Bifunctional Application of Viologen-MoS₂-CNT/Polythiophene Device as Electrochromic Diode and Half-Wave Rectifier

A dual purpose solid state electrochromic diode has been fabricated using polythiophene (P3HT) and ethyl Viologen (EV), predoped with multiwalled carbon nanotubes (MWCNTs) and MoS₂. The device has been designed by considering two important aspects, first, the complementary redox activity of P3HT and EV and second, the electron holding properties of MoS₂ and MWCNTs. The latter is found to enhance the electrochromic performance of the solid state device. On the other hand, the complementary redox nature gives the asymmetric diodic I-V characteristic to the device which has been exploited to use the electrochromic device for rectification application. The MoS₂ nanoflower and MWCNTs are synthesized by one-step hydrothermal and pyrolysis techniques and well characterized by scanning electron microscopy (SEM), X-ray analysis (XRD), and Raman spectroscopy. Electrochromic properties of the device have been studied in detail to reveal an improvement in device performance in terms of faster speed and high coloration efficiency and color contrast. In situ bias-dependent Raman spectroscopy has been performed to understand the operation mechanism of the electrochromic diode which reveals (bi-)polaron formation as a result of dynamic doping eventually leading to color change. A half-wave rectifier has been realized from the electrochromic diode which rectifies an AC voltage of frequency 1 Hz or less making it suitable for low frequency operation. The study opens a new possibility to design and fabricate multipurpose frequency selective electrochromic rectifiers.