Thin Solid Films, Vol.403-404, 197-203, 2002
Production technology for CIGS thin film solar cells
Composition ratios such as Cu/(In+Ga) and Ga/In have a great influence not only on performances but an yields of Cu(In,Ga)Se-2 (CIGS) solar modules. We demonstrated on a composition monitoring of a Cu/(In+Ga) ratio and control of a Ga/In profile in the CIGS films using a Cu rich composition in Cu rich growth stage. A composition monitoring method based on emissivity of CIGS films is proposed and developed for the preparation of large area CIGS films. The substrate temperature cooling rate immediately after the deposition increases with increasing the Cu/(In+Ga) ratio in Cu-rich films, while Cu poor films have almost the same cooling rate. Measurement of the temperature cooling rate therefore enables the determination of whether the deposited film has Cu rich or poor composition. In and Ga depth profiles in completed CIGS films depend on the Cu/(In+Ga) ratios in Cu rich growth stage. Smooth gradient profile near the surface was formed in the CIGS film prepared from a heavily Cu rich film due to the fast diffusion rate of Ga into an excess Cu,Se layer. The bandgap profile, induced by the Ga/In depth profile, can be controlled by the Cu rich composition in Cu rich growth stage to improve performance of solar cells.