Improved CdTe Solar-Cell Performance by Plasma Cleaning the TCO Layer

A hollow-cathode plasma-cleaning source, designed for uniformity, was added to the load-lock region of an existing single-vacuum CdTe-cell fabrication system. This plasma source cleans the transparent-conductive-oxide layer of the cell prior to the deposition of the CdS and CdTe layers. This plasma exposure enables both thinner CdS layers and enhanced cell voltage. The net result is a reduction in CdS thickness by approximately 20 nm, while maintaining the same cell voltage or, equivalently, an increase in voltage of as much as 80 mV for the same thickness of CdS. Maps that are generated by electroluminescence and light-beam-induced current show modest uniformity improvement with plasma-cleaning treatment.