Ageing of an electrochromic device, especially of the electrolytic layer
Final Report Abstract
Electrochromic systems (ECDs) are characterized by the fact that their optical properties (transmittance and/or reflection) can be reversibly changed by an electrical voltage, which makes them interesting for applications where incident radiation (light/heat) is to be regulated (e.g. building and vehicle glazing, eye protection). Depending on the application, this can increase comfort (blinds) and/or reduce energy consumption (cooling), as well as the number of components (additional shading). By manufacturing ECDs on plastic substrates (film/plate) and further processing them in plastic processing operations (film back injection, thermoforming) to 3D-molded and, compared to glass-based ECDs, lightweight and low-cost products, on the one hand the application range of ECDs can be extended (e.g. ski goggles, visors, vehicle glazing), on the other hand a significant cost reduction can be achieved, since these are established, automatable and scalable manufacturing processes. Furthermore, a certain type (battery type) can be manufactured as a multilayer system with coating processes suitable for large-scale production (e.g. slot die and doctor blade coating) (except for the most commonly used ITO current collector layer). Extensive aging tests were carried out on such a layer structure, consisting of polycarbonate film as substrate, current collector layers made of ITO, a working and counter electrode made of PEDOT:PSS and TiO2, respectively, which are connected via a polymer electrolyte, focusing on the electrolyte. This shows elastomeric behavior due to its wide-mesh crosslinking polyurethane matrix and is suitable for the aforementioned processing methods due to its mechanical strength and deformability. First, the ECD, the working and counter electrode and the electrolyte were characterized in detail with regard to their properties. Major findings of the following aging investigations are that the solvent propylene carbonate is not suitable, that the susceptibility to cracking/brittleness of the ITO layer on polycarbonate film under thermal and mechanical stress is problematic considering the conditions in processing operations, and that the ECD exhibits a fast switching time and a high transmittance in the bright state at low voltages, but only a moderately stable switching behavior under dry argon atmosphere and a loss of function in normal climate already after a short time. An adapted layer system is realized in which the ITO is replaced by a polymeric and thermomechanically resistant current collector layer, the solvent is substituted by ionic liquid, and a Prussian Blue counter electrode is used. The cycling resistance under air atmosphere before and after four weeks of storage at normal climate is shown for a demonstrator (145 cm²). The layer system also allows further processing by back injection molding to form a compact component.
Publications
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Polyurethane-Based Gel Electrolyte for Application in Flexible Electrochromic Devices. Polymers, 14(13), 2636.
Johannes, Christopher; Hartung, Michael & Heim, Hans-Peter
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Back Injection Molding of Electrochromic Multilayer Films on Polycarbonate Substrates. Material Research Society, Spring Meeting, San Francisco
Johannes, C.
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Flexible Electrochromic Device on Polycarbonate Substrate with PEDOT:PSS and Color-Neutral TiO2 as Ion Storage Layer. Polymers, 15(9), 1982.
Johannes, Christopher; Macher, Sven; Niklaus, Lukas; Schott, Marco; Hillmer, Hartmut; Hartung, Michael & Heim, Hans-Peter
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The Influence of Thermal and Mechanical Stress on the Electrical Conductivity of ITO-Coated Polycarbonate Films. Polymers, 15(11), 2543.
Johannes, Christopher; Lins, Fabian; Meyer, Miriam; Hartung, Michael & Heim, Hans-Peter
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Weathering of a Polyurethane-Based Gel Electrolyte. Polymers, 15(6), 1448.
Johannes, Christopher; Hartung, Michael & Heim, Hans-Peter
