The properties of thin p-type microcrystalline silicon (p-mu c-Si:H) films prepared onto boron-doped amorphous silicon carbide (p-a-SiC:H) have been investigated. At the initial growth regime (< 100 Angstrom) of the p-mu c-Si:H onto p-a-SiC:H, Si nanocrystallites were proved to be formed in amorphous matrix. The thin p-mu c-Si:H was introduced as a novel constant band gap buffer at the p/i interface of amorphous silicon solar cells. The open circuit voltage and the blue response of the cell were improved significantly by inserting the p-mu c-Si:H at the p/i interface as a buffer when compared with those of the bufferless cell. Our numerical modeling on the constant band gap buffer elucidates clearly that the buffering effects of the thin p-mu c-Si:H originate from the shrinkage of highly defective region with a short lifetime in the vicinity of the p/i interface. (C) 2000 American Institute of Physics. [S0021-8979(00)03912-8].