A High Contrast Hybrid Electrochromic Device Containing PEDOT, Heptyl Viologen, and Radical Provider TEMPO

An anodic radical provider, 2,2,6,6-tetramethyl-1-piperidinyloxy ͑TEMPO͒, and two electrochromic ͑EC͒ materials, poly͑3,4-ethylenedioxythiophene͒ ͑PEDOT͒ and heptyl viologen ͓HV͑BF 4 ͒ 2 ͔, were utilized to fabricate a hybrid electrochromic device ͑ECD͒.PEDOT and HV͑BF 4 ͒ 2 were used as film and solution-type cathodic EC materials, respectively.The ECD exhibited two-stage redox reactions with high absorbance attenuation in the visible region.With the variation in the operating voltage, a maximum transmittance change ͑⌬T͒ of 20% at 610 nm was observed in the first stage ͑Ϫ0.5 to 0.8 V͒, whereas a maximum ⌬T of 68% was observed in the second stage ͑0.8-1.5 V͒.Furthermore, fast switching times of 6.9 and 2.1 s were estimated for bleaching and darkening, respectively.The coloration efficiencies at 610 nm were 171.9 and 91.0 cm 2 C -1 for the first and second stages, respectively.