MRS Proceedings

Table of Contents - Volume  1120  - Symposium M – Energy Harvesting–Molecules and Materials  

Editors : D.L. Andrews, K.O. Ghiggino, T. Goodson, III, A.J. Nozik

Articles

Utilizing Quantum Dots to Enhance Solar Spectrum Conversion Efficiencies for Photovoltaics

2008 MRS Fall Meeting.

Richard N Savagea1, Hans Mayera2, Matthew Lewisa3 and Dan M Marrujoa4

a1 rsavage@calpoly.edu, Cal Poly State University, Materials Engineering, San Luis Obispo, California, United States

a2 hmayer@calpoly.edu, Cal Poly State University, Mechanical Engineering, San Luis Obispo, California, United States

a3 mlewis01@calpoly.edu, Cal Poly State University, Materials Engineering, San Luis Obispo, California, United States

a4 dmarrujo@calpoly.edu, Cal Poly State University, Materials Engineering, San Luis Obispo, California, United States

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%.

(Received November 23 2008)

(Accepted February 02 2009)

Key Words

  • photovoltaic;
  • nanostructure;
  • semiconducting
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