The Effect of H 2 Dilution on the Stability of a-Si:H based Solar Cells

We have systematically investigated the effect of H 2 dilution on the stability of a-Si:H based solar cells. The results clearly show that the device stability against light soaking improves substantially with increasing H 2 dilution until a threshold is reached. Beyond this threshold which depends on the substrate temperature, the stability no longer changes with further increase in H 2 dilution. On the other hand, at a given ratio of H 2 to the reactant gases, the device stability generally improves with increasing substrate temperature. Multi-step light soaking experiments have shown that devices made with H2 dilution saturate much faster (∼100 hours) under one-sun illumination and exhibit little overshoot effect in the recovery process, in sharp contrast to devices made without H 2 dilution. Based on the simple two-component model for defect kinetics, these observations and the fact that the apparent saturation time coincides with the time constant of the “fast” defects strongly suggest that negligible amount of “slow” defects exist in materials made with H 2 dilution. While H 2 dilution generally suppresses the formation of microstructure giving rise to dihydride bonding and microvoids, the differences in the kinetics of light induced degradation cannot always be traced to obvious differences in these structural properties.