Angle-dependent XPS analysis of silicon nitride film deposited on screen-printed crystalline silicon solar cell

Abstract

In this work silicon nitride (Si 3N 4) film was deposited as an antireflection coating (ARC) on crystalline silicon solar cell (cell♯A) using plasma-enhanced chemical vapor deposition (PECVD). Two solar cells XA and XB of approximately equal area were diced from cell#A and characterized by angle-dependent X-ray photoelectron spectroscopy (XPS). The XPS profiling shows the presence of silicon (Si), nitrogen (N), carbon (C) and oxygen (O) in the Si 3N 4 film. The presence of C and O indicates that organic substances, involved in processing steps were not released completely from the surface and may diffuse in Si 3N 4 ARC during deposition. The XPS spectra corresponding to Si2p, N1s, C1s and O1s were recorded at angles 0° (normal to the surface), 30° and 45°, as angle increases spectra becomes more surface sensitive. Peak positions in Si2p and N1s spectra explain the oxygen contamination in the Si 3N 4 film. The shift in the peak positions of C1s and O1s as angle increases from 0° to 45° explains the surface contamination of carbon and oxygen. The atomic composition of elements Si, N, C and O show more carbon, oxygen concentration and smaller N/Si ratio than stoichiometry, i.e. Si 3N 4 in cell XB. However, cell XA not only show better photovoltaic performance in terms of parameters open-circuit voltage ( V oc), short-circuit current density ( J sc), fill factor (FF) and efficiency ( η) but also have more uniform texturization and regular pyramids on the surface as revealed by scanning electron microscopy (SEM). The presence of higher concentration of impurities (carbon and oxygen), non-uniformity in texturization and in the Si 3N 4 film as well could be responsible for less satisfactory photovoltaic performance of cell XB.