CdTe devices have reached a remarkable success in the market due to the robustness of the material and the simplicity of producing stoichiometric absorbers. For many years one of the strong limitations of this material was its high electron affinity that needs copper in the back contact degrading the cells. However a wide community of researchers has investigated and partially solved this issue, but very little has been done on the effect of the front contact on the degradation of the cells. In this paper we analyze the effect of different TCOs on the stability of CdTe solar cells. Solar cell efficiencies show similar values but with some differences in Jsc, mostly due to the effect on the transmission spectra. However most interesting results come from the analysis of the capacitance-voltage and drive level capacitance profiling and from the aging of the different devices. Results show a different distribution of the defects for the solar cells with ITO front contact, compared to ITO/ZnO based devices. This difference is confirmed also by the aging results in open circuit, CV-DLCP measurements suggests diffusion of impurities from the glass/ITO stack.
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