Why can't an a-Si:H solar cell rely on diffusion to separate the photogenerated carriers as much as a c-Si solar cell does?

Question

The higher bandgap (around 1.7 eV) prevents the photogenerated carriers from diffusing through the intrinsic layer of the a-Si:H cell.

Because the absorption coefficient of a-Si:H is 70 times higher than that of c-Si in the visible region of the solar spectrum.

Because the diffusion length is around 300 nm, while in c-Si it is around 300 microns.

Because a-Si:H suffers from light induced degradation.