Optimization of Optical Properties of VO2 Films Through Manipulation of Periodic Structure (2015)

Undergraduate: Kasey Evans

Faculty Advisor: Rene Lopez
Department: Physics & Astronomy

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Heat lost through windows accounts for an estimated 15% of the 150,000 TWh of energy consumed annually in the US. To reduce this waste, our research group investigates passive VO2 window coatings that adaptively regulate the amount of heat that radiates through windows without the need of electrical power. VO2 is a thermochromic material: In response to heat, its optical properties change. Above room temperatures, VO2 reflects infrared (IR) light that would otherwise continue to undesirably heat an indoor environment. Below room temperatures, it transmits IR, helping to warm the indoors. The difference in IR reflectance between the two phases is referred to as IR modulation. Current approaches to utilizing VO2 window coverings poorly modulate IR light, heavily attenuate visible light transmittance, and appear orange. In response to this, we explore an aspect of the technology mostly ignored by other groups: films comprised of periodic arrays of VO2. Through the use of simulation software, we investigate the effects of various parameters of periodic arrays (such as periodicity, height, shape, and multiple layerings) on the IR modulation and visible transmittance of the films. Through this process, we design patterns which optimize the IR modulating affect while minimally impacting the visible light transmittance. We hope to present cheap, easily mass-produced, and highly functional VO2 coatings that can be retrofitted onto existing windows for the general consumer.