Gold-free Cu-metallized III-V solar cell

Au-free, fully Cu-metallized InGaP/InGaAs/Ge triple-junction solar cells using Pd/Ge/Cu as front contact and Pt/Ti/Pt/Cu/Cr as back contact were fabricated and the results are reported for the first time. From the specific contact resistance measurement, these Cu-metallized ohmic contacts have low contact resistance in the order of 10^-6 Ω-cm². AES and TEM results clearly show the formation mechanisms of the Cu-metallization ohmic structures, for Pd/Ge/Cu contact, it was due to the formation of Ge diffusion into the GaAs layer, and for the Pt/Ti/Pt/Cu/Cr contact, it was due to high work function of Pt layer, these copper metallized ohmic contacts were quite stable even after 310 °C annealing. The I-V curves of the Cu-metallized InGaP/InGaAs/Ge triple-junction solar cells showed similar electrical characteristics to the solar cells with Au-metallized triple junction solar cell. Overall, the Pd/Ge/Cu and Pt/Ti/Pt/Cu ohmic contacts have been successfully applied to the InGaP/InGaAs/Ge triple-junction solar cells and demonstrated excellent performance.