Effect of PEDOT-PSS resistivity and work function on PLED performance

The effect of a commonly used hole injection layer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT-PSS), on polymer light-emitting diode (PLED) performance has been investigated. A series of four different types of commercial PEDOT-PSS, with varying resistivity and work function were examined in devices with the structure Indium Tin Oxide (ITO)/PEDOT-PSS/High Molecular Weight Poly(n-vinylcarbazole) (PVKH): 30% N, N'-bis(3-methylphenyl)-N, N'-diphenylbenzidine (TPD)/Low molecular Weight Poly (n-vinylcarbazole) (PVKL): 40% 2-(4-Biphenyl)-5-(4-tert-butylphenyl)-1,2,4-oxadiazole (PBD): 8% Ir(ppy)(3). It was found that the PEDOT-PSS with the highest work function and resistivity produced the devices with the highest efficiencies; this is due to the improved hole injection effect, the decrease in electron leakage current and the prevention of pixel crosstalk. A maximum device current efficiency of 33.4 cd A 1 has been achieved for the most resistive PEDOT; this corresponded to an external quantum efficiency (E.Q.E.) of 11%. Increasing the work function of the PEDOT used resulted in a 60% increase in E.Q.E. and device efficiency for PEDOTs in the same resistivity range. Drift-diffusion simulations, carried out using SEmiconducting Thin Film Optics Simulation software (SETFOS) 3.2, produced J-V curves in good agreement with the experimentally observed results; this allowed us to extract qualitative values for the effective device mobility along with the PEDOT work function and resistivity. (C) 2013 Elsevier B.V. All rights reserved.