Utilizing Electroplex Emission to Achieve External Quantum Efficiency up to 18.1% in Nondoped Blue OLED.

Xuejun Zhan,Yanbin Gong,Zhen Li,Qianqian Li,Jin Tu,Qian Peng,Yujun Xie,Dongge Ma,Zhongbin Wu

doi:10.34133/2020/8649102

Abstract

For the first time, electroplex emission is utilized to enhance the performance of nondoped blue organic light-emitting diodes (OLEDs). By decorating the twisted blue-emitting platform and adjusting the electronic structure, three molecules of 3Cz-Ph-CN, 3Cz-mPh-CN, and 3Ph-Cz-CN with a donor-acceptor structure are synthesized and investigated. When external voltage is applied, electroplex emission, which contributes to the emission performance of OLED, can be realized at the interface between the emitting layer and the electron-transporting layer. Accordingly, high external quantum efficiency of 18.1% can be achieved, while the emission wavelength of the device can be controlled in the blue region. Our results provide the possibility to enhance the performance of OLED through electroplex emission, in addition to the generally investigated thermally activated delayed fluorescence (TADF). Excitedly, when 3Ph-Cz-CN is used as host material in orange-emitting phosphorous OLEDs (PO-01 as the dopant), unprecedented high external quantum efficiency of 27.4% can also be achieved.

Highlights

Since its discovery in the last century, thanks to unremitting efforts of scientists, organic electroluminescence has witnessed great progress [1,2,3,4,5,6,7]
While heavy-atom-induced spin-orbit coupling could make it possible for effectively harvesting triplet excitons (75% of the total electrogenerated excitons) [14], accompanied with higher external quantum efficiencies, the notorious stability problem and difficulty to tune the phosphorous emission of phosphorous organic lightemitting diodes (OLEDs) (PhOLEDs) bothered their wide applications
Electroplex could be formed at the interface between the emitting layer (EML) and the electron-transporting layer (ETL), when 3Ph-Cz-CN was used as EML in nondoped OLEDs

Summary

Introduction

Since its discovery in the last century, thanks to unremitting efforts of scientists, organic electroluminescence has witnessed great progress [1,2,3,4,5,6,7]. The newly formed redshifted broad bands were employed to realize white emission [27, 28], and there were no efforts of using electroplex or exciplex to enhance the device performance while controlling the red-shifted bands. Electroplex could be formed at the interface between the emitting layer (EML) and the electron-transporting layer (ETL), when 3Ph-Cz-CN was used as EML in nondoped OLEDs. As expected, the high external quantum efficiency of 18.1% could be achieved, while the emission wavelength of the device could be controlled in the blue region. To the best of our knowledge, this is the first time that electroplex has been successfully utilized to enhance the performance of nondoped blue OLEDs. by utilizing 3PhCz-CN as host material in orange-emitting PhOLEDs (PO-01 as the dopant), unprecedented high external quantum efficiency of 27.4% could be realized. We would like to present the synthesis and thermal, photophysical, electrochemical, and electroluminescent properties in detail

Results

Materials and Methods

Conflicts of Interest