Results of optical absorption spectroscopy during doping/undoping of poly(3,4-ethylene-dioxythiophene (PEDOT) acting as an electrode in a solid state electrochromic cell are presented. We found that PEDOT is well suited for applications in electrochromic displays. The change in optical absorption in the visible region is appropriate for a smart window and the required applied voltage is small (+/- 1.5 V). The switching time at room temperature, from fully coloured to fully bleached is about 4 s and the stability upon repeated switching is very good. We attempted to use in situ Raman spectroscopy for identification of the ions moving into and out of a PEDOT polymer electrode during electrochemical cycling. Unfortunately, the Raman signal from the conjugated material is strong enough to dominate the cell spectra, preventing the identification of the moving ions. But this also means that the solid state electrochemical cell can be used for in situ Raman studies on conjugated polymers during electrochemical doping.