Positron Annihilation Studies on the Damp Heat Degradation of ZnO: Al Transparent Conductive Oxide Layers for CIGS Solar Cells

Wenqin Shi, Mirjam Theelen, Andrea Illiberi, Maik Butterling, Henk Schut, Christoph Hugenschmidt, Miro Zeman, Ekkes Bruck, Stephan W.H. Eijt, More Authors

Research output: Contribution to journalArticleScientificpeer-review

10 Citations (Scopus)

Abstract

Positron annihilation depth-profiling is used as an innovative tool to monitor the evolution of vacancy defects in two series of ZnO:Al transparent conductive oxide (TCO) layers for Cu(In,Ga)Se2 (CIGS) solar cells under accelerated degradation at 85 °C/85% relative humidity. The first series of ZnO:Al layers are deposited directly on flat glass substrates, leading to low densities of (extended) grain boundaries in the ZnO:Al. These ZnO:Al layers only show an increase in open volume upon degradation in the near-surface range. The second series of ZnO:Al layers are deposited on the more corrugated surface of CdS/CIGS/Mo solar cells, and show, on the other hand, a pronounced formation of open volume throughout the layer. Its depth-dependence is consistent with in-diffusion of molecules such as H2O and CO2 into the ZnO:Al layer via the grain boundaries, as primary driver for the degradation. The detected time-dependence of the growth of open volume at the grain boundaries in the ZnO:Al TCO layer matches the time scale of the observed reduction in solar cell efficiency and series resistance, suggesting that the generated open volume induces a significant barrier against charge carrier transport.

Original languageEnglish
Pages (from-to)1847-1851
Number of pages5
JournalIEEE Journal of Photovoltaics
Volume8
Issue number6
DOIs
Publication statusPublished - 2018

Keywords

  • Buffer layers, and back contacts
  • CIGS and CdTe thin film solar cells
  • degradation
  • grain boundaries
  • positrons
  • transparent conductors
  • ZnO:Al

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