Fundamental bounds for harvesting sunlight with aperture antennae

The tantalizing prospect of using antennae for solar power conversion received preliminary consideration, but was not pursued in earnest due to the daunting challenges in suitable materials, fabrication procedures, and the rectification (conversion to DC power) of frequencies approaching 1 PHz (1015 s-1). Recent advances in nano-materials and nano-fabrication technologies have prompted revisiting the solar antenna strategy. Coherence theory informs us that even ostensibly incoherent radiation is partially coherent on a sufficiently small scale. Based on a generalized broadband analysis, we show how the partial coherence of sunlight, exhibiting transverse partial coherence on a scale of two orders of magnitude larger than its characteristic wavelengths, impacts the potential of harvesting solar energy with aperture antennae (coherent detectors), and establish a fundamental bound. These results quantify the tradeoff between intercepted power and averaged intensity with which the effect of increasing antenna size (and hence greater system simplicity) can be evaluated.