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.
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.
Combining these theoretical results with experimental techniques opens new avenues for designing cost-effective and high-efficiency thin-film solar cells.
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.
Director, Light-Material Interactions in Energy Conversion (LMI) EFRC
Caltech (LMI-EFRC Assistant Director)
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.
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.2012.2198434]
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/nl203351k]
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.109.138701]
Light-Material Interactions in Energy Conversion (LMI) EFRC
LMI EFRC Website
The related publications were highlighted in the following press pieces:
University, DOE Laboratory