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Special coating greatly improves solar cell performance
February 25, 2008The energy from sunlight falling on only 9 percent of California's Mojave Desert could power all of the United States' electricity needs if the energy could be efficiently harvested, according to some estimates. Unfortunately, current-generation solar cell technologies are too expensive and inefficient for wide-scale commercial applications.
A team of Northwestern University researchers has developed a new anode coating strategy that significantly enhances the efficiency of solar energy power conversion. A paper about the work, which focuses on "engineering" organic material-electrode interfaces in bulk-heterojunction organic solar cells, is published online this week in the Proceedings of the National Academy of Sciences (PNAS).
This breakthrough in solar energy conversion promises to bring researchers and developers worldwide closer to the goal of producing cheaper, more manufacturable and more easily implemented solar cells. Such technology would greatly reduce our dependence on burning fossil fuels for electricity production as well as reduce the combustion product: carbon dioxide, a global warming greenhouse gas.
Tobin J. Marks, the Vladimir N. Ipatieff Research Professor in Chemistry in the Weinberg College of Arts and Sciences and professor of materials science and engineering, and Robert Chang, professor of materials science and engineering in the McCormick School of Engineering and Applied Science, led the research team. Other Northwestern team members were researcher Bruce Buchholz and graduate students Michael D. Irwin and Alexander W. Hains.
Of the new solar energy conversion technologies on the horizon, solar cells fabricated from plastic-like organic materials are attractive because they could be printed cheaply and quickly by a process similar to printing a newspaper (roll-to-roll processing).
To date, the most successful type of plastic photovoltaic cell is called a "bulk-heterojunction cell." This cell utilizes a layer consisting of a mixture of a semiconducting polymer (an electron donor) and a fullerene (an electron acceptor) sandwiched between two electrodes -- one a transparent electrically conducting electrode (the anode, which is usually a tin-doped indium oxide) and a metal (the cathode), such as aluminum.
When light enters through the transparent conducting electrode and strikes the light-absorbing polymer layer, electricity flows due to formation of pairs of electrons and holes that separate and move to the cathode and anode, respectively. These moving charges are the electrical current (photocurrent) generated by the cell and are collected by the two electrodes, assuming that each type of charge can readily traverse the interface between the polymer-fullerene active layer and the correct electrode to carry away the charge -- a significant challenge.
The Northwestern researchers employed a laser deposition technique that coats the anode with a very thin (5 to 10 nanometers thick) and smooth layer of nickel oxide. This material is an excellent conductor for extracting holes from the irradiated cell but, equally important, is an efficient "blocker" which prevents misdirected electrons from straying to the "wrong" electrode (the anode), which would compromise the cell energy conversion efficiency.
In contrast to earlier approaches for anode coating, the Northwestern nickel oxide coating is cheap, electrically homogeneous and non-corrosive. In the case of model bulk-heterojunction cells, the Northwestern team has increased the cell voltage by approximately 40 percent and the power conversion efficiency from approximately 3 to 4 percent to 5.2 to 5.6 percent.
The researchers currently are working on further tuning the anode coating technique for increased hole extraction and electron blocking efficiency and moving to production-scaling experiments on flexible substrates.
Northwestern University
Tobin J. Marks, the Vladimir N. Ipatieff Research Professor in Chemistry in the Weinberg College of Arts and Sciences and professor of materials science and engineering, and Robert Chang, professor of materials science and engineering in the McCormick School of Engineering and Applied Science, led the research team. Other Northwestern team members were researcher Bruce Buchholz and graduate students Michael D. Irwin and Alexander W. Hains.
Of the new solar energy conversion technologies on the horizon, solar cells fabricated from plastic-like organic materials are attractive because they could be printed cheaply and quickly by a process similar to printing a newspaper (roll-to-roll processing).
To date, the most successful type of plastic photovoltaic cell is called a "bulk-heterojunction cell." This cell utilizes a layer consisting of a mixture of a semiconducting polymer (an electron donor) and a fullerene (an electron acceptor) sandwiched between two electrodes -- one a transparent electrically conducting electrode (the anode, which is usually a tin-doped indium oxide) and a metal (the cathode), such as aluminum.
When light enters through the transparent conducting electrode and strikes the light-absorbing polymer layer, electricity flows due to formation of pairs of electrons and holes that separate and move to the cathode and anode, respectively. These moving charges are the electrical current (photocurrent) generated by the cell and are collected by the two electrodes, assuming that each type of charge can readily traverse the interface between the polymer-fullerene active layer and the correct electrode to carry away the charge -- a significant challenge.
The Northwestern researchers employed a laser deposition technique that coats the anode with a very thin (5 to 10 nanometers thick) and smooth layer of nickel oxide. This material is an excellent conductor for extracting holes from the irradiated cell but, equally important, is an efficient "blocker" which prevents misdirected electrons from straying to the "wrong" electrode (the anode), which would compromise the cell energy conversion efficiency.
In contrast to earlier approaches for anode coating, the Northwestern nickel oxide coating is cheap, electrically homogeneous and non-corrosive. In the case of model bulk-heterojunction cells, the Northwestern team has increased the cell voltage by approximately 40 percent and the power conversion efficiency from approximately 3 to 4 percent to 5.2 to 5.6 percent.
The researchers currently are working on further tuning the anode coating technique for increased hole extraction and electron blocking efficiency and moving to production-scaling experiments on flexible substrates.
Northwestern University
Solar Cell Current Events and Solar Cell News RSSNanometric butterfly wings created
A team of researchers from the State University of Pennsylvania (USA) and the Universidad Autónoma de Madrid (UAM) have developed a technique to replicate biological structures, such as butterfly wings, on a nano scale. The resulting biomaterial could be used to make optically active structures, such as optical diffusers for solar panels.
Looking deeply into polymer solar cells
Researchers from the Eindhoven University of Technology and the University of Ulm have made the first high-resolution 3D images of the inside of a polymer solar cell.
Carbon nanotubes could make efficient solar cells
Using a carbon nanotube instead of traditional silicon, Cornell researchers have created the basic elements of a solar cell that hopefully will lead to much more efficient ways of converting light to electricity than now used in calculators and on rooftops.
Bringing solar power to the masses
On a 104-degree Friday in July when sunlight bathed The University of Arizona campus, doctoral student Dio Placencia sat before a noisy vacuum chamber in the Chemical Sciences Building trying to advance the renewable energy revolution.
Plastics that convert light to electricity could have a big impact
Researchers the world over are striving to develop organic solar cells that can be produced easily and inexpensively as thin films that could be widely used to generate electricity.
NIST scientists study how to stack the deck for organic solar power
A new class of economically viable solar power cells-cheap, flexible and easy to make-has come a step closer to reality as a result of recent work* at the National Institute of Standards and Technology (NIST), where scientists have deepened their understanding of the complex organic films at the heart of the devices.
Nanopillars Promise Cheap, Efficient, Flexible Solar Cells
Researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the University of California at Berkeley have demonstrated a way to fabricate efficient solar cells from low-cost and flexible materials.
Low-cost solution processing method developed for CIGS-based solar cells
Though the solar industry today predominately produces solar panels made from crystalline silicon, they remain relatively expensive to make.
Flexible Solar Strips Light Up Campus Bus Shelter
There won't be anymore waiting in the dark at this campus bus shelter. New flexible solar cell technology developed by a group of engineering researchers at McMaster University has been installed to power lighting for night-time transit users.
Lasers are making solar cells competitive
Solar electricity has a future: It is renewable and available in unlimited quantities, and it does not produce any gases detrimental to the climate.
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