‐range charge migration in these matrixes.…”

“…Herein, we use a series of phosphine oxide (PO) electron‐transporting materials, m ‐ (diphenylphosphoryl)dibenzothiophene sulfone ( m DBSOSPO, m = 2, 3, and 4) as the acceptors [ 20 ] to construct the exciplex matrixes with hole‐transporting 4,4'‐bis(9‐carbazolyl)‐2,2'‐dimethylbiphenyl (CDBP) as the donor, namely, CDBP: m DBSOSPO ( Figure a). The varied substitution position of diphenylphosphine oxide (DPPO) leads to the different steric hindrances of m DBSOSPO and D‐A intermolecular CT effects of the exciplexes, giving rise to their diverse excited‐state properties and host–dopant interactions.…”