Effects of Hydrogen Dilution on Voc in a-Si:H pin Solar Cells

We study the effects of hydrogen dilution on the open circuit voltage of a-Si:H pin solar cells fabricated by rf glow discharge growth. We keep the p and n layers the same and only vary the i layer properties. A normal a-Si:H i layer, an H-diluted i layer, and a thin H-diluted layer inserted between p and normal i layer are selected for this study. We measure the JV characteristics and theinternal electric field distribution using a transient-null-current technique both in annealed and light soaked stated. We find that hydrogen dilution does stabilize the Voc either in a bulk H-diluted i layer or in a thin layer between p and normal i layer after 100 hours AM1 sun light soaking. From dark IV measurement, both H-diluted cells show little change in current at voltage near Vocbefore and after light soaking; while the normal a-Si:H cell does show a noticeable change. Also the internal field measurements find a stronger electric field starting from p and i interface for both H-diluted cells compared to the normal a-Si:H cell. Furthermore, there are no measurable changes in the field profiles after 100 hour AM1 light-soaking for both H-diluted and normal a-Si cells. Allthese suggest that hydrogen dilution increases the field strength near p and i interface, which is the key that leads to a more stable Voc of H-diluted cells.