World Community Grid and researchers in Harvard University's Department of Chemistry and Chemical Biology are working together to develop efficient and inexpensive solar cells using organic molecules, which will satisfy the world's future energy needs through renewable energy resources.
Energy is the oxygen our modern society breathes, the juice we need for our most basic daily needs, including food, transportation, and entertainment. Combining oil, gas, coal, nuclear, hydroelectric, biological, solar, and wind energy sources, the world uses an average of 15 terawatts (TW) of power or 130 trillion kilowatt-hours per year – enough to light 150 billion 100-watt bulbs!
By the year 2050, as the population grows and the standard of living in developing countries increases, the amount of energy the world consumes will likely double, reaching 30 TW. However, the world's power supply will be unable to keep up with this heightened demand. Oil and hydroelectric energy sources are running short; wind power is not sufficient to meet our needs, and there are serious environmental concerns surrounding gas, coal, and nuclear power.
As a result, a great number of scientists are focusing their attention on bio- and solar-powered energy sources. But bio-powered sources also have limitations. If current bio-power sources, such as biodiesel, were used, it would require 20% of the earth's available surface to satisfy new energy demands, resulting in devastating ecological and social consequences. Thus, solar energy offers the most viable option. The sun is an abundantly available resource and harnessing its energy requires a much smaller ecological footprint; using only 0.16% of the earth's surface, the world could produce about 18 TW of power!
However, scientists have not yet found the optimal material to convert this massive amount of energy into electricity. Energy in light is converted into electrical energy through the use of devices called solar cells or photovoltaics. At present, common materials used for solar cells are based on silicon semiconductor technology. These conventional solar cells can harvest as much as 24% of the incoming solar energy; unfortunately, the fabrication of such efficient devices requires high temperatures and difficult manufacturing conditions, leading to relatively high production costs.
Toward the goal of inexpensive renewable energy sources, scientists in companies and universities worldwide are now involved in developing solar cells based on organic molecules, which are composed primarily of carbon and other light atoms such as nitrogen or oxygen. These materials can potentially combine the electronic properties of conventional semiconductors with the excellent mechanical and processing properties of polymeric, or "plastic", materials.
Although these organic solar cells may not have the same high efficiency as silicon (harvesting as much as 6.5% of the incoming solar energy, as announced last year by Nobel Laureate Alan Heeger, professor of physics at the University of California at Santa Barbara), they could be chemically modified to improve their efficiency. Indeed, the number of potential molecules that can be used in an organic solar cell is limited only by the imagination of a synthetic chemist. In this respect, organic molecules can be combined in a myriad of ways to build millions and millions of different molecules. While some of these molecules will not be efficient, a handful may provide the answer we are searching for in order to support modern society's global demand for energy.
World Community Grid and The Clean Energy Project
World Community Grid and the Clean Energy Project are assembling a virtual laboratory to build thousands of organic compounds in order to discover those that are the best candidates for future solar cell research. With the aid of World Community Grid, new molecular materials with specific properties will be designed in software, instead of having to actually synthesize and test the molecules in an actual chemical experiment. Thus rather than measuring the response of the molecules to sunlight, scientists from the Aspuru-Guzik group at Harvard University will be able to look at their calculated molecular properties and estimate their performance as solar cells. To be successful, they will need to achieve the highest levels of accuracy available with current computational chemistry methods - and must do so for tens of thousands of molecules.
Plastic materials are made out of polymers - that is, chemical compounds made of thousands of repetitions of a molecular motif linked end-to-end. The project will begin by selecting a handful of motifs, modifying each one with various chemical substituents, and changing the size of the altered motifs; this results in tens of thousands of compounds to study. The first phase will enable the researchers to determine the general electronic properties of these molecules.
After this stage, scientists will be able to select a few dozen promising candidates. These candidates will be subject to extremely detailed simulations that will uncover their energy transport properties, including the effects of temperature and the environment.
The PC's of World Community Grid volunteers will calculate the quantum mechanical and classical properties of each one of these molecules to determine which ones are the best candidates for the next generation of light-harvesting devices.
After these massive computations are completed, the project will be able to identify a few prospective finalists that will be passed on to other experimental researchers for actual synthesis to undergo real testing in the laboratory.
Ultimately, with World Community Grid's support, scientists are expecting to create successful materials to produce efficient and inexpensive solar cells that will serve as viable solutions for our future energy needs.
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