• Current Photovoltaic Research
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• v.7 no.1
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• pp.1-8
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• 2019

The $Cu(In,Ga)Se_2$ (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 $500^{\circ}C$ the CIGS film consisted of CIGS phase and secondary phases including $In_4Se_3$, InSe, and $Cu_9(In,Ga)_4$. 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 $450^{\circ}C$ and subsequent Se annealing $550^{\circ}C$ showed a densely-packed grains with smooth surface, well-aligned bamboo grains on the top of the film, little voids 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.

• Current Photovoltaic Research
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• v.10 no.2
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• pp.39-48
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• 2022

A Se-containing Cu/SnSe₂/ZnSe precursor was employed to introduce S to the precursor to form Cu₂ZnSn(S,Se)₄ (CZTSSe) film. The morphology of CZTSSe films strongly varied with two different pre-annealing environments: S and N₂. The CZTSSe film with S pre-annealing showed a dense morphology with a smooth surface, while that with N₂ pre-annealing showed a porous film with a plate-shaped grains on the surface. CuS and Cu₂Sn(S,Se)₃ phases formed during the S pre-annealing stage, while SnSe and Cu₂SnSe₃ phases formed during the N₂ pre-annealing stage. The SnSe phase formed during N₂ pre-annealing generated SnS₂ phase that had plate shape and severely aggravated the morphology of CZTSSe film. The power conversion efficiency of the CZTSSe solar cell with S pre-annealing was low (1.9%) due to existence of Zn(S.Se) layer between CZTSSe and Mo substrate. The results indicated that S pre-annealing of the precursor was a promising method to achieve a good morphology for large area application.