Simultaneously measuring the electrical and optical response of electrochromic materials
Simultaneously measuring the electrical and optical response of electrochromic materials lead image
Electrochromic materials can adjust their optical properties in a reversible manner by means of an external electrical stimulus. For example, smart windows made with electrochromic materials can vary their optical transmission upon application of an electrical voltage. Such windows can save energy by reducing the need for climate regulation inside of a building.
A new article presents an experimental setup for simultaneously studying both the dynamic electrical and optical response of electrochromic materials. The method combines electrochemical impedance spectroscopy (EIS) and color impedance spectroscopy (CIS). The results of detailed test measurements on a tungsten oxide thin film demonstrate the versatility of the setup for investigating materials with voltage-modulated optical properties.
EIS, an often-used and well-understood technique, uses a small voltage oscillation as an excitation and measures the resulting oscillating current response. However, CIS, which measures the resulting oscillating optical response, is still in an early stage of development.
The researchers devised theoretical frameworks and a robust experimental setup for simultaneous EIS and CIS measurements. Tests were performed on amorphous tungsten oxide at different optical wavelengths and excitation voltage amplitude values. The researchers were able to estimate the uncertainty of the CIS technique for the first time, which is essential to judge the validity of the experimental data and make comparisons to theoretical models. For intercalation materials like tungsten oxide, the signal-to-noise ratio associated with CIS is too small at high frequencies but could be improved by the use of a variable-amplitude method.
Fundamental studies based on simultaneous EIS and CIS measurements may help unravel the coloration-charge dynamics in electrochromic systems and, as a result, lead to improvements in certain features of the technology.
Source: “Setup for simultaneous electrochemical and color impedance measurements of electrochromic films: Theory, assessment, and test measurement,” by Edgar A. Rojas-González and Gunnar A. Niklasson, Review of Scientific Instruments (2019). The article can be accessed at http://doi.org/10.1063/1.5115119 .
