The relationship between the grain size of poly-Si after SPC and the structure of a-Si before SPC was studied. The structure of a-Si was characterized by TA/TO: the Raman intensity ratio of the Transverse Acoustic (TA) like band and the Transverse Optical (TO) like band. A good positive correlation between the grain size and TS/TO was revealed for the first time. The nucleation and growth kinetics were speculated by using a thermodynamic model. The grain size could be enlarged up to 6 μ m by applying textured substrates to a-Si with a large structural disorder. This film was applied to the active layer of solar cells, and a collection efficiency of 51% at 900 nm was obtained.