10% Efficiency Cu(In,Ga)Se2 Solar Cell with Strongly (220)/(204) Oriented Cu-Poor Absorber Layers Sputtered Using Single Quaternary Target

Cu-poor CIGS thin films were fabricated by RF magnetron sputtering from a single quaternary target with the composition of Cu_0.7In_0.7Ga_0.3Se₂, in an effort to improve the cell efficiency of CIGS solar cells. The Cu-poor thin films with the ([Cu]/[In]+[Ga]) composition ratios of 0.70–0.77 were obtained showing that the composition of the target can be transferred to the film. It was also observed that the strongly (220)/(204) preferred orientation appeared at the substrate temperatures higher than 600 °C, which is known to be essential for achieving high-quality CIGS solar cells. This result indicates that the Cu–Se compounds present in trace amounts of CIGS films hinder the (112) orientation and promotes the growth of the (220) orientation. As a result, the CIGS absorber layer with the Cu-poor composition and the (220)/(204) preferred orientation exhibited a drastically improved cell efficiency of 10.02%.