Magnetron Sputtering Route to Efficiency-Enhanced Cu2ZnSnS4 Thin Films as the Counter Electrode of Dye-Sensitized Solar Cells

High quality Cu2ZnSnS4 and Cu2ZnSn(S,Se)(4) (CZTS and CZTSSe) thin films were prepared by a simple two-stage process, in which Cu-Zn-Sn ternary alloy precursor layer was first sputtered on FTO substrate from a single target and then CZTS and CZTSSe thin films were obtained by the subsequent sulfurization and selenization. The as-prepared CZTS and CZTSSe thin films were used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Photovoltaic performances of these cells can be optimized by controlling the thickness and selenization time of both CZTS and CZTSSe thin films. The best power conversion efficiency (PCE) of these films can reach 8.42%, which is comparable to that of Pt CE (8.16%). Cyclic voltammograms (CVs) and electrochemical impedance spectra (EIS) measurements demonstrate that these as-prepared thin films possess outstanding electrocatalytic activity and conductivity, which are ideal CE materials.