Europhys. Lett.
Volume 66, Number 3, May 2004
Page(s) 399 - 404
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 April 2004
Europhys. Lett., 66 (3) , pp. 399-404 (2004)
DOI: 10.1209/epl/i2003-10211-3

Spectroscopy of electronic defect states in $\chem{Cu(In,Ga)(S,Se)_2}$-based heterojunctions and Schottky diodes under damp-heat exposure

C. Deibel, V. Dyakonov and J. Parisi

Department of Energy and Semiconductor Research, Faculty of Physics University of Oldenburg - 26111 Oldenburg, Germany

(Received 12 August 2003; accepted in final form 19 February 2004)

The changes of defect characteristics induced by accelerated lifetime tests on the heterostructure n- $\chem{ZnO}$/ i- $\chem{ZnO/CdS}$/ $\chem{Cu(In,Ga)(S,Se)_2}$/ $\chem{Mo}$ relevant for photovoltaic energy conversion are investigated. We subject heterojunction and Schottky devices to extended damp-heat exposure at 85 $\un{{}^{\circ}C}$ ambient temperature and 85% relative humidity for various time periods. In order to understand the origin of the pronounced changes of the devices, we apply current-voltage and capacitance-voltage measurements, admittance spectroscopy, and deep-level transient spectroscopy. The fill factor and open-circuit voltage of test devices are reduced after prolonged damp-heat treatment, leading to a reduced energy conversion efficiency. We observe the presence of defect states in the vicinity of the $\chem{CdS}$/chalcopyrite interface. Their activation energy increases due to damp-heat exposure, indicating a reduced band bending at the $\chem{Cu(In,Ga)(S,Se)_2}$ surface. The Fermi-level pinning at the buffer/chalcopyrite interface, maintaining a high band bending in as-grown cells, is lifted due to the damp-heat exposure. We also observe changes in the bulk defect spectra due to the damp-heat treatment.

73.20.Hb - Impurity and defect levels; energy states of adsorbed species.
73.50.Pz - Photoconduction and photovoltaic effects.
73.61.Le - Other inorganic semiconductors.

© EDP Sciences 2004