Electrochromic supercapacitor electrodes based on viologen-derived cross-linked thin films

Abstract

Viologens are an important class of materials in organic electrochromic technology due to their n-type semiconductor properties and the high color intensity in their radical cation state. Due to their charged structures, viologens are generally ideal molecules for gel-based organic electrochromic devices, but with specific modifications, they can also be employed in thin-film-based electrochromic devices (ECDs). In this study, crosslinking reactions of viologen-based molecules (ALV-X) with various allyl group-containing counterions were conducted on ITO/Glass surfaces in the presence of a tetra-thiol-based crosslinker. The surface roughness of the resulting films varied from 4.64 nm to 8.46 nm depending on the counterion exchange. Electrochemical characterizations of the prepared viologen-based crosslinked electrodes indicated that the LUMO energy levels ranged between −4.267 eV and −4.297 eV. Viologen-based cross-linked thin films with transmittance changes close to 30 % in the visible region, 50 % in the UV region and 20 % in the NIR region with specific capacitances of 0.25 mF cm⁻² have been found to be highly suitable materials, especially as cathodic layers in electrochromic/supercapacitor devices.