Band-gap-graded Cu2ZnSn(S1-x,Se-x)(4) Solar Cells Fabricated by an Ethanol-based, Particulate Precursor Ink Route

Abstract

Solution processing of earth-abundant Cu2ZnSn(S1-x,Se-x)(4) (CZTSSe) absorber materials is an attractive research area in the economical and large-scale deployment of photovoltaics. Here, a band-gap-graded CZTSSe thin-film solar cell with 7.1% efficiency was developed using non-toxic solvent-based ink without the involvement of complex particle synthesis, highly toxic solvents, or organic additives. Despite the high series resistance due to the presence of a thick Mo(S,Se)(x) layer and Zn(S,Se) aggregates, a high short-circuit current density (J(SC)) was generated. In addition, there was no significant difference in open circuit voltages (V-OC) between CZTS (0.517 V) and CZTSSe (0.505-0.479 V) cells, despite a significant band gap change from 1.51 eV to 1.24 eV. The high J(SC) and less loss of V-OC are attributed to the effect of band gap grading induced by Se grading in the CZTSSe absorber layer. Our environmentally benign ink approach will enable the realization of low-cost, large-area, high-efficiency thin-film solar cells.