Current Photovoltaic Research ISSN:2288-3274(Print) 2508-125X(Online)

The Cu(In,Ga)Se₂ (CIGS) thin film obtained by two-step process (metal deposition and Se annealing) has a rough surface morphology and many voids at the CIGS/Mo interface. To solve the problem a precursor that contains Se was employer by depositing a (In,Se)/(Cu,Ga) stacked layer. We devised a two-step annealing (vacuum pre-annealing and Se annealing) for the precursor because direct annealing of the precursor in Se environment resulted in the small grains with unwanted demarcation between stacked layers. After vacuum pre-annealing up to 500°C the CIGS film consisted of CIGS phase and secondary phases including In₄Se₃, InSe, and Cu₉(In,Ga)₄. The secondary phases were completely converted to CIGS phase by a subsequent Se annealing. A void-free CIGS/Mo interface was obtained by the two-step annealing process. Especially, the CIGS film prepared by vacuum annealing 450°C and subsequent Se annealing 550°C showed a densely-packed grains with smooth surface, well-aligned bamboo grains on the top of the film, little oids in the film, and also little voids at the CIGS/Mo interface. The smooth surface enhanced the cell performance due to the increase of shunt resistance.