Electrochromic Performance of Silver Nanowires Based Transparent Electrode Films: an Approach to ITO-Free Electrochromic Devices

Transparent electrodes (TE) have been widely studied as a key component of many optoelectronic devices such as solar cells, flexible light-emitting devices, transparent heaters and smart windows. Currently, indium tin oxide (ITO) is extensively used as transparent electrode for these devices owing to its high transparency, electrical conductivity and chemical stability. However, the scarcity of indium, the expensive deposition method and brittleness of ITO prompted the search for new flexible, stable and low-cost TEs. Silver nanowire (AgNW) networks appear as a promising alternative thanks to their high optical transparency, excellent electrical properties and mechanical flexibility [1], and are indeed gaining much attention in the last years. In order to improve the integration of AgNW networks into industrial devices, their stability against electrical and/or thermal stresses needs to be enhanced. One of the applications of TE is smart windows that have attracted great attention due to their potential applications in energy-efficient devices. Thanks to electrochromic materials that can alter their transparency as a response to an electrical input, [2] smart windows can decrease the need for energy-intensive heating or air conditioning in buildings. Strong direction of improvement in ECDs consists of replacing the commonly used ITO as transparent electrode with a flexible TE. In this context, AgNW networks are promising candidates however, their stability to oxidation and corrosion in electrolyte remains a key issue for the application. Moreover, the method and experimental conditions of electrochromic oxide deposition on AgNW networks also influence the stability of AgNW networks.<br/>The aim of the present work is to prepare ITO-free electrochromic devices using stable AgNW networks as TE. The network is deposited through spray-coating on transparent glass substrates. To overcome the instability issues, AgNW networks are coated with a thin conformal protective oxide layer using atmospheric pressure spatial atomic layer deposition [3]. The influence of post deposition treatment on the properties and stability of AgNW networks are discussed. The electrochromic oxide is deposited through radio frequency magnetron sputtering (RFMS) technique and the electrochromic performance is determined through cyclic voltammetry and chronoamperometric characterizations. The performance of AgNW based electrochromic film is compared with the ITO based electrochromic film.<br/><b>References:</b><br/>1. Muñoz-Rojas, D., et al., <i>Spatial Atomic Layer Deposition (SALD), an emerging tool for energy materials. Application to new-generation photovoltaic devices and transparent conductive materials.</i> Comptes Rendus Physique, 2017. <b>18</b>(7-8): p. 391-400.<br/>2. Mjejri, I., et al., <i>Crystallized V₂O₅ as oxidized phase for unexpected multicolor electrochromism in V₂O₃ thick film.</i> ACS Applied Energy Materials, 2018. <b>1</b>(6): p. 2721-2729.<br/>3. Khan, A., et al., <i>Stability enhancement of silver nanowire networks with conformal ZnO coatings deposited by atmospheric pressure spatial atomic layer deposition.</i> ACS applied materials & interfaces, 2018. <b>10</b>(22): p. 19208-19217.