Progress in triple-junction amorphous silicon alloy solar cells with improved current mismatch in component cells

We have achieved a new world record stable efficiency of 11.8% for amorphous silicon alloy solar cells using a spectrum-splitting, triple-junction structure. In addition to our previously reported key factors leading to high performance multijunction solar cells, we have improved the current matching among the component cells. We have designed the triple structure such that the top cell, which usually exhibits the highest fill factor, remains to be the current-limiting cell in the degraded state. One critical requirement for achieving the desired current matching without sacrificing the triple cell current is to obtain a high quality narrow bandgap bottom cell capable of producing sufficient red current. Details on this narrow bandgap amorphous silicon germanium alloy cell as well as stability data on the triple-junction cell are presented.