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New Generation Silicon Solar Cells

2.7 Direct/indirect band gap

New Generation Silicon Solar Cells

Indirect:

need a photon, a phonon, and a charge

 carrier happens more seldom

  longer absorption length

recombination at grain boundarys and

 point defects

Direct:

need just the right photon

 for band transition

higher transition probability

Material

c-Si

a-Si:H

GaAs

Band gap

1,12 eV  (indirekt)

1,8 eV

(„direct“)

1, 43 eV (direct)

Absorption coefficient

(hν = 2,2) [cm-1]

6*103

2*104

5*104

Indirect and direct band gap

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