Silicontetrachloride based microcrystalline silicon for application in thin film silicon solar cells

摘要

The replacement of the process gas silane by Silicontetrachloride for the deposition of microcrystalline silicon thin films is explored. The films were prepared by plasma enhanced chemical vapor deposition from mixtures of Silicontetrachloride and hydrogen. Deposition conditions similar as employed for efficient silane-based microcrystalline silicon solar cells of high deposition rate were applied. Structural and electronic properties of the films are studied by infrared optical absorption and Raman spectroscopies and conductivity measurements. Increasing the flow ratio of Silicontetrachloride to hydrogen, the transition from the crystalline to the amorphous state is found to occur in a similar range of flow ratio as in silane-based material. The lowest porosity is observed for a crystalline fraction near 80%. Porosity, void-related microstructure and chlorine content are found to decrease with increasing substrate temperature. For boron doped material deposited at a substrate temperature of 250℃, conductivity values exceeding 50 (Ω cm)~(-1) were achieved. This latter material was incorporated as p-layer into microcrystalline pin silicon solar cells. Solar cell efficiencies similar as for solar cells with a silane-based p-layer were obtained.