title: Grain-to-Grain Compositional Variations and Phase Segregation in Copper-Zinc-Tin-Sulfide Films.
abstract: We have performed a rigorous investigation of the structure and composition of individual grains in copper-zinc-tin-sulfide (CZTS) films realized by sulfurization of a sputtered metal stack. Although on average close to the ideal CZTS stoichiometry, elemental analysis shows significant grain-to-grain variations in composition. High-resolution Raman spectroscopy indicates that this is accompanied by grain-to-grain structural variations as well. The intensity from the 337 cm(-1) Raman peak, generally assigned to the kesterite phase of CZTS, remains constant over a large area of the sample. On the other hand, signals from secondary phases at 376 cm(-1) (copper-tin-sulfide) and 351 cm(-1) (zinc-sulfide) show significant variation over the same area. These results confirm the great complexity inherent to this material system. Moreover, structural and compositional variations are recognized in the literature as a factor limiting the efficiency of CZTS photovoltaic devices. This study demonstrates how a seemingly homogeneous CZTS thin film can actually have considerable structural and compositional variations at the microscale, and highlights the need for routine microscale characterization in this material system.
authors.affiliation: Department of Mechanical Engineering, ‡Materials Science and Engineering Program, and §Department of Electrical and Computer Engineering, University of California-Riverside , Riverside, California 92521, United States.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Alvarez Barragan
authors.affiliation: Department of Mechanical Engineering, ‡Materials Science and Engineering Program, and §Department of Electrical and Computer Engineering, University of California-Riverside , Riverside, California 92521, United States.
authors.forename: Hoda
authors.initials: H
authors.lastname: Malekpour
authors.affiliation: Department of Mechanical Engineering, ‡Materials Science and Engineering Program, and §Department of Electrical and Computer Engineering, University of California-Riverside , Riverside, California 92521, United States.
authors.forename: Stephen
authors.initials: S
authors.lastname: Exarhos
authors.affiliation: Department of Mechanical Engineering, ‡Materials Science and Engineering Program, and §Department of Electrical and Computer Engineering, University of California-Riverside , Riverside, California 92521, United States.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Balandin
authors.affiliation: Department of Mechanical Engineering, ‡Materials Science and Engineering Program, and §Department of Electrical and Computer Engineering, University of California-Riverside , Riverside, California 92521, United States.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Mangolini
keywords: CZTS; Raman spectroscopy; earth-abundant photovoltaic materials; energy dispersive spectroscopy; phase segregation; thin films