High efficiency multi-junction solar cells using amorphous silicon and amorphous silicon-germanium alloys

Using a novel cell design the authors have achieved a 13.7% conversion efficiency with amorphous silicon and amorphous silicon-germanium alloys in a three-cell stacked-junction configuration. 13.0% conversion efficiency was achieved in the tandem configuration. The efficiency value was measured using a triple-source solar simulator adjusted for global AM1.5 test conditions. This device has a structure of stainless steel/textured silver/zinc oxide/ni/sub 1/p/ni/sub 2/p/ni/sub 3/p/ITO/grid. The authors used an amorphous silicon-germanium alloy with the new design in the i/sub 1/ layer, and amorphous silicon alloys in the i/sub 2/ and i/sub 3/ layers. The J-V characteristic shows J/sub sc/=7.66 mA/cm/sup 2/, V/sub oc/=2.55 V, and fill factor= 0.70 with an active area of 0.25 xcm/sup 2/. The quantum efficiency of this device is 60% collection at 400 nm, 93% at the peak, 55% at 800 nm, and 21% at 850 nm. The total photocurrent density obtained by integrating the quantum efficiency envelope with the global AM1.5 spectrum is 23.5 mA/cm/sup 2/.<
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