Optimization of CBD CdS process in high-efficiency Cu(In,Ga)Se2-based solar cells

We present an optimization of the US chemical bath deposition process as applied to high-efficiency Cu(In,Ga)Se-2 photovoltaic thin-film absorber materials. Specifically, we investigated deposition time (thickness), bath temperature (65, 80 and 90degreesC) and a Cd2+ partial-electrolyte treatment of the chalcopyrite absorber prior to US deposition. We found that thinner US layers (grown on as-deposited absorbers) allowing more light to reach the junction are not necessarily conducive to higher short-circuit current density. Device performance was found to be dependent on the CdS layer thickness, but rather independent of the growth temperature. On the other hand, devices prepared from absorbers subjected to a Cd2+ partial electrolyte treatment show that the device performance dependence on US thickness is somewhat alleviated, and devices incorporating thinner US layers are possible without loss of parameters, such as open-circuit voltage and fill factor. (C) 2002 Elsevier Science B.V. All rights reserved.