Degradation mechanisms in Silicon solar cells

In the mix of renewable energies, photovoltaics plays an important role. However, the prolonged illumination of solar cells with sunlight usually leads to a slow reduction of the efficiency of the energy conversion. This effect is particularly pronounced in solar cells made from hydrogenated amorphous silicon (a-Si:H). It is known that the concentration of deep defects in this material increases upon illumination, which leads to a reduction of the life time of photogenerated charge carriers and therefore to the reduction of the efficiency. What is not known is the exact microscopic structure of these defects. Detailed knowledge of this microstructure could however lead to improved deposition techniques which, in turn, might allow a suppression of the defect formation and the fabrication of more efficient thin-film solar cells.

The photogenerated defects in a-Si:H are so-called dangling bonds as shown in the figure for a similar defect in crystalline Si. These unsaturated bonds are occupied with a single electron only and can therefore be studied with electron spin resonance (ESR). To obtain relevant new spectroscopic information on these defects, several German groups are developing new ESR techniques in a concerted effort such as electrically detected magnetic resonance at high magnetic fields and ESR at THz frequencies obtained from synchrotron radiation. In this context, we build a novel microscope at the Schottky Institut which will allow the sensitive spatial mapping of dangling bond defects via electrically detected magnetic resonance.

Selected publications

  • Excitons and light-induced degradation of amorphous hydrogenated silicon
    Applied Physics Letters 58 1620 (1991)
    M. S. Brandt, M. Stutzmann
  • Fast Metatstable-defect creation in amorphous-silicon by femtosecond light-pulses
    Physical Review Letters 67 2347 (1991)
    M. Stutzmann, J. Nunnenkamp, M. S. Brandt, A. Asano
  • An alternative degradadtion method for amorphous hydrogenated silicon: The constant degradation method
    Journal of Applied Physics 75 2507 (1994)
    M. S. Brandt, M. Stutzmann
  • Electrically detected magnetic resonance of a-Si:H at low magnetic fields: the influence of hydrogen on the dangling bond resonance
    Journal of Non-Crystalline Solids 230 343 (1998)
    M. S. Brandt, M.W. Bayerl, M. Stutzmann, C.F.O. Graeff
  • Microscopic identification of the origin of generation-recombination noise in hydrogenated amorphous silicon with noise-detected magnetic resonance
    Physical Review Letters 84 5188 (2000)
    S.T.B. Goennenwein, M.W. Bayerl, M. S. Brandt, M. Stutzmann



BMBF Verbundprojekt EPR-Solar
Funding Number 03SF0328B

TUM Technische Universität München TUM Technische Universität München Physik Department Elektrotechnik und Informationstechnik TUM Technische Universität München

Recent publications

Interaction of Strain and Nuclear Spins in Silicon: Quadrupolar Effects on Ionized Donors

Phys. Rev. Lett. 115, 057601 (2015)

D. Franke | F. Hrubesch | M. Künzl | H. W. Becker | K. M. Itoh | M. Stutzmann | F. Hoehne | L. Dreher | M. S. Brandt

Online Reference

see also: Nuclear Spins of Ionized Phosphorus Donors in Silicon

Phys. Rev. Lett. 108, 027602 (2012)

L. Dreher | F. Hoehne | M. Stutzmann | M. S. Brandt

Online Reference

Ultrafast electronic read-out of diamond NV centers coupled to graphene

Nature Nanotechnology 10, 135 (2015)

A. Brenneis | L. Gaudreau | M. Seifert | H. Karl | M. S. Brandt | H. Huebl | J. A. Garrido | F. H. L. Koppens | A. Holleitner

Online Reference

Bipolar polaron pair recombination in polymer/fullerene solar cells

Physical Review B 92, 245203 (2015)

A. Kupijai | K. M. Behringer | F. Schäble | N. Galfe | M. Corazza | S. A. Gevorgyan | F. C. Krebs | M. Stutzmann | M. S. Brandt

Online Reference

Broadband electrically detected magnetic resonance using adiabatic pulses

Journal of Magnetic Resonance 254, 62 (2015)

F. Hrubesch | G. Braunbeck | A. Voss | M. Stutzmann | M. S. Brandt

Online Reference

High cooperativity coupling between a phosphorus donor spin ensemble and a superconducting microwave resonator

Appl. Phys. Lett. 107, 142105 (2015)

C. W. Zollitsch | K. Mueller | D. Franke | S. T. B. Goennenwein | M. S. Brandt | R. Gross | H. Huebl

Online Reference

Submillisecond Hyperpolarization of Nuclear Spins in Silicon

Phys. Rev. Lett. 114, 117602 (2015)

F. Hoehne | L. Dreher | D. Franke | M. Stutzmann | L. S. Vlasenko | K. M. Itoh | M. S. Brandt

Online Reference