Consistent processing and long term stability of CdTe devices

A technology for processing of thin film CdS/CdTe devices has been developed in our laboratory. This in-line, continuous, pilot system enables unique processing steps and conditions not available with batch processing and allows the fabrication of a large number of devices. Results from the pilot scale system are applicable to systems processing larger areas. Utilizing the pilot system, significant progress has been made towards demonstrating consistent stability (resistance to degradation) for thin film CdTe photovoltaics. We have repeatedly shown that devices with good stability can be produced if processed at the optimum set of conditions. Small changes in processes can lead to significant differences in device stability. Among the processing steps for fabrication of CdTe devices, the CdCl₂ treatment has a significant effect on performance and stability. A metric has been developed to predict the stability of devices at the time of device fabrication. Accelerated stress testing is ongoing. Extremely long duration stress testing (65°C, open circuit conditions for ∼30,000 hours with 5 hours of illumination out of 8 hour cycle) has demonstrated that the rate of efficiency loss levels out with final efficiencies in the range of 8.5% ∼ 9.5%. A production prototype system for processing nominally 2 MW/yr. is currently under construction. This system utilizes the process definition developed in the pilot system.