Preparation of (Cu,Ag) 2 SnS 3 Thin‐Film Solar Cells by Sulfurizing Metal Precursors Featuring Various Ag Contents

To enlarge the bandgap of Cu2SnS3 (CTS), Ag-incorporating CTS thin films are successfully deposited by sulfurizing Ag-Cu-Sn precursors featuring various Ag contents and the constant Cu/Sn ratio of 1.75, which is the optimal value for CTS thin-film solar cells. To control the Ag content of the films, the thickness of the Ag layers of the precursors is varied from 0 to 200 nm, which corresponds to the Ag/(Ag + Cu) ratio of the films varying from 0 to 0.32. The films featuring Ag/(Ag + Cu) ratios smaller than 0.16 are solid solutions of CTS and Ag2SnS3, that is, (Cu,Ag)(2)SnS3 (CATS), while the film featuring the Ag/(Ag + Cu) ratio of 0.32 appears to be a mixture of CATS and Ag-Sn-S related crystals, such as Ag8SnS6. The grain size and bandgap increase as the Ag/(Ag + Cu) ratio increases up to 0.16. The highest power conversion efficiency (PCE) of 3.6% is obtained for the cell featuring the Ag/(Ag + Cu) ratio of 0.08. The highest open cell voltage (V-OC) for the CATS thin-film solar cells is obtained to be 0.284 mV. However, the improvement in PCE is attributed to the increase in the short-circuit current density and fill factor of the cell rather than the increase in V-OC.