Surface Effects of the Cu S Film

The carrier transport in the very thin Cu S layer is sensitively affected by surface effects of this layer. The dipping process does not readily lead to optimum photovoltaic operation of the Cu S film. Appropriate treatments have to be applied in order to improve the properties of the Cu S and to reduce surface recombination. 

A window of a thin CU2O layer on the surface reduces surface recombination drastically. This layer however can only be formed on highly stoichiometric Cu2Soron a metallic copper layer, which can be provided either by the deposition of the additional copper or by the extraction of S from the Cu S layer in a H2 glow-discharge and a siibsequent heat-treatment in air /37/. This heat-treatment causes on the one hand copper diffusion into the Cuj S and thereby an improvement of the stoichiometry, on the other hand the formation of CU2O on the surface. 

Excessive heating in air results in the formation of CuO which presents no suitable window layer on the Cu S surface, hence the surface recombination increases as described in chapter 6,4. The kinetics of the post-dip treatment has been investigated by Pfisterer et al. /37/. 

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