Understanding charge transport in Ir(ppy)₃:CBP OLED films

Sanderson, Stephen, Philippa, Bronson, Vamvounis, George, Burn, Paul L., and White, Ronald D. (2019) Understanding charge transport in Ir(ppy)₃:CBP OLED films. Journal of Chemical Physics, 150 (9). 094110.

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Abstract

Ir(ppy)₃:CBP blends have been widely studied as the emissive layer in organic light emitting diodes (OLEDs), yet crucial questions about charge transport within the layer remain unaddressed. Recent molecular dynamics simulations show that the Ir(ppy)₃ molecules are not isolated from each other, but at concentrations of as low as 5 wt. % can be part of connected pathways. Such connectivity raises the question of how the iridium(iii) complexes contribute to long-range charge transport in the blend. We implement a kinetic Monte Carlo transport model to probe the guest concentration dependence of charge mobility and show that distinct minima appear at approximately 10 wt. % Ir(ppy)₃ due to an increased number of trap states that can include interconnected complexes within the blend film. The depth of the minima is shown to be dependent on the electric field and to vary between electrons and holes due to their different trapping depths arising from the different ionization potentials and electron affinities of the guest and host molecules. Typical guest-host OLEDs use a guest concentration below 10 wt. % to avoid triplet-triplet annihilation, so these results suggest that optimal device performance is achieved when there is significant charge trapping on the iridium(iii) complex guest molecules and minimum interactions of the emissive chromophores that can lead to triplet-triplet annihilation.

Item ID: 57527
Item Type: Article (Research - C1)
ISSN: 1089-7690
Copyright Information: © 2019 Author(s). Published under license by AIP Publishing.
Funders: Australian Government Research Training Program, Australian Research Council (ARC)
Projects and Grants: Australian Government Research Training Program Scholarship, ARC Laureate Fellow No. FL160100067
Date Deposited: 21 Mar 2019 01:05
FoR Codes: 02 PHYSICAL SCIENCES > 0204 Condensed Matter Physics > 020404 Electronic and Magnetic Properties of Condensed Matter; Superconductivity @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970102 Expanding Knowledge in the Physical Sciences @ 100%
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