The Creation and Annealing Kinetics of Fast Light Induced Defect States created by 1 Sun Illumination in a-Si:H

Preliminary results are presented on the kinetics of fast states at 25°C created by 1 sun illumination in protocrystalline hydrogen diluted a-Si:H films. The results are for the bulk properties of the a-Si:H films which was confirmed by the similarity of results obtained on corresponding intrinsic layers in p-i-n solar cells. It is found that the kinetics exhibit two regimes. The first regime is in the form of a delay before the onset of an A·log(t) time dependence indicative of a dispersive process. Despite the unexpected effect of a dependence of this first regime on the degradation/annealing history of the samples, it was possible to characterize the highly reproducible logarithmic dependences for different illumination times as well as in the presence of different carrier generation/recombination rates. It is found that for the degradation times studied, the annealing kinetics associated with the second regime are independent of the 1 sun illumination time but are dependent on the recombination introduced by illuminations as low as ∼0-5 of 1 sun. These fast states are located close to midgap, similar to the position of dangling bond defects. The results presented raise interesting questions that still need to be answered about the nature and origin of the fast defects in order to assess their contribution to the long term degradation and the overall stability a-Si:H materials.