K. Podhájeckáa, O. Dammera, J. Pflegera
a Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského nám. 2, CZ-162 06 Praha 6, Czech Republic
The composite of P3HT and gold nanoparticles was prepared by in-situ reduction of tetrachloroauric acid, HAuCl4, by sodium borohydride in presence of poly(3-hexylthiophene-2,5-diyl), P3HT, and tetraoctylammoniumbromide. TEM images prove formation of Au nanoparticles with size distribution between 3 and 10 nm.
Electrical properties of P3HT/Au composite containing 1:1 P3HT/Au weight ratio were compared to those of pure P3HT. Measurements of thin films performed on a ceramic substrate with golden interdigital electrode indicate conductivity s=2.0×10-5 Scm-1 for both pure P3HT and P3HT/Au composite. This value corresponds to values given in literature for P3HT in its unintentionally doped form. The presence of Au nanoparticles below percolation threshold (5 vol. %) does not influence the electrical behavior within the rage of experimental limits.
The presence of Au nanoparticles however influences properties of sandwich structures. Films of thickness approx. 300 nm sandwiched between conductive transparent ITO and Al electrodes show the distinct behavior of the pure polymer and the nanocomposite. Pure P3HT behaves as a Schottky barrier photovoltaic device giving open circuit voltage Uoc=0.3V and short circuit current Isc=10-6 Acm-2 under white light illumination (P=20 mW/cm-2). On the other hand, the composite system containing Au nanoparticles does not show a diode behavior in the dark and no photocurrent appears under illumination. The Schottky barrier between composite layer and Al electrode is significantly decreased suggesting that the presence of Au nanoparticles modifies the interface between the conjugated polymer and Al electrode.