Study of the Effect of Absorber Etching on the Back Contact Performance of CdTe Solar Cells

The application of copper in the CdTe back contact is believed to be crucial to form an ohmic contact with CdTe. On the other hand it has actually shown other beneficial effects such as increasing the carriers concentration, indeed the highest conversion efficiencies have been obtained only with copper insertion. However it is not clear if this is due to a compensation reduction or to a formation of new defects in bulk CdTe. Moreover, the role of the etching process is also very important, it is believed that a tellurium rich layer is formed which might react with copper forming CuxTe. We have prepared CdTe devices with Cu/Au back contact on differently etched CdTe surface and tested them by applying thermal, luminous and electrical stresses. The devices and their degradation effects are studied by current-voltage, capacitance voltage, drive level capacitance profiling and admittance spectroscopy characterization techniques and the etching effect is analyzed by Raman measurements.