RESUMO
Inorganic electrochromic (EC) materials, which can reversibly switch their optical properties by current or potential, are at the forefront of commercialization of displays and smart windows. However, most inorganic EC materials have challenges in achieving multicolor tunability. Here, we propose that the Burstein-Moss (BM) effect, which could widen the optical gap by carrier density, could be a potential mechanism to realize the multicolor tunable EC phenomenon. Degenerated semiconductors with suitable fundament band gaps and effective carrier masses could be potential candidates for multicolor tunable EC materials based on the BM effect. We select bulk Y2CF2 as an example to illustrate multicolor tunability based on the BM effect. In addition to multicolor tunability, the BM effect also could endow EC devices with the ability to selectively modulate the absorption for near infrared and visible light, but with a simpler device structure. Thus, we believe that this mechanism could be applied to design novel EC smart windows with unprecedented functions.
RESUMO
Novel electrochromic (EC) materials were developed and formed by a two-step chemical deposition process. First, a self-assembled monolayer (SAM) of 2,2':6',2â³-terpyridin-4'-ylphosphonic acid, L, was deposited on the surface of a nanostructured conductive indium-tin oxide (ITO) screen-printed support by simple submerging of the support into an aqueous solution of L. Further reaction of the SAM with Fe or Ru ions results in the formation of a monolayer of the redox-active metal complex covalently bound to the ITO support (Fe-L/ITO and Ru-L/ITO, respectively). These novel light-reflective EC materials demonstrate a high color difference, significant durability, and fast switching speed. The Fe-based material shows an excellent change of optical density and coloration efficiency. The results of thermogravimetric analysis suggest high thermal stability of the materials. Indeed, the EC characteristics do not change significantly after heating of Fe-L/ITO at 100 °C for 1 week, confirming the excellent stability and high EC reversibility. The proposed fabrication approach that utilizes interparticle porosity of the support and requires as low as a monolayer of EC active molecule benefits from the significant molecular economy when compared with traditional polymer-based EC devices and is significantly less time-consuming than layer-by-layer growth of coordination-based molecular assemblies.