a-Si:H (Hydrogenated amorphous Si) based solar cell cannot rely on diffusion to

Question

a-Si:H (Hydrogenated amorphous Si) based solar cell cannot rely on diffusion to separate the photogenerated carriers compared to c-Si (crystalline) solar cell choose one answer below: a) Because the higher bandgap (1.7 eV) prevents the photogenerated carriers from diffusing through the intrinsic layer of the a-Si :H cell b) Because the absorption coeficlent ofa SilH salmost one orderfntude higher than that of c-Si in the visible region (400nm-800nm). c) Because the diffusion length in a-Si:H is much shorter than in c-Si.

Explanation / Answer

In the c-Si(crystalline solar cell) carrier collection is by minority carrier diffusion with in p and n type layers. That is diffusion lengths are long(>200 micrometer) which assist collection of photogenerated carriers over the whole useful range of solar cell thikness where optical absorption take place.

In case of Si-H, minority carrier diffusion lengths are extremely small(around 0.1 micrometer), that is device cannot rely on collection of photogenerated carriers by diffusion alone.

That means option C is correct.

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