Damage control at the SnO2/Si interface in optoelectronic amorphous silicon devices: an Auger and electrical study

The interface between the transparent conductive oxide (TCO) SnO ₂ and the first amorphous-silicon layer in optoelectronic devices (e.g. solar cells) can be damaged as a result of the interaction between the TCO and the plasma used for the glow-discharge deposition of the a-Si:H layers. Electrical barriers at the nominally ohmic contact and diffusion of tin into the active layers may result from chemical reduction of SnO₂ and oxidation of Si. Auger depth-profiling techniques are used to measure the TCO damage directly on the devices. A method for quantifying the total amount of reduced tin from the profile data is developed. The extent of the TCO reduction is correlated with the preparation procedures and with the photovoltaic performance of the cells. In particular, the beneficial role of thin protecting metal layers on TCO is investigated by both Auger and electrical measurements