High-Conductivity Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) Film and Its Application in Polymer Optoelectronic Devices

• Published in: Advanced functional materials 2005-02, Vol.15 (2), p.203-208
• Main Authors: Ouyang, J., Chu, C.-W., Chen, F.-C., Xu, Q., Yang, Y.
• Format: Article
• Language: English
• Subjects: 4-ethylenedioxythiophene) (PEDOT; Conducting polymers; Light-emitting diodes; Light‐emitting diodes, organic; organic; Photovoltaic devices; Poly; Poly(3,4‐ethylenedioxythiophene) (PEDOT)
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200400016

The conductivity of a poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film can be enhanced by more than two orders of magnitude by adding a compound with two or more polar groups, such as ethylene glycol, meso‐erythritol (1,2,3,4‐tetrahydroxybutane), or 2‐nitroenthanol, to an aqueous solution of PEDOT:PSS. The mechanism for this conductivity enhancement is studied, and a new mechanism proposed. Raman spectroscopy indicates an effect of the liquid additive on the chemical structure of the PEDOT chains, which suggests a conformational change of PEDOT chains in the film. Both coil and linear conformations or an expanded‐coil conformation of the PEDOT chains may be present in the untreated PEDOT:PSS film, and the linear or expanded‐coil conformations may become dominant in the treated PEDOT:PSS film. This conformational change results in the enhancement of charge‐carrier mobility in the film and leads to an enhanced conductivity. The high‐conductivity PEDOT:PSS film is ideal as an electrode for polymer optoelectronic devices. Polymer light‐emitting diodes and photovoltaic cells fabricated using such high‐conductivity PEDOT:PSS films as the anode exhibit a high performance, close to that obtained using indium tin oxide as the anode. The conductivity of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films is enhanced by the addition of ethylene glycol, meso‐erythritol, or 2‐nitroethanol, which change the conformation of the PEDOT chains. High‐performance polymer light‐emitting diodes (see Figure) and solar cells using enhanced PEDOT:PSS films as the anode are demonstrated.