Photovoltaics are the fastest-growing renewable energy source over the last three years and have the potential to supply a significant fraction of our electricity needs. Conventional silicon cells are made of thick crystals because silicon is a weak absorber in the infrared and much of the visible. Thin solar cells require less energy and material to make and may lead more swiftly to cost competitiveness with conventional sources of electricity. A challenge facing thin cells is to maximize the absorption of the solar spectrum. We explore the enhancements to absorption in thin-film cells made possible by metallic nanoparticles and other structures designed to scatter incident radiation into guided modes propagating parallel to the cell’s surface.