Solar Tech Finding Claims 50% Efficiency

by Susan DeFreitas, August 6th, 2010

The “black swan theory” refers to real events beyond the realm of normal expectations–and that’s how an international team of researchers at SciTech Solar (lead by a former professor emeritus from Penn State) are referring to their latest breakthrough, a technology that allows for ultra high-efficiency solar cells to generate DC, or direct current electricity.

Why is this such a big deal in the solar world? Apparently because it makes possible the design and fabrication of a new class of solar energy converters which could allow for a dramatic increase in energy conversion efficiency and cost savings of solar cells. According to Penn State, this is a technology that can successfully compete with today’s semiconductor-based solar cells while exceeding efficiencies and decreasing costs. They’re hailing it as a scalable, sustainable, adaptable and environmentally-friendly technology that will allow manufacturers to quickly and economically shift to new materials if a shortage of any one type occurs.

image via SciTech Associates

The technology is based on a new “optical rectification” process that makes use of a simple, cost-effective, single element system that extracts energy from the solar spectrum from the infrared through the visible light spectrum. This broad-spectrum absorption significantly contributes to the gain in efficiency as compared to today’s solar cells, allowing these single element cells to act simultaneously as both a receiving antenna and as a rectifier to absorb and convert solar energy to an electric current. Such a device is historically termed a “rectenna” and was developed for microwave power transmission.

In extensive computer simulations, scientists from United States, Belgium and Korea performed quantum-mechanical calculations that agree with the rectification results of the actual operation of the device, showing rectification of light throughout the visible region and a significant DC current output. The scientists obtained efficiencies comparable to and exceeding those of current solar cell devices (efficiencies as high as 50% were recorded). The scientists are currently developing prototype devices which include more robust antenna structures and plasmonic effects to enhance output and efficiency.

Source

United States Patent Application	20090308443
Kind Code	A1
Cutler; Paul H.	December 17, 2009

---

Apparatus and system for a single element solar cell

Abstract

A device for receiving and converting incident radiation into DC current, the device including a transparent conductor, at least one point-contact diode, the at least one point-contact diode having a nanowire/mCNT providing a receiving antenna function and a rectification function, a thin insulating layer situated between the transparent conductor and the nanowire/mCNT, and a point contact junction at which the nanowire/mCNT contacts the thin insulating layer.

---

Inventors:	Cutler; Paul H.; (State College, PA)
Correspondence Address:	KENYON & KENYON LLP ONE BROADWAY NEW YORK NY 10004 US
Serial No.:	157842
Series Code:	12
Filed:	June 13, 2008

Current U.S. Class:	136/256
Class at Publication:	136/256
International Class:	H01L 31/00 20060101 H01L031/00

---

Claims

---

1. A device for receiving and converting incident radiation into DC current, the device comprising:a transparent conductor; at least one point-contact diode, the at least one point-contact diode having a nanowire providing a receiving antenna function and a rectification function; a thin insulating layer, situated between the transparent conductor and the nanowire; and a point-contact junction, at which the nanowire contacts the thin insulting layer.

1-Solar Cell 2-Solar Radiation 3-Transparent Cover 4-Metal Electrode 5-Thin Insulating Layer 6-mCNT Rectifying Antenna
7-Contact Area 8-Sharp Edge 9-High Frequency Diode

See also WO2009152435

Researchers Generate Hydrogen Without The Carbon Footprint

ScienceDaily (July 15, 2008) — A greener, less expensive method to produce hydrogen for fuel may eventually be possible with the help of water, solar energy and nanotube diodes that use the entire spectrum of the sun's energy, according to Penn State researchers.

"Other researchers have developed ways to produce hydrogen with mind-boggling efficiency, but their approaches are very high cost," says Craig A. Grimes, professor of electrical engineering. "We are working toward something that is cost effective."

Currently, the steam reforming of natural gas produces most of our hydrogen. As a fuel source, this produces two problems. The process uses natural gas and so does not reduce reliance on fossil fuels; and, because one byproduct is carbon dioxide, the process contributes to the carbon dioxide in the atmosphere, the carbon footprint.

Grimes' process splits water into its two components, hydrogen and oxygen, and collects the products separately using commonly available titanium and copper. Splitting water for hydrogen production is an old and proven method, but in its conventional form, it requires previously generated electricity. Photolysis of water solar splitting of water has also been explored, but is not a commercial method yet.

Grimes and his team produce hydrogen from solar energy, using two different groups of nanotubes in a photoelectrochemical diode. They report in the July issue of Nano Letters that using incident sunlight, "such photocorrosion-stable diodes generate a photocurrent of approximately 0.25 milliampere per centimeter square, at a photoconversion efficiency of 0.30 percent."

"It seems that nanotube geometry is the best geometry for production of hydrogen from photolysis of water," says Grimes.

In Grimes' photoelectrochemical diode, one side is a nanotube array of electron donor material -- n-type material -- titanium dioxide, and the other is a nanotube array that has holes that accept electrons - p-type material -- cuprous oxide titanium dioxide mixture. P and n-type materials are common in the semiconductor industry. Grimes has been making n-type nanotube arrays from titanium by sputtering titanium onto a surface, anodizing the titanium with electricity to form titanium dioxide and then annealing the material to form the nanotubes used in other solar applications. He makes the cuprous oxide titanium dioxide nanotube array in the same way and can alter the proportions of each metal.

While titanium dioxide is very absorbing in the ultraviolet portion of the sun's spectrum, many p-type materials are unstable in sunlight and damaged by ultraviolet light, they photo-corrode. To solve this problem, the researchers made the titanium dioxide side of the diode transparent to visible light by adding iron and exposed this side of the diode to natural sunlight. The titanium dioxide nanotubes soak up the ultraviolet between 300 and 400 nanometers. The light then passes to the copper titanium side of the diode where visible light from 400 to 885 nanometers is used, covering the light spectrum.

The photoelectrochemical diodes function the same way that green leaves do, only not quite as well. They convert the energy from the sun into electrical energy that then breaks up water molecules. The titanium dioxide side of the diode produces oxygen and the copper titanium side produces hydrogen.

Although 0.30 percent efficiency is low, Grimes notes that this is just a first go and that the device can be readily optimized.

"These devices are inexpensive and because they are photo-stable could last for years," says Grimes. "I believe that efficiencies of 5 to 10 percent are reasonable."

Grimes is now working with an electroplating method of manufacturing the nanotubes, which will be faster and easier.

Working with Grimes are Gopal K. Mor, Oomman K. Varghese and Karthik Shankar, research associates; Rudeger H. T. Wilke and Sanjeev Sharma, Ph.D. candidates; Thomas J. Latempa, graduate student, all at Penn State; and Kyoung-Shin Choi, associate professor of chemistry, Purdue University.

The U.S. Department of Energy supported this research.

Source