Amorphous Ge Passivation Effects on Ge Solar Cells

Amorphous Ge (α-Ge) deposited from a high purity Ge source was adopted to study the passivation applications for Ge solar cells. The measured results indicate that postannealing treatment onto the solar cell with α-Ge plays an important role in determining the solar cell performance. For samples with α-Ge and a GaAs contact layer outside the front metal grid region, more than one-order decrease of dark current can be obtained after conducting a postannealing step at 300 °C for 2-10 min. In addition, solar cell performance characteristics are dramatically improved with 1-sun V_oc from 0.035 to 0.16 V, J_sc from 16.1 mA/cm ² to 27 mA/cm ² , fill factor from 0.17 to 0.40, and efficiency η from 0.1% to 1.7% after completing the postannealing process. Furthermore, after removing the GaAs contact layer outside the front metal-grid region, solar cells with α-Ge show 1-sun efficiency 1.19% (6.54% versus 5.35%) and fill factor 0.14 (0.68 versus 0.54) higher than those samples without α-Ge, which correspond to 22.2% and 25% relative increase in the efficiency and the fill factor, respectively.