helena_biegler.jpg Host Laboratory TAKAHASHI LAB.
Position in LIMMS EUJO-LIMMS Researcher (IMTEK)
Main  Research Topic in LIMMS

NANOTECH - Investigation of the surface potential change of CIGS solar cell material under monochromatic illumination by using Kelvin probe force microscopy


 Photovoltage, KFM, surface potential, CIGS solar cells, bandgap grading 


Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
Phone:+81 (0)3 5452 6036 / Fax:+81 (0)3 5452 6088


IMTEK - Department of Microsystems Engineering
Microsystem Materials Laboratory (MML), University of Freiburg
Georges-Koehler-Allee 103, 79110 Freiburg, Germany

E-mail   hb-01 at iis.u-tokyo.ac.jp
Download icon_pdf.gifAbstract2014_HBiegler.pdf


Short resume :
2012-now Actual position
2008 - 2012 Here
2004-2008 Here
2001-2004 Here

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Research Projects in Limms

1- Investigation of the surface potential change of CIGS solar cell material under monochromatic illumination by using Kelvin probe force microscopy
Context :
CIGS thin film solar cells improved over the last years but the electrical properties are not yet fully understood. The theoretical efficiency maximum is at 1.4 eV bandgap energy, however, CIGS materials exhibit an efficiency decay at bandgap energies > 1.1 eV. For a better understanding of the electrical properties of polycrystalline CIGS materials, it was intended to determine surface potential change of CIGS materials both at the grain interior and the grain boundary.
Objectives & Methods :
The surface potential change of bandgap graded CIGS solar cell material under the illumination with monochromatic laser light with different wavelengths was measured. For that purpose the photovoltage at the grain interior and grain boundaries of the polycrystalline material, caused by the irradiation of the surface, was measured by using a combined AFM/KFM system. 
Results :
The photovoltage that was expected to increase with higher photon energy of the irradiating light starts dropping when the photon energy exceeds a certain amount of energy over the minimum bandgap energy of the sample. A possible explanation could be, that due to the bandgap grading a low energy barrier might be established in the depletion region of the p‑n junction that can be overcome by charge carriers if the conduction band is laterally evenly filled. This should be the case for lower energetic light with a higher penetration depth before absorption. With higher photon energies, however, due to the smaller penetration depth of the photons a charge carrier gradient in the depletion region might be established that induces a charge carrier motion towards the bulk material.
References and publications :
[1] M. Takihara, Doctoral dissertation, 2009.
[2] S. Minoura et al., J. Appl. Phys., 113 (063505), 2013.

Main publication List (papers, conferences and patent)







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