Investigation of CdZnTe for Thin-Film Tandem Solar Cell Applications: Preprint

Research output: Contribution to conferencePaper

Abstract

Modeling of two-junction tandem devices shows that for optimal device performance, the bandgap of the top cell should be around 1.6-1.8 eV. CdZnTe alloys can be tailored to yield bandgaps in the desired range. In this study, we considered were used to fabricate these films, using close-spaced sublimation (CSS) and radio-frequency sputtering (RFS) techniques. In the first approach, we used mixedpowders of CdTe and ZnTe as the source for film deposition by CSS. Even for the ZnTe/CdTe (95:5 ratio) source material, the deposited films were entirely CdTe due to higher vapor pressure of CdTe. In the second approach, we used pre-alloyed CdZnTe powders (CERAC, Inc.) as the source. Due to the lower sticking coefficient of Zn, even for the source composition of 75% Zn, these films containedvery low quantities of Zn (~5%). We tried unsuccessfully to increase the Zn content in the films by confining Zn vapor by enclosing the region between the source and substrate, reducing the substrate temperature to 400 deg C, and adjusting the source/substance distance. Finally, we used thin-film couples consisting of 300-nm-thick CdTe deposited by CSS and 300-nm-thick ZnTe deposited by RFS; thesamples were then heat-treated in cadmium chloride vapor. Compositional analysis of the samples showed extensive interdiffusion of Cd and Zn for the annealed samples. We will present the data on the various stack configurations of CdTe and ZnTe, the effect of different post-deposition anneals, the effect of oxygen on the interdiffusion and alloy formation and its possible correlation to thedevice performance degradation.
Original languageAmerican English
Number of pages9
StatePublished - 2003
Event2003 Materials Research Society Spring Meeting - San Francisco, California
Duration: 21 Apr 200325 Apr 2003

Conference

Conference2003 Materials Research Society Spring Meeting
CitySan Francisco, California
Period21/04/0325/04/03

NREL Publication Number

  • NREL/CP-520-33965

Keywords

  • atomic force microscopy (AFM)
  • auger electron spectroscopy (AES)
  • bandgap
  • CdZnTe
  • close-space sublimation (CSS)
  • couple
  • interdiffusion
  • post-deposition anneal
  • PV
  • radio-frequency sputtering (RFS)
  • secondary ion mass spectrometry (SIMS)
  • tandem devices
  • thin films
  • x-ray diffraction (XRD)

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