SOLVING THE ENERGY CRISIS
WITH INTERMEDIATE BAND SOLAR CELLS
Editor's Note: Giancarlo S. ('16) describes his work in Science Research in this DuPont Challenge essay.
For 650,000 years carbon dioxide levels did not surpass 300 parts per million. As of 2014, carbon dioxide levels are at a historic high (400 ppm), and show no signs of slowing or stopping (NASA, 2011). Carbon dioxide, along with methane, nitrous oxide and a handful of other organic molecules, fall under a category of gases known as greenhouse gases (EPA, 2014). Scientists agree that the increase in emission of greenhouse gasses is the main contributor to a well documented, thoroughly supported, and scientifically validated effect known as global warming (National Geographic, 2015).
Global warming is the gradual increase in Earth’s surface temperature and has been shown to pose a threat to the survival of our planet. The increased volume of greenhouse gases in our environment creates an insulative layer in Earth’s upper atmosphere that traps the sun's rays (and consequently their heat energy) on the Earth’s surface. Scientists predict that the temperature of the Earth will rise 3-9 degrees by the end of the century (NRDC, 2005). While this rise does not seem very significant numerically, its practical repercussions are immense. Since 2000, record high temperatures, melting polar ice caps, and the increased frequency of extreme weather events have already been documented and correlated to the gradual warming of planet Earth (NMSEA, 2011).
The main source of these greenhouse gas pollutants in our atmosphere comes from the production of electrical energy. In the U.S. alone, 2.5 billions tons of carbon dioxide are produced from coal burning power plants every year (NRDC, 2005). Not only is this dependence on fossil fuels destroying the worlds' atmosphere, it also contributes to many other global concerns such as political unrest and war. It has thus become a major focus of scientists and engineers to create renewable and reliable sources of energy that don't require the use of fossil fuels.
Among the multitude of renewable energy sources, solar power stands out as being one of the most effective and widespread technologies (Solar Energy USA, 2013). There are still, however, many improvements to be made. At any one time the Earth receives 3.4865335 × 1017 joules of the suns energy per second (Christian, 2005). Just 0.01% of that energy would be enough to power the entire world... twice (EIA, 2012).
The main limiting factor in solar cell technology today is the inefficiencies of the cells themselves. The current top of the line, commercially available solar cells are about 21.5% efficient (Shahan, 2014). This means that 21.5% of the photons (particles of light) striking the surface of the cells get converted into electrical current. The maximum theoretical efficiency for a conventional solar cell, given by the Shockley–Queisser limit, is approximately 33.7% (Shockley, 1961).
A new type of solar cell may pose a solution to this limiting efficiency. The cell, named an intermediate band solar cell, utilizes a new chemical composition and structure to raise the efficiency of a single cell to about 63% (SISER, 2015). This higher efficiency would effectively triple the electrical output achieved by today's commercial cells. Intermediate band solar cells can achieve this high efficiency due to the fabrication of a so-called “intermediate band” within the host semiconductor material. This intermediate band absorbs photons that would otherwise be lost to heat (or some other form of dissipated energy) and then converts them into electrical energy (Dhomkar, 2013). By investigating various materials systems, scientists have been able to fabricate some very rudimentary samples. Although these cells show great progress, they are still a long way from being fully realized. Production hurdles, such as the structural stability of the device and limited financial resources, are two of the largest restrictions to the finalization of the technology.
Scientists predict that by 2100, if greenhouse gas emissions remain unchecked, sea levels around New York City could rise by as much as three feet, putting the area I live in, Battery Park, under water (Bradford, 2014). Not only is this threat very real, it is also very current. For many years politicians and lawmakers have put the issue of climate change at the bottom of the list, focusing on other concerns. Unfortunately, this global threat is happening now and it will be our generation's crisis to address when we grow up. We can no longer continue to delay climate change action and we must focus on ways to stop and reverse global warming before it is too late.
Global warming is the gradual increase in Earth’s surface temperature and has been shown to pose a threat to the survival of our planet. The increased volume of greenhouse gases in our environment creates an insulative layer in Earth’s upper atmosphere that traps the sun's rays (and consequently their heat energy) on the Earth’s surface. Scientists predict that the temperature of the Earth will rise 3-9 degrees by the end of the century (NRDC, 2005). While this rise does not seem very significant numerically, its practical repercussions are immense. Since 2000, record high temperatures, melting polar ice caps, and the increased frequency of extreme weather events have already been documented and correlated to the gradual warming of planet Earth (NMSEA, 2011).
The main source of these greenhouse gas pollutants in our atmosphere comes from the production of electrical energy. In the U.S. alone, 2.5 billions tons of carbon dioxide are produced from coal burning power plants every year (NRDC, 2005). Not only is this dependence on fossil fuels destroying the worlds' atmosphere, it also contributes to many other global concerns such as political unrest and war. It has thus become a major focus of scientists and engineers to create renewable and reliable sources of energy that don't require the use of fossil fuels.
Among the multitude of renewable energy sources, solar power stands out as being one of the most effective and widespread technologies (Solar Energy USA, 2013). There are still, however, many improvements to be made. At any one time the Earth receives 3.4865335 × 1017 joules of the suns energy per second (Christian, 2005). Just 0.01% of that energy would be enough to power the entire world... twice (EIA, 2012).
The main limiting factor in solar cell technology today is the inefficiencies of the cells themselves. The current top of the line, commercially available solar cells are about 21.5% efficient (Shahan, 2014). This means that 21.5% of the photons (particles of light) striking the surface of the cells get converted into electrical current. The maximum theoretical efficiency for a conventional solar cell, given by the Shockley–Queisser limit, is approximately 33.7% (Shockley, 1961).
A new type of solar cell may pose a solution to this limiting efficiency. The cell, named an intermediate band solar cell, utilizes a new chemical composition and structure to raise the efficiency of a single cell to about 63% (SISER, 2015). This higher efficiency would effectively triple the electrical output achieved by today's commercial cells. Intermediate band solar cells can achieve this high efficiency due to the fabrication of a so-called “intermediate band” within the host semiconductor material. This intermediate band absorbs photons that would otherwise be lost to heat (or some other form of dissipated energy) and then converts them into electrical energy (Dhomkar, 2013). By investigating various materials systems, scientists have been able to fabricate some very rudimentary samples. Although these cells show great progress, they are still a long way from being fully realized. Production hurdles, such as the structural stability of the device and limited financial resources, are two of the largest restrictions to the finalization of the technology.
Scientists predict that by 2100, if greenhouse gas emissions remain unchecked, sea levels around New York City could rise by as much as three feet, putting the area I live in, Battery Park, under water (Bradford, 2014). Not only is this threat very real, it is also very current. For many years politicians and lawmakers have put the issue of climate change at the bottom of the list, focusing on other concerns. Unfortunately, this global threat is happening now and it will be our generation's crisis to address when we grow up. We can no longer continue to delay climate change action and we must focus on ways to stop and reverse global warming before it is too late.
NASA. (2011). Global Climate Change: Evidence. Retrieved from http://climate.nasa.gov/evidence/
EPA. (2014, April 15). Greenhouse Gas Emissions: Greenhouse Gases Overview. Retrieved from http://www.epa.gov/climatechange/ghgemissions/gases.html
National Geographic. (2015). Global warming causes, climate change causes. Retrieved from http://environment.nationalgeographic.com/environment/global-warming/gw-causes/
Natural Resources Defense Council (NRDC). (2005, October 18). Global warming basics. Retrieved from http://www.nrdc.org/globalwarming/f101.asp
New Mexico Solar Energy Association (NMSEA). (2011). What is global warming? Retrieved from http://www.nmsea.org/Curriculum/Primer/Global_Warming/fossil_fuels_and_global_warming.htm
Solar Energy USA. (2013). Solar Power Facts. Retrieved from http://solarenergy-usa.com/solar-info/solar-facts/
Christian, E. (2005). Solar Constant. Retrieved from http://helios.gsfc.nasa.gov/qa_sun.html#power
U.S. Energy Information Administration (EIA). (2012). International energy statistics. Retrieved from http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm?tid=44&pid=44&aid=2
Shahan, Z. (2014, February 2). Which solar panels are most efficient? Retrieved from http://cleantechnica.com/2014/02/02/which-solar-panels-most-efficient/
Shockley, W., & Queisser, H. J. (1961). Detailed Balance Limit of Efficiency of p-n Junction Solar Cells. Journal of Applied Physics, 32(3), 510. doi:10.1063/1.1736034
Scottish Institute for Solar Energy Research (SISER). (2015). Intermediate band solar cells. Retrieved from http://siser.eps.hw.ac.uk/research/next-generation/intermediate-band-solar-cells
Dhomkar, S., Manna, U., Peng, L., Moug, R., Noyan, I., Tamargo, M., & Kuskovsky, I. (2013). Feasibility of submonolayer ZnTe/ZnCdSe quantum dots as intermediate band solar cell material system. Solar Energy Materials and Solar Cells, 117, 604-609. doi:10.1016/j.solmat.2013.07.037
Bradford, A. (2014, December 17). Effects of global warming. Retrieved from http://www.livescience.com/37057-global-warming-effects.html
EPA. (2014, April 15). Greenhouse Gas Emissions: Greenhouse Gases Overview. Retrieved from http://www.epa.gov/climatechange/ghgemissions/gases.html
National Geographic. (2015). Global warming causes, climate change causes. Retrieved from http://environment.nationalgeographic.com/environment/global-warming/gw-causes/
Natural Resources Defense Council (NRDC). (2005, October 18). Global warming basics. Retrieved from http://www.nrdc.org/globalwarming/f101.asp
New Mexico Solar Energy Association (NMSEA). (2011). What is global warming? Retrieved from http://www.nmsea.org/Curriculum/Primer/Global_Warming/fossil_fuels_and_global_warming.htm
Solar Energy USA. (2013). Solar Power Facts. Retrieved from http://solarenergy-usa.com/solar-info/solar-facts/
Christian, E. (2005). Solar Constant. Retrieved from http://helios.gsfc.nasa.gov/qa_sun.html#power
U.S. Energy Information Administration (EIA). (2012). International energy statistics. Retrieved from http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm?tid=44&pid=44&aid=2
Shahan, Z. (2014, February 2). Which solar panels are most efficient? Retrieved from http://cleantechnica.com/2014/02/02/which-solar-panels-most-efficient/
Shockley, W., & Queisser, H. J. (1961). Detailed Balance Limit of Efficiency of p-n Junction Solar Cells. Journal of Applied Physics, 32(3), 510. doi:10.1063/1.1736034
Scottish Institute for Solar Energy Research (SISER). (2015). Intermediate band solar cells. Retrieved from http://siser.eps.hw.ac.uk/research/next-generation/intermediate-band-solar-cells
Dhomkar, S., Manna, U., Peng, L., Moug, R., Noyan, I., Tamargo, M., & Kuskovsky, I. (2013). Feasibility of submonolayer ZnTe/ZnCdSe quantum dots as intermediate band solar cell material system. Solar Energy Materials and Solar Cells, 117, 604-609. doi:10.1016/j.solmat.2013.07.037
Bradford, A. (2014, December 17). Effects of global warming. Retrieved from http://www.livescience.com/37057-global-warming-effects.html
