A WO3-poly(butyl viologen) layer-by-layer film/ruthenium purple film based electrochromic device switching by 1 volt application

Abstract

A layer-by-layer (LbL) assembly of poly(butyl viologen) (PBV) and poly(peroxotungstate) was used for preparing a cathodically coloring dual electrochrome WO3-PBV film. A new formulation containing ferrocenecarboxaldehyde and potassium hexacyanoruthenate(II) was employed for the first time and anodically coloring ruthenium purple (RP) thin films were electrodeposited. X-ray photoelectron spectroscopy and Fourier transform infrared analyses confirmed the RP film structure to be an inorganic coordination polymer: K-x center dot Fe-x(III)[Ru-II(CN)(6)](y), wherein Fe3+ and Ru2+ color centers are flanked by CN- ligands. Nanoscale electrical conductivities determined by conducting atomic force microscopy were deduced to be 1.03 and 147.4 mS cm(-1), for the RP and WO3-PBV LbL films respectively, which confirmed their ability to function as mixed conductors, attributes pertinent during optical switching. Reversible bias induced transition between purple and colorless hues was attained in the RP film and between deep blue and colorless states was achieved for the WO3-PBV LbL film with coloration efficiencies of 188 and 380 cm(2) C-1 respectively. A complementarily coloring electrochromic device of WO3-PBV/RP was fabricated with an environmentally benign, inexpensive aqueous electrolyte, which switched between blue, purple, and colorless states. The device exhibited an electrochromic efficiency of 476 cm(2) C-1 at 580 nm, an outstanding transmission modulation of 49%, and short switching times (similar to 1 s); all under remarkably low operating voltages of +/- 1V. The WO3-PBV/RP device can deliver high optical contrast under low operating bias, and is highly scalable and durable, which demonstrates it to be ideal for practical optical switching devices like fast changing displays or smart windows. (C) 2014 Elsevier B.V. All rights reserved.