Waveguide-Imprinted Slim Polymer Films: Beam Steering Coatings for Solar Cells

We report that transparent polymer coatings imprinted with tilted planar waveguides significantly reduce optical loss caused by the scattering of incident light by front metal contacts of solar cells. A periodic array of planar waveguides oriented at specific angles with respect to the film's surface normal efficiently captures and steers incident light away from contacts and, in this way, suppresses scattering. These beam steering films are fabricated in a single, room temperature step by self-trapped incandescent beams. The beams inscribe multimode planar waveguides oriented at angles ranging from 0° to 2.7° inphotopolymerizable epoxide resin. We characterized the microstructural and optical properties of the films and demonstrated their ability to deflect incident white light, comparable to sunlight, by as much as 180 μm. Solar cells coated with beam steering films showed significant enhancements in external quantum efficiency (EQE) of up to 4.42% relative to unstructured films. This first demonstration of waveguide-based deflection of light from metal contacts represents a facile, inexpensive, low energy approach to EQE enhancement, which can be integrated without disrupting well-established solar cell manufacturing technologies.