Black to Transmissive Switching in a Pseudo Three-Electrode Electrochromic Device

We introduce the first π-conjugated polymer-based, black-to-transmissive and multicolored switching electrochromic device (ECD) constructed in a Pseudo 3-Electrode Electrochromic Device (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 diester-substituted poly(3,4-propylenedioxythiophene) (PProDOT-(CH 2 CO 2 C 12 H 25 ) 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-ethylenedioxythiophene (EDOT), 2-ethylhexyloxy-substituted 3,4-propylenedioxythiophene ProDOT-(CH 2 O(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 PProDOT-BTD in 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 state with color coordinates of L* = 75, a* = −7, b* = −7. The device has a high Michelson contrast of 0.8 (which can range from 0 to 1). Separate potential control over the electrodes allows color mixing 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.