'total internal reflection' ?
The researcher's cells use iron oxide and tungsten oxide to do the light-capturing. Iron oxide absorbs visible light and tungsten oxide absorbs ultraviolet. Also tungsten oxide has a high refractive index. This means that light finds it hard to escape once it is inside a piece of tungsten oxide because it is bounced back and forth by a phenomenon called total internal reflection, increasing the chance it will be absorbed. p.78.Source:
Solar Cells: Tiny Balls of Fire, The Economist, June 28th-July 4th 2014, 411: 8893, 78-79.