Wet-chemical passivation and characterization of silicon interfaces for solar cell applications

The interface properties of silicon solar cell structures were characterized by the two non-destructive and highly surface-sensitive spectroscopic techniques: surface photovoltage and spectroscopic ellipsometry. The resulting charge and density of interface states as well as the microscopic surface roughness and oxide coverage were investigated during silicon wafer preparation and during sample storage in air. The surface state density of hydrogen-terminated silicon surfaces as well as the long-time stability of the hydrogen termination were found to primarily depend on the surface morphology resulting from the wet-chemical oxidation procedures applied before. The smallest interface state densities were obtained by NH4F treatment subsequent to oxidation in ultra-pure water at 80°C. Surfaces prepared using this procedure are found to be much more stable upon exposition to clean-room air than those prepared by conventionally prepared H-terminated surfaces. ccessful application of the new passivation procedures in photovoltaics is shown for selected examples of different solar cell concepts.