Evaluation of Cu2ZnSnS4 Absorber Films Sputtered from a Single, Quaternary Target
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Cu2ZnSnS4 (CZTS) is a promising absorber material for thin-film solar cells since it contains no rare or toxic elements, has a high absorption coefficient and a near ideal bandgap energy. It does, however, present some challenges due to the limited single-phase region of the desired kesterite phase and its instability towards decomposition. Sputtering of CZTS from quaternary, compound targets using RF magnetron sputtering is known. In this thesis work CZTS absorbers were made using pulsed DC magnetron sputtering on stainless steel substrates. The effects of varying substrate temperature and adding seed layers to promote grain growth were investigated, as well as the effects of a rapid thermal anneal in a S-rich atmosphere.
Film compositions determined by X-ray fluorescence were found to be inside or close to the kesterite single-phase region in the phase diagram, but were generally too Cu-rich and Zn-poor to yield good results. The kesterite phase was confirmed with X-ray crystallography and Raman spectroscopy, indicating that it is possible to sputter CZTS from a single target with a high deposition rate. It was found that Cu2S seed layers could induce a significant increase in grain size, and preliminary experiments showed no evidence of the seed layer remaining after deposition of the absorber. Higher substrate temperatures also lead to increased grain size, but excessive heating caused the decomposition of the CZTS. Annealing induced grain growth, relaxed internal stress in the material and improved the electrical properties of the CZTS films, primarily by the removal of shunts.
Place, publisher, year, edition, pages
2013. , 72 p.
UPTEC K, ISSN 1650-8297 ; 13005
Cu2ZnSnS4, CZTS, kesterite, sputtering, compound, quaternary
IdentifiersURN: urn:nbn:se:uu:diva-199838OAI: oai:DiVA.org:uu-199838DiVA: diva2:621657
Subject / course
Master Programme in Chemical Engineering
Ericson, Tove, DoktorandSterner, Jan, Doktor
Platzer-Björkman, Charlotte, DocentLarsson, Karin, Professor