Optical absorption enhancement in silicon nanowire and nanohole arrays for photovoltaic applications

In this proceeding, we simulate the optical properties of vertically-aligned silicon nanowire and nanohole arrays using the transfer matrix method. We find that the optical absorption in both silicon nanowire and nanohole arrays improves with increasing lattice constant up to 600nm - 700nm. We attribute the observed optical absorption enhancement effect to an increase in the field concentration inside the active silicon region and the excitation of guided resonance modes. For optimized parameters, both structures can be more absorptive than an equally-thick silicon solid film with an optimal single layer Si3N4 anti-reflection coating. This conclusion holds true for both optically thin (2.33μm) and optically thick (100μm) structures. For optically thin structures, the enhancement in the optimal nanohole array exceeds the conventional light trapping limit. For optically thick structures, the enhancement in both optimal nanohole and nanowire arrays exceeds the light trapping limit. Additionally, we show that the overall absorption efficiencies for hexagonal and square lattices of nanowires are very similar.

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