Rapid laser annealing of Cu(In,Ga)Se2 thin films by using a continuous wave Nd:YAG laser (λ0= 532 nm)

Abstract

Rapid laser annealing of a Cu(In,Ga)Se2 (CIGS) thin film absorber was proposed and demonstrated using a continuous 532-nm Nd:YAG laser, following sputtering with Cu0.9In0.7Ga0.3Se2 target, because the conventional annealing temperature for improving the crystallinity of CIGS thin films is higher than the decomposition temperature of a typical flexible polymer substrate. When the laser optical power was incrementally increased over the range from 2.00 to 3.00 W, for 200 s, XRD patterns showed the formation of CIGS chalcopyrite (112), (220/204), and (312/116) phases in the laser-annealed CIGS thin films, at laser optical powers of 2.75 and 3.00 W. The band gaps of these laser-annealed CIGS thin films varied from 1.45 to 1.83 eV and depended on the laser optical power. The relative mean absorbance of the laser-annealed CIGS thin films was 1.806, suggesting that approximately 98.44% of the incident photons were observed by the 600-nm-thick film in the visible spectral region. Conductivity type varied with changes in the laser optical power. The resistivities of the laser-annealed CIGS thin films were of order of 10−3 - 101 Ω-cm.