Solution-processable bipolar host materials composed of fluorenyl, carbazolyl and 1,3,4-oxadiazolyl derivatives: synthesis and application in phosphorescent organic light-emitting diodes?

Journal of Materials Chemistry C Pub Date: 2016-04-25 DOI: 10.1039/C6TC01108J

Abstract

Carrier transport in a host is crucial for enhancing the emission efficiency of phosphorescent organic light-emitting diodes (PhOLEDs). The study prepared two new solution-processable bipolar hosts (FC3O and FC4O) containing fluorenyl, hole-transporting carbazolyl and electron-transporting oxadiazolyl moieties to investigate their applicability to PhOLEDs. The ratios of oxadiazolyl over carbazolyl groups are 3/1 and 4/2 for FC3O and FC4O, respectively. It was found that both hosts reveal good thermal stability (Td > 360 °C, Tg > 145 °C) attributable to rigid and non-planar structures; moreover, homogeneous films (rms roughness <0.75 nm) were readily obtained by the spin-coating process. Multilayer green-emitting PhOLEDs were successfully fabricated (ITO/PEDOT:PSS/EML/BCP/LiF/Al), using FC3O or FC4O doped with Ir(ppy)3 as the emission layer (EML) which was deposited by the spin-coating process. The maximum luminance and maximum current efficiency of the FC4O-based device were 10?232 cd m?2 and 18.2 cd A?1, respectively, higher than 9358 cd m?2 and 14.9 cd A?1 of the FC3O-based one. Furthermore, both FC3O and FC4O outperform the conventional host PVK (1567 cd m?2, 4.0 cd A?1) in terms of device performance, indicating their potential for general applicability to hosts of organic light-emitting diodes.

Graphical abstract: Solution-processable bipolar host materials composed of fluorenyl, carbazolyl and 1,3,4-oxadiazolyl derivatives: synthesis and application in phosphorescent organic light-emitting diodes
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