Cu2ZnSn(S,Se)4 (CZTSSe) solar cells

Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have gained recent researchattention as lab-scale devices have achieved 12.6% power conversion efficiency (p.c.e.) [1]. However, CZTSSe performance is limitedby low open-circuit voltages (VOC) which can be associated withthe detrimental defect properties of the bulk absorber [2]. Oneroute to improve device performance of CZTSSe absorbers isthrough material alloying, where various elements can be incorporated into the tetragonal crystal lattice to modify the optoelectronic properties of the absorber. Notably, Ge-alloyed Cu2Zn(Sn,Ge)(S,Se)4 (CZTGeSSe) has demonstrated improved performancefor CZTSSe absorbers through improved optoelectronic propertiesand the ability for band gap tuning/grading of the film [3]. In thiswork, we further expand our research in kesterite-based alloymaterial systems to include Ag-alloyed (Ag,Cu)2ZnSnSe4 (ACZTSe),where modification of the absorber properties has similarly beenachieved. Here we report the successful formation of ACZTSe solarcells from heterogeneous nanocrystal inks and characterize therole of Ag on the grain-growth, absorption, defect, and deviceproperties of this material. Nominal atomic Ag-alloy concentrations of [Ag]/([Ag]þ[Cu]) at 0%, 5%, and 50% are considered here