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E16.04 - An EXAFS Analysis of Copper-Based Ternary and Quaternary Materials for Extremely Thin Absorber Layer 
April 25, 2014   9:00am - 9:15am

Earth-abundant absorbers become even more cost-effective when used in an extremely thin absorber solar cell. Atomic layer deposition (ALD) and chemical vapor deposition (CVD) deposit highly conformal films and hence are important tools for developing nanostructured solar cells with scalability.We present local structure studies of ZnS/CuS, CuSnS and CuZnSnS composite films prepared with ALD and CVD, using extended x-ray absorption fine structure (EXAFS) technique. The EXAFS technique has the ability to probe the local environment about different atoms, and can also give very precise ratios of elements using their fluorescence peaks. Previous work has shown that individual thin films of Zinc Sulfide (ZnS) and Copper (I) Sulfide (CuS) resemble bulk structure. Yet multi-layer films of ZnS/CuS, prepared using a wide range of parameters, produce films that are predominantly either ZnS or CuS, with the other material being highly disordered. This can be attributed to the crystal structure mismatch of ZnS and CuS, making ALD with these precursors unsuitable for a CuZnS alloy.Another copper-based material, CuSnS (CTS), has a stable structure with good electrical and optical absorption properties. Composite films of CTS were made using CVD layers of CuS and Tin (IV) Sulfide (SnS), with an anneal step. The metal precursors were Tin (IV) Acetate for SnS and KI5 (a direct descendant of CupraSelect from Air Products) for CuS. Of special note, the metal precursors are all non-pyrophoric, which is safer. The sulfur source was HS, generated in situ via a reaction between aluminum sulfide powder (AlS) and water. CuSnS also has the same structure as ZnS, which allows for the formation of the quaternary CuZnSnS (CZTS). CZTS composite films were also made, using Zn(TMHD) for the ZnS, which deposited on top of the CuS and SnS layers determined for CTS. Stoichiometric control was established by varying the deposition times of the binary compounds, and was measured using energy-dispersive x-ray spectroscopy (EDX), x-ray diffraction (XRD), and EXAFS techniques. Optical absorption results are promising for forming a photovoltaic device with copper-based ternary and quaternary materials as the absorber.

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Keynote Address
Panel Discussion - Different Approaches to Commercializing Materials Research
Business Challenges to Starting a Materials-Based Company
Fred Kavli Distinguished Lectureship in Nanoscience
Application of In-situ X-ray Absorption, Emission and Powder Diffraction Studies in Nanomaterials Research - From the Design of an In-situ Experiment to Data Analysis