Optical anisotropy in thin films of poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate)

Anisotropic optical constants spectrum of spin-coated thin films of poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate) (PEDOT-PSS) from 200 to 1700 nm were determined using variable-angle spectroscopic ellipsometry and polarized intensity transmission data together with absorption spectroscopy. PEDOT-PSS was found to be very anisotropic, uniaxial with the optic axis parallel to the surface normal. The result is in good agreement with results obtained of chemically polymerized PEDOT layers doped with toluenesulfonate. By adding sorbitol to the PEDOT-PSS dispersion before spin-coating, layers with a higher conductivity were obtained. A detailed study was made of the optical response of these layers in comparison to the PEDOT-PSS prepared from dispersions without sorbitol. The optical anisotropy is important to consider when using PEDOT-PSS in optoelectronic devices, such as polymer light-emitting diodes and photovoltaic devices. (C) 2002 Elsevier Science B.V. All rights reserved.