Improving tin oxide/hydrogenated amorphous silicon interfaces for solar cell applications

To suppress the electron injection barrier at the tin oxide/hydrogenated amorphous silicon (a-Si:H) interface, the SnO₂ work function was modified by evaporating thin layers of palladium on the SnO₂ substrate prior to a-Si:H deposition. The determination of the barrier height from the current-voltage characteristics in the dark and under illumination shows that it is possible to change the barrier height between SnO₂ and a-Si:H by adjusting the thickness of the palladium interfacial layer. Moreover, no reduction of the optical transmission of the SnO₂/a-Si:H structure is observed when thin layers of palladium (20 angstrom) are introduced at the SnO₂/a-Si:H interface. This is interpreted as being a result of the protective effect of the palladium, which prevents the reduction of SnO₂ by the silane plasma and reacts with the a-Si:H layer to form a silicide compound. Auger and secondary ion mass spectroscopy measurements show that the thin palladium layers may be efficient for avoiding the interaction between SnO₂ and a-Si:H. The results are discussed in view of the improvement of the open-circuit voltage in a-Si:H-based solar cells.