Issue 20, 2016

High-performance bipolar host materials for blue TADF devices with excellent external quantum efficiencies

Abstract

New bipolar host molecules composed of carbazole, pyridoindole, and dibenzothiophene (DBT) were synthesized for blue thermally activated delayed fluorescence (TADF)-based organic light-emitting diodes (OLEDs). 2,8-Di(9H-carbazol-9-yl)dibenzo[b,d]thiophene, 9-(8-(9H-carbazol-9-yl)dibenzo[b,d]thiophen-2-yl)-9H-pyrido[2,3-b]indole, and 2,8-bis(9H-pyrido[2,3-b]indol-9-yl)dibenzo[b,d]thiophene were prepared based on the selective reactivity at the 2,8-positions of DBT. The new symmetric and asymmetric host materials exhibited high triplet energies (2.89–2.95 eV). 4,5-Di(9H-carbazol-9-yl)phthalonitrile (2CzPN) was selected as an emitting dopant for achieving sky-blue emissions in TADF-OLEDs. 2CzPN-doped TADF-OLEDs, whose configuration is ITO (50 nm)/HATCN (7 nm)/TAPC (75 nm)/host:6% 2CzPN (20 nm)/TmPyPB (50 nm)/LiF (15 nm)/Al (100 nm), showed low driving voltages and high external quantum efficiencies (EQEs). These results are attributed to the well-controlled bipolar character of the host giving a better charge balance in the emitting layer. In particular, the device containing ZDN:6% 2CzPN showed an unprecedentedly high EQE of 25.7% (at 0.074 mA cm−2).

Graphical abstract: High-performance bipolar host materials for blue TADF devices with excellent external quantum efficiencies

Supplementary files

Article information

Article type
Paper
Submitted
27 Janv. 2016
Accepted
02 Apr. 2016
First published
04 Apr. 2016

J. Mater. Chem. C, 2016,4, 4512-4520

High-performance bipolar host materials for blue TADF devices with excellent external quantum efficiencies

J. S. Kang, T. R. Hong, H. J. Kim, Y. H. Son, R. Lampande, B. Y. Kang, C. Lee, J. Bin, B. S. Lee, J. H. Yang, J. Kim, S. Park, M. J. Cho, J. H. Kwon and D. H. Choi, J. Mater. Chem. C, 2016, 4, 4512 DOI: 10.1039/C6TC00385K

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