Solution-Processible Carbazole Dendrimers as Host Materials for Highly Efficient Phosphorescent Organic Light-Emitting Diodes

• Published in: Advanced functional materials Vol. 23; no. 5; pp. 619 - 628
• Main Authors: Li, Jiuyan, Zhang, Ting, Liang, Yunjing, Yang, Ruixia
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 05-02-2013; WILEY‐VCH Verlag
• Subjects: carbazole; Dendrimers; Devices; Dopants; host materials; Organic light emitting diodes; phosphorescent OLEDs; Polyvinyl carbazole; solution-processible; Spin coating; Spreads
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201201326

A group of dendrimers with oligo‐carbazole dendrons appended at 4,4′‐ positions of biphenyl core are synthesized for use as host materials for solution‐processible phosphorescent organic light‐emitting diodes (PHOLEDs). In comparison with the traditional small molecular host 4,4′‐N,N′‐dicarbazolebiphenyl (CBP), the dendritic conformation affords these materials extra merits including amorphous nature with extremely high glass transition temperatures (ca. 376 °C) and solution‐processibility, but inherent the identical triplet energies (2.60–2.62 eV). In comparison with the widely‐used polymeric host polyvinylcarbazole (PVK), these dendrimers possess much higher HOMO levels (–5.61 to –5.42 eV) that facilitate efficient hole injection and are favorable for high power efficiency in OLEDs. The agreeable properties and the solution‐processibility of these dendrimers makes it possible to fabricate highly efficient PHOLEDs by spin coating with the dendimers as phosphorescent hosts. The green PHOLED containing Ir(ppy)3 (Hppy = 2‐phenyl‐pyridine) dopant exhibits high peak efficiencies of 38.71 cd A−1 and 15.69 lm W−1, which far exceed those of the control device with the PVK host (27.70 cd A−1 and 9.6 lm W−1) and are among the best results for solution‐processed green PHOLEDs ever reported. The versatility of these dendrimer hosts can be spread to orange PHOLEDs and high efficiencies of 32.22 cd A−1 and 20.23 lm W−1 are obtained, among the best ever reported for solution‐processed orange PHOLEDs.
The dendritic analogues of small molecular phosphorescent host (4,4′‐N,N′‐dicarbazolebiphenyl (CBP)) inherit similar triplet energies and HOMO/LUMO levels to those of CBP, but exhibit extra merits of amorphous nature and solution‐processible capability. These dendrimers greatly enhance device performance in comparison with traditional polyvinylcarbazole (PVK) when used as hosts in phosphorescent organic light‐emitting diodes (PHOLEDs), representing perfect alternatives to PVK as solution‐processible phosphorescent hosts for PHOLEDs.