The microstructure,optoelectronic property and the application in solar cell of Si films and SiGe alloy films near phase transition from amorphous to microcrystalline are outlined.The proto-crystalline Si films(proto-Si)with improved medium range order are grown at the amorphous phase side of the phase transition region,showing remarkable stability against light soaking.The high quality nano-crystalline Si films(nano-Si)with low defect density are grown just at the microcrystalline phase side of the phase t...