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

A. Ennaoui, M. Bär, J. Klaer, T. Kropp, R. Sáez-Araoz, M. Ch Lux-Steiner

Research output: Contribution to journalArticle

66 Citations (Scopus)

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 (CED) 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 = 2.4eV) 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 ∼1mA/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 700.4mV, a fill factor of 65-8% and a short-circuit current density of 24.5mA/cm2 (total area: 22.5mA/cm2). These results are comparable to the performance of CdS buffered reference cells. First integrated series interconnected mini-modules on 5 Times; 5 cm2 substrates have been prepared and already reach an efficiency (active area: 17.2 cm2) of above 8%.

Original languageEnglish
Pages (from-to)499-511
Number of pages13
JournalProgress in Photovoltaics: Research and Applications
Volume14
Issue number6
DOIs
Publication statusPublished - Sep 2006
Externally publishedYes

Fingerprint

Buffer layers
Short circuit currents
baths
Solar cells
Buffers
Current density
buffers
solar cells
modules
Commonwealth of Independent States
Thin films
Wavelength
Thioureas
Open circuit voltage
Auger electron spectroscopy
thin films
absorbers
Surface structure
Transparency
short circuit currents

Keywords

  • Buffer layer
  • Cadmium-free
  • CuInS
  • Efficiency
  • Solar cell
  • Thin film
  • ZnS

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Fuel Technology
  • Physics and Astronomy (miscellaneous)
  • Renewable Energy, Sustainability and the Environment

Cite this

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. / Ennaoui, A.; Bär, M.; Klaer, J.; Kropp, T.; Sáez-Araoz, R.; Lux-Steiner, M. Ch.

In: Progress in Photovoltaics: Research and Applications, Vol. 14, No. 6, 09.2006, p. 499-511.

Research output: Contribution to journalArticle

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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 (CED) 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 = 2.4eV) 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 ∼1mA/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 700.4mV, a fill factor of 65-8{\%} and a short-circuit current density of 24.5mA/cm2 (total area: 22.5mA/cm2). These results are comparable to the performance of CdS buffered reference cells. First integrated series interconnected mini-modules on 5 Times; 5 cm2 substrates have been prepared and already reach an efficiency (active area: 17.2 cm2) of above 8{\%}.",
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