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High resolution EBIC and TEM investigations on CdTe solar cells

: Zywitzki, O.


Nowak, S. ; European Commission:
27th European Photovoltaic Solar Energy Conference and Exhibition, EU PVSEC 2012. DVD-ROM : Proceedings of the international conference held in Frankfurt, Germany, 24 - 28 September 2012
München: WIP-Renewable Energies, 2012
ISBN: 3-936338-28-0
European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) <27, 2012, Frankfurt>
Fraunhofer FEP ()
thin film solar cell; CdTe; CdS; electron beam induced current; field emission scanning; electron microscopy

By the use of an ion beam preparation technique polished cross sections of cadmium telluride thin film solar cells are prepared, which enables a high resolution FE-SEM imaging of microstructure and interfaces and simultaneously the measurement of the electron beam induced current (EBIC). The effect of electron beam accelerating voltage on EBIC signal distribution was investigated. The best lateral resolution of the EBIC signal could be obtained for a relative low EB accelerating voltage of 2 keV. After increasing the accelerating voltages to 5 and 10 keV the lateral resolution is deteriorated, which can be explained by the increasing electron range.
EBIC results with high lateral resolution show that mainly areas near to the grain boundaries of the CdTe crystallites contribute to the measured signal, which can be interpreted as evidence for grain boundary near states passivation. Further it could be shown that especially small CdTe grains near the CdS interface possesses to a high EBIC signal. These results can be discussed as an effect of the chlorine diffusion during activation treatment. Because of small volume diffusion coefficient of chlorine in CdTe the diffusion occurs preferably along the grain boundaries. By the further slow volume diffusion mainly the outer regions of the grains are affected.