Factors that Determine the Length Scale for Uniform Tinting in Dynamic Windows Based on Reversible Metal Electrodeposition

Abstract

Dynamic windows based on reversible metal electrodeposition are attractive compared to conventional electrochromics because they can have neutral color, high contrast, and potentially lower cost, yet they are not nearly as developed, and the design rules for making them function at large scale are not presented in the literature. We model the voltage drops that occur in the transparent electrodes to get insight on how to obtain uniform electrodeposition of metals over large area. By optimizing the surface and density of the Pt nanoparticles used to nucleate metal growth, we lower the nucleation barrier for electrodeposition by 70 mV. We show that the growth rate of the metal films is determined by diffusion rather than reaction kinetics, which makes it possible to achieve uniform film deposition over a range of potentials from −300 to −700 mV. We demonstrate 100 cm2 dynamic windows that are color-neutral and tint uniformly from a clear state (>60%) to a dark state (<5%) in less than 1 min.

Reversible Metal Electrodeposition Devices: An Emerging Approach to Effective Light Modulation and Thermal Management

“…Therefore, bistability is necessary for RMEDs applied to smart windows. Excellent bistability was obtained in RMEDs based on Bi-Cu deposition, [25,26,28,34,39] and attempts have been made to improve the open-circuit stability of Agbased RMEDs to avoid unnecessary power consumption. [40][41][42][43] The idea of using RMEDs to modulate IR radiation was originally proposed in 2008.…”

“…[19,39,40,42,43] Another RME reaction at counter electrode is also reported. [8,25,26,34,53,54] It is easily noticeable that, to achieve reversible electrodeposition, the electrolyte solution must contain an appropriate reductive species (indicated by blue balls in Figure 2b), which remain stable after oxidation. Put differently, the corresponding oxidation product will not self-decompose and no gas is produced during the deposition process, as component decomposition and gas leakage will lead to an irreversible change to the electrolyte.…”

“…To improve the lattice matching of metals and ITO, Barile et al proposed a method that utilizes a self-assembled monolayer of Pt nanoparticles (NPs), as shown in Figure 4b. [8,25,26,85,86] As Pt itself is a metal that can be used as the seed for metal deposition, electrodeposited metal nuclei tend to form around these Pt NPs. In a 25 cm 2 device using Pb and Cu as the active metals, compared with the flower-shaped dendritic crystals deposited on an unmodified ITO electrode, uniform platelet crystals and a dense deposition layer were obtained on the Pt-modified ITO electrode.…”

“…Poor conductance leads to a considerable potential drop between the central and peripheral areas of the device. [26] To ensure that the deposition layer covers all the electrodes, a large operating voltage must be used, which may cause instability of the electrode, electrolyte decomposition, and nonuniform switching. 3.…”

“…The best performance reported for RMEDs are listed in Table 1.In the last century and the first decade of the 21th century, sustained efforts have been invested to apply the reversible electrodeposition mechanism to display devices. [19][20][21][22][23][24] In recent years, research on RMEDs has been progressing owing to their potential applications in energy-saving fields, especially in light modulation [8,[25][26][27][28] and thermal management. [18,29,30] Ag, Bi, and Cu are the most widely studied metals for reversible electrodeposition because of their high reversibility and the use of hazard-free electrolytes.…”