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Issue 11, 2014
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Oxadiazole based bipolar host materials employing planarized triarylamine donors for RGB PHOLEDs with low efficiency roll-off

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Abstract

A series of 6 novel triarylamine-containing oxadiazole compounds (o-PCzPOXD, o-ICzPOXD, o-TPATOXD, o-PCzTOXD, o-ICzTOXD, o-CzTOXD) have been designed, synthesized and characterized concerning applications as host materials in PHOLED devices. To further improve the ortho-linkage concept, the impact of incorporating planarized electron-donating triarylamine (TAA) structures on intramolecular charge transfer was examined. The effect was evaluated for two series of electron-accepting oxadiazole scaffolds, realizing ortho-linkage on the benzene (POXD) and the thiophene (TOXD) cores. Thermal analysis shows increased glass-transition temperatures for planarized structures indicating an improved morphological stability. A higher degree of planarization also results in significantly increased singlet and triplet energy values, revealing the impact on the intramolecular charge transfer. Employing the developed materials, red (o-TPATOXD: CEmax: 28.8 cd A−1, EQEmax: 16.9%), green (o-PCzPOXD: CEmax: 62.9 cd A−1, EQEmax: 17.1%) and blue (o-PCzPOXD: CEmax: 29.8 cd A−1, EQEmax: 13.4%) devices were achieved showing remarkably low efficiency roll-off for planarized donors. Hence, this is the first report of efficient blue devices for this specific class of host materials. It is proposed that the results correlate with an increasing ortho-linkage effect and decreasing donor strength of the TAA moiety by planarization and, thus, tackling one of the major challenges in PHOLED research: improving both triplet energy and compound stability.

Graphical abstract: Oxadiazole based bipolar host materials employing planarized triarylamine donors for RGB PHOLEDs with low efficiency roll-off

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Supplementary files

Article information


Submitted
26 Nov 2013
Accepted
04 Jan 2014
First published
07 Jan 2014

J. Mater. Chem. C, 2014,2, 2069-2081
Article type
Paper
Author version available

Oxadiazole based bipolar host materials employing planarized triarylamine donors for RGB PHOLEDs with low efficiency roll-off

P. Kautny, D. Lumpi, Y. Wang, A. Tissot, J. Bintinger, E. Horkel, B. Stöger, C. Hametner, H. Hagemann, D. Ma and J. Fröhlich, J. Mater. Chem. C, 2014, 2, 2069
DOI: 10.1039/C3TC32338B

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