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Effect of chlorine activation treatment on electron beam induced current signal distribution of cadmium telluride thin film solar cells

: Zywitzki, Olaf; Modes, Thomas; Morgner, Henry; Metzner, Christoph; Siepchen, Bastian; Späth, Bettina; Drost, Christian; Krishnakumar, Velappan; Frauenstein, Sven


Journal of applied physics 114 (2013), No.16, Art. 163518, 6 pp.
ISSN: 0021-8979
ISSN: 1089-7550
Journal Article
Fraunhofer FEP ()
solar cells; cadmium tellurid; electron beam

We have investigated CdTe thin film solar cells without activation treatment and with CdCl2activation treatment at temperatures between 370 and 430 C using a constant activation time of25 min. For this purpose, CdS/CdTe layers were deposited by closed-space-sublimation on FTO coated float glass. The solar cells were characterized by measurements of the JV characteristics and quantum efficiencies. In addition, ion polished cross sections of the solar cells were prepared for high-resolution FE-SEM imaging of the microstructure and the simultaneous registration of electron beam induced current (EBIC) signal distribution. By measurement of the EBIC signal distribution, it can be shown that without activation treatment the CdTe grain boundaries itself and grain boundary near regions exhibit no EBIC signal, whereas centres of some singular grains already show a distinct EBIC signal. In contrast, after the chlorine activation treatment, the grain boundary near regions exhibit a significant higher EBIC signal than the centre of the grains. The results can be discussed as a direct evidence for defect passivation of grain boundary near regions by the chlorine activation treatment. At activation temperature of 430 C, additionally, a significant grain growth and agglomeration of the CdS layer can be recognized, which is linked with the formation of voids within the CdS layer and a deterioration of pn junction properties.