Based on our experimental research on diphasic silicon films, the parameters suc h as absorption coefficient, mobility life- time product and bandgap were estima ted by means of effective-medium theory. And then computer simulation of a-Si:H/ μc-Si:H diphasic thin film solar cells was performed. It was shown that the mor e crystalline fraction in the diphasic silicon films, the higher short circuit d ensity, the lower open-circuit voltage and the lower efficiency. From the spectr al response, we can see that the response in long wave region was improved signi ficantly with increasing crystalline fraction in the silicon films. Taking Lamb ertian back refraction into account, the diphasic silicon films with 40%—50% cr ystalline fraction was considered to be the best intrinsic layer for the bottom solar cell in micromorph tandem.