The use of online diagnostic systems for real-time quality assurance, control (and future continuous online optimization) in roll-to-roll amorphous silicon PV manufacturing

In partnership with the NREL/DOE PV Manufacturing R&D Program, Energy Conversion Devices, Inc. (ECD) has developed a comprehensive set of online diagnostic systems that allow real-time measurement of PV device characteristics in-situ during amorphous silicon (a-Si) deposition, prior to deposition of ITO, PV device characteristics measured include open-circuit voltage (V_oc), charging rate (CR), and thickness (t) of each of the three cells in the triple-junction device. Measurements are made with an rms precision of about 0.05%, and at periods of 1 s to 1 min (1 cm to 1 m). The information from these systems is displayed real-time in the control room for online quality assurance (QA) and trouble-shooting. The diagnostics systems have been incorporated into software feedback loops to control film thicknesses. We are now beginning the development of programs for continuous online optimization.