Investigation of unintentional doping at the p-i interface of homojunction amorphous silicon solar cells

Defect formation due to boron diffusion at the p-i interface of a single junction amorphous silicon solar cell has been investigated. A test device including a boron lightly doped layer has been manufactured in order to emphasize the effect of doping induced defects. Current voltage measurements on the test structure under AM1.5 show a very low photovoltaic performances due two the large defect density and to the low electric field. The structure has been characterized through capacitance versus frequency measurements in dark conditions and under medium infrared radiation (4µm). This measurement setup allowed us to detect the presence of trap states lying around 0.3-0.4 eV above the valence band.