Optimisation of Processing, Conductivity and Adhesion of PEDOT:PSS Films

Lead Research Organisation: University of Birmingham
Department Name: Metallurgy and Materials

Abstract

Poly(3,4-ethylene dioxythyophene) doped with Poly(styrene sulfonate) (often shortened to PEDOT:PSS) is a semi-conducting polymer system, normally formed into films from an aqueous solution, that could replace indium tin oxide (ITO) in optoelectric devices. However, PEDOT:PSS conductivity cannot match that of ITO on its own so further conductivity enhancements are employed to improve the conductivity. Current methods utilise volatile solvents to create the required conductivity but they are not environmentally friendly and are difficult to use on a bulk manufacturing scale. Furthermore, the adhesion of PEDOT:PSS to flexible substrates (which could be used for flexible flat panel displays for example) is relatively poor. This project will focus on the enhancement of conductivity through the use of the non-toxic surfactant Tween 80 and the improvement of adhesion to flexible substrates through the use of a polydopamine coating.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509590/1 01/10/2016 30/09/2021
1952982 Studentship EP/N509590/1 25/09/2017 30/09/2020 Joseph Carter
 
Description Poly(3,4-ethylene dioxythyophene) doped with Poly(styrene sulfonate) (often shortened to PEDOT:PSS) is a semi-conducting polymer system, nomally formed into films from an aquious solution, that could replace indium tin oxide (ITO) in optoelectric devices. On its own, PEDOT:PSS cannot match the conductivity of ITO, so further conductivity enhancements are employed to improve the conductivity. Furthermore, the adhesion of PEDOT:PSS to flexible substrates is relatively poor. This project has focussed on the addition of the non-toxic surfactant Tween 80 to enhance conductivity, and the use of the biopolymer polydopamine (PDA) as a pre coating to improve adhesion. The current key findings are follows:
- The processing and treatment method of PEDOT:PSS on its own (i.e. without Tween 80) has been investigated and a standard for annealing times and temperatures has been suggested.
- The conductivity of PEDOT:PSS can be enhanced with the addition of Tween 80 to the solution proir to film forming. There appears to be an optimum amount in that too little and there is only a small amount of conductivity enhancement, too much and the quality of the formed films deteriorates.
- Conductivoty of the films can also be improved by washing with MEK, ethanol and methanol.
- Tween 80 also alters the rheological and surface tension properties of PEDOT:PSS solution which has implictions for the processing methods used in bulk manufcturing.
- Applying further layers of PEDOT:PSS to an existing PEDOT:PSS film significanly improves the conductivity of the final film formed.
- Adhesion can be improved with the use of a PDA layer prior to PEDOT:PSS film forming
- There may also be an improvement in adhesion with just the use of Tween 80 without the need to add a PDA layer.
Exploitation Route In future optoelectric devices when ITO can no longer be used (either due to availability or the need for flexibility), it will become necessary to have an aquious PEDOT:PSS system that can match the conductivity of ITO and can be manufactured on a bulk scale. By mimicing conditions for bulk manufacturing processes and using a non-toxic addition to the PEDOT:PSS solution this research will contribute to help find a suitable PEDOT:PSS system.
Sectors Electronics,Manufacturing, including Industrial Biotechology