In the process of the high growth rate μc-Si：H film deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD)， the high energy ion impinging on the growing surface could deteriorate the device performance. Incorporation of a low growth rate intrinsic μc-Si：H p/i buffer layer was advanced in this paper. The results show that the introduced low growth rate buffer layer could improve the characteristics of p/i interface and the vertical uniformity of the intrinsic layer. It was found that the defects in intrinsic layer first decreased and then increased with increasing thickness of the buffer layer. These results led to an optimal thickness for the buffer layers. The efficiency of solar cells was increased about 1% when the thickness was optimized. As a result， the efficiency of 8.11% has been achieved at an i-layer deposition rate of 8.5nm/s.