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.

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► Versatile in situ processing procedure of PEDOT:DDQ on substrate.
► Processing solution has a relatively long pot life, less acidic than PEDOT:PSS.
► Can take on mechanical properties of polymer additive including hydrophobicity.
► Orders of magnitude lower contact resistance relative to PEDOT:PSS.
► Relatively high conductivity for first PEDOT:DDQ report of continuous thin film formation.