Spectroscopy of electronic defect states in -based heterojunctions and Schottky diodes under damp-heat exposure

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

Corresponding author: parisi@ehf.uni-oldenburg.de

Received: 12 August 2003
Accepted: 19 February 2004

Abstract

The changes of defect characteristics induced by accelerated lifetime tests on the heterostructure n-/i-// relevant for photovoltaic energy conversion are investigated. We subject heterojunction and Schottky devices to extended damp-heat exposure at 85 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 /chalcopyrite interface. Their activation energy increases due to damp-heat exposure, indicating a reduced band bending at the  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.