Hierarchical NiO microflake films with high coloration efficiency, cyclic stability and low power consumption for...

We have demonstrated that thin films of hierarchical NiO microflakes assembled from nanoleaves can be grown directly on FTO-coated glass substrates using a facile and template-free hydrothermal technique. This hierarchical structure holds the advantages of both nanometre-sized building blocks and microsized assemblies. Thus, the films exhibit highly enhanced electrochromic performances and cyclic stability due to their high surface area and good electrochemical stability. Moreover, a complementary electrochromic device combining the hierarchical NiO microflake film with a self-weaving WO3 nanoflake film is fabricated to further improve the electrochromic performance. As a result, the complementary electrochromic device shows a high optical modulation (73.2% at 550 nm), large coloration efficiency (146.9 cm(2) C(-1) at 550 nm by applying a low coloration voltage of -1.0 V) and fast switching responses with a coloring time of 1.8 s and a bleaching time of 3.2 s. It is also observed that there is no significant degradation of the electrochromic properties after 2000 continuous coloration/bleaching cycles, making it attractive for practical applications.