Experimental scheme for a stable molybdenum bilayer back contacts for photovoltaic applications

Sreejith Karthikeyan, Liyuan Zhang, Sehyun Hwang, Stephen A. Campbell

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Molybdenum (Mo) back contacts have been widely used for thin film based solar cells, especially for CuIn 1-x Ga x Se 2 (CIGS) and Cu 2 ZnSnS 4 (CZTS) based devices. Traditionally, a bilayer approach at two different sputtering pressures is used to produce highly conducting and adhesive films on glass substrates. Mo bilayers undergo a harsh heat treatment during the absorber layer (CIGS/CZTS) deposition or formation process, which in turn changes the residual stress and the morphological properties of the back contact layers and can cause poor adhesion of the absorber layers. This is a key layer for the photovoltaic industry because the entire device is deposited on top of this layer. Adhesion issues can degrade device performance and can affect the long-term stability of the solar cell. This work reports in-situ study of Mo stress variation during anneals ranging from 20 °C to 500 °C and compares the film's morphological and electrical properties before and after heating to develop a thermally stable Mo bilayer. For bilayer films with a total thickness of 1 μm, this study revealed that the optimum pressure and thickness are 5 mTorr and 150 nm, and 1 mTorr and 850 nm for the bottom and top layers, respectively.

Original languageEnglish (US)
Pages (from-to)647-653
Number of pages7
JournalApplied Surface Science
Volume449
DOIs
StatePublished - Aug 15 2018

Bibliographical note

Funding Information:
This project was funded by Sunshot program of Department of Energy, USA. SK acknowledges the support of (Initiative for Renewable Energy and the Environment) IREE. This work was conducted in Minnesota Nano Center (MNC), University of Minnesota, an NNIN-supported facility. Parts of this work were carried out in the University of Minnesota I.T. Characterization Facility, which receives partial support from NSF through the MRFN program.

Funding Information:
This project was funded by Sunshot program of Department of Energy, USA. SK acknowledges the support of (Initiative for Renewable Energy and the Environment) IREE . This work was conducted in Minnesota Nano Center (MNC), University of Minnesota, an NNIN-supported facility. Parts of this work were carried out in the University of Minnesota I.T. Characterization Facility, which receives partial support from NSF through the MRFN program.

Publisher Copyright:
© 2017 Elsevier B.V.

Keywords

  • Back contact layer
  • In-situ stress
  • Molybdenum bilayer
  • Molybdenum stress
  • Sputtering

How much support was provided by MRSEC?

  • Shared

Reporting period for MRSEC

  • Period 4

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