Abstract
Optical rectennas are an attractive technology for high-efficiency, low-cost solar cells if several technological issues can be addressed. These devices combine submicron antennas with ultra-high speed diodes to rectify incident radiation. Visible light frequency operation requires a quantum approach to analyze the rectification process and design the devices. The small coherence area for sunlight limits the power per rectenna, which affects the conversion efficiency. In assessing the broadband ultimate efficiency obtainable from rectenna solar cells it turns out that operating voltage plays the same role that band gap energy plays in conventional solar cells, leading to a single cell limit of 44 %. Parallel plate diodes cannot provide the 0.1 fs RC time constant that is required to rectify visible light frequencies, and so other potential solutions such as traveling-wave diodes, sharp-tip diodes, or geometric diodes are required. Waste heat harvesting and thermophotovoltaics using optical rectennas would relax the RC constraints because the infrared frequencies are lower than those for visible light, but with substantial coherence impediments. With innovation and careful development rectenna solar cells have the potential to provide an exciting new photovoltaics technology.
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