Microstructural and electrical properties of silicon-oxy-nitride layers for photovoltaic applications

Silicon heterojunction solar cells (SHJ) attracted a lot of attention in recent years due to their high efficiency potential and low temperature production process. In the present study nano-crystalline Silicon Oxy-Nitrides layers (nc-SiOxNy) are studied in view of their application in SHJ cells since they suffer less parasitic absorption. SiOxNy films deposited by Plasma Enhanced Chemical Vapour Deposition with different parameters were subsequently annealed in order to obtain the formation of nanocrystals. Structural and compositional analyses were performed by Raman and Fourier-Transform Infra-Red (FTIR) spectroscopy and optical characterization. IV measurements were carried out in order to investigate the electrical properties of the layers. Microscopical analyses were performed with Scanning Electron and Atomic Force Microscope (AFM). Samples show high conductivity ranging from 1-40 S/cm demonstrating that the dopants become electrically active and that the layers become nanocrystalline. Through AFM phase contrast analysis we found differences in tip-sample energy dissipation that can be due to variations in the composition and/or crystalline/amorphous phase. Raman spectroscopy has allowed us to detect the evolution of the crystallinity with deposition conditions and annealing time. FTIR shows peak shifts with deposition and annealing parameters. The combination of macroscopical and microscopical techniques gives a fundamental insight on the properties of the material.