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BAND TAIL STATES IN MICROCRYSTALLINE SILICON SOLAR CELLS PROBED BY PHOTOLUMINESCENCE AND OPEN CIRCUIT VOLTAGE

R. Carius1,* , T. Merdzhanova1,2, S. Klein1, F. Finger1

Affiliation

  1. Institut für Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
  2. Central Laboratory for Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria

Abstract

Thin film p-i-n microcrystalline silicon (µc-Si:H) solar cells were studied by photoluminescence (PL) spectroscopy and open circuit voltage, Voc. By this means, the cause of the commonly observed increase of Voc when the silane concentration in the gas phase for the preparation of the intrinsic absorber layers is raised is addressed. The hot wire chemical vapour deposition (HW-CVD) technique was used for the preparation of films and intrinsic absorber layers of solar cells with efficiencies higher than 9%. By monitoring Voc and the PL energy, EPL, as a function of temperature, information on the photogenerated carrier distributions and the splitting of the quasi-Fermi energies was gained and the effect of states in the gap was studied by comparison with results from a crystalline p-i-n diode. An increase of EPL and Voc for increasing SC and decreasing temperature is attributed to the shift of the excess carrier distributions to higher energies. It is proposed that this shift is limited by band tail states. It is proposed that increasing SC leads to a reduction of the density of band tail states, due to structural relaxation of the µc-Si:H network by the presence of hydrogen or hydrogenated amorphous silicon..

Keywords

Photoluminescence, Open circuit voltage, Solar cells, Microcrystalline silicon.

Submitted at: Dec. 9, 2004
Accepted at: Jan. 26, 2005

Citation

R. Carius, T. Merdzhanova, S. Klein, F. Finger, BAND TAIL STATES IN MICROCRYSTALLINE SILICON SOLAR CELLS PROBED BY PHOTOLUMINESCENCE AND OPEN CIRCUIT VOLTAGE, Journal of Optoelectronics and Advanced Materials Vol. 7, Iss. 1, pp. 121-128 (2005)