Abstract
Improving the modulation depth and switching speed of electrochromic devices is important for expanding the field of electrochromic functional materials applications. The previous study demonstrates that semiconducting (SC-) single-wall carbon nanotube (SWNT) thin film based electrochromic cells with ionic liquid as the electrolyte and metallic (MT-) SWNT counter electrode can operate with fast switching times in the millisecond range. However, achieving a high modulation depth requires an increasing thickness of the electrochromically active SC-SWNT layer resulting in a slowdown of the switching time by more than order of magnitude. Here it is reported that milliseconds range switching time can be restored by increasing the thickness of MT-SWNT thin film counter electrode thus matching the electrochemical capacitances of the two sides of the electrochromic cell while reaching a high modulation depth of 20 dB and high coloration efficiency exceeding 1800 cm(2) C-1 at an infrared wavelength of 1770 nm. The results are interpreted in terms of considering the SWNT cell as a supercapacitor with two connected in series electric double layer 3D capacitors associated with two opposing SWNT electrodes.