Highly Transparent Conjugated Polymer as the Counter Electrode in Electrochromic Smart Windows

Abstract

mirrors, [2] electronic paper, [3] spacecraft thermal control, [4] and military camouflage, [5] etc.Generally, there are five functional layers in one electrochromic device (ECD): two conductive layers, one electrochromic layer, one electrolyte layer, and one counter electrode layer (i.e., the ion storage layer). Among those, the electrochromic layer is responsible for the color transformation. The counter electrode layer coordinates the redox reaction of the electrochromic layer, storing the counter ions to achieve the charge balance concurrently. [6,7] Therefore, the counter electrode layer plays an essential role in the optical performance and long-term stability of ECDs. Compared to the mature research on electrochromic materials, [8] counter electrode materials (CEMs) have been largely ignored. Due to the very limited options for CEMs, many reported works just simply use bare tin-doped indium oxide (ITO), without a counter electrode layer, when evaluating electrochromic materials in a device set-up. This is a simple way to construct an ECD, whereas, the redox process of ITO is irreversible, leading to serious degradation in its conductivity and transparency, [9] which makes it unsuitable for the industrial application of ECDs.

Recent advances in electrochromic materials and devices for camouflage applications

“…The ion storage layer functions as a counter electrode layer, undergoing reversible electrochemical oxidation (reduction) to coordinate the reduction (oxidation) of the EC material to balance the charge shuttling from the EC layer through the electrolyte. [45][46][47] The electrolyte layer sits in the center of the device, which can separate the EC layer and ion storage layer to prevent direct electrical contact and transport ions inside the device. 48 Substrates and conducting layers as conductive electrodes which determine the mechanical properties of the devices are commonly discussed together.…”

“…The result demonstrated that the device retained the color switching of EC materials while also showing high longterm durability (95% retention of the contrast after 3300 steps), fast response time (less than 4 s) and excellent coloration efficiency. In addition, other colorless ionic storage layers, such as inorganic oxides, 129,130 poly(2,2,6,6-tetramethylpiperidinyloxy-4-ylmethacrylate) (PTMA) derivatives, [131][132][133] and conjugated polymers, 43,46 could also be applied to camouflage devices. Notably, the matched electroactive voltage window of the ion storage material and the EC material is also a major influence on device performance.…”

“…However, the irreversibility of ITO redox leads to a large driving voltage and poor stability of the device. 46 This makes it unsuitable for industrial applications of EC camouflage devices.…”

Hydrogen‐Bonding Induced Crosslinked Polymer Network for Highly Stable Electrochromic Device and a Construction Strategy for Black‐Bilayer Electrochromic Film

“…Conjugated polymers are an attractive class of electrochromic materials owing to their easily modified structure, tunable bandgaps, and facile optical properties. [1][2][3] Solution-processable conjugated polymers are likely to play an important role in DOI: 10.1002/smll.202303359 low-cost and large-scale production of electrochromic materials, which is of great value in their practical applications. [4,5] Conventionally, the introduction of solubilizing groups (such as long alkyl chain or alkoxy chain) is a necessary and common method to obtain solution-processable polymers.…”

Dual Polymer Complementarity Induced Truly Black Electrochromic Film and the Construction of Intelligent Eye-Protection Filters

“…As a new generation of electrochromic (EC) materials, conjugated polymers are widely used for their fast switching time, high contrast, and coloration efficiency, as well as easy structural modification, providing a broad platform for designing and preparing high-performance electrochromic materials. − Solution-processable conjugated polymers have important applications in low-cost, large-scale production of electrochromic materials. − Black-to-transparent solution-processable conjugated polymers are a special and rare class of materials used in reflective and transmissive electrochromic devices, including user-controlled protective eyewear, dimmable windows, and electronic paper, which have received much attention in the field of electrochromic materials. − …”