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

Ju Sik Kang, Tae Ryang Hong, Hyung Jong Kim, Young Hoon Son, Raju Lampande, Byoung Yeop Kang, Chiho Lee, Jong Kwan Bin, Bang Sook Lee, Joong Hwan Yang, Jinwuk Kim, Sungnam Park, Min Ju Cho, Jang Hyuk Kwon, Dong Hoon Choi

Research output: Contribution to journalArticlepeer-review

61 Citations (Scopus)

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).

Original languageEnglish
Pages (from-to)4512-4520
Number of pages9
JournalJournal of Materials Chemistry C
Volume4
Issue number20
DOIs
Publication statusPublished - 2016
Externally publishedYes

Bibliographical note

Funding Information:
This research was supported by National Research Foundation of Korea (NRF2012R1A2A1A01008797) and by Key Research Institute Program (NRF20100020209). DH Choi is particularly thankful for the support from LG display Co. Limited (2014-2015). And this work was also supported by the Industrial Strategic Technology Development Program of MKE/KEIT [10048317, Development of red and blue OLEDs with external quantum efficiency over 20% using delayed fluorescent materials].

Publisher Copyright:
© 2016 The Royal Society of Chemistry.

ASJC Scopus subject areas

  • General Chemistry
  • Materials Chemistry

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