Optimization Of Intrinsic Silicon Passivation Layers In Nc-Si:H/C-Si Silicon Heterojunction Solar Cells

A series of intrinsic silicon thin films were prepared using radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at low temperature and low power density. We investigated the influence of silane concentration (C-s) on the structural, optical, and electronic properties, and passivation quality of the intrinsic silicon films, and the performances of hydrogenated nanocrystalline silicon/crystalline silicon (nc-Si:H/c-Si) silicon heterojunction (SHJ) solar cells. The results show that with decreasing silane concentration, substantial changes in the crystalline volume fraction, hydrogen concentration, structure factor, optical bandgap, and photosensitivity of the film take place in the transition zone. The passivation quality of intrinsic silicon thin films is decided by the hydrogen content and bonding structure of the film. Films close to the transition zone show good compactness and photosensitivities, high hydrogen content, and low state densities, and contain abundant SiH bonds. The films provide excellent passivation for c-Si surfaces and significantly enhance the open-circuit voltages of nc-Si:H/c-Si SHJ solar cells. However, the passivation quality deteriorates seriously when the film is too thin. In this work, the optimum silane concentration was found to be 6% (molar fraction). By optimizing the film thickness of the passivation layers with C-s=6%, we obtained an nc-Si:H/c-Si SHJ solar cell with an open-circuit voltage of 672 mV, short-circuit current density of 35.1 mA.cm(-2), fill factor of 0.73, and efficiency of 17.3%.