SUMMARY

Carbon nanotube arrays have shown recent promise in the development of optical rectennas for solar energy harvesting. A rectenna (‘rectifying antenna’) is a device that incorporates two elements: an antenna that captures electromagnetic radiation, and a diode that rectifies the AC antenna oscillations into useable DC power. Optical-frequency rectennas are a burgeoning alternative technology to semiconductors for energy harvesting and photodetection. Realizing an optical rectenna requires an antenna that can efficiently capture optical radiation, and a diode that can operate at nearly PHz frequencies.

This proposal details an optical rectenna device that uses forests of carbon nanotubes (CNTs). The CNTs act as individual antennas that absorb visible light. The tips of each CNT are fabricated into metal-insulator-metal tunnel diodes to rectify the light into electricity. In this work, the diode’s insulating layer is characterized to find the ideal balance of high diode asymmetry and low resistance. Another development describes the use of multiple insulators in combination to enhance diode rectification efficiency by nearly 100-fold. This work also models the optical behavior using photon-assisted tunneling theory. The approach seeks to better understand the fundamental device mechanisms and shed light on the principle performance limits with the goal of guiding future device development. Lastly, this work introduces a proposed concept of an organic-based infiltrated-forest CNT rectenna design. This design is a scalable approach that promises to enhance conversion efficiency with a flexible and commercially viable design.