Universal Polymeric Hole Transporting Material for Solution-Processable Green and Blue Thermally Activated Delayed Fluorescence OLEDs

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(9H-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.

Charge transporting and thermally activated delayed fluorescence materials for OLED applications

“…Je et al developed a new vinyl polymer ( 44 ) containing a universal HTM via radical polymerization reaction. 67 The synthesized compound showed high thermal stability and comparable E T to that of the commercial poly( N -vinyl carbazole) (PVK) HTM. The T d and E T of the developed material were found to be 476 °C and 2.96 eV, respectively, which can be applied in optoelectronic devices.…”

Carbazole‐Decorated Organoboron Emitters with Low‐Lying HOMO Levels for Solution‐Processed Narrowband Blue Hyperfluorescence OLED Devices

“…Comparison of the maximum EQE of the solution-processed MR-TADF OLEDs reported in the literature. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Angewandte Chemie safely demonstrate that the performance improvement of Cz-DABNA and t-BuCz-DABNA hyperfluorescence devices is mainly due to the suppression of hole traps by energy level regulation.…”

“…[20][21][22] Compared with evaporation, solution-processing methods have been intensively demonstrated as more economical approaches for the mass production of large-area OLED displays. [23][24][25] However, the efficiency of reported solutionprocessed MR-TADF OLEDs remains far inferior to that of their vacuum-deposited counterparts, [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] among which pure blue devices with y color coordinate below 0.20 show extremely low efficiency with EQE of only 16.6 %. [29] The hyperfluorescence is formed by adding a conventional TADF material with high reverse intersystem crossing (RISC) rate in the emissive layer as the sensitizer, which could obviously improve the efficiency of MR-TADF devices by accelerating the triplet exciton upconversion for avoiding exciton annihilation events of long-lived triplets, [29,33,44,45] such as triplet-triplet and triplet-polaron interactions.…”

Carbazole‐Decorated Organoboron Emitters with Low‐Lying HOMO Levels for Solution‐Processed Narrowband Blue Hyperfluorescence OLED Devices

“…Comparison of the maximum EQE of the solution-processed MR-TADF OLEDs reported in the literature. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] safely demonstrate that the performance improvement of Cz-DABNA and t-BuCz-DABNA hyperfluorescence devices is mainly due to the suppression of hole traps by energy level regulation.…”