Nanostructured electrochromic and photoelectrochemical materials and devices

Nanostructured tungsten oxide (WO 3 ) and hydrated tungsten oxide (WO 3 •H 2 O) films were assembled on fluorine doped tin oxide (FTO) coated glass substrates by seed-assisted hydrothermal methods.Plate-like, brick-like and sticklike nanostructured WO 3 or hydrated WO 3 films were obtained by using sodium sulfate (Na 2 SO 4 ), ammonium sulfate ((NH 4 ) 2 SO 4 ) and ammonium acetate (CH 3 COONH 4 ) as capping agents, respectively.The electrochromic (EC) characteristics of the as-prepared films were investigated in single EC layer devices and complementary EC devices with Prussian blue (PB) as the counter electrode.Compared to the films without capping agent, the plate-like nanostructured 3WO 3 •H 2 O film grown with Na 2 SO 4 shows significantly improved EC performance.A high coloration efficiency value of 112.7 cm 2 C -1 at 632.8 nm is obtained, and the response time for 90% transmittance changes is found to be 4.3 s for coloration and 1.4 s for bleaching for a sample size ~2 cm 2 (FTO sheet resistance:15 Ω/□), respectively, while the brick-like monoclinic WO 3 film displays a comparable switching response of t c ,90% = 272 s and t b, 90% = 364 s (sample size ~2 cm 2 , FTO sheet resistance: 15 Ω/□) and a coloration efficiency of 38.2 cm 2 C -1 at 632.8 nm.Both films show adjustable transmittance modulation under different voltages and a good reversible coloration/bleaching stability.The single layer EC devices based on these films demonstrate promising applications in smart windows and large-area information displays.