High contrast all-solid-state electrochromic device with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), heptyl viologen, and succinonitrile☆

Abstract A high contrast all-solid-state electrochromic device (ECD) is fabricated, using the device heptyl viologen (HV(BF 4 ) 2 ) as the cathodic coloring solution (electrochromic), 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as the anodic radical provider (ion-storage layer), and crystals of succinonitrile (SN)-plastic as the solid-matrix. The electrochemical and electrochromic properties of HV(BF 4 ) 2 and TEMPO molecules are analyzed from their individual perspectives in a 0.1 M electrolyte of tetrabutylammonium tetrafluoroborate (TBABF 4 ) in propylene carbonate (PC). A solid-matrix is prepared by mixing PC with SN (heated at 70 °C) at the volume ratio of 30/70 for PC/SN, and then mixing this content with 0.1 M TBABF 4 . Furthermore, 6 wt% silicon dioxide (SiO 2 ) nanoparticles are added to the matrix to eliminate its crystalline nature. This all-solid-state ECD made with this non-crystalline solid-matrix shows a high optical contrast with coloration efficiencies of ca. 65.5 and 342.2 cm 2 /C at 610 nm at two stages. The transmittance of the ECD at 610 nm can be changed reversibly from 80.7% (bleached) to 6.7% (darkened), with applied potentials of 0 and 1.5 V, respectively. Electrochemical and electrochromic properties of the ECD are verified using cyclic voltammetry (CV), in-situ potential-UV–vis absorption 3D spectra, and optical transmittance kinetic curves. ECDs with SN and all-solid-state electrolyte are shown at the stages of bleaching and darkening through their optical microscopic images.