Making PV from Any Semiconductor
August 28, 2012 Editor 0
A new technology has been developed by researchers from the United States Department of Energy, the Berkeley Lab and the University of California (Berkeley). This technology will be capable of solving one of the most complicated problems concerning solar energy; that problem is high-cost production. This recent and innovative technology will enable the production of low-cost solar cells. In addition, these cells will be extremely effective when it comes to generating electrical energy. In the past metal oxides such as phosphides or sulfides were considered inappropriate for cells because they couldn’t properly fit chemical means.
The physicist Alex Zettl who headed this outstanding study alongside with his colleague Feng Wang says now is the right time to take bad material and give them a good and proper use; their technology gives them the possibility to overcome the difficulty of tailor much earth abundant when it comes to chemical tailoring. They can tailor those materials by simply applying an electric field.
Alex Zettl is the corresponding author of a paper published in the journal Nano Letters; the paper’s title is ‘Screening-Engineered Field-Effect Solar Cells’,’ and it is co-authored by Onur Ergen, Steven Byrnes, William Regan, Will Gannett, Feng Wang and Oscar Vazquez-Mena Alex Zettl also holds joint arrangements with the Division of Materials Science (Berkeley Lab), and with the Physics Department (UC Berkeley) there he leads the COINS, stands for Center of Integrated Nanomechanical Systems.
Using semiconductor materials, solar cells convert solar energy into electricity; this shows the PV (Photovoltaic) effect; which means that those cells absorb photons, and then they release electrons. Later, those electrons can be directed into an electric current. Obviously, PV is the latest resource for green, clean and renewable energy; however, nowadays technologies use limited and expensive semiconductors (e.g. copper indium gallium selenide; large crystals of silicone or cadmium Telluride). Substances like these can be difficult to fabric into devices, and they are costly.
Zettl said that international interest in solar energy slowed because the cost/efficiency ratio is very low; by using their technology they will decrease not only the costs related to production of such material. But also the complexity when it comes to the fabrication; this will result in an international increased use and interested in this type of environment-friendly energy. This recent technology is named SFPV (SFPV stands for Screening Engineered Field Effect Photovoltaic); the technology was given this name because it uses an electric field effect that is a well-known phenomenon; where the concentration of charge-carries present in a semiconductor is modified by applying an electric field. Using the Screening Engineered Field Effect Photovoltaic technology, a wisely planned partially screening top conductor lets the gate electric field infiltrates the electrode and more homogeneously control the semiconductor transporter type.
William Regan (lead author) said that their technology needs only gate and conductor deposition; without the need of using chemical doping, high temperatures, ion implantation or other harmful and expensive procedures. According to Regan, the key to their success is the slight screening of the gate field (that was accomplished by using geometric shaping of the top conductor). This allows carrier modulation of the semiconductor and electrical contact to be performed at the same time.
According to the SFPV system, the top electrode’s structure is modified; that will allow at least one of the conductor’s dimensions to be restricted. Berkeley researchers managed to modify the electrode contact into thin fingers (working with copper oxide); in a different configuration (working with silicon), they built the top contact ultra-fine through the surface. Possessing the necessary narrow fingers the gate field will generate a low electrical opposition inversion ‘coat’ in the middle of the fingers and a possible barrier underneath them. A homogeneously tinny top contact will enable gate fields to infiltrate and turn upside down or up to the underlying semiconductor.
Feng Wang (co-author) said that their demonstrations showed that electrically stable p-n junctions could be accomplished with almost any semiconductor and any conductor material using the application to a gate field; once the conductor is properly geometrically organized. Researchers were capable of demonstrating the Screening Engineered Field Effect Photovoltaic effect in a self gating structure;
Regan stated that self gating structure will eliminate the need of having an outside gate power font; this will result in simplification in the implementation of the Screening Engineered Field Effect Photovoltaic devices. Regan also adds to his statement the gate will have another two important roles
– The gate will serve as an anti-reflection coat;
– Secondly, as a necessary and common feature for high-productivity PVs.
Both the Department of Energy Office of Science and the National Science Foundation supported this research.
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