Photovoltaic Measurements in Single-Nanowire Silicon Solar Cells

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Abstract
Single-nanowire solar cells were created by forming rectifying junctions in electrically contacted vapor−liquid−solid-grown Si nanowires. The nanowires had diameters in the range of 200 nm to 1.5 μm. Dark and light current−voltage measurements were made under simulated Air Mass 1.5 global illumination. Photovoltaic spectral response measurements were also performed. Scanning photocurrent microscopy indicated that the Si nanowire devices had minority carrier diffusion lengths of ∼2 μm. Assuming bulk-dominated recombination, this value corresponds to a minimum carrier lifetime of ∼15 ns, or assuming surface-dominated recombination, to a maximum surface recombination velocity of approximately 1350 cm s-1. The methods described herein comprise a valuable platform for measuring the properties of semiconductor nanowires, and are expected to be instrumental when designing an efficient macroscopic solar cell based on arrays of such nanostructures.