Antireflective (AR) coatings have a wide array of applications like glare reduction on eyeglasses, smart-phone display, and computer monitors. Researchers at Penn State have newly developed an anti-reflective coating that improvises existing coating to such an extent that it can turn transparent plastics like Plexiglas practically invisible. Chris Geibink, an associate professor at Penn State, said that the discovery was made while trying to create high-efficiency solar panels. The process involved concentrating light using plastic lenses on small and highly efficient solar cells. Reducing reflection loss was essential.
The research group wanted an AR coating that would work well at multiple angles and over the entire solar spectrum as the sun crossed the sky. The team also wanted a coating that can withstand various weather conditions for over a long period. The research team would have made use of an off-the-shelf solution, but there was not any solution that met their requirements, and this led to innovation.
It is easier to make a solution that would eliminate reflection at a particular wavelength, angles or direction but the coating never fulfilled the required criteria. Eyeglass coating cannot be used because it is pointed towards the narrow visible portion of the spectrum. A solar spectrum is five-time broader as visible spectrum, so eyeglass coating would not perform well for a concentrating solar cell system. Reflections happen when light travels from one medium to another. The difference in refractive index will determine how fast the light can travel from one medium to another. For air, the refractive index is 1 and plastic has a refractive index of 1.5 so when the reflection would be significantly higher.
Natural coating materials like Teflon or magnesium fluoride have a refractive index of 1.3 this can be slowly varied to 1.5 by blending various materials. The team discovered a new process, they made use of sacrificial molecule to form nanoscale pores in Teflon, therefore, conceiving a graded index Teflon-air film that deceives light into seeing a transition from 1 to 1.5, eliminating all reflections.