The evolution of excess defects in hydrogenated amorphous Si p-i-n solar cells, induced by a forward current in the dark, was studied by modeling their measured dark and illuminated current-voltage and quantum efficiency characteristics at different stages of degradation. The electrical-optical model was based upon the solution of the Poisson’s and continuity equations. Modeling revealed that metastable defects were mainly produced in regions where tail-to-tail recombination of injected electrons and holes was high. These regions were characterized by either a high defect density or a low electric field. Simulation of experimental characteristics after 1h of current injection indicated that the spatial generation of current-induced defects was highly non-uniform, with the main defect formation occurring near to the p/i interface and, to a lesser extent, towards the n/i interface. Few defects were generated over the bulk intrinsic layer. Modeling of the characteristics after a longer duration of current injection indicated a broadening of the current-induced defect zone from the interfaces to the bulk intrinsic layer. After prolonged current injection, the density of excess dangling-bond defects in the bulk intrinsic layer increased significantly, while the defect density near to the p/i interface decreased; resulting in a more uniform distribution of excess metastable defects. Evidence from modeling suggested that some metastable defects migrated from the interfaces, and towards the bulk. It was concluded that prolonged current injection not only produced excess metastable defects, but also caused these defects to migrate to regions of lower defect density.

Metastable Defect Migration under High Carrier Injection in Hydrogenated Amorphous Silicon p-i-n Solar Cells. U.Dutta, P.Chatterjee, S.Tchakarov, M.Uszpolewicz, P.Roca i Cabarrocas: Journal of Applied Physics, 2005, 98[4], 044511 (8pp)