Residual stress in CIGS thin film solar cells on polyimide: simulation and experiments

Sputtering technique is used to prepare Cu(In,Ga)Se₂ (CIGS) thin film solar cells on a UPILEX-S 50S polyimide substrate in order to investigate the residual stress in the Mo back contact and CIGS absorber layer after selenized annealing with various the thickness ratios of the Mo contact, R_Mo. A comparison between the results of numerical simulation and those obtained from X-ray diffractometry, indicate the existence of compressive residual stress in both the Mo contact and the CIGS absorber layer. The residual stress in the Mo contact was inversely proportional to the residual stress in the CIGS absorber layer. Residual stress decreased with an increase in the thickness ratio of the Mo contact. The empirical formulae for the residual stresses as a function of R_Mo in the Mo and CIGS films were deduced, from the results of this study.