Synergistic Effect of Mn on Bandgap Fluctuations and Surface Electrical Characteristics in Ag-based Cu2ZnSn(S,Se)4 Solar Cells

In Cu2ZnSn(S,Se)4 photovoltaic devices, the exceptionally high density of 2CuZn + SnZn donor defects may induce bandgap fluctuations and thus limit Voc and PCE enhancement. We have previously reported that the partial substitution of Ag for Cu in Cu2ZnSn(S,Se)4 provides a promising way to effectively suppress CuZn defects and considerably enhance the cell performance for Cu2ZnSn(S,Se)4 photovoltaic devices. However, the bandgap fluctuations and detrimental band tailing fundamentally still limit cell performance. On the basis of a Ag-substituted CZTSSe system, in this paper, we demonstrate that partially substituting Zn with Mn could be a feasible tactic to pronouncedly decrease the bandgap fluctuations and prevent detrimental band tailing. Our in-depth investigation reveals that Mn substitution could increase depletion width, decrease the defect densities of the CuZn acceptor and 2CuZn + SnZn donor, and enable grain boundary (GB) inversion in a (Cu,Ag)2ZnSn(S,Se)4-based cell. As a result, an impressive PCE of 11.81% was achieved when the Mn substitution level was 10%, with a Voc of 478 mV, a Jsc of 37.89 mA cm−2, and an FF of 65.23%. This is so far the highest efficiency among Mn-substituted CZTSSe-based photovoltaic devices. By thoroughly understanding these photoelectric properties of the CZTSSe-based photovoltaic devices, we believe that the breakthrough in device efficiency will come soon through our continuous efforts.