Oxidative-Reductive Near-Infrared Electrochromic Switching Enabled by Porous Vertically Stacked Multilayer Devices

Here, we demonstrate for the first time the ability ofa porous pi-conjugated semiconducting polymer film to enable facile electrolytepenetration through vertically stacked redox-active polymer layers,thereby enabling electrochromic switching between p-type and/or n-typepolymers. The polymers P1 and P2, with structuresdiketopyrrolopyrrole (DPP)-pi(bridge)-3,4,-ethylenedioxythiophene(EDOT)-pi(bridge) [pi(bridge) = 2,5-thienylfor P1 and pi(bridge) = 2,5-thiazolyl for P2] are selected as the p-type polymers and N2200 (a known naphthalenediimide-dithiophene semiconductor) asthe n-type polymer. Single-layer porous and dense (control) polymerfilms are fabricated and extensively characterized using optical microscopy,atomic force microscopy, scanning electron microscopy, and grazingincidence wide-angle X-ray scattering. The semiconducting films arethen incorporated into single and multilayer electrochromic devices(ECDs). It is found that when a p-type (P2) porous toplayer is used in a multilayer ECD, it enables electrolyte penetrationto the bottom layer, enabling oxidative electrochromic switching ofthe P1 bottom layer at low potentials (+0.4 V versus+1.2 V with dense P2). Importantly, when using a porous P1 as the top layer with an n-type N2200 bottomlayer, dynamic oxidative-reductive electrochromic switchingis also realized. These results offer a proof of concept for developmentof new types of multilayer electrochromic devices where precise controlof the semiconductor film morphology and polymer electronic structureis essential.

Automated summary

For the first time, we demonstrate the ability of a porous semiconducting polymer film to enable easy penetration of electrolyte through vertically stacked polymer layers, enabling electrochromic switching between different types of polymers. The fabricated films are extensively characterized and incorporated into single and multilayer electrochromic devices. These results provide a proof of concept for the development of new types of electrochromic devices with precise control over semiconductor film morphology and polymer electronic structure.