Carbon nanotube/PEDOT:PSS electrodes for organic photovoltaics^*

¹ Electrical Engineering Department & Center For Materials Technology and Lasers, Technological Educational Institute (TEI) of Crete, PB 1939, Heraklion 71 004, Crete, Greece
² Department of Materials Science and Technology, University of Crete, PB 2208, 71003, Heraklion, Crete, Greece
³ Mechanical Engineering Department, TEI of Crete, 71500, Crete, Greece
⁴ Sciences Department & Photovoltaic Park, TEI of Crete, Heraklion, 71500, Crete, Greece

Corresponding author: kymakis@stef.teiher.gr

Received: 25 July 2006
Accepted: 12 October 2006
Published online: 10 January 2007

Abstract

High conductive and transparent thin films based on carbon nanotube – poly(3,4-ethylene-dioxythiophene)-poly(styrene sulfonate), PEDOT-PSS blends have been used to replace the conventional indium tin oxide (ITO) as the hole collecting electrode in organic photovoltaic cells. Using PEDOT:PSS as the host material, excellent dispersion of functionalized single wall carbon nanotubes can be achieved enhancing the polymer's conductivity, while maintaining its excellent optical transparency. Photovoltaic cells with Poly(3-hexylthiophene), P3HT and [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM as the electron donor and acceptor on respectively on polymer-nanotube substrates have been fabricated and characterized. A power conversion efficiency of 1.3%, with a fill factor of 0.4, an open-circuit voltage of 0.6 V and a short-circuit current of 5.6 mA/cm² under 100 mW/cm² white light illumination are reported. These values are close with the reference cells made on ITO glass substrates with the same device structure and fabrication process. The only drawback is on the fill factor which is considerably smaller due to the high resistance of the polymer-nanotube film. Nevertheless, the results indicate that the spin casted polymer-nanotubes thin films are a low cost alternative to ITO for organic electronics.