Si wire arrays are a promising architecture for solar-energy-harvesting applications, and may offer a mechanically flexible alternative to Si wafers for photovoltaics1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17. To achieve competitive conversion efficiencies, the wires must absorb sunlight over a broad range of wavelengths and incidence angles, despite occupying only a modest fraction of the array’s volume. Here, we show that arrays having less than 5% areal fraction of wires can achieve up to 96% peak absorption, and that they can absorb up to 85% of day-integrated, above-bandgap direct sunlight. In fact, these arrays show enhanced near-infrared absorption, which allows their overall sunlight absorption to exceed the ray-optics light-trapping absorption limit18 for an equivalent volume of randomly textured planar Si, over a broad range of incidence angles. We furthermore demonstrate that the light absorbed by Si wire arrays can be collected with a peak external quantum efficiency of 0.89, and that they show broadband, near-unity internal quantum efficiency for carrier collection through a radial semiconductor/liquid junction at the surface of each wire. The observed absorption enhancement and collection efficiency enable a cell geometry that not only uses 1/100th the material of traditional wafer-based devices, but also may offer increased photovoltaic efficiency owing to an effective optical concentration of up to 20 times.
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This work was supported by BP and in part by the Department of Energy EFRC program under grant DE-SC0001293, and made use of facilities supported by the Center for Science and Engineering of Materials, an NSF Materials Research Science and Engineering Center at Caltech. S.W.B. acknowledges the Kavli Nanoscience Institute for fellowship support. The authors acknowledge D. Pacifici for useful discussions and assistance in generating the quasi-periodic hole-array patterns, B. Kayes and M. Filler for their contributions at the outset of this project and M. Roy and S. Olson for their advice and skill in machining the components of the experimental apparatus.
The authors declare no competing financial interests.
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Kelzenberg, M., Boettcher, S., Petykiewicz, J. et al. Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications. Nature Mater 9, 239–244 (2010). https://doi.org/10.1038/nmat2635
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