Published By
IDTechEx
Follow us:
follow us on twitter
subscrive to our rss feed
follow us on facebook
Email
Password
IDTechEx
Energy Harvesting USA 2014 40% Discount
Energy Harvesting Journal

Scientists report solar breakthrough

ZoomScientists report solar breakthrough
Researchers from the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have reported the first solar cell that produces a photocurrent that has an external quantum efficiency greater than 100 percent when photoexcited with photons from the high energy region of the solar spectrum.
 
The external quantum efficiency for photocurrent, usually expressed as a percentage, is the number of electrons flowing per second in the external circuit of a solar cell divided by the number of photons per second of a specific energy (or wavelength) that enter the solar cell. None of the solar cells to date exhibit external photocurrent quantum efficiencies above 100 percent at any wavelength in the solar spectrum. The external quantum efficiency reached a peak value of 114 percent. The newly reported work marks a promising step toward developing Next Generation Solar Cells for both solar electricity and solar fuels that will be competitive with, or perhaps less costly than, energy from fossil or nuclear fuels.
 
The mechanism for producing a quantum efficiency above 100 percent with solar photons is based on a process called Multiple Exciton Generation (MEG), whereby a single absorbed photon of appropriately high energy can produce more than one electron-hole pair per absorbed photon.
 
The researchers achieved the 114 percent external quantum efficiency with a layered cell consisting of antireflection-coated glass with a thin layer of a transparent conductor, a nanostructured zinc oxide layer, a quantum dot layer of lead selenide treated with ethanedithol and hydrazine, and a thin layer of gold for the top electrode.
 
The new results published in Science by the NREL research team is the first report of MEG manifested as an external photocurrent quantum yield greater than 100 percent measured in operating quantum dot solar cells at low light intensity; these cells showed significant power conversion efficiencies (defined as the total power generated divided by the input power) as high as 4.5 percent with simulated sunlight. While these solar cells are un-optimized and thus exhibit relatively low power conversion efficiency (which is a product of the photocurrent and photovoltage), the demonstration of MEG in the photocurrent of a solar cell has important implications because it opens new and unexplored approaches to improve solar cell efficiencies.
 
Another important aspect of the new results is that they agree with the previous time-resolved spectroscopic measurements of MEG and hence validate these earlier MEG results. Excellent agreement follows when the external quantum efficiency is corrected for the number of photons that are actually absorbed in the photoactive regions of the cell. In this case, the determined quantum yield is called the internal quantum efficiency. The internal quantum efficiency is greater than the external quantum efficiency because a significant fraction of the incident photons are lost through reflection and absorption in non-photocurrent producing regions of the cell. A peak internal quantum yield of 130% was found taking these reflection and absorption losses into account.
 
Source: NREL
Top image of solar spectrum source: Association of Universities for Research in Astronomy Inc
 
 
 
IoT USA 2014
 
Webinars Generic Banner
Wireless Sensor Networks (WSN) 2012-2022
Green_Plug
Energy Harvesting and Storage for Electronic Devic
Thermoelectric Energy Harvesting 2014-2024

IDTechEx ReportsIDTechEx Reports

Energy Harvesting and Storage 2014-2024: Forecasts, Technologies, Players
Updated in Oct 2014
Thermoelectric Energy Harvesting 2014-2024: Devices, Applications, Opportunities
Brand new for May 2014
Piezoelectric Energy Harvesting 2013-2023: Forecasts, Technologies, Players
Updated in Jan 2014
Wireless Power Transmission for Consumer Electronics and Electric Vehicles 2014-2024
Full details here
Energy Harvesting/ Regeneration for Electric Vehicles Land, Water & Air 2014-2024
Full details here
Organic Photovoltaics (OPV) 2013-2023: Technologies, Markets, Players
Full details here
Dye Sensitized Solar Cells (DSSC/DSC) 2013-2023: Technologies, Markets, Players
Full details here
Analysis of Energy Harvesting Applications
Full details here
Wireless Sensor Networks (WSN) 2014-2024: Forecasts, Technologies, Players
Updated in March 2014
Electrochemical Double Layer Capacitors: Supercapacitors 2014-2024
Full details here
Batteries & Supercapacitors in Consumer Electronics 2013-2023: Forecasts, Opportunities, Innovation
Updated in Feb 2014
Thin Film Photovoltaics 2012-2022: Forecasts, Technologies, Analysis
Updated in Aug 2013

IDTechEx EventsIDTechEx Events