Transparent Solid Polymer Electrolyte Thin Film Via Layer-By-Layer Deposition for Electrochromic Devices

Polymer solid-state ionic conducting materials are of high interests because of their great applied potential in flexible and wearable devices. Layer-by-Layer (LbL) deposition is a facile method to fabricate thin film with precise control of structures and functionalities. In this work, a new solid polymer thin film constructed by layer-by-layer deposition as Li⁺ ion conductor is presented. Unlike traditional polymeric LbL films, which usually involve two individual polymers as components, here we demonstrate a novel strategy for LbL assembly method by using poly(ethylene oxide) (PEO)-poly(acrylic acid) (PAA) and PAA-PEO complexes as building blocks. Compared with non-complexing polymers, polymeric complexes possess unique steric structures and interfacial behaviors, providing more possibilities to modulate the final structure and properties of the LbL film. We studied a series of LbL films-- PAA/PEO, PAA-PEO/PEO, PEO-PAA/PAA and PEO-PAA/PAA-PEO, investigating the growth kinetics and ionic conduction of those films. We found out that the polymeric complexes not only contributed to a fast growing behavior of LbL films, but also led to an improved ionic conductivity. We further present the use of PEO-PAA/PAA-PEO multilayers as solid electrolyte for a working electrochromic device.