ZnSnxGe1-xN2 as electron-selective contact for silicon heterojunction solar cells

This work reports the electrical characterization of ZnSnxGe1-xN2 (ZTGN) layers deposited on glass by sputtering and further assesses for the first time the performance of SHJ solar cells featuring them as electron-selective contacts. Bandgap, conductivity, and activation energy were found to significantly change between Sn and Ge-rich samples, but poor performance was observed when ZTGN layers were employed as electron-selective contacts for SHJ solar cells, with similar results despite changes in material properties. A non-moving Fermi level around mid-gap silicon, strong limitation due to series resistance, and poor conductivity of Ge-rich samples can account for the observed behavior. Doping of Ge-rich ZTGN appears thus necessary to build efficient devices with a ZTGN contact layer. Using an ex-situ phosphine palsma followed by annealing did not prove successful to this regard, making in-situ doping probably necessary.