High‐Performance Ultraviolet Organic Light‐Emitting Diode Enabled by High‐Lying Reverse Intersystem Crossing

Abstract

Ultraviolet (UV) organic emitters that can open up applications for future organic light-emitting diodes (OLEDs) are of great value but rarely developed. Here, we report a highquality UV emitter with hybridized local and charge-transfer (HLCT) excited state and its application in UV OLEDs. The UV emitter, 2BuCz-CNCz, shows the features of low-lying locally excited (LE) emissive state and high-lying reverse intersystem crossing (hRISC) process, which helps to balance the color purity and exciton utilization of UV OLED. Consequently, the OLED based on 2BuCz-CNCz exhibits not only a desired narrowband UV electroluminescent (EL) at 396 nm with satisfactory color purity (CIE x, y = 0.161, 0.031), but also a record-high maximum external quantum efficiency (EQE) of 10.79 % with small efficiency roll-off. The state-ofthe-art device performance can inspire the design of UV emitters, and pave a way for the further development of highperformance UV OLEDs.

Deep Blue Emitter Based on Tris(triazolo)triazine Moiety with CIEy < 0.08 for Highly Efficient Solution‐Processed Organic Light‐Emitting Diodes Via Molecular Strategy of “Hot Excitons”

“…With this in mind, many HLCT-based deep/ pure blue materials have been developed recently. [29][30][31][32][33][34][35][36][37][38][39][40][41][42] However, most of these emitters were utilized in OLED via vacuum deposition method. Very few exploration has been performed on the solution processable OLED based on deep/pure blue HLCT emitters.…”

“…[41] Furthermore, the EQE max of deep-blue HLCT emitters rarely reaches 10% and is difficult to meet the practical requirements. [40] Moreover, only few acceptor fragments, e.g., phenanthro [9,10-d]-imidazole and cyano, have been employed in HLCT molecules. [31,33,34] Therefore, there is still a large room to enrich the HLCT molecules as well as further improve their EL performance, especially in the deep blue cases.…”

Toward phosphorescent and delayed fluorescent carbon quantum dots for next-generation electroluminescent displays

“…In the past few years, TADF with MR effect induced HOMO–LUMO separation has shown great potential to deliver a narrow EL band. 91–94 For example, Hatakeyama et al first reported two MR-TADF compounds with a B–N-containing core skeleton, which exhibited blue EL with a small FWHM of only 28 nm, a high maximum EQE max of 20.2%, and high color purity with CIE coordinates of (0.13, 0.09) which are close to the National Television System Committee (NTSC) blue light standard (CIE: (0.14, 0.08)). 95 The as-synthesized compounds with tert -butyl and carbazolyl units were subsequently modified and achieved blue OLEDs with a FWHM of only 27 nm, a high EQE max of 32.1%, and low efficiency roll-off.…”

Nearly 100% Exciton Utilization via Hybridized Inter‐ and Intramolecular Triplet Exciton Harvesting Channels in Blue Fluorescent Organic Light‐Emitting Diodes

“…HLCT or hot exciton mechanisms can also be used to upconvert triplet excitons into singlet excitons within the ns scale time range. [37][38][39][40][41][42][43][44] High-lying excited states can contribute to the quick exciton conversion, providing high external quantum efficiency (EQE) over 10% in the nondoped blue OLEDs. However, the exciton utilization efficiency (EUE) of the devices operated by the hot exciton mechanism needs to be further enhanced to reach a high EQE.…”