September 2012

Future Solar Cells: Thinner, Brighter, and Better

New theory describes light management in thin-film solar cells.

Click to enlarge photo. Enlarge Photo

Image courtesy of Harry Atwater, Caltech

Large-area nanostructured solar cells. The substrate contains many cells and nanostructures, with each metallic nanopattern designed to increase solar absorption. Individual solar cells are 4 mm x 4 mm and the substrate is 10 cm long.

The Science

Researchers developed a new theoretical description of thin-film solar cells based on photon recycling in highly-fluorescent materials. These results, along with incorporation of a realistic prediction of enhancements and losses from metallic nanostructures, demonstrate that highly efficient photovoltaic devices could be created using ultra-thin semiconductor layers.

The Impact

Combining these theoretical results with experimental techniques opens new avenues for designing cost-effective and high-efficiency thin-film solar cells.

Summary

Thin-film solar cells have numerous advantages including reduced material cost, lower weight, and flexible platforms. However, thin layers absorb less sunlight, making them less efficient than solar cells with thick layers. Researchers in the Light-Material Interactions in Energy Conversion EFRC developed a new theory for light management in thin-film Gallium Arsenide solar cells, and demonstrated that the most efficient photovoltaic device also emits light suggesting that “a great solar cell is a great LED (Light Emitting Diode).” This theory of photon recycling in highly fluorescent materials inspired the geometry of Alta Devices’ solar cell, which broke the world record for efficiency in 2011. LMI researchers also engineered the local density of optical modes to better trap sunlight, providing a pathway to surpass the traditional ray optic limit for solar cell efficiency in an ultrathin device. An additional theoretical refinement allowed an accurate prediction of losses sustained in ultra-thin film photovoltaics coupled with metallic nanopatterns. Combining these theoretical results will enable new design improvements and cost reductions in thin-film solar cells.

Contact

Harry Atwater
Director, Light-Material Interactions in Energy Conversion (LMI) EFRC
haa@caltech.edu

Carrie Hofmann
Caltech (LMI-EFRC Assistant Director)
carrie.hofmann@caltech.edu

Funding

DOE Office of Science, Basic Energy Sciences, Energy Frontier Research Centers (EFRC) Program; D.M. Callahan supported by DOE Office of Science; O.D. Miller supported by NSF graduate fellowship.

Publications

O.D. Miller, E. Yablonovitch, and S.R. Kurtz, “Strong Internal and External Luminescence as Solar Cells Approach the Shockley-Queisser Limit.” IEEE Journal of Photovoltaics 2, 121121 (2012) [DOI: 10.1109/JPHOTOV.2012.2198434External link]

D.M. Callahan, J.N. Munday, and H.A. Atwater, “Solar Cell Light Trapping Beyond the Ray Optic Limit.” Nano Letters 12, 214-218 (2012) [DOI: 10.1021/nl203351kExternal link]

A. Niv, M. Ghargi, C. Gladden, O.D. Miller, and X. Zhang, “Near-Field Electromagnetic Theory for Thin Solar Cells.” Physical Review Letters 109, 138701 (2012) [DOI: 10.1103/PhysRevLett.109.138701External link]

Related Links

Light-Material Interactions in Energy Conversion (LMI) EFRC

LMI EFRC WebsiteExternal link

The related publications were highlighted in the following press pieces:

Highlight Categories

Program: BES, EFRCs

Performer/Facility: University, DOE Laboratory

Last modified: 12/6/2013 1:26:23 PM