We investigated the properties of a novel p-type nanocrystalline Si (p-nc-Si) prepared onto p-a-SiC and the effect of using the buffer with an energy bandgap over 1.9 eV at the p/i interface on the performance of p/i/n type amorphous silicon based solar cells. At the initial growth stage of the p-nc-Si onto p-a-SiC, Si nanocrystallites are proved to be formed in amorphous matrix within the thickness of less than 100Å. The open circuit voltage and the blue response of the cell were improved significantly by inserting the film at the p/i interface as a buffer as compared with the bufferless cell. We found from a numerical simulation using the Gummel-Sharfetter method that the buffering effect of the p-nc-Si is originated from the reduction of highly defective region with a short life-time in the vicinity of the p/i interface.