The role of exciplex states in phosphorescent OLEDs with poly(vinylcarbazole) (PVK) host

Abstract

NOTICE: this is the author's version of a work that was accepted for publication in Psychology of Organic Electronics. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be re ected in this document. Changes may have been made to this work since it was submitted for publication. A de nitive version was subsequently published in Organic Electronics, 20, May 2015, 10.1016/j.orgel.2015 Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. PLEDs would enable printing of display or lighting panels on large area substrates that could substantially reduce fabrication costs by avoiding expensive vacuum processes presently used in OLED technologies. PVK is one of the most popular hosts for blue PLEDs. However, PVK has very poor electron transport properties and oxadiazole based electron dopants, e.g.PBD or OXD-7, are used to improve charge transport. This is generally ascribed to capture and transport of electrons on the PBD or OXD-7. Here we show that this is not necessarily the only reason for improved efficiency upon PVK doping. We demonstrate that devices with PVK doped with PBD or OXD-7 have emission lasting up to 1 ms which in some cases may be greater than prompt emission from excitons formed initially on the dopant. This long-lived emission is arising mainly due to formation of an exciplex between the PVK and PBD / OXD-7. This exciplex state then repopulates dopant iridium complexes over a long period of 2 time giving very long-lived emission. We also note, that this exciplex-fed long-lived emission from heavy metal complexes is observed in several PLEDs with PBD and PVK (and also OXD-7) doped with blue or green iridium phosphors indicating this to be a general phenomenon.Manuscript text

Extended ligand conjugation and dinuclearity as a route to efficient platinum-based near-infrared (NIR) triplet emitters and solution-processed NIR-OLEDs

“…Blend, exciplex hosts were selected as host materials, having previously been found to be very good candidates for use with metal complex phosphors. 43,[60][61][62] Two such bi-component hosts were studied: TCTA:PO-T2T 63 , which is soluble in chloroform:chlorobenzene mixture, and TPD:PBD 43 with good solubility in toluene. [The motivation for considering the former lies in that it has been found to exhibit thermally activated delayed fluorescence (TADF), though this property has been found not to be relevant for its performance as an OLED host for 5; detailed discussion is provided in the Supporting Information, Section 5.1].…”

Thermally Activated Delayed Fluorescence in Polymer–Small-Molecule Exciplex Blends for Solution-Processed Organic Light-Emitting Diodes

“…This blend can be easily processed from solution and, to the best of our knowledge, is the first attempt to produce a polymer–small-molecule exciplex, for the purpose of strong TADF emission. Because of the prominent film-forming properties of poly­( N -vinylcarbazole), , the blend can potentially be used in inkjet or slot-die printing. 2,4,6-Tris­[3-(diphenylphosphinyl)­phenyl]-1,3,5-triazine (PO-T2T), which is used as an acceptor, shows excellent solubility in toluene, which helps in the formation of high-quality films.…”

Abnormal Carrier Dynamics of Non‐Doped “P‐Type” Poly(N‐vinylcarbazole)

“…The HOMO of PVK is 5.6 eV, [ 14 ] which has 0.6 eV difference to the work function of ITO (5.0 eV). So the additional NPB has to be added for hole‐only device ITO/NPB/PVK/Al, where the 5 nm NPB was used to induce hole injection.…”