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The influence of oxygen and nitrogen impurities on the performance of thin-film solar cells based on microcrystalline silicon (mu c-Si:H) has been systematically investigated. Single mu c-Si:H layers and complete mu c-Si:H solar cells have been prepared with intentional contamination by admitting oxygen and/or nitrogen during the deposition process. The conversion efficiency of similar to 1.2 mu m thick mu c-Si: H solar cells is deteriorated if the oxygen content in absorber layers exceeds the range from 1.2 x 10(19) to 2 x 10(19) cm(-3); in the case of nitrogen contamination the critical impurity level is lower ([N](critical)=6 x 10(18)-8 x 10(18) cm(-3)). It was revealed that both oxygen and nitrogen impurities thereby modify structural and electrical properties of mu c-Si:H films. It was observed that the both contaminant types act as donors. Efficiency losses due to oxygen or nitrogen impurities are attributed to fill factor decreases and to a reduced external quantum efficiency at wavelengths of >500 nm. In the case of an air leak during the mu c-Si:H deposition process, the cell performance drops at an air leak fraction from 140 to 200 ppm compared to the total gas flow during i-layer deposition. It is demonstrated that oxygen and nitrogen impurities close to the p/i-interface have a stronger effect on the cell performance compared to impurities close to the n/i-interface. Moreover, thick mu c-Si:H solar cells are found to be more impurity-sensitive than thinner cells

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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.

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