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Working at the scanning electron microscope at the Center for Functional Nanomaterials are: (seated) Brookhaven Lab researchers Raluca Gearba and Charles Black, and (standing) Katy Bosworth, Cornell University, and Brookhaven’s Chang-Yong Nam.
Scientists at Brookhaven’s Center for Functional Nanomaterials (CFN) are working on converting solar energy to electricity using new materials and new methods for controlling the structure of these materials. The research involves overcoming challenges to using inexpensive, organic materials or nanostructured inorganic materials in efficient solar cells.
Today, only a small fraction of the electricity we use is generated by solar cells because these devices are made of crystalline silicon, an expensive material. Over the lifetime of a solar panel — about 30 years — the average cost of electricity is about five to ten times higher than electricity generated by conventional fossil-fuel based methods. If solar cell manufacturing costs could be reduced to one-tenth of their present value, these devices could provide cost-competitive electricity and may be deployed on a more widespread basis.
Brookhaven scientists are studying low-cost polymer materials for possible use in solar cells. Their goal is rooted in both basic and applied science: They want to understand how the materials function and determine if they may be suitable for improving solar panels for the marketplace. At the CFN, the scientists use sophisticated tools to determine how the materials function on the nanoscale (one nanometer is a billionth of a meter). In complementary studies at Brookhaven’s National Synchrotron Light Source, x-rays are being used to probe the structure of organic semiconducting polymers, an essential part of solar cells.
Compared to conventional silicon solar cells, polymer solar cells have the potential to be lighter in weight, potentially better for the environment, and less expensive to fabricate.
Solar cells made of polymers are composed of electron donor- and acceptor- materials. When sunlight hits the electron-donor region of the cell, excitons — electronically excited pairs of electrons and holes, spaces where electrons previously resided — are created. To break the bound state of the electron and hole to create a current, the exciton must pass through an interface, which is constructed with two thin materials sandwiched together. A polymer-based material in the interface, the donor, absorbs photons, or energy from the sun, and the acceptor material, a fullerene, a carbon molecule in the shape of a nanotube, attracts the electron. An electric field at the interface of the solar cell is able to rip apart the electron and hole to create an electric charge needed for electrical power.
If the excitons move efficiently and quickly, and separate so that electrons are freed from holes, they will create a current. The cell’s electric field provides the voltage, which, when combined with current, gives power to the solar cell. Brookhaven scientists are focusing on how to get excitons to find an interface before they are scattered and lost. The exciton must travel a distance of ten nanometers to get to the interface and the conducting metal wires that protrude from each side of the cell. By fabricating new architecture for the interface and the wires, researchers can give the interface a jagged surface and make the wires protrude like fingers, pointing in the direction of the excitons. Then the excitons have a shorter distance to travel, and more surface space to which they can bind.
Using sophisticated fabrication techniques at the CFN, the scientists can correlate structure and function. If they are able to build a more efficient solar cell using polymers on the nanoscale, they may revolutionize the solar power industry, leading the way to clean, renewable, economical electricity powered by the sun.
The objectives of the National Photovoltaics (PV) Environmental Research Center are to: a) Identify potential environmental, health and safety (EHS) barriers for photovoltaic materials, processes or applications and define strategies to overcome such barriers; b) assist the industry, the DOE and its contractors in maintaining safe and environmentally friendly facilities, minimizing EHS risks and reducing EHS related costs, to ensure the public support and economic viability of PV; c) maintain the center as the world’s best source on PV-EHS, providing accurate information related to EHS issues and perceptions.
The Center has supported the DOE headquarters, the National Renewable Laboratory’s (NREL), SNL, and the PV industry since the 1980s. It has strong relationships with most PV manufacturers, the NREL solar energy projects, and the DOE’s small business research projects. Initially, the Center’s activities were focused on PV manufacturing EH&S. The Center now also performs research on PV product recycling and life cycle assessment.
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Last Modified: November 6, 2009