Previously, we reported a conversion efficiency of 15.5% on Se-free Cu(In,Ga)S2 solar cell via KCN-free process. It was the highest conversion efficiency on the Se-free Cu(In,Ga)S2 solar cells, however, it is still lower compared with Cu(In,Ga)Se2, CdTe and perovskite solar cells. There are three big restricting factors of the Eff enhancement on Se-free Cu(In,Ga)S2 solar cell. First, the carrier density is very low. This low carrier density is assumed that the degradation of all electric parameters, especially, open-circuit voltage and fill-factor. Secondly, the life time of absorber is very short, which is assumed to be the restrict of the open-circuit voltage. At last, Se-free Cu(In,Ga)S2 absorber has surface roughness after sulfurization. It is presumed that the fill-factor degradation was caused by the roughness of absorber. To improve them, we have been trying a variety of experiments on Se-free Cu(In,Ga)S2. In this paper, we mainly focus on the improvement of the carrier density, and report our latest progress. As a result, our champion cell demonstrated over 16% efficiency via in-house measurement, contributed by enhancement of carrier density. Additionally, we conducted some other experiments to boost the efficiency on Se-free Cu(In,Ga)S2 solar cells, for example, rapid thermal sulfurization, Ag doping, Cd-free buffer layer and so on. At the conference, we will show each effect of above experiments and reveal which trial was more effective for the Se-free Cu(In,Ga)S2 solar cells.
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