Amorphous Silicon Alloy Triple-Junction Solar Cell with 14.6% initial and 13.0% Stable Efficiencies

An initial conversion efficiency of 14.6 percent has been achieved using amorphous silicon-based alloy in a spectrum splitting triple-junction structure. After 1000 hours of indoor one-sun light soaking at 50 degrees C, the stabilized efficiency is 13.0 percent. Both efficiencies are the highest reported to date for amorphous silicon alloy solar cells and have been independently confirmed by theNational Renewable Energy Laboratory. The device was deposited onto a stainless steel substrate coated with textured silver/zinc oxide back reflector. The bottom and middle cells use amorphous silicon-germanium alloys, employing high hydrogen dilution in the gas mixture and bandgap profiling in the cell design. The top cell uses amorphous silicon alloy with high hydrogen dilution. Key factorsleading to the achievement include a) improvement of the bottom cell that exhibits an AM1.5 efficiency of 10.4 percent and quantum efficiency of 45 percent at 850 nm; b) improvement of the tunnel junctions between the component cells by incorporating a novel multilayered structure with microcrystalline p and n layers; and c) improvement of transparent conductive oxide for enhancing the shortwavelength response of the top cell.