Helianthos : Roll-to-Roll deposition of flexible solar cell modules

In the development of the roll-to-roll deposition of amorphous silicon by means of plasma enhanced chemical vapor deposition, a number of different plasma aspects have been of importance. First, the understanding of process windows in terms of a dust free plasma has led to the formulation of an empirical scaling law for the dust free to dust forming transition in terms of the crucial process parameters such as, e.g., power and gas flows. Second, the homogeneity of deposition on an effective width of 30 cm has been demonstrated to be better than 5%. Increasing the deposition rate might be achieved by increasing the power density, but it scales only as (power density) 0.77 . A last important issue in roll-to-roll processing of long runs is process stability and on-line quality control. The accurate measurement of self bias voltage and optical thickness of the deposited stacks have proven to be very useful in this context.