Universal Polymeric Hole Transporting Material for Solution-Processable Green and Blue Thermally Activated Delayed Fluorescence OLEDs
Hyeondoo Je, Min Ju Cho, Na Yeon Kwon, Su Hong Park, Min Ji Kang, Heume Il Baek, Junho Youn, Chang Wook Han, Dong Hoon Choi
Abstract
To obtain high-efficiency solution-processed organic light-emitting diodes (OLEDs), a hole transport material (HTM) capable of solution processing with excellent charge transport properties is required. In this study, a new vinyl polymer ( PmCP ) containing hole-transporting 1,3-di(9 H -carbazol-9-yl)benzene (mCP) in the side chain was successfully synthesized via radical polymerization. PmCP showed good film-forming ability and thermal stability. Moreover, PmCP has a higher triplet energy value and hole mobility than poly( N -vinylcarbazole) (PVK) used as a reference HTM, which can be applied as a hole transport layer (HTL) in thermally activated delayed fluorescence (TADF) OLEDs, providing green and blue emissions. PmCP -based solution-processable TADF-OLEDs containing green- and blue-emitting layers were easily fabricated without damaging the lower HTL while using ethyl acetate as an orthogonal solvent. The corresponding OLEDs possess high external quantum efficiencies of 29.60% and 11.00% for the green- and blue-emitting devices, respectively. They show superior performances compared to PVK-based devices used as a reference. It was confirmed that PmCP as a solution-processable HTM can replace PVK and is universally applicable to both green- and blue-emitting devices.