Band-gap profiling for improving the efficiency of amorphous silicon alloy solar cells

We have developed an amorphous silicon alloy based solar cell with a novel structure in which the optical gap of the intrinsic layer changes in a substantial portion of the bulk. Computer simulation studies show that for a given short circuit current, it is possible with this structure to obtain higher open circuit voltage and fill factor than in a conventional cell design. Experimental cell structures have been made and confirm the theoretical prediction. The new cell design shows a considerable improvement in efficiency. Incorporation of this structure in the bottom cell of a triple device has resulted in the achievement of 13.7% efficiency under global AM1.5 illumination.