Microstructure and photoelectric properties of P-doped silicon-rich SiN_x film as an n-type layer for PIN-type amorphous silicon thin film solar cells

In this study, the phosphorus doped silicon nanocrystals embedded in silicon-rich SiN_x:H thin films were fabricated using a radio frequency plasma enhanced chemical vapor deposition technique, from a SiH₄, pH₃, H₂and NH₃mixture. The effects of nitrogen incorporation on the microstructure and photoelectric properties of the nc-Si:H film were systematically investigated. Raman and transmission electron microscope observation revealed the fact that nitrogen incorporation inhibited the growth of Si nanocrystals, and their sizes and densities of them could be adjusted by varying the incorporation flow ratio NH₃/(SiH₄ + H₂ + pH₃). The reduction of refractive index and improvement of conductivity of the prepared films were observed with increasing nitrogen impurity, and a maximal conductivity was obtained when the flow ratio was 0.02. In addition, the P-doped nc-SiN_x:H film was used as an n-type layer for the amorphous silicon thin film solar cells to optimize its efficiency, and the solar cell with high fill factor (0.624) and efficiency (9.26%) has been obtained when the flow ratio was 0.02. As a result, the P-doped nc-SiN_x:H film with proper nitrogen incorporation was able to efficiently improve the performance of the thin film solar cells.