Synthetic Metals 161 (2011) 1105–1112 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Limitations of dual and complementary inorganic–organic electrochromic device for smart window application and its colorimetric analysis S.S. Kalagi a , S.S. Mali b , D.S. Dalavi b , A.I. Inamdar c , Hyunsik Im c , P.S. Patil b,∗ a G.S.Sc. College, Belgaum, Karnataka 590006, India b Thin Film Materials Laboratory Shivaji University, Kolhapur 416004, India c Department of Semiconductor Science, Dongguk University, Seoul, South Korea article info Article history: Received 21 January 2011 Received in revised form 18 March 2011 Accepted 25 March 2011 Available online 6 May 2011 Keywords: WO3 PANI IOECD Thin films Colorimetric Limitations abstract Inorganic tungsten oxide (WO 3 ) and organic polyaniline (PANI) films were used as the cathodic and anodic electrodes of an inorganic–organic electrochromic device (IOECD). WO 3 was deposited by sputtering while PANI films were electrodeposited on transparent Indium doped Tin Oxide (ITO) glass substrates, respectively. Optical and electrochemical studies were performed to find the optical attenuation, col- oration efficiencies, reversibility and response time separately for the individual films as well as for the assembled IOECD. The change in transmittance of WO 3 film was found to be 63.92%. PANI film showed an optical attenuation of 50.69% while the transmission change through the IOECD was equal to 57%. Colorimetric analysis was done to define the colors in the bleached and colored states in terms of L*ab values and xy chromaticity diagram. Factors limiting the performance of an IOECD were analyzed. It was found that in a charge unbalanced dual complementary IOECD, the coloration efficiency is always less than that of one of the constituent electrodes. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Electrochromism is defined as a reversible and visible change in the transmittance or reflectance of a material as a result of electro- chemical oxidation or reduction. The property of electrochromism can be found in a variety of organic and inorganic materials and conducting polymers. The radical change in the optical absorp- tion spectrum of conducting polymers upon doping and inorganic materials on the insertion/extraction of ions makes these materials prime candidates for the construction of electrochromic devices. Of all electrochemical reactions entailing at least some visible change at the electrode, only a limited number of them are of sufficient intensity to be useful in devices, and a lower limit of color change or contrast specified to define usefulness could limit those described as electrochromic. While a system showing only changes of color is technically electro chromic, one of the states evoked in most applications needs to be a colorless one, though a weak yellow often suffices [1]. Significant effort has been put forth on elec- trochromic devices based on inorganic electrochromic materials and organic conducting polymers. Hybrid organic/inorganic mate- rials in general represent the natural interface between two worlds of material science. The main challenge is managing to synthe- ∗ Corresponding author. Tel.: +91 231 2609229; fax: +91 231 2691533. E-mail addresses: psp phy@unishivaji.ac.in, icnama2008@gmail.com (P.S. Patil). size inorganic–organic hybrid combinations that keep or enhance the best properties of each of the components while eliminating or reducing their particular limitations. Undertaking this challenge provides an opportunity for developing new materials and devices with synergic behavior leading to improved performance or to new useful properties. Indeed, hybrid materials frequently involve a combination of components that have been thoroughly studied in their respective fields but provide an additional dimension to their properties in becoming part of the hybrid compound/device. Environmental friendly production and energy economization are the new areas drawing world’s attention. With this, the demand for energy savings in buildings will increase in the coming years. Windows that are able to dynamically control the solar radiation throughput will play an important role. Such windows play an important role in controlling the thermal conditions by reducing the winter heating and summer cooling requirements [2–5]. How- ever, while designing such windows, a number of factors that play a detrimental role in the optimum performance of the device need to be addressed. This underlines the need of detailed study of each individual component of the working device. These factors include the electrochemical, thermal and at rest stabilities in order to real- ize successful electrochromic systems. Czanderna and Lampert [6] have reported about the electrochemical and thermal issues. Ho [7] has addressed the problems of at rest stabilities in detail for a num- ber of devices. However to our knowledge, no one has addressed the limitations of such devices with respect to the colorimetric aspect. 0379-6779/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2011.03.028