Hydrogen content, transport properties and light degradation of a-Si:H films containing artificially generated interfaces

Using different methods, intrinsic a-Si:H/a-Si:H interfaces were artificially generated in hydrogenated amorphous silicon films. Three types of interfaces were studied: (i) interfaces in which only the regrowth mechanisms were present; (ii) interfaces where both the regrowth mechanisms and the initial transient state of the discharge were present; and (iii) interfaces in which the initial transient state of the discharge was the dominant mechanism. The resulting material was characterized by measuring the hydrogen content, the electronic density of states, the transport properties and the film stability as a function of the interface type and density. It was found that samples containing interfaces of the first type are not very different from samples without interfaces and that transient discharge processes produce accumulation of hydrogen in the interface, which could relieve strains in the network. In order to investigate the influence of this strain-relieving mechanism on the Staebler-Wronski effect, p-i-n solar cells containing these H-rich interfaces were prepared and measured, together with "normal" cells. It was found that the former cells are more stable than the "normal" cells. The results of the present paper provide a new and promising way to circumvent the problem of the long term stability of hydrogenated amorphous solar cells.