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 2Cu(Zn) + Sn-Zn donor defects may induce bandgap fluctuations and thus limit V-oc 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 Cu-Zn 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 Cu-Zn acceptor and 2Cu(Zn) + Sn-Zn donor, and enable grain boundary (GB) inversion in a (Cu,Ag)(2)ZnSn(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 V-oc of 478 mV, a J(sc) 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.