Fabrication of Cu2SnS3 thin film solar cells using Cu/Sn layered metallic precursors prepared by a sputtering process

Abstract

As an alternative to Cu(In,Ga)(S,Se)2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTS)-based thin film solar cells (TFSCs), the ternary chalcogenide semiconductor Cu2SnS3 (CTS) is an emerging material with suitable optical band gap energy ranging from 0.93 to 1.77eV and high absorption coefficients (>104cm−1). In this study, we report the preparation of high-quality CTS thin films by the annealing of the sputtered Cu-Sn metallic precursor under S vapor atmosphere in a graphite box using the RTA process. Furthermore, the influence of different S vapor partial pressures in the graphite box during annealing on the properties of the CTS thin films has been investigated systematically. It is observed that the properties and photovoltaic performance of the CTS thin films are strongly dependent on the S vapor partial pressure during annealing. The monoclinic crystal structure is observed from X-ray diffraction (XRD) of the (112), (220), and (312) planes, and it is further confirmed using Raman spectroscopy by the presence of Raman peaks at 295 and 354cm−1. The direct band gap energy is found to be 0.91eV by extrapolation from external quantum efficiency (EQE) measurement of a CTS thin film annealed using 60mg of S powder. The preliminary best power conversion efficiency (PCE) of 2.21% with a short circuit current density of 29.7mA/cm2, an open circuit voltage of 179.5mV, and a fill factor of 41% have been obtained for a CTS thin film annealed using 60mg of S powder, although the processing parameters have not been optimized.