High temperature life testing of the Advanced Triple Junction (ATJ) solar cell

We present high temperature life testing data on Emcore's GaInP2/InGaAs/Ge Advanced Triple-Junction (ATJ) solar cell. One of the most complex materials structures in a solar cell is the metal-semiconductor interconnect interface. Solid-state diffusion of metal into the semiconductor at this interface can lead to shunting and degradation of the solar cell. The rate of diffusion is well known in device physics to be dependent on temperature and the specific metal and semiconductor materials. The purpose of this study was to characterize the survivability and diffusion characteristics of the top metal contacts to the ATJ solar cell. A large number of cells were subjected to accelerated high temperature life tests at 200 degrees C, 220 degrees C, 240 degrees C, and 260 degrees C, for up to 5,000 hours. Bare cells, as well as cells with welded and soldered interconnects were studied. No failures (degradation > 2% relative) were observed. Critical conclusions regarding the reliability of the ATJ cell are presented.