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Lithium trapping as degradation mechanism of electrochromic properties of all-solid-state WO3//NiO device

Abstract

There has been keen interest for years in the research of all-solid-state transmittance-type electrochromic (EC) devices for their various applications especially in “smart windows”. A step forward has been taken in the successful preparation of full multilayered devices with enlarged optical contrast and fast switching response. However, a limited durability remains a severe issue. Upon cycling, EC devices suffer from decline of charge capacity as well as optical modulation while the detailed degradation mechanisms remain poorly understood. Here, we demonstrate unambiguous ion-trapping evidence to interpret the charge density decay of the EC device induced using various voltammetric cycling protocols, namely long term cycling and accelerated one. Pronounced comparable ion trapping occurs in cathodically colored WO3 films whatever the cycling procedure is, suggesting the existence of trapping “saturation” phenomenon. From second-ion-mass-spectroscopy analysis, the 7Li+/184W+ ratio in degraded WO3 films is more than 100 while it is almost zero in the as-prepared films. On contrast, for anodically colored NiO, a larger number of trapped cations is determined in the long-term cycled films than in the accelerated ones. In combination with x-ray-photoelectron-spectroscopy, variable bonding energies indicate the ions are trapped in different types of sites, depending on cycling procedure, and they can reside into the structural channels or break the network’ chains to form new chemical bondings, thus resulting in significant color difference. In addition, a clear upward trend in trapped Li concentration along with depth is observed. All our findings provide a deep insight into the degradation phenomenon taking place in electrochromic films as well as in full devices and offer valuable information for the understanding of micro mechanisms.

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Publication details

The article was received on 22 Mar 2018, accepted on 05 Aug 2018 and first published on 07 Aug 2018


Article type: Paper
DOI: 10.1039/C8TC01372A
Citation: J. Mater. Chem. C, 2018, Accepted Manuscript
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    Lithium trapping as degradation mechanism of electrochromic properties of all-solid-state WO3//NiO device

    D. Dong, W. Wang, A. Rougier, A. Barnabé, G. Dong, F. Zhang and X. Diao, J. Mater. Chem. C, 2018, Accepted Manuscript , DOI: 10.1039/C8TC01372A

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