Abstract
Omnidirectional broadband absorption of the solar radiation is pivotal to solar energy harvesting and particularly to low-cost non-tracking photovoltaic (PV) technologies. The current work numerically examines the utilization of surface arrays composed of Fresnel nanosystems (Fresnel arrays), which are reminiscent of the known Fresnel lenses, for the realization of ultra-thin silicon PV cells. Specifically, the optical and electrical performances of PV cells integrated with Fresnel arrays are compared with those of a PV cell incorporated with an optimized surface array of nanopillars (NP array). It is shown that the broadband absorption of specifically tailored Fresnel arrays can provide an enhancement of ∼20% over that of an optimized NP array. The performed analysis suggests that broadband absorption in ultra-thin films decorated with Fresnel arrays is driven by two light trapping mechanisms. The first is light trapping governed by light concentration, induced by the arrays, into the underlying substrates, which increases the optical coupling between the impinging illumination and the substrates. The second mechanism is light trapping motivated by refraction, as the Fresnel arrays induce lateral irradiance in the underlying substrates, which increases the optical interaction length and hence the overall probability for optical absorption. Finally, PV cells incorporated with surface Fresnel arrays are numerically calculated, with short-circuit current densities (J(sc)) which are ∼50% higher than that of a PV cell incorporated with an optimized NP array. Also, the effect of increased surface area, due to the presence of Fresnel arrays, and its effect on surface recombination and open-circuit voltage (V(oc)) are discussed.