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

A high contrast all-solid-state electrochromic device (ECD) is fabricated, using the device heptyl viologen (HV(BF4)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(BF4)2 and TEMPO molecules are analyzed from their individual perspectives in a 0.1 M electrolyte of tetrabutylammonium tetrafluoroborate (TBABF4) 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 TBABF4. Furthermore, 6 wt% silicon dioxide (SiO2) 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 cm2/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.

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► A high contrast all-solid-state electrochromic device (ECD) is studied.
► This ECD is based on 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and heptyl viologen (HV).
► Silicon oxide (SiO2) is used for eliminating the dendrites of succinonitrile (SN).
► The proposed ECD shows high transmittance variation from 80.74% to 6.71% at 610 nm.
► A high coloration efficiency of 342.2 cm2/C at 610 nm is achieved.