A transparent−green−blue electrochromic device based on 2, 2, 6, 6−tetramethyl−1−piperidinyloxy (TEMPO), polyaniline, and HV(BF4)2

Abstract A novel hybrid type electrochromic device (ECD) was fabricated, using a stable radical provider, 2,2,6,6−tetramethyl−1−piperidinyloxy (TEMPO) and two electrochromic (EC) materials, polyaniline (PANI) and heptyl viologen (HV(BF 4 ) 2 ). The PANI thin film and HV(BF 4 ) 2 solution were chosen as anodically and cathodically coloring materials, respectively. The TEMPO was selected to act as the anion storage species in pair with either of the electrochromic material. This type of assembly thus formed two electrochromic systems in one device, i.e., TEMPO−HV and TEMPO−PANI. The electrolyte for the ECD was composed of 0.1 M TEMPO, 0.05 M HV(BF 4 ) 2 , 0.1 M TBABF 4 , and 1.0 mM HClO 4 in propylene carbonate (PC), and was placed in between two ITO glasses. By varying the operating voltage between 0 and 1.5 V, the TEMPO−HV system showed a transmittance change (ΔT) of 46.2% at 550 nm. By varying the operating voltage between 0 and −1.0 V, the TEMPO−PANI system showed a ΔT of 45.5% at 700 nm. The complete system activation (both TEMPO−HV and TEMPO−PANI) was achieved by setting the operating voltage between −1.0 and 1.5 V, obtaining a ΔT of 53.3% at 550 nm. The estimated switching times for the total system were 3.1 and 3.4 s for bleaching and darkening, respectively. The coloration efficiencies of the ECD at 700 and 500 nm, for the green to blue transition, were 159.7 and 169.2 cm 2 C -1 , respectively, while 88.8 and 23.5 cm 2 C -1 for the transparent to green transition. The proposed hybrid ECD was characterized by cyclic voltammetry (CV), UV–Vis absorbance spectra, dynamic transmittance curves, and long-term stability test.