The recombination mechanism and defect energy levels of Ag-doped ZnSnN2/ZnSnN2 pn homojunction solar cells

The photovoltaic performance of ZnSnN2 homojunction has never been studied. Here, ZnSnN2 homojunction solar cells with Ag-doped ZnSnN2 as the p-type layer are fabricated with magnetron sputtering deposition, and the mechanism limiting the photovoltaic performance is revealed. The junction is abrupt. The current transport is dominated by thermionic emission below 320 K and generation-recombination (GR) in the space charge region in 330–380 K. Below 320 K, the short circuit current density and the open circuit voltage are limited by nonradiative interface recombination. The open circuit voltage loss also results from interfacial barrier height inhomogeneity, which obeys the Gaussian distribution model or the temperature fluctuation of interface barrier heights for holes. At higher temperatures, deep energy levels in the middle of the bandgap result in the GR in the space charge region. One shallow energy level at 0.13 eV and one interface energy level at 0.72 eV above the valence band maximum are observed. The former is likely induced by substitutional Ag-doping.