Integrated Inline Characterisation Techniques for Improved Silicon Heterojunction Solar Cell Production

Silicon heterojunction (SHJ) technology is gaining market share in photovoltaics due to its lean process sequence, high efficiency potential and low CO2 footprint. Margins for improvement in performance, yield and cost are decreasing, while at the same time the benefit of even small gains is growing with production volume. It is therefore worthwhile to implement detailed monitoring of process parameters as well as inline characterisation of the cell precursors during production. In this contribution, we present an overview of inline characterisation techniques that are relevant to SHJ cell production and critically discuss their benefits and weaknesses with the help of some showcase examples. We find that inline characterisation is useful at multiple stages of production. Measurements between processing steps allow early detection of defective wafers, preventing unnecessary processing. They also permit evaluation of the performance of individual manufacturing processes. As one prominent example, we demonstrate the generation of highly-resolved thickness maps of the amorphous silicon and transparent conducting oxide layers using reflection spectroscopy combined with multispectral imaging, as well as physical and machine learning models. This method provides information at an unprecedented level of detail about the layer deposition processes that are at the heart of SHJ technology.