Atomic-Scale Characterization of CdTe PV Through Atom Probe Tomography
Kevin S. Boxer
1, Dr. Brian Gorman
1, Dr. Teresa Barnes
21Colorado School of Mines, Golden, CO, 2National Renewable Energy Laboratory, Golden, CO
CdTe Solar Cell Technology
First Solar 40-MW CdTe PV Array
(Photo courtesy of JUWI Group) Transmittance vs. Wavelenthof CdTe (www.sttic.com.ru)
● Thin Film Photovoltaic Device
● Increasingly Cost Competitive
● GE & First Solar Heavily Invested
● Potential to Reduce the Use of Fosil Fuels
● Favorable Balance of Cost & Efficiency
Atom Probe Tomography (APT)
CAMECA LEAP 4000X Si Schematic of LEAP Electrode and Detector (http://www.cameca.com)
● Local Electrode Atom Probe (LEAP)
● Laser-Induced Field Evaporation
● Chemical Composition Measurements at the Atomic Scale
● Time of Flight Mass Spectrometry
● 3D Imaging and Analysis
Sample Preparation
Ti (~500 nm)
ZnTe:Cu (~500 nm) CdTe (4-6 microns)
CdS (80-100 nm, before CdTe processing) SnO2:F (~300-400 nm)
SnO2 (100 nm)
Glass (1.1mm, alkali free) * CdCl2 anneal (no thickness)
● Samples Prepared at National Renewable Energy Lab
● Thin Film Deposited with Chemical Vapor Deposition (CVD)
● Photolithographically Processed Into 0.25 cm2 Mesas
● Sample Variations in CdTe Temp. and Annealing Conditions
● Utilized Focused Ion Beam (FIB) to Mill Sample [1]
● FEI Company Helios 600i FIB with Ga Source
● Specimen Was Attached to Si Microtip Array
● Sample Was Milled to ~ 300 nm Diameter
3D-Imaging
Cd Zn Zn+Cd+Metallic Impurity
Zn+Te CdTe Sample
Mass Spectrum
Future Work
Perform Additional APT Trials with Variations in Composition to Determine Effect on Properties and Increase Energy Conversion
References
[1] K. Thompson, D. Lawrence, D. J. Larson, J. D. Olson, T. F. Kelly, and B. Gorman, “In situ site-specific specimen preparation for atom probe to-mography,” Ultramicroscopy, vol. 107, no. 2–3, pp. 131–139, Mar. 2007.
Acknowledgements
Thank you to Dr. Chuck Stone, Dr. Brian Gorman, Dr. David Diercks, Dr. Teresa Barnes, Dr. Craig Taylor, Phyllis Johnson, and Linda Crow, and the support of the National Science Foundation through the REMRSEC REU under grant No. DMR-1063150.
