Angular refractive path for optical enhancement and evaluation of dye solar cells

Abstract

Here we report a fundamental angle resolved study on bare dye solar cells, DSCs, and those coupled to two different prisms (hemi-cube and hemi-cylinder). The natural angular enhancement of incident photon-to-current conversion efficiency of DSCs is shown to further increase in the prisms case. This is partially due to the higher external transmittance and mainly to the longer optical path, achieved thanks to the tilted surfaces and optical density of the coupling elements. Results suggest possible use of DSCs with thin active layers (below 10μm) and micrometric refractive prisms or nanometric diffraction gratings on the surface, compensating the incomplete light absorption by an enhanced optical path. A simplified yet robust angular refractive path model, which includes Fresnel reflection, Snell’s refraction and Lambert–Beer absorption, can clearly explain the results and predict enhancements at larger angles than the used ones. The angular photo-electronic measurements revealed also an elegant tool to retrieve a dispersion curve for the effective refractive index neff(λ) of such a complex and absorbing medium as the sensitized porous titania filled with electrolyte. Such information could be used in the design and simulation of different photon management structures, from the macroscopic size of 3D photovoltaics architectures to the micro- and nano-scale of anti-reflection, refractive or diffraction texturing.