On-substrate polymerization of solution-processed, transparent PEDOT: DDQ thin film electrodes with a hydrophobic polymer matrix

Thin conductive, hydrophobic films of poly(3,4-ethylenedioxythiophene) or PEDOT were synthesized on-substrate in the presence of the organic electron acceptor and dehydrogenating agent 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) using a versatile processing procedure. Significant polymerization in the processing solution was delayed by using common aprotic, ethereal solvents with low dielectric constants to prevent solvating the EDOT:DDQ charge transfer complex into radicals. Polymerization was initiated by an increase in concentration upon solvent evaporation during spin coating. A hydrophobic polymer matrix additive of polyvinyl acetate was used to aid in film formation, and a post-treatment rinse with acetonitrile was necessary to obtain a conductive film. Conductivities ranged from 17 to 59 S/cm, where the higher values were achieved at the cost of transparency. A work function of 4.62 eV was determined by UV photoelectron spectroscopy for one film recipe. When comparing conductive AFM results of PEDOT: DDQ to highly conductive, ethylene glycol-treated PEDOT: poly(styrenesulfonate) or PSS, surface currents were orders of magnitude higher for PEDOT: DDQ than for PEDOT: PSS. If optimized further, less acidic and hydrophobic PEDOT: DDQ films have the potential to replace PEDOT: PSS for use as a transparent electrode or charge transport layer in organic solar cells, organic light emitting diodes, touch screens, and other optoelectronic devices. (C) 2011 Elsevier B.V. All rights reserved.