Intermediate Band Solar Cell

1
Intermediate Band Solar Cell

• Device physics
• University of Utrecht
• 24 January 2004
• Rob Harmsen

2
Overview

• Introduction
• Main principles of IBSC
• Conditions
• Efficiency
• Shockley Read Hall recombination
• IBSC Materials
• Conclusion

3
Single gab solar cell makes poor use of solar
spectrum

• Multi Junction cell
• Solar thermo-photovoltaic
• Molecular based cells
• Intermediate band solar cell (IBSC)

4
Intermediate band (IB)

• Extra current without voltage degradation

5
Conditions

• Each band is described by its own quasi Fermi
  level
• Band to band transitions must be radiative
• Infinite carrier mobility, Ideal contacts etc

6
Efficiency

• Single gab 40.7
• Tandem cell 55.4
• IBSC 64.1
• Better quantum efficiency then tandem.

7
Shockley Read Hall recombinationTrap v.s. IB

• Traps between CB and VB are normally considered
  as a source of non-radiative recombination
  (SRH).
• How can the IB be only a radiative recombination
  source?
• TrapLocalized v.s. IBDelocalized

8
Shockley Read Hall recombinationEnergy

• Phonon energy tenths of meV
• Bandgap hundreds of meV
• IB, simultaneous interaction with tenths of
  phonons (unlikely).
• Trap, impurity is excited, then emission of
  phonons (not simultaneous).

9
Shockley Read Hall recombination Not likely if

• Impurities are in periodical pattern.
  Vibrational modes tenths meV
• Quantum dots. thousands of atoms, not a single
  impurity

10
IB Materials

• Ga4X3M XAs or P, Mmetal

11
Quantum Dot

• InyGa1-yAs Dot in AlxGa1-xAs material
• Materials have been made
• No increase of efficiency observed
• Quantum efficiency/photon energy indicate
  principles of IBSC

12
Nanoporous Materials

• Nanoporous material TiO2
• Cavities filled with PbS as Quantum dot
• Electrolyte CH3OH as P contact forms HCOOH. Even
  if illuminated with low energy photons.
• solid state P-type contact photovoltaic behavior
  is lost.
• Evidence of IBSC principles has not been found yet

13
Conclusions

• IBSC, theoretically efficiency of 63
• Each band must have a separate quasi Fermi
  level.
• Band to band transitions must be radiative.
• If IB is de-localized SRH recombination plays no
  role (i.e. QDs).
• New materials have been found, indicating these
  work according to IBSC principles
• No improvement of efficiency has been found yet.