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Local Band Gap Measurements by VEELS of Thin Film Solar Cells

Published online by Cambridge University Press:  02 April 2014

Debora Keller ,
Stephan Buecheler ,
Patrick Reinhard ,
Fabian Pianezzi ,
Darius Pohl ,
Alexander Surrey ,
Bernd Rellinghaus ,
Rolf Erni Open the ORCID record for Rolf Erni [Opens in a new window]  and
Ayodhya N. Tiwari
Debora Keller*
Affiliation:
Empa—Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Thin Films and Photovoltaics, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland Empa—Swiss Federal Laboratories for Materials Science and Technology, Electron Microscopy Center, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
Stephan Buecheler
Affiliation:
Empa—Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Thin Films and Photovoltaics, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
Patrick Reinhard
Affiliation:
Empa—Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Thin Films and Photovoltaics, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
Fabian Pianezzi
Affiliation:
Empa—Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Thin Films and Photovoltaics, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
Darius Pohl
Affiliation:
Institute for Metallic Materials, IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany
Alexander Surrey
Affiliation:
Institute for Metallic Materials, IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany Institut für Festkörperphysik, TU Dresden, D-01062, Germany
Bernd Rellinghaus
Affiliation:
Institute for Metallic Materials, IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany
Rolf Erni
Affiliation:
Empa—Swiss Federal Laboratories for Materials Science and Technology, Electron Microscopy Center, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
Ayodhya N. Tiwari
Affiliation:
Empa—Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Thin Films and Photovoltaics, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland
*
*Corresponding author. debora.keller@empa.ch
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Abstract

This work presents a systematic study that evaluates the feasibility and reliability of local band gap measurements of Cu(In,Ga)Se2 thin films by valence electron energy-loss spectroscopy (VEELS). The compositional gradients across the Cu(In,Ga)Se2 layer cause variations in the band gap energy, which are experimentally determined using a monochromated scanning transmission electron microscope (STEM). The results reveal the expected band gap variation across the Cu(In,Ga)Se2 layer and therefore confirm the feasibility of local band gap measurements of Cu(In,Ga)Se2 by VEELS. The precision and accuracy of the results are discussed based on the analysis of individual error sources, which leads to the conclusion that the precision of our measurements is most limited by the acquisition reproducibility, if the signal-to-noise ratio of the spectrum is high enough. Furthermore, we simulate the impact of radiation losses on the measured band gap value and propose a thickness-dependent correction. In future work, localized band gap variations will be measured on a more localized length scale to investigate, e.g., the influence of chemical inhomogeneities and dopant accumulations at grain boundaries.

Keywords

VEELSmonochromated STEMband gapCu(InGa)Se2chalcopyritesolar cell
Type
Materials Applications
Information
Microscopy and Microanalysis , Volume 20 , Issue 4 , August 2014 , pp. 1246 - 1253
Copyright
© Microscopy Society of America 2014 

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