Nanotechnology Now

Our NanoNews Digest Sponsors



Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > NREL Scientists Report First Solar Cell Producing More Electrons In Photocurrent Than Solar Photons Entering Cell

Abstract:
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.

NREL Scientists Report First Solar Cell Producing More Electrons In Photocurrent Than Solar Photons Entering Cell

Golden, CO | Posted on December 15th, 2011

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.

Multiple Exciton Generation is key to making it possible

A paper on the breakthrough appears in the Dec. 16 issue of Science Magazine. Titled "Peak External Photocurrent Quantum Efficiency Exceeding 100 percent via MEG in a Quantum Dot Solar Cell," it is co-authored by NREL scientists Octavi E. Semonin, Joseph M. Luther, Sukgeun Choi, Hsiang-Yu Chen, Jianbo Gao, Arthur J. Nozikand Matthew C. Beard. The research was supported by the Center for Advanced Solar Photophysics, an Energy Frontier Research Center funded by the DOE Office of Science, Office of Basic Energy Sciences. Semonin and Nozik are also affiliated with the University of Colorado at Boulder.

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.

NREL scientist Arthur J. Nozik first predicted in a 2001 publication that MEG would be more efficient in semiconductor quantum dots than in bulk semiconductors. Quantum dots are tiny crystals of semiconductor, with sizes in the nanometer (nm) range of 1-20 nm, where 1 nm equals one-billionth of a meter. At this small size, semiconductors exhibit dramatic effects because of quantum physics, such as:
rapidly increasing bandgap with decreasing quantum dot size,
formation of correlated electron-hole pairs (called excitons) at room temperature,
enhanced coupling of electronic particles (electrons and positive holes) through Coulombic forces,
and enhancement of the MEG process.
Quantum dots confine the charges and harvest excess energy

Quantum dots, by confining charge carriers within their tiny volumes, can harvest excess energy that otherwise would be lost as heat - and therefore greatly increase the efficiency of converting photons into usable free energy.

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.

In a 2006 publication, NREL scientists Mark Hanna and Arthur J. Nozik showed that ideal MEG in solar cells based on quantum dots could increase the theoretical thermodynamic power conversion efficiency of solar cells by about 35 percent relative to today's conventional solar cells. Furthermore, the fabrication of Quantum Dot Solar Cells is also amenable to inexpensive, high-throughput roll-to-roll manufacturing.

Such potentially highly efficient cells, coupled with their low cost per unit area, are called Third (or Next) Generation Solar Cells. Present day commercial photovoltaic solar cells are based on bulk semiconductors, such as silicon, cadmium telluride, or copper indium gallium (di)selenide; or on multi-junction tandem cells drawn from the third and fifth (and also in some cases fourth) columns of the Periodic Table of Elements. All of these cells are referred to as First- or Second-Generation Solar Cells.

First experiment to show 100-percent-plus in operating solar cells

MEG, also referred to as Carrier Multiplication (CM), was first demonstrated experimentally in colloidal solutions of quantum dots in 2004 by Richard Schaller and Victor Klimov of the DOE's Los Alamos National Laboratory. Since then, many researchers around the world, including teams at NREL, have confirmed MEG in many different semiconductor quantum dots. However, nearly all of these positive MEG results, with a few exceptions, were based on ultrafast time-resolved spectroscopic measurements of isolated quantum dots dispersed as particles in liquid colloidal solutions.

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.

####

About National Renewable Energy Laboratory (NREL)
NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for DOE by the Alliance for Sustainable Energy, LLC.

For more information, please click here

Contacts:
Media may contact:
William Scanlon
303-275-4051

Copyright © National Renewable Energy Laboratory (NREL)

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Iranian Researchers Synthesize Stable Ceramic Nanopowders at Room Temperature September 20th, 2014

Arrowhead to Present at BioCentury's NewsMakers in the Biotech Industry Conference September 19th, 2014

SouthWest NanoTechnologies (SWeNT) Receives NIST Small Business Innovation Research (SBIR) Phase 1 Award to Produce Greater than 99% Semiconducting Single-Wall Carbon Nanotubes September 19th, 2014

Toward optical chips: A promising light source for optoelectronic chips can be tuned to different frequencies September 19th, 2014

New research points to graphene as a flexible, low-cost touchscreen solution September 19th, 2014

Physics

Toward optical chips: A promising light source for optoelectronic chips can be tuned to different frequencies September 19th, 2014

Elusive Quantum Transformations Found Near Absolute Zero: Brookhaven Lab and Stony Brook University researchers measured the quantum fluctuations behind a novel magnetic material's ultra-cold ferromagnetic phase transition September 15th, 2014

Laboratories

Elusive Quantum Transformations Found Near Absolute Zero: Brookhaven Lab and Stony Brook University researchers measured the quantum fluctuations behind a novel magnetic material's ultra-cold ferromagnetic phase transition September 15th, 2014

'Squid skin' metamaterials project yields vivid color display: Rice lab creates RGB color display technology with aluminum nanorods September 15th, 2014

Berkeley Lab Licenses Boron Nitride Nanotube Technology: New material has unique mechanical and electronic properties September 13th, 2014

Advanced Light Source Sets Microscopy Record| Berkeley Lab Researchers Achieve Highest Resolution Ever with X-ray Microscopy September 11th, 2014

Govt.-Legislation/Regulation/Funding/Policy

SouthWest NanoTechnologies (SWeNT) Receives NIST Small Business Innovation Research (SBIR) Phase 1 Award to Produce Greater than 99% Semiconducting Single-Wall Carbon Nanotubes September 19th, 2014

Big Results Require Big Ambitions: Three young UCSB faculty receive CAREER awards from the National Science Foundation September 18th, 2014

Scientists refine formula for nanotube types: Rice University theorists determine factors that give tubes their chiral angles September 17th, 2014

New non-invasive technique could revolutionize the imaging of metastatic cancer September 17th, 2014

Announcements

Iranian Scientists Separate Zinc Ion at Low Concentrations September 20th, 2014

Arrowhead to Present at BioCentury's NewsMakers in the Biotech Industry Conference September 19th, 2014

SouthWest NanoTechnologies (SWeNT) Receives NIST Small Business Innovation Research (SBIR) Phase 1 Award to Produce Greater than 99% Semiconducting Single-Wall Carbon Nanotubes September 19th, 2014

Toward optical chips: A promising light source for optoelectronic chips can be tuned to different frequencies September 19th, 2014

Energy

Iranian Researchers Synthesize Stable Ceramic Nanopowders at Room Temperature September 20th, 2014

IEEE International Electron Devices Meeting To Celebrate 60th Anniversary as The Leading Technical Conference for Advanced Semiconductor Devices September 18th, 2014

Rice rolls 'neat' nanotube fibers: Rice University researchers' acid-free approach leads to strong conductive carbon threads September 15th, 2014

Simple, Cost-Effective Method Proposed for Synthesizing Zinc Oxide Nanopigments September 15th, 2014

Quantum Dots/Rods

Nano-pea pod model widens electronics applications: A new theoretical model explains how a nanostructure, such as the nano-pea pod, can exhibit localised electrons September 4th, 2014

Interaction between Drug, DNA for Designing Anticancer Drugs Studied in Iran August 17th, 2014

NANOPARTICLES INDIA August 8th, 2014

Researchers create quantum dots with single-atom precision June 30th, 2014

Solar/Photovoltaic

Simple, Cost-Effective Method Proposed for Synthesizing Zinc Oxide Nanopigments September 15th, 2014

Indium/Copper Sulfide Compound Semi-Conductor Synthesized through New Method September 8th, 2014

Material development on the nanoscale: Doped graphene nanoribbons with potential September 8th, 2014

Layered graphene sandwich for next generation electronics September 8th, 2014

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More














ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE