RESUMO
Electrochromic (EC) glass has the potential to significantly improve energy efficiency in buildings by controlling the amount of light and heat that the building exchanges with its exterior. However, the development of EC materials is still hindered by key challenges such as slow switching time, low coloration efficiency, short cycling lifetime, and material degradation. Metal doping is a promising technique to enhance the performance of metal oxide-based EC materials, where adding a small amount of metal into the host material can lead to lattice distortion, a variation of oxygen vacancies, and a shorter ion transfer path during the insertion and de-insertion process. In this study, we investigated the effects of niobium, gadolinium, and erbium doping on tungsten oxide using a single-step solvothermal technique. Our results demonstrate that both insertion and de-insertion current density of a doped sample can be significantly enhanced by metal elements, with an improvement of about 5, 4 and 3.5 times for niobium, gadolinium and erbium doped tungsten oxide, respectively compared to a pure tungsten oxide sample. Moreover, the colouration efficiency increased by 16, 9 and 24% when doping with niobium, gadolinium and erbium, respectively. These findings suggest that metal doping is a promising technique for improving the performance of EC materials and can pave the way for the development of more efficient EC glass for building applications.
RESUMO
The transport of both electrons and ions in organic mixed ionic and electronic conductors such as phthalocyanines, is essential to allow redox reactions of entire films and, hence, to impart electrochromism. Thin films of a new type, tetrakis-perfluoroisopropyl-perfluoro phthalocyanine, F40PcCu of different thicknesses were obtained via vapor deposition. The extent of the intermolecular coupling within the F40PcCu films established by van der Waals interactions was investigated by in situ optical spectroscopy during film growth. The transfer of electrons and diffusion of counter cations in these films, as well as their electrochromic performance were characterized by electrochemical and spectroelectrochemical measurements with an aqueous solution of KCl as electrolyte. A moderate degree of intermolecular interaction of the F40PcCu molecules in the solid state was observed, compared to non-fluoroalkylated perfluoro phthalocyanine, F16PcCu and octakis-perfluoroisopropyl-perfluorophthalocyanine, F64PcCu, which exhibit stronger and weaker coupling, respectively. The replacement of F by perfluoroisopropyl is, thereby, established as a valuable approach to tune this coupling of chromophores and, hence, the transport coefficients of electrons and ions in the solid films. Reversible changes of the films upon reduction and intercalation of K+ counter ions and re-oxidation and expulsion of the counter ions were confirmed by simultaneously measured optical absorption spectra. Thin films of F40PcCu showed a well-balanced, equally fast transport of electrons and ions. The films provided a fast and reversible switching process over at least 200 cycles indicating the stability of these materials.
