Harvesting solar energy using optical frequency rectennas is a potential low-cost solution for high efficiency photovoltaics. Unlike conventional semiconductor solar cells, in which the solar energy efficiency is fundamentally limited to approximately 30%, an optical rectenna is not constrained by that limitation; therefore conversion efficiency greater than 85% would be possible.
An optical rectenna operates the same way as a well-known radio antenna at lower frequencies. Rectification based on electron tunneling between closely positioned metal electrodes is the only way to transform optical radiation of petahertz frequency directly into electrical power. However, to date, no one has developed feasible rectification for 500THz. It can be explained mostly by the fact that existing planar metal-insulator-metal (MIM) tunnel diode (MIMTD) cannot provide a sufficiently low RC time constant to rectify visible light.
Moreover, all contemporary conventional planar nanotechnology treatments exhibit many disadvantages including lithography limitations and undesirably high skin resistance of metal electrodes due to imperfections introduced by processing, thus drastically limiting the operating efficiency of fabricated tunnel-junctions at the frequencies higher than 1THz.
My design of the MIMTD potentially operating at frequencies of the sunlight overcomes disadvantages in existing designs and methods by providing non-planar configuration of the MIMTD and developing a special method of their fabrication. The distinct feature of the patented solution consists of using permanently formed nano-holes through the thickness of the film-substrate as a self-alignment mask for forming arrays of nanoscale MIMTDs, thus eliminating the need for lift-off processing in the vicinity of formed MIM-structures. The junction area of the MIM-structure is controlled by the size of a hole as well as by combination of methods of metal deposition and deposition geometry. Furthermore, the inventive designs allow formation of the MIMTD with independent control of both capacitance and resistance, which results in capability of reaching a unity coupling efficiency between the antenna and the diode.
In short, my patent claims designs that cover all situations, in which an overlapped by two metal zone is formed within the hole by deposition of metals from the opposite sides of the sheet substrate. This is the only possible combination of the sources and the substrate positioning for the deposition.
The potential payoff would be fundamentally new solar power conversion technology combining both higher efficiency and lower production cost. Imagine deployable Kapton film with inventive MIM-arrays instead of metal coating on silicon wafers, which produce 850 Watt per square meter of the electrical power! Imagine a spaceship having a sail made of ultrathin film with a built-up of rectenna arrays that transform solar energy directly into electrical power that further may be transformed into the thrust allowing easy achievement of extraterrestrial speeds!
One of significant benefits for organizations developing according to the invention is that, at an intermediate stage of successful development, the technology may achieve the level of capability sufficient for producing innovative ultrafast uncooled nanoscale high-speed infrared detectors for use in in military and civilian applications. The market could be potentially as big as a billion dollar industry.