Plasmonic and biomimetic light-trapping for photovoltaics

The challenge when applying photonics to photovoltaics is the need to provide broadband, multiple-angle solutions to problems and both plasmonics and biomimetics offer broadband approaches to reducing reflection and enhancing lighttrapping. Over millions of years nature has optimised nanostructures to create black, transparent, white and mirrored surfaces, the antireflective "moth-eye" structures are perhaps the best known of these biophotonic materials. In this paper we use simulated and experimental studies to illustrate how careful optimisation of nanoscale features is required to ensure the optimum match between reflectivity, spectral bandwidth and device quantum efficiencies. In the case of lighttrapping by plasmonic scattering there is more room for design and specific spectral regions can be targeted by precise control of the size, shape and density of particular metal nanoparticles. We describe how the best opportunity for plasmonics within inorganic solar cells appears to be enhanced light-trapping of near-band edge photons.