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Built-in light concentrators enhance solar cell efficiency

11 December 2015

Crystal growth on a nano/microscale level results in the formation of 'match-head-like, three-dimensional structures that enhance light absorption.

Left: silicon wires with match heads and (right) light absorption profile of a single match-head wire at 587nm absorption (image courtesy of the Center for Integrated Nanotechnologies, a US DoE facility at Los Alamos National Laboratory)

Match-head semiconductor nanowires, developed by a US Department of Energy (DoE) facility at the Los Alamos National Laboratory, focus incident light for greater overall efficiency. The match heads are naturally formed during the wire-growth process, which can be applied to various materials and structures for photonic and optoelectronic devices.

The new technology provides a novel method for enhancing optical absorption and photovoltaic efficiency via crystal growth. Controlled silicon crystal growth on the tops of silicon wires creates a match-head structure, the match head acting as a light concentrator.

This is believed to be the first large structure grown on a nanowire tip and it creates a completely new architecture for harnessing energy.

Enhanced light absorption and efficient, photo-generated carrier collection are essential characteristics of highly efficient solar cells. Nanowires with embedded radial junctions are promising building blocks for highly efficient photovoltaics because of their ability to achieve these two characteristics.

Light absorptance is increased by 36 percent and photovoltaic efficiency increased by 20 percent. Because the match-head crystal is naturally grown and minimises surface energy, this technique is applicable for a wide range of materials and device architectures to boost performance. The ability to control the shape of the nanostructure is essential for manufacturing next-generation semiconductor devices, such as photodetectors and light emitters.

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