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E7.04 - Nanostructured Copper Iron Sulfide Solar Light Absorbers 
April 23, 2014   11:15am - 11:30am

Copper iron sulfide materials are potentially useful earth-abundant solar light absorbers that incorporate the favorable qualities of copper sulfide with enhanced phase stability. Copper sulfide served as a component in some of the earliest commercial photovoltaics and retains promise as an earth-abundant solar absorber due to its optical properties and availability.1 Use of Cu2S in photovoltaics was discontinued due to phase instability and the related high copper conductivity. This phase instability resulted in deposition of metallic copper at interfaces and alteration in the band gap and minority carrier diffusion length. We have demonstrated that these issues are exacerbated in nanostructured Cu2S,2 an issue we sought to address by synthetic manipulation of copper sulfide chemistry. Solvatothermal synthesis of such nanoparticles enables synthetic control over phase and extent of iron incorporation. Notably, incorporation of even very small amounts of iron produced materials with optical properties similar to the copper sulfide phase sought after for thin film cells, but which resisted phase transformation over time.3 We have expanded on this finding to explore a range of copper iron sulfide nanoparticles. In this ternary system, an array of phases were accessed by variation of the amount of iron incorporated. Phases produced range from tetragonal Cu2S to CuFeS2. Solid solution formation allowed a linear relationship between ratio of Cu:Fe in solution and solid, resulting in gradual tuning of the optical behaviors and phase stability. The band gaps and plasmon band absorption of these copper iron sulfide nanoparticles were controllably altered by the extent of iron incorporation, yet the band gaps generally fall in the range optimal for a solar absorber. The presence of plasmon band absorption is one measure of the phase instability and resultant loss of copper, and is systematically eliminated as iron incorporation increases. This is supported by cyclic voltammetry and X-ray diffraction measurements. For species with low iron concentrations, the phase stability is greatly enhanced by surface passivation using metal sulfide ions. (1) (a) Wadia, C.; Alivisatos, A. P.; Kammen, D. M. Environ. Sci. Technol. 2009, 43, 2072-2077; (b) Zhao, Y. X.; Burda, C. Energy Environ. Sci 2012, 5, 5564-5576.(2) Lotfipour, M.; Machani, T.; Rossi, D. P.; Plass, K. E. Chem. Mater. 2011, 23, 3032-3038.(3) Machani, T.; Rossi, D. P.; Golden, B. G.; Jones, E. C.; Lotfipour, M.; Plass, K. E. Chem. Mater. 2011, 23, 5491-5495.

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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