Exciplex Organic Light-Emitting Diodes with Nearly 20% External Quantum Efficiency: Effect of Intermolecular Steric Hindrance between the Donor and Acceptor Pair

Authors:
Publisher website
Google Scholar
Abstract
Exciplex emitters have emerged as an important class of thermally activated delayed fluorescence (TADF) materials for highly efficient OLEDs. A TADF exciplex emitter requires an intermolecular donor/acceptor pair. We have synthesized a bipolar donor-type material, DPSTPA, which was used to pair with known acceptor materials (2CzPN, 4CzIPN or CzDBA). The OLEDs based on the exciplex emitters DPSTPA/X, where X = 2CzPN and CzDBA give green and orange-red colors with record-high external quantum efficiencies (EQEs) of 19.0±0.6% and 14.6±0.4%, respectively. In contrast, the exciplex pair DPSTPA/4CzIPN gave very low photoluminescence quantum yield (PLQY) and EQE of the device. The DFT calculations indicate that the intermolecular distance between the donor and the acceptor plays a key factor for the PLQY and EQE. The observed low PLQY and the poor device performance for the DPSTPA/4CzIPN pair are probably due to the relative long distance between the DPSTPA and 4CzIPN in the thin film caused by the four congested carbazole (Cz) groups of 4CzIPN which effectively block the interaction of the nitrile acceptor with the triphenylamino donor of DPSTPA.
Funding Information
  • Ministry of Education
  • Ministry of Science and Technology, Taiwan (MOST 107-3017-F-007-002, MOST 107-2113-M-007-004)

This publication has 39 references indexed in Scilit: