Achieving High Electroluminescence Efficiency and High Color Rendering Index for All‐Fluorescent White OLEDs Based on an Out‐of‐Phase Sensitizing System

• Published in: Advanced functional materials 2021-08, Vol.31 (33), p.n/a
• Main Authors: Liu, Hao, Chen, Jinke, Fu, Yan, Zhao, Zujin, Tang, Ben Zhong
• Format: Article
• Language: English
• Subjects: Configurations; Dopants; Electroluminescence; Energy transfer; Excitons; Fluorescence; Förster energy transfer; Interlayers; Materials science; Organic light emitting diodes; out‐of‐phase sensitizing systems; Rendering; Sensitizing; thermally activated delayed fluorescence; White light; white organic light‐emitting diodes
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202103273

Sensitizing conventional fluorescence (CF) dopants with thermally activated delayed fluorescence (TADF) materials has achieved considerable progress, by which the advantages of TADF materials and CF dopants can be fully harnessed. However, the usually used co‐phase configuration of CF dopant‐engaged sensitizing systems often encounters exciton loss due to Dexter energy transfer (DET). Herein, an effective out‐of‐phase configuration is proposed to sensitize CF dopants in the fabrication of white organic light‐emitting diodes (WOLEDs). Based on a new efficient sky‐blue TADF luminogen DCP‐BP‐DPAC which has an electroluminescence (EL) peak at 486 nm and an EL efficiency of 26.6%, a green TADF material BDMAC‐XT, and a red CF dopant DBP sensitized by BDMAC‐XT through an out‐of‐phase configuration without interlayer, efficient WOLEDs are successfully fabricated. By further adopting orange TBRB or 4CzTPNBu as intermediate sensitizers, more efficient energy transfer to DBP is achieved via Förster energy transfer. Through step‐by‐step energy transfer and elimination of excess DET process, high‐performance all‐fluorescent WOLEDs are achieved, providing excellent EL efficiencies over 23.0%, and highly stable white light with a high color rendering index of 87. The outstanding EL performance and high‐quality emission color demonstrate the great potential of the proposed out‐of‐phase design for sensitizing systems of WOLEDs. An out‐of‐phase configuration without interlayer for sensitizing system is proposed, based on which efficient step‐by‐step Förster energy transfer from thermally activated delayed fluorescence hosts to fluorescence dopant is realized, and thus high‐performance all‐fluorescent white organic light‐emitting diodes are achieved, providing excellent electroluminescence efficiencies over 23.0%, and highly stable white light with a high color rendering index of 87.