Dynamic radiative properties of the Cu(In,Ga)Se2layer during the co‐evaporation process

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Abstract
A study of the wavelength‐integrated emissivity has been performed on the optical stack CuxSe/Cu(In,Ga)Se2/Mo. The wavelength interval used in the study was 2–20 µm, which covers 95% of the radiated heat from a black body heated to 500°C. Substrate temperatures around 500°C are commonly used in production of Cu(In,Ga)Se2thin films for solar cells. The integrated emissivity was obtained from directional reflectivity measurements of experimental samples with different thicknesses of the CuxSe layers. It was subsequently compared to the emissivity from numerical simulations based on newly obtained values of the refractive index values for Cu(In,Ga)Se2and CuxSe at these wavelengths. Good agreement was found between the measured and simulated values. At a Cu(In,Ga)Se2thickness of 1.8 µm and a Mo thickness of 400 nm, a maximum in the integrated emissivity was found for a CuxSe thickness of 30 nm. The results are valuable input into understanding the dynamics of the change in emissivity between Cu‐rich Cu(In,Ga)Se2with segregated CuxSe and Cu‐poor single phase Cu(In,Ga)Se2at temperatures around 500°C. In co‐evaporation of Cu(In,Ga)Se2, this emissivity change is often monitored and used as a process control (end‐point detection). Copyright © 2010 John Wiley & Sons, Ltd.