Light management for photovoltaics using high-index nanostructures

Strategies to increase light-trapping in solar cells can significantly improve the power-conversion efficiency of these devices. This Review discusses the use of nanostructured high-index layers to manipulate photons in thin-film solar cells, as well as the recent efforts aimed at integrating such layers in large-area devices. High-performance photovoltaic cells use semiconductors to convert sunlight into clean electrical power, and transparent dielectrics or conductive oxides as antireflection coatings. A common feature of these materials is their high refractive index. Whereas high-index materials in a planar form tend to produce a strong, undesired reflection of sunlight, high-index nanostructures afford new ways to manipulate light at a subwavelength scale. For example, nanoscale wires, particles and voids support strong optical resonances that can enhance and effectively control light absorption and scattering processes. As such, they provide ideal building blocks for novel, broadband antireflection coatings, light-trapping layers and super-absorbing films. This Review discusses some of the recent developments in the design and implementation of such photonic elements in thin-film photovoltaic cells.