PC 35

CHARACTERIZATION OF FLUORENE-THIOPHENE COPOLYMER LAYERS BY THE SURFACE PHOTOVOLTAGE METHOD

J. Toušek^a, P. Pavlačková^b, V. Cimrová^b

^aDepartment of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Prague 8, Czech Republic

^bInstitute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic

(tousek@karlov.mff.cuni.cz, cimrova@imc.cas.cz)

FIPT

The surface photovoltage (SPV) method was utilized for the photophysical study of thin polymer layers made of poly{[(9,9-dihexylfluorene-2,7-diyl)[3-(3-methylbutyl)thiophene-2,5-diyl]} prepared by spin-coating on ITO substrates. The SPV in a thin polymer layer is a result of dissociation of photogenerated free excitons in the electric field of the space charge region (SCR) which is created spontaneously at the surface. The photovoltage (PV) signal was measured between a transparent electrode capacitively coupled to the surface of the sample and the back ITO electrode. Photovoltaic spectra were measured for the illumination from both the free surface (SPV_fs) and ITO substrate (SPV_ITO) side and for various layer thicknesses. The SPV_fs spectrum differs from the SPV_ITO spectrum, which follows very well the absorption spectrum, whereas the maximum of SPV_fs spectrum is shifted to longer wavelengths. The thickness of the space charge region and the diffusion lengths were evaluated by fitting theory to the experimental data. The results are discussed also in relation to photoluminescence study of thin films.

We acknowledge the support of the Ministry of Education, Youth and Sports of the Czech Republic (grant No.1M06031) and of the Grant Agency of the Academy of Sciences of the Czech Republic (grant No. IAA4050409).