Electrochromic Metallo-Organic Nanoscale Films: Fabrication, Color Range, and Devices

In this study, we demonstrate a versatile approach for the formation of electrochromic nanoscale assemblies on transparent conductive oxides on both rigid and flexible substrates. Our method is based on the application of alternating spin-coated layers of well-defined metal polypyridyl complexes and a palladium(II) salt to form electrochemically addressable films with a high chromophore density. By varying the central metal ion of the polypyridyl complexes (Os, Ru, and Fe) and their ligands and by mixing these complexes, coatings with a wide range of colors can be achieved. These coatings cover a large area of RGB color space. The coloration intensities of these nanoscale films can be tuned by the number of deposition steps. The materials have very attractive ON/OFF ratios, electrochemical stabilities, and coloration efficiencies. Reversible color-to-colorless and color-to-color transitions were demonstrated, and the films were further integrated into sandwich cells.