A carbon nanotube optical rectenna for energy harvesting
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The optical rectenna (rectifying antenna) is a burgeoning alternative solar technology that incorporates an antenna to capture electromagnetic radiation and a diode that rectifies the a.c. antenna oscillations into useable d.c. power. In 2015, Cola et al. provided the first optical rectenna demonstration, accomplished with a forest of aligned carbon nanotubes (CNTs) that are capable of absorbing solar radiation and then rectifying the optical frequencies using a coupled high-speed (~PHz) tunneling diode. This work overcomes the limitations of the original CNT rectenna by providing important device developments as well as advancing fundamental understanding of the CNT optical rectenna mechanism. The CNT tunneling diode was explored by incorporating multiple insulators to tailor diode current and asymmetry with air-stable materials. The excellent diodes facilitated the first air-stable demonstration of optical rectification in addition to a 100-fold improvement in conversion efficiency. Furthermore, optical measurements were validated with rectenna simulations, which elucidate loss mechanism and proffers valuable efficiency limits to guide future improvements. Lastly, a novel device modification was developed to incorporate polymer materials in conjunction with the CNTs. The design is facile, scalable, and flexible, promising a commercially viable approach to solar rectenna applications. The progress made in this work will ultimately enable better solar and thermal energy harvesting in CNT rectenna devices.