Electrochromic devices incorporating an electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) film and a free standing, transparent film of a proton conducting polymer electrolyte with high ambient temperature ionic conductivity of 10(-2) S cm(-1) have been fabricated with and without the ion storage electrodeposited Prussian blue (PB) counter electrode layer. While coloration efficiency increases as a function of applied potential in the sole PEDOT device with largest values of CE(max,VIS) similar to 120 cm(2) C-1 and CE(max,NIR) similar to 133 cm(2) C-1 attained at V-c = -1.9 V, the PEDOT:PB device shows a digression from this trend. Much higher coloration efficiencies in the visible(247 cm(2) C-1 at 570nm) and NIR (116 cm(2) C-1 at 1100 nm) regions are achieved for the PEDOT:PB device at a relatively lower reducing voltage of -0.8 V. The PEDOT:PB device shows fast switching redox process (t(c) = 2.6 s and t(b) = 1.3 s for a 50% optical contrast at 632.8 nm) and a highly reversible charge density as the ratio of Q(inserted) to Q(extracted) was found to vary between 0.8 and 1.0. When switched between the clear and blue states for 2000 cycles, the insignificant drop in peak current density maxima observed for the PEDOT:PB device, i.e. the good cycling stability, the facile fabrication of device assembly, the ease of scaling LIP the electrolyte and electrochromic coatings, indicate that this method can be adapted as a simple and inexpensive alternative to conventional electrochromic windows with high cost components. (c) 2008 Elsevier Ltd. All rights reserved.