Apparatus surface conditioning effects in copper sulfide reactive sputtering for photovoltaic applications

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Abstract
The electrical requirements of the CdS/Cu x S solar cell place severe requirements on the Cu x S stoichiometry. While using Cu–Ar–H2S cylindrical magnetron reactive sputtering to depositcoatings for use in CdS/Cu x S solar cells, we encountered film property variations which were traced to relatively long time constants (∠100 min) for equilibration of the cathode and wall surfaces. This paper describes experiments in which equilibration times were determined for cases where: (a) cathode and wall surfaces were initially both in a ’’clean’’ fresh copper state, (b) cathode was in the clean state and walls were in the conditioned state, and (c) cathode was in the conditioned state and walls were in the clean state. The time constants were found to be determined primarily by the initial state of the cathodesurface, the H2S injection rate, and the discharge current. Heterojunctions with sputteredCu2S deposited after proper conditioning onto evaporated CdS and (CdZn)S have yielded short circuit currents ∠19 mA/cm2 which are comparable to those obtained with copper sulfide deposited by the more conventional ion exchange processes. An efficiency of ∠7% has been achieved for a (CdZn)S/Cu x S cell with sputteredCu2S.

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