Exciplex Cohosts Employing Nonconjugated Linked Dicarbazole Donors for Highly Efficient Thermally Activated Delayed Fluorescence-Based Organic Light-Emitting Diodes

Yi-Tzu Hung; Zhi-Yang Chen; Wen-Yi Hung; Deng-Gao Chen; Ken-Tsung Wong

doi:10.1021/acsami.8b14070

Exciplex Cohosts Employing Nonconjugated Linked Dicarbazole Donors for Highly Efficient Thermally Activated Delayed Fluorescence-Based Organic Light-Emitting Diodes

ACS Appl Mater Interfaces. 2018 Oct 10;10(40):34435-34442. doi: 10.1021/acsami.8b14070. Epub 2018 Sep 28.

Authors

Yi-Tzu Hung¹, Zhi-Yang Chen², Wen-Yi Hung², Deng-Gao Chen¹, Ken-Tsung Wong^{1

3}

Affiliations

¹ Department of Chemistry , National Taiwan University , Taipei 10617 , Taiwan.
² Institute of Optoelectronic Sciences , National Taiwan Ocean University , Keelung 202 , Taiwan.
³ Institute of Atomic and Molecular Science, Academia Sinica , Taipei 10617 , Taiwan.

PMID: 30222304
DOI: 10.1021/acsami.8b14070

Abstract

Two new nonconjugated linked dicarbazole materials, dCzPSi and dCzPSO₂, with high triplet energy were synthesized and characterized. dCzPSi and dCzPSO₂ were adopted as unipolar host materials for the green thermally activated delayed fluorescence (TADF) emitter (4CzIPN) to achieve high-efficiency organic light-emitting diodes (OLEDs). The electron-transporting acceptor, PO-T2T, was introduced to mix with dCzPSi and dCzPSO₂ to give two new exciplex-forming systems that can improve the exciton formation propensity in the emitting layer. The relevant properties of these new exciplexes were characterized, and they were suggested as promising cohosts for the green TADF emitter, 4CzIPN. The characteristics of the devices employing single hosts (dCzPSi and dCzPSO₂) and exciplex-forming cohosts (dCzPSi:PO-T2T and dCzPSO₂:PO-T2T) were explored. The obtained results indicate that the Si-bridged dicarbazole compound dCzPSi outperforms its counterpart dCzPSO₂ in which two carbazole groups are linked by an SO₂ group. The device employed with the dCzPSi:PO-T2T cohost with 10 wt % 4CzIPN achieved a low V_on of 2.2 V and maximum efficiencies of 21.1% (external quantum efficiency), 56.4 cd A^-1 (current efficiency), 59.1 lm W^-1 (power efficiency), as compared to those (18.7%, 56.6 cd A^-1, and 68.5 lm W^-1) of the dCzPSO₂:PO-T2T-hosted device. This work verifies the advantages of using a cohost that can form an exciplex for boosting the device efficiency with reduced efficiency roll-off of TADF-based OLEDs.

Keywords: cohost; dicarbazole; exciplex; high triplet energy; non-conjugated linkage; thermally activated delayed fluorescence.