Research

Highly-efficient Cd-free CuInS2 thin-film solar cells and mini-modules with Zn(S,O) buffer layers prepared by an alternative chemical bath process

  1. A. Ennaoui1,*,
  2. M. Bär1,†,
  3. J. Klaer1,
  4. T. Kropp1,
  5. R. Sáez-Araoz1,
  6. M. Ch. Lux-Steiner1,2

Article first published online: 17 FEB 2006

DOI: 10.1002/pip.682

Issue

Progress in Photovoltaics: Research and Applications

Progress in Photovoltaics: Research and Applications

Volume 14, Issue 6, pages 499–511, September 2006

Additional Information

How to Cite

Ennaoui, A., Bär, M., Klaer, J., Kropp, T., Sáez-Araoz, R. and Lux-Steiner, M. Ch. (2006), Highly-efficient Cd-free CuInS2 thin-film solar cells and mini-modules with Zn(S,O) buffer layers prepared by an alternative chemical bath process. Prog. Photovolt: Res. Appl., 14: 499–511. doi: 10.1002/pip.682

Author Information

  1. 1

    Solar Energy Research, Department of Heterogeneous Material Systems (SE2), Hahn-Meitner-Institut Berlin, Glienicker Street 100, 14109 Berlin, Germany

  2. 2

    Freie Universität Berlin, 14195 Berlin, Germany

  1. †

    Department of Chemistry, University of Nevada, Las Vegas, NV 89154, USA.

*Solar Energy Research, Department of Heterogeneous Material Systems (SE2), Hahn-Meitner-Institut Berlin, Glienicker Street 100, 14109 Berlin, Germany.

Publication History

  1. Issue published online: 15 AUG 2006
  2. Article first published online: 17 FEB 2006
  3. Manuscript Revised: 25 SEP 2005
  4. Manuscript Received: 8 AUG 2005

Funded by

  • European Commission. Grant Number: ENK6-2002-00664
  • German BMBF. Grant Number: 01SF0007
  • German BMWA. Grant Number: 0329889

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Keywords:

  • ZnS;
  • CuInS2;
  • thin film;
  • solar cell;
  • efficiency;
  • cadmium-free;
  • buffer layer

Abstract

Recent progress in fabricating Cd- and Se-free wide-gap chalcopyrite thin-film solar devices with Zn(S,O) buffer layers prepared by an alternative chemical bath process (CBD) using thiourea as complexing agent is discussed. Zn(S,O) has a larger band gap (Eg = 3·6–3·8 eV) than the conventional buffer material CdS (Eg = 2·4 eV) currently used in chalcopyrite-based thin films solar cells. Thus, Zn(S,O) is a potential alternative buffer material, which already results in Cd-free solar cell devices with increased spectral response in the blue wavelength region if low-gap chalcopyrites are used. Suitable conditions for reproducible deposition of good-quality Zn(S,O) thin films on wide-gap CuInS2 (‘CIS’) absorbers have been identified for an alternative, low-temperature chemical route. The thickness of the different Zn(S,O) buffers and the coverage of the CIS absorber by those layers as well as their surface composition were controlled by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray excited Auger electron spectroscopy. The minimum thickness required for a complete coverage of the rough CIS absorber by a Zn(S,O) layer deposited by this CBD process was estimated to ∼15 nm. The high transparency of this Zn(S,O) buffer layer in the short-wavelength region leads to an increase of ∼1 mA/cm2 in the short-circuit current density of corresponding CIS-based solar cells. Active area efficiencies exceeding 11·0% (total area: 10·4%) have been achieved for the first time, with an open circuit voltage of 700·4 mV, a fill factor of 65·8% and a short-circuit current density of 24·5 mA/cm2 (total area: 22·5 mA/cm2). These results are comparable to the performance of CdS buffered reference cells. First integrated series interconnected mini-modules on 5 × 5 cm2 substrates have been prepared and already reach an efficiency (active area: 17·2 cm2) of above 8%. Copyright © 2006 John Wiley & Sons, Ltd.

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