|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
LIMMS/CNRS-IIS (UMI 2820)
IMTEK - Department of Microsystems Engineering
|hb-01 at iis.u-tokyo.ac.jp|
|Short resume :|
|2008 - 2012||Here|
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 :
-  M. Takihara, Doctoral dissertation, 2009.
-  S. Minoura et al., J. Appl. Phys., 113 (063505), 2013.
Main publication List (papers, conferences and patent)