In-situ transmission measurements as process control for thin-film silicon solar cells

In this work, in-situ transmission measurements using plasma as light source are presented for the determination of growth rate and crystallinity during silicon thin-film growth. The intensity of distinct plasma emission lines was measured at the backside of the transparent substrates on which silicon films, ranging from amorphous to microcrystalline, were deposited. Using this configuration, the growth rate of thin-films was determined with high accuracy. In addition, we show that the crystallinity of the films can be monitored in the most critical range (between 40% and 80%) for microcrystalline silicon solar cells by evaluating the intensity ratio of two transmitted wavelengths in-situ. The gradual change in the absorption behaviour of the films during the phase transition is reflected by this ratio of two wavelengths as demonstrated by the good correlation with the crystallinity fraction determined by ex-situ Raman spectroscopy. This approach of in-situ transmission spectroscopy provides an easy-to-implement monitoring and control system for the industrial deposition of thin-film silicon solar cells, as critical material properties can be determined real-time during the deposition process even on rough substrates that are optimized for light trapping in solar cells.

► Transmission measurements were performed during the growth of device grade thin-film silicon for photovoltaic application.
► The plasma emission of the PECVD process was used as light source.
► Distinct plasma wavelengths were recorded over the time to determine the thickness and the crystallinity of the silicon layer.Figure optionsDownload as PowerPoint slideHighlights
► Transmission measurements during silicon growth for photovoltaic application.
► Plasma emission is used as the light source.
► In-situ determination of growth rate and film thickness.
► In-situ determination of silicon film crystallinity.
► Absorption characteristic of silicon.