Photon management for photovoltaics

Photovoltaics are expected to play an important role in the future energy infrastructure. However, achieving simultaneously high efficiency in both light absorption and carrier collection remains a challenging tradeoff. Photon management, which refers to the engineering of materials and device structures to control the spatial distribution of optical energy, offers a number of promising routes to optimizing this tradeoff. Progress in fabrication of nanostructured materials combined with advances in the understanding of nanophotonic devices has enabled new strategies for photon management in a range of photovoltaic devices. Prominent among these are structures with pronounced surface topography or graded refractive-index profiles that reduce surface reflectivity; materials processing that increases optical absorption in materials such as silicon; incorporation of semiconductor nanostructures that enables simultaneous improvements in optical absorption and photogenerated carrier collection; and coherent light trapping in optical waveguide modes via plasmonic or optical scattering effects. The articles in this issue review some of these emerging directions.