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Utilizing Quantum Dots to Enhance Solar Spectrum Conversion Efficiencies for Photovoltaics

Published online by Cambridge University Press:  01 February 2011

Richard N Savage ,
Hans Mayer ,
Matthew Lewis  and
Dan M Marrujo
Richard N Savage
Affiliation:
rsavage@calpoly.edu, Cal Poly State University, Materials Engineering, San Luis Obispo, California, United States
Hans Mayer
Affiliation:
hmayer@calpoly.edu, Cal Poly State University, Mechanical Engineering, San Luis Obispo, California, United States
Matthew Lewis
Affiliation:
mlewis01@calpoly.edu, Cal Poly State University, Materials Engineering, San Luis Obispo, California, United States
Dan M Marrujo
Affiliation:
dmarrujo@calpoly.edu, Cal Poly State University, Materials Engineering, San Luis Obispo, California, United States
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Abstract

Silicon-based photovoltaics typically convert less than 30% of the solar spectrum into usable electric power. This study explores the utilization of CdSe based quantum dots as spectral converters that absorb the under utilized UV portion of the solar spectrum and fluoresce at wavelengths near the band-gap of silicon-based solar cells. A flexible 1 mm thick thin-film structure that contains an array of microfluidic channels is designed and fabricated in polydimethylsiloxane (PDMS) using soft-lithographic techniques. The channels are approximately 85 microns wide by 37 microns tall and are filled with a solution containing the quantum dots. The thin-film structure can easily be attached to the surface of a single-junction solar cell. As a result, solar energy striking the coated solar cell with wavelengths less than 450 nm, which would normally experience low conversion efficiency, are absorbed by the quantum dots which fluoresce at 620nm. The high energy photons are converted to photons near the band-gap which increase the overall conversion efficiency of the solar cell. The quantum dots employed in this study are fabricated with a CdSe core (5.2 nm) and a ZnS outer shell and they exhibit a 25 nm hydrodynamic diameter. The UV-VIS spectral transmission properties of PDMS, along with its refractive index, are determined in order to characterize the spectral conversion efficiency of the thin-film structure. A model is developed to predict the optimum path length and concentration of quantum dots required to improve the power output of an amorphous silicon solar cell by 10%.

Keywords

photovoltaicnanostructuresemiconducting
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1120: Symposium M – Energy Harvesting–Molecules and Materials , 2008 , 1120-M09-06
Copyright
Copyright © Materials Research Society 2009

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