Effect of diffuse illumination.
(a) Contour plot showing the influence of diffuse illumination on nanostructured PV as the cut-off energy for nanoscale concentration (Ecut-off) is varied, assuming maximum concentration (X = 46,050). Esc corresponds to the semiconductor bandgap of the device. (b) 3 slices of the contour plot in (a) corresponding to Ecut-off = 1.43 eV (traditional PV), Ecut-off = 1.74 eV (concentration for photons from Esc to Ecut-off) and Ecut-off →∞ (concentration for all incident photons); similar calculations performed for X = 1,000 are also shown. The nanostructured device with complete concentration (i.e. concentration for all energies of incident photons) outperforms traditional PV when diffuse illumination accounts for <20% of the incident light. The nanostructured device with partial concentration (corresponding to concentrating only light with energies 1.43–1.74 eV) outperforms the traditional device when the incident light is <60% diffuse. With only modest concentration (X = 1,000), the device has an efficiency of 35.5% under 25% diffuse illumination. (c) Absorption contour plot and schematic depicting a nanoscale device that is able to concentrate light with energies Esc to Ecut-off but unable to concentrate light with energy greater than Ecut-off.