2 Fundamentals of silicon photovoltaics

• Radiation quantum must have at least the energy of the band gap

• Only the energy of the radiation quantum is necessary for charge separation

• in addition to the energy gap, there

  is also an impulse gap.

• To generate the electron-hole pair,

  a three-body impact must occur:

  1. Photon

  2. Phonon

  3. Charge carrier

• Phonons are the energy quanta of

  the lattice vibration.

• Probability much smaller

Direct semiconductors have a

significantly higher absorption rate

than indirect semiconductors.

Therefore, much less material can

be used.

Thin film solar cells are always

direct semiconductors.

• The path length of the light through the atmosphere weakens it and changes the spectral composition (blue sky at noon, morning or evening red)

• AM0 is outside of the atmosphere

• AM1 with vertical passage through the atmosphere

• AM1.5 is standard spectrum for solar cell measurement

Future solar cells will be characterized by low manufacturing costs, not by a large efficiency improvement.

Monocrystalline silicon (mono-Si)

• Homogeneous crystal structure

• Efficiency ~ 20-23%

• Energy-intensive and expensive production

Polycrystalline silicon (poly-Si)

• No uniform crystal direction, but different alignment

• Efficiency ~ 15-20%

• Lower energy demand for production

30 years lifetime, maybe longer

cell test

glass cleaning

foil cut

cell soldering

cross soldering

inspection

lamination

Final inspection of the laminates

final assembly

high-voltage test

performance test

quality control

encampments

• Metal: Fermi level in the middle

  between valence and conduction band;

  overlapping of valence and conduction

  band

• Insulators: Fully occupied valence band

  and a large energy gap to the

  conduction band; thermally excited

  electrons cannot overcome it at room

  temperature

• Semiconductors: Fully occupied

  valence band and a smaller band gap

p-doped

• The Fermi level is closer to the valence band

• Having an excess of free holes

n-doped

• The Fermi level is closer to the conduction band

• Having an excess of free electrons