Multi-walled carbon nanotubes doping for fast and efficient hybrid solid state electrochromic device

Abstract

Overall performance of a polythiophene-ethyl viologen-based solid state electrochromic device has been improved by doping with multi-walled carbon nanotubes (MWCNTs) to exploit its ballistic transport capabilities. The finished hybrid (organic–inorganic) device is free from liquid electrolyte and shows the most efficient color switching with a very small bias and high color contrast while switching between magenta and blue color states. The MWCNTs have been synthesized using the simple pyrolysis method and doped in the viologen containing layer after proper characterization using x-ray diffraction, electron microscopy, and Raman spectroscopy. In situ UV-Vis spectroscopy has been used to quantify the performance of the device that works on the mutual redox-based mechanism of viologen-polythiophene layers. In situ Raman microscopy and spectroscopy have been used to establish the working mechanism duly validated by electrical I-V characteristics of the device. The simple doping process makes the device the most efficient one in the family of polythiophene-based devices. Overall, a liquid electrolyte less, power efficient solid state electrochromic device with a switching time of 1s/0.5 s, a coloration efficiency of 401 cm2/C, a contrast ratio of 79%, and a stability of more than 100 cycles has been achieved.