Improving the contrast of all-printed electrochromic polymer on paper displays

PEDOT:PSS-based electrochromic displays have been explored for manufacture on flexible paper substrates in roll-to-roll printing presses at high volumes and low costs. Here, we report the improvement of the optical contrast of such devices by adding an extra layer of a dihexyl-substituted poly(3,4-propylenedioxythiophene) (PProDOT-Hx2) to complement the optical absorption spectrum of PEDOT: PSS. The oxidized state of PProDOT-Hx2 is highly transparent and is an intense magenta color while in the reduced state. By adding a layer of PProDOT-Hx2 directly on top of PEDOT: PSS, we were able to improve the optical contrast by nearly a factor of two. In this report, we present optical and electrochemical data of PProDOT-Hx2/PEDOT: PSS-based electrochromic paper displays and compare their performance with PEDOT: PSS-only equivalents.