Using phosphorus doped hydrogenated silicon oxycarbide film as a window layer on the light entrance side of silicon heterojunction solar cells: The role of phase separation on electron transport

The phosphorus doped hydrogenated nanocrystalline silicon oxycarbide (n-nc-SiCO:H) layer can be used as a window layer on the light incident side of silicon heterojunction solar cells (HJT). The chemical composition, structural organization and properties of the n-nc-SiCO:H layer deposited from plasma enhanced chemical vapor deposition (PECVD) method can be easily manipulated via radio frequency power density tuned. Phase separation is observed in the n-nc-SiCO:H layer in which nanoscale silicon crystallites were embedded in amorphous silicon oxycarbide matrix. The optical properties of the n-nc-SiCO:H layer are depended on oxygen and carbon atoms incorporation ratio. The conductivity of the n-nc-SiCO:H layer is dominated by activated phosphorus concentration and the phase separation. The activated phosphorus atoms which play an important role on electron transportation are distributed in both crystalline silicon phase and amorphous silicon phase. Both activated phosphorus concentration and band gap value for oxygen rich amorphous silicon oxycarbide layer are determined by incorporation ratio of O atoms. The interplay effects of optical and electrical properties of the n-nc-SiCO:H layers on HJT cells electric performance variation are revealed out in this report. An average efficiency (across ∼120 cells) of 26.3 % was achieved in cells with optimized power density for the n-nc-SiCO:H layer. The results demonstrate that phase separation in the n-nc-SiCO:H layer plays a critical role on electron transportation.