Technical: The scientific goal of this project is to understand and control film growth and penetration of atomic layer deposited copper sulfide semiconductors onto mesoporous oxide templates. Critical to this research is use of atomic layer deposition to control the material growth at atomic resolutions to achieve ultrathin conformal copper sulfide-based semiconducting films that follow the contours of nanostructured oxides, and a suite of characterization tools to understand the mechanisms for film growth and resulting materials properties. The industrial partner, Air Products and Chemicals, Inc., provides custom metal organic precursors, which enable unprecedented control over material stoichiometry and phase, a major issue with previous attempts to utilize Cu-based materials for solar energy conversion. The ability of the atomic layer deposition precursors to conformally coat the mesoporous nanoparticle and nanowire templates as a function of material processing conditions is studied using high resolution electron microscopy and optical studies. Focus is placed on understanding and controlling the material phase and homogeneity, trap state density, structural defects, and electronic structure as evaluated by X-ray synchrotron measurements, photothermal deflection spectroscopy, and the transport properties of materials and devices.

Nontechnical Abstract

The project addresses basic research issues in a topical area of materials science with high technological relevance. It contributes to the development of semiconductor materials based on abundant, non-toxic elements that could be used for solar energy conversion. The PIs plan to expand their successful track record of training underrepresented physics students through collaborations with local Hispanic-serving community colleges and organizations. Much of this work is performed at the UCSC Advanced Studies Laboratory, providing students exposure to both NASA and industrial collaborators.

Project Report

Intellectual Merit: The laboratory built a new low cost ALD/CVD materials deposition system that can deposit up to 3-different precursors for making metal sulfide alloy films via pulsed-CVD and ALD. This system is specifically designed to work with non-pyrophoric precursors and with insitu generated hydrogen sulfide, providing a much safer alternative to more commonly used systems for CVD and ALD deposition systmes. Using this system, we were able to successfully deposit Cu2S, ZnS and SnS2 ALD and CVD thin films using a low temperature and less corrosive organometallic precursors. We also demonstrated how (Cu,Zn) and (Cu,Sn), and (Cu,Zn,Sn) sulfide alloys form using multilayer deposition, and the role of the temperature, substrate (i.e. glass, silicon, ZnS, TiO2, etc), and post annealing conditions in controlling the resulting stoichiometry. The local structure of these alloys, probed by EXAFS, revealed that the (Cu,Zn) sulfur system fully phase separates on the nanoscale producing ZnS and CuS, the (Cu, Sn) sulfur system successfully forms into Cu2SnS3, and the (Cu,Zn,Sn) sulfur system shows features of both. (Cs, Zn, Sn) sulfur nanoparticles were also studied to demonstrate how the synthesis method and dimension of the nanophase (0D versus 2D) affects overall composition and structure or sulfide alloys. These materials were incorporated into PV device structures to understand the impact of the structural phases on device performance. These results will be important for any group working on ALD or CVD sulfide films or on cupper sulfide alloys for solar energy conversion. Broader Impact: This grant resulted in the support and training of 3 Ph.D. students in Physics, namely Ian Carbone (now tenure-track assistant professor of Environmental Studies at Allegheny), Andrew Short (now research scientist at Applied Materials) and Leila Jewell (Ph.D. 2015) who all learned CVD/ALD material deposition, structural characterization using EXAFS, and electrical and optical characterization. Anthony Bielecki completed his MS thesis research on this project, and undergraduate students participating in this research include Mikaela Hoffman-Stepleton, Brian Vollbrecht, Chris Doohan, Alannah Meyers, David Shugar, and Sophia Rocco. These students presented the results of this research at the Materials Research Society Spring meeting and American Physical Society March Meeting, the EDS Society chapter meeting, and the ALD and PV Specialist conferences. The research resulted in 1 invention disclosure, 4 published papers, and an additional 2 publications in progress. For outreach, Carter’s lab participated in the SACNAS (Society for the Advancement of Chicanos and Native Americans in Science) conference in Anaheim in 2010 and in San Jose in 2011. Carter and her students also ran an Expanding Your Horizons workshop focused on teaching high school students about solar energy. Finally, Carter stated the IRIS Science Academy to teach hands-on science education to students who do not currently have access to this training. Some of the students supported under this grant volunteered to help in the Summer Science Camps.

Agency
National Science Foundation (NSF)
Institute
Division of Materials Research (DMR)
Application #
1006190
Program Officer
Z. Charles Ying
Project Start
Project End
Budget Start
2010-07-01
Budget End
2014-06-30
Support Year
Fiscal Year
2010
Total Cost
$420,000
Indirect Cost
Name
University of California Santa Cruz
Department
Type
DUNS #
City
Santa Cruz
State
CA
Country
United States
Zip Code
95064