Effects of Germanium Incorporation on Electrical Properties and Photovoltaic Performance of Tin Germanium Sulfide Solar Cells

This study investigated the effects of Ge incorporation on the electrical properties and photovoltaic performance of tin(II) sulfide (SnS) solar cells. The effect of Ge content (x) in Sn_1–xGe_xS on its structural, optical, and electrical characteristics were analyzed. X-ray diffraction revealed that increasing the Ge content led to a decrease in the interplanar spacings, in accordance with Vegard’s law. The Sn_1–xGe_xS solar cells exhibited enhanced photovoltaic performance with increasing x, reaching an optimal power conversion efficiency (η) of 1.39% at x = 0.37. The formation of Ge-related shallow defect levels that act as radiative recombination centers (RCs) and the suppression of crystal defects that act as nonradiative recombination centers (NRCs), due to the promotion of grain growth with Ge incorporation, could contribute to the improvement in η. However, a high Ge concentration leads to an increased number of NRCs and a reduction in RCs in thin films. Additionally, the current density and open circuit voltage decrease due to the worsening of the cliff structure, thereby decreasing the η of solar cells. These findings indicate that controlled Ge incorporation into SnS is a viable strategy for enhancing the solar cell performance, and the Sn_1–xGe_xS alloy is a promising material for next generation solar cells.