Stability studies of component cells for multijunction amorphous silicon alloy solar cells

The authors have studied the light-induced degradation and saturation behavior of component cells for double- and triple-junction a-Si alloy solar cells. Top a-Si alloy cells reach saturation after 300 hours of one-sun light soaking with 10-12% degradation. Both middle and bottom a-SiGe alloy cells show signs of saturation at around 600 hours under simulated light illumination appropriate for these cells; the degradation after 1000 hours of exposure is 16-18%. Based on this study it is estimated that double-junction cells will degrade by 12-18%, and triple-junction cells will degrade by 10-18%. Experimental results also reveal that the degradation of top cells, particularly in open-circuit voltage, is determined by the bulk properties instead of the interface between p and i layers. Further improvement of bulk intrinsic layer quality of top cells can reduce the degradation of multijunction solar cells