New 3D Solar Technology Boosts Efficiency

oakridgeAnyone who follows news on new solar technology is probably aware that conversion efficiency, that is, the amount of solar light, that actually becomes electricity, is the top challenge for this industry. Currently the top conversion rate is around 18% which means there’s definitely room for much more efficiency.

In a recent interview, Hypersolar’s CEO Tim Young said what we should be looking for “disruptive technologies”, which are technologies that represent game-changing breakthroughs, not traditional technologies that may not be economically viable over the long term without government subsidies. “We need technologies that will boost performance by 500% or 1,000%, not 1% or 2%”, Mr. Young told Energy Refuge.

A new technology developed by Oak Ridge National Laboratory doesn’t quite do that, but it succeeds in improving light-to-power conversion efficiency of photovoltaics by almost 80%.

The technology was developed by Jun Xu and consists of a 3-D nanocone-based solar cell platform made of zinc oxide. The n-type nanocones are surrounded by a p-type semiconductor and serve as the junction framework and the electron conductor. The p-type matrix is made of polycrystalline cadmium telluride and serves as the primary photon absorber medium and hole conductor.

“We created a nanocone-based solar cell, invented methods to synthesize these cells and demonstrated improved charge collection efficiency," said Xu, who is a member of ORNL's Chemical Sciences Division.

Xu and his colleagues said they were able to achieve a light-to-power conversion efficiency of 3.2%. The usual rate for conventional planar structure of the same material is 1.8%.

"We designed the three-dimensional structure to provide an intrinsic electric field distribution that promotes efficient charge transport and high efficiency in converting energy from sunlight into electricity," Xu said. The important concept behind our invention is that the nanocone shape generates a high electric field in the vicinity of the tip junction, effectively separating, injecting and collecting minority carriers, resulting in a higher efficiency than that of a conventional planar cell made with the same materials.

The laboratory said some of the key features of the solar material include its unique electric field distribution that achieves efficient charge transport; the synthesis of nanocones using inexpensive proprietary methods; and the minimization of defects and voids in semiconductors. The latter provides enhanced electric and optical properties for conversion of solar photons to electricity.

Another positive quality of the new solar cell is that it can tolerate defective materials and reduce cost in fabricating next-generation solar cells.

The research behind this technology was accepted by this year's Institute of Electrical and Electronics Engineers photovoltaic specialist conference and will be published in the IEEE Proceedings. The papers are titled "Efficient Charge Transport in Nanocone Tip-Film Solar Cells" and "Nanojunction solar cells based on polycrystalline CdTe films grown on ZnO nanocones."

With information provided by Oak Ridge National Laboratory

Image credit: Oak Ridge National Laboratory

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