Charge-transfer-featured materials—promising hosts for fabrication of efficient OLEDs through triplet harvesting via triplet fusion

Abstract

A charge-transfer-featured naphthalimide derivative with a small exchange energy but a lower lying (3)ππ* state than (3)CT state is found to contribute to triplet harvesting through a P-type rather than an E-type delayed fluorescence, and could act as a quite promising host to achieve highly efficient OLEDs.

High performance fluorescent and phosphorescent organic light-emitting diodes based on a charge-transfer-featured host material

“…In the solid film state, where CzPhONI molecules are tightly packed, the interactions become stronger, leading to the more bathochromic spectrum with an emission peak at $493 nm. More detailed investigations have shown that CzPhONI exhibits a twisted intramolecular CT character, and it has been reported elsewhere [16]. The density functional theory calculations show that the overlap between HOMO and LUMO is zero.…”

“…It has been demonstrated that CzPhONI is a triplet-fusion delayed fluorescence (TFDF) material, which is related to a triplet up-conversion mechanism [16]. The up-conversion mechanism originates from the triplet-triplet annihilation (TTA) process, and the value of g r is higher than the maximum value in conventional fluorescent OLEDs [24][25][26].…”

“…To further enhance the EL performance, more investigations deserve to be carried out, by enhancing the up-conversion efficiency, optimizing the device architecture, doping concentration and film thickness. Moreover, applying novel CT-featured host materials with thermally activated delayed fluorescence (TADF) property is also a promising strategy, when the conflict between small DE ST and high PL quantum yield in developing high performance TADF materials is well addressed [16,[35][36][37].…”

“…Recently, a CT-featured complex, 6-{3,5-bis-[9-(4-t-butylphenyl)-9H-carbazol-3-yl]-phenoxy}-2-(4-t-butylphenyl)-benzo[de]isoquinoline-1,3-dione (CzPhONI) [16], which possessed small DE ST resulting from the intramolecular CT state, was realized. It was used as the host of a fluorescent dye, and the results showed that the external quantum efficiency (EQE) of the device exceeded the theoretical limit, ascribed to a triplet-fusion up-conversion mechanism.…”

High performance organic ultraviolet photodetector with efficient electroluminescence realized by a thermally activated delayed fluorescence emitter

“…When under a forward bias, holes and electrons are injected from corresponding electrodes, and excitons will be formed in CzPhONI layer for emission. Although the EL emission takes advantage of the triplet-triplet annihilation (TTA) up-conversion mechanism of CzPhONI emitter, 22 the TTA process is not as efficient as the reverse intersystem crossing (RISC) of thermally activated delayed fluorescence (TADF) materials. 23 Herein, we demonstrate a high performance organic UVPD with high EL yields.…”