Overcoming the Challenge of High Surface Recombination in Thin-Film Photovoltaic Cells Based on Subwavelength Arrays for Elevated Light Trapping

Surface arrays of subwavelength photoactive structures have been demonstrated for photovoltaic (PV) applications with elevated omnidirectional and broadband absorption. However, this approach suffers from an increase in surface recombination and loss of photovoltage. Herein, surface decoration with subwavelength dielectric (SiO₂) arrays that provide enhanced light trapping without compromising the photovoltage performance is proposed. An increase of ≈ 50% in broadband absorption is shown in an ultrathin film of 200 nm due to the presence of a top surface SiO₂ nanopillar array in comparison with the same film decorated with an optimized antireflective coating of 50 nm of Si₃N₄. Interestingly, the broadband enhancement is not due to lower reflection, but rather the presence of the arrays forces a considerable lower transmission. The distribution of the optical power flux density suggests that the low transmission is due to appreciable refraction, which is induced by the presence of the dielectric arrays. Finally, the photovoltaic performance is examined for various array geometries and absorber acceptor concentrations and an overall increase of >60% in PV efficiency is calculated for a decorated photovoltaic cell in comparison with a PV cell with an antireflection coating of 50 nm Si₃N₄.