Black to transmissive switching in a Pseudo three-electrode electrochromic device

Abstract

We introduce the first π-conjugated polymer-based, black-to-transmissive and multicolored switching electrochromic device (ECD) constructed in a Pseudo 3-ElectrodeElectrochromicDevice (P3-ECD) architecture. In this ECD, the non-electrochromic, yet electroactive, polymer poly(3,4-propylenedioxypyrrole-N- propionitrile) (PProDOP-N-EtCN) serves as a counter electrode material.This transmissive polymer helps eliminate the contrast limitations seen in dual polymer ECDs that use combinations of anodically and cathodically coloring polymers. The P3-ECD adds colors by transmitting light through two independently controlled working electrodes (coated with two different electrochromic polymer films) and two counter electrodes (coated with PProDOP-N-EtCN) stacked together with a gel electrolyte. The two cathodically coloring EC polymers that were used in this work are, a diestersubstituted poly(3,4-propylenedioxythiophene) (PProDOT-(CH2CO2C12H25) 2) for the first one, namely PProDOT-ester, and a donor-acceptor analogue, namely PProDOT-BTD, which consists of a specific alternation of donor and acceptor building units spanning the electron-rich 3,4-thylenedioxythiophene (EDOT), 2-ethylhexyloxy-substituted 3,4-propylenedioxythiophene ProDOT-(CH 2O(2-EtHx))2 and the electron-deficient 2,1,3-benzothiadiazole (BTD). The PProDOT-ester switches from a deep purple (L* = 41 a* = 22 b* = -48) to a highly transmissive gray/blue (L* = 87 a*=-2 b*=-7),while the PProDOT-BTD switches from a deep green (L*=60, a*=-23, b*= 12) to transmissive sky blue (L*=84, a*=-4, b*=-6). Utilizing PProDOT-ester and PProDOTBTDin their neutral form in the P3-ECD yields a deep blue-black with color coordinates of L*=26 ,a* =-3, b*=-17 switching to a transmissive statewith color coordinates of L*=75, a*=-7, b*=-7. The device has a highMichelson contrast of 0.8 (which can range from0 to 1). Separate potential control over the electrodes allows colormixing of the polymers in intermediate oxidation states in the P3-ECD. As such, a full palette of colors is accessible through proper choice of EC materials as desired for the construction of multicolored information displays, and in the case of black-to-transmissive electronic paper. © 2009 American Chemical Society.