CdS is used as a passivation layer in CIGS based thin film solar application. For accurate measurement of the CdS layer on the product one need to know optical constants of the material. This is easily done with the MProbe VisNIR system.( http://www.semiconsoft.com/wp/mprobe20desktop/)
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CdS layer: measurement of thickness and n&k
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CdS Measurement
CdS is used as a passivation layer in CIGS based thin –film solar cells. It is
deposited on top of the absorber (CIGS) in the solar cell stack. Surface of the CIGS layer
is very rough and, during on-product measurement ,only thickness of the CdS is,
typically, determined using known optical constants data.
To determine optical dispersion of the CdS, two samples of the CdS on glass were
prepared using same procedure as on product deposition.
MProbe VisNIR system (400-1700nm wavelength range) was use to measure these
sample and the data was analyzed to determine thickness and n& k of the CdS layer.
CdS dispersion was represented using Tauc-Lorentz approximation to account for
differences with standard library material. Light scattering effect from surface roughness
was corrected using Kirchhoff scalar approximation and estimated roughness was
determined from the measurement along with thickness and n, k values.
Fig. 1 CdS sample #1 the fit of the model to measured data. CdS layer thickness was
determined as 50nm, surface roughness: 12 nm, dispersion (see Fig.2)
83 Pine Hill Rd. Southborough, MA 01772
Phone +1.617.388.6832 Fax. +1.508.858.5473
email: info@semiconsoft.com http://www.semiconsoft.com
2. Fig. 2 CdS sample #1 dispersion determined from the measurement.
Fig. 3 CdS sample #2 the fit of the model to measured data. CdS layer thickness was
determined as 121nm, surface roughness: 22 nm, dispersion (see Fig.2)
83 Pine Hill Rd. Southborough, MA 01772
Phone +1.617.388.6832 Fax. +1.508.858.5473
email: info@semiconsoft.com http://www.semiconsoft.com
3. Fig. 4 CdS sample #2 dispersion determined from the measurement
CdS dispersion determined from sample #1 and #2 is almost identical with only minor
differences.
The results were saved as a CdS material in the database for use for on-product
measurement of the TCO/CdS/CIGS/Mo stack.
83 Pine Hill Rd. Southborough, MA 01772
Phone +1.617.388.6832 Fax. +1.508.858.5473
email: info@semiconsoft.com http://www.semiconsoft.com
