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Effects of 2nd Phases, Stress, and Na at the Mo/Cu2ZnSnS4 Interface

Published online by Cambridge University Press:  01 February 2011

Jeffrey L. Johnson
Affiliation:
jeff.l.johnson@utah.edu
Haritha Nukala
Affiliation:
harithanukala@gmail.com, University of Central Florida, AMPAC, Orlando, Florida, United States
Ashish Bhatia
Affiliation:
ashish.bhatia@utah.edu, UNIVERSITY OF UTAH, MATERIALS SCIENCE AND ENGG., 122 S CENTRAL CAMPUS DRIVE, SALT LAKE CITY, Utah, 84112, United States
W.M. Hlaing Oo
Affiliation:
w.hlaing@utah.edu, University of Utah, Materials Science and Engineering, Salt Lake City, Utah, United States
Loren W Rieth
Affiliation:
loren.rieth@utah.edu, University of Utah, Electrical and Computer Engineering, Salt Lake City, Utah, United States
Michael A Scarpulla
Affiliation:
scarpulla@ece.utah.edu, University of Utah, Materials Science and Engineering, Salt Lake City, Utah, United States
Elizabeth A Lund
Affiliation:
liz.lund@utah.edu, University of Utah, Chemical Engineering, Salt Lake City, Utah, United States
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Abstract

Cu2ZnSnS4 (CZTS) is an alternative material to Cu(In,Ga)Se2 (CIGSe) for use in thin film photovoltaic absorber layers composed solely of commodity elements [1,2]. Thus, if similar material quality and performance can be realized, its use would allow scale-up of terrestrial thin film photovoltaic production unhindered by material price or supply constraints. Here we report on our research on the deposition of CZTS by RF sputtering from a single CZTS target and co-sputtering from multiple binary sources on Mo-coated glass. We find some samples delaminate during post-sputtering furnace annealing in S vapor. Samples on borosilicate glass (BSG) delaminate much more frequently than those on soda-lime glass (SLG). We investigate the influences of the formation of frangible phases such as MoS2 at the CZTS/Mo interface and residual and thermal mismatch stress on delamination. We implicate fracture in a layer of MoS2 as the mechanism of delamination between the Mo and CZTS layers using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Wafer curvature measurements show significant (˜400 MPa) deposition stress for minimally optimized Mo deposition; however nearly stress-free Mo layers with good adhesion can be deposited using a multi-step Mo deposition recipe. Co-sputtering CZTS adds 100 MPa of stress on both BSG and SLG, however delamination is nearly absent for samples deposited on low-stress Mo layers. We investigate metallic diffusion barrier layers to prevent the formation of MoS2 at the interface. Lastly we discuss the importance of removing Mo oxide by sputter etching before CZTS deposition and its effects on adhesion and series resistance.

Type
Research Article
Copyright
Copyright © Materials Research Society 2010

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References

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