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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. [email protected]
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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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References

Abou-Ras, D., Caballero, R., Fischer, C.-H., Kaufmann, C.A., Lauermann, I., Mainz, R., Mönig, H., Schöpke, A., Stephan, C., Streeck, C., Schorr, S., Eicke, A., Döbeli, M., Gade, B., Hinrichs, J., Nunney, T., Dijkstra, H., Hoffmann, V., Klemm, D., Efimova, V., Bergmaier, A., Dollinger, G., Wirth, T., Unger, W., Rockett, A.A., Perez-Rodriguez, A., Alvarez-Garcia, J., Izquierdo-Roca, V., Schmid, T., Choi, P.-P., Müller, M., Bertram, F., Christen, J., Khatri, H., Collins, R.W., Marsillac, S. & Kötschau, I. (2011). Comprehensive comparison of various techniques for the analysis of elemental distributions in thin films. Microsc Microanal 17, 728–751.CrossRefGoogle ScholarPubMed
Aguiar, J.A., Reed, B.W., Ramasse, Q.M., Erni, R. & Browning, N.D. (2013). Quantifying the low-energy limit and spectral resolution in valence electron energy loss spectroscopy. Ultramicroscopy 124, 130–138.CrossRefGoogle ScholarPubMed
Alonso, M.I., Wakita, K., Pascual, J., Garriga, M. & Yamamoto, N. (2001). Optical functions and electronic structure of CuInSe2, CuGaSe2, CuInS2, and CuGaS2 . Phys Rev B 63, 075203.CrossRefGoogle Scholar
Bangert, U., Harvey, A., Davidson, J., Keyse, R. & Dieker, C. (1998). Correlation between microstructure and localized band gap of GaN grown on SiC. J Appl Phys 83, 7726.CrossRefGoogle Scholar
Batson, P.E., Kavanagh, K.L., Woodall, J.M. & Mayer, J.W. (1986). Electron-energy-loss scattering near a single misfit dislocation at the GaAs/GaInAs interface. Phys Rev Lett 57, 2729–2732.CrossRefGoogle Scholar
Bolton, J.P.R. & Chen, M. (1995). Electron energy loss in multilayered slabs. Ultramicroscopy 60, 247–263.CrossRefGoogle Scholar
Chirilă, A., Buecheler, S., Pianezzi, F., Bloesch, P., Gretener, C., Uhl, A.R., Fella, C., Kranz, L., Perrenoud, J., Seyrling, S., Verma, R., Nishiwaki, S., Romanyuk, Y.E., Bilger, G. & Tiwari, A.N. (2011). Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films. NatMater 10, 857–861.Google ScholarPubMed
Chirilă, A., Reinhard, P., Pianezzi, F., Bloesch, P., Uhl, A.R., Fella, C., Kranz, L., Keller, D., Gretener, C., Hagendorfer, H., Jaeger, D., Erni, R., Nishiwaki, S., Buecheler, S. & Tiwari, A.N. (2013). Potassium-induced surface modification of Cu(In,Ga)Se2 thin films for high efficiency solar cells. Nat Mater 12, 1107–1111.CrossRefGoogle ScholarPubMed
Erni, R. & Browning, N.D. (2005). Valence electron energy-loss spectroscopy in monochromated scanning transmission electron microscopy. Ultramicroscopy 104, 176–192.CrossRefGoogle ScholarPubMed
Erni, R. & Browning, N.D. (2007). Quantification of the size-dependent energy gap of individual CdSe quantum dots by valence electron energy-loss spectroscopy. Ultramicroscopy 107, 267–273.CrossRefGoogle ScholarPubMed
Erni, R. & Browning, N.D. (2008). The impact of surface and retardation losses on valence electron energy-loss spectroscopy. Ultramicroscopy 108, 84–99.CrossRefGoogle ScholarPubMed
Erni, R., Lazar, S. & Browning, N.D. (2008). Prospects for analyzing the electronic properties in nanoscale systems by VEELS. Ultramicroscopy 108, 270–276.CrossRefGoogle ScholarPubMed
Gu, L., Srot, V., Sigle, W., Koch, C., Van Aken, P., Scholz, F., Thapa, S., Kirchner, C., Jetter, M. & Rühle, M. (2007). Band-gap measurements of direct and indirect semiconductors using monochromated electrons. Phys Rev B 75, 195214.CrossRefGoogle Scholar
Han, S.-H., Hasoon, F.S., Al-Thani, H.A., Hermann, A.M. & Levi, D.H. (2005). Effect of Cu deficiency on the optical properties and electronic structure of CuIn1−xGaxSe2 . J Phys Chem Solids 66, 1895–1898.CrossRefGoogle Scholar
Hegedus, S.S. & Shafarman, W.N. (2004). Thin-film solar cells: Device measurements and analysis. Prog Photovolt 12, 155–176.CrossRefGoogle Scholar
Kimoto, K., Kothleitner, G., Grogger, W., Matsui, Y. & Hofer, F. (2005). Advantages of a monochromator for bandgap measurements using electron energy-loss spectroscopy. Micron 36, 185–189.CrossRefGoogle ScholarPubMed
Kröger, E. (1968). Berechnung der Energieverluste schneller Elektronen in dünnen Schichten mit Retardierung. Z Physik 216, 115–135.CrossRefGoogle Scholar
Lazar, S., Botton, G.A., Wu, M.-Y., Tichelaar, F.D. & Zandbergen, H.W. (2003). Materials science applications of HREELS in near edge structure analysis and low-energy loss spectroscopy. Ultramicroscopy 96, 535–546.CrossRefGoogle ScholarPubMed
Malis, T., Cheng, S.C. & Egerton, R.F. (1988). EELS log-ratio technique for specimen-thickness measurement in the TEM. J Electron Microsc Tech 8, 193–200.CrossRefGoogle ScholarPubMed
Minoura, S., Kodera, K., Maekawa, T., Miyazaki, K., Niki, S. & Fujiwara, H. (2013). Dielectric function of Cu(In,Ga)Se2-based polycrystalline materials. J Appl Phys 113, 063505–063505–14.CrossRefGoogle Scholar
Nadenau, V., Rau, U., Jasenek, A. & Schock, H.W. (2000). Electronic properties of CuGaSe2-based heterojunction solar cells. Part I. Transport analysis. J Appl Phys 87, 584.CrossRefGoogle Scholar
Rafferty, B. & Brown, L. (1998). Direct and indirect transitions in the region of the band gap using electron-energy-loss spectroscopy. Phys Rev B 58, 10326–10337.CrossRefGoogle Scholar
Schamm, S. & Zanchi, G. (2003). Study of the dielectric properties near the band gap by VEELS: Gap measurement in bulk materials. Ultramicroscopy 96, 559–564.CrossRefGoogle ScholarPubMed
Specht, P., Ho, J.C., Xu, X., Armitage, R., Weber, E.R., Erni, R. & Kisielowski, C. (2005). Band transitions in wurtzite GaN and InN determined by valence electron energy loss spectroscopy. Solid State Commun 135, 340–344.CrossRefGoogle Scholar
Van Benthem, K., French, R.H., Sigle, W., Elsässer, C. & Rühle, M. (2001). Valence electron energy loss study of Fe-doped SrTiO3 and a Σ13 boundary: Electronic structure and dispersion forces. Ultramicroscopy 86, 303–318.CrossRefGoogle Scholar
Wei, S.-H., Zhang, S.B. & Zunger, A. (1998). Effects of Ga addition to CuInSe2 on its electronic, structural, and defect properties. Appl Phys Lett 72, 3199–3201.CrossRefGoogle Scholar
Zhang, L., Erni, R., Verbeeck, J. & Van Tendeloo, G. (2008). Retrieving the dielectric function of diamond from valence electron energy-loss spectroscopy. Phys Rev B 77, 195119.CrossRefGoogle Scholar