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Novel Devices ♦ news digest 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-optimised and 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 EQE 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 (IQE).


The IQE is greater than the EQE 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.


This research was supported by the Centre for Advanced Solar Photophysics, an Energy Frontier Research Centre funded by the DOE Office of Science, Office of Basic Energy Sciences. Scientists affiliated with the University of Colorado at Boulder also contributed to the study.


Further details of this work are published in the online publication, “Peak External Photocurrent Quantum Efficiency Exceeding 100 percent via MEG in a Quantum Dot Solar Cell ”, Science, published online on 16 December 2011, Vol. 334 no. 6062 pp. 1530-1533.


DOI: 10.1126/science.1209845


Dr. Philippe Roussel to present at CS Europe Conference 2012


Defining the next steps for the Compound Semiconductor Industry,Dr. Philippe Roussel of Yole Développement will present the talk “Wide Bandgap device market update”.


Following the success of CS Europe 2011, next year’s conference is expanding to 2 days and offers a fantastic mix/quality of speakers making it the must attend industry event for 2012.


Register at www.cseurope.net & book your delegate place now as numbers will be limited. The conference takes place on 12th/13th March 2012 at Hilton Hotel, Frankfurt, Germany.


A networking dinner will also be held on the night of 12th March.


Conference Chair Dr Andrew W Nelson, President & CEO, IQE


January / February 2012 www.compoundsemiconductor.net 239


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