LayTec is currently developing the product for in-line monitoring of thin-film solar cell production processes. The upcoming sensor systems will measure the thickness of all functional layers and provide information on optical properties of the layer materials as well as surface roughness and formation of interdiffusion regions between layers.
Fig. 1:
Typical reflectance
spectrum
of a Mo/
CIGS(1500 nm)/
CdS (60 nm)/
TCO(750 nm) test
structure.
We have already approved our methods in CdTe and CIGS based processes, both for photovoltaic cells on glass and metallized polymer foils.
The future of chalcopyrite and II-VI thin-film solar cell production heavily depends on reliable in-line thickness monitoring methods. The current methods are insufficient for two reasons: 1) accurate film thickness measurements by specular reflectance are hindered by diffuse scattering on rough textured CIGS or CdTe absorbers; 2) in high temperature processes, inter-diffusion of adjacent layers takes place.
For accurate measurements of rough materials we are developing a new optical head with highly sensitive detectors which suppresses the upper listed artefacts. For the precise analysis of the spectra, we have successfully extended the conventional thin-film optical equation by correcting terms for texture, light scattering and inter-diffusion effects.
LayTec has conducted numerous tests for CdTe and CIGS absorbers, CdS buffers on absorber layers and various TCOs, both on substrates and on top of multi-layer stacks. Fig. 1 shows one of these test spectra.
The new product is designed to be integrated into virtually any deposition processes ranging from in-line processes on glass to roll-to-roll processes on polymer or metal foil.
Dr. Steffen Uredat of LayTec will present first results at the 18th International Photovoltaic Science and Engineering Conference (PVSEC 18) in Kolkata, India on 19-23 January 2009. The product release is planned for the 3rd quarter of 2009.