Research focus--The principal research effort of Dr. Compaan, on the deposition of semiconductor thin films for solar cells, is supported by the National Renewable Energy Laboratory (NREL). Complete CdS/CdTe thin film solar cells are being fabricated at Toledo with the CdS, CdTe, and CdCl2 deposited by pulsed laser deposition and radio frequency (rf) planar magnetron sputtering. The research emphasizes techniques scalable to large-area, thin-film modules for applications of photovoltaic power generation. Most of our research effort involves the use of glass substrates which are coated with fluorine-doped tin oxide which serves as the transparent conductor. However, some research is directed to the development of CdS/CdTe cells on flexible substrates such as molybdenum foil and high temperature polymers. There are currently two major projects supported by NREL. The first involves continuing research to improve the performance of the CdTe-based cells and to study defects and non-uniformities in the thin films which can lead to long term degradation of the cell performance. The second project involves “next-generation” devices such as developing CdTe alloys suitable for a top cell in a two-junction tandem configuration. This to cell needs to have a band gap of about 1.7 eV compared with the 1.5 eV band gap of CdTe. We are also working on the development of a transparent back contact (and/or “tunnel junction”) for the top cell so that sunlight (and current) can pass to the smaller-gap bottom cell.
Other faculty collaborate in this work. These include Profs. Victor Karpov, Randy Bohn, Xunming Deng in Physics and Astronomy, and Dean Giolando of the Chemistry Department.
Another related research effort of our group involves the development of improved thin films for flat-panel plasma display panel (PDP) technology and the study of vacuum-ultraviolet emission spectroscopy from PDP structures with time resolution of nanoseconds.
In our labs we use a wide variety of characterization and diagnostic techniques including Raman scattering, photoluminescence, x-ray diffraction, scanning electron microscopy (SEM) with energy dispersive x-ray analysis (EDS), laser-induced time-resolved fluorescence, photoreflectance and electroreflectance, spectral quantum efficiency, and I-V device measurements. We collaborate with other research groups in using atomic force microscopy (AFM), spectroscopic ellipsometry, Rutherford backscattering (RBS), and synchrotron-based x-ray studies (grazing incidence x-ray fluorescence, x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS).
Recent selected publications:
M. Shao, A. Fischer, D. Grecu, U. Jayamaha, E. Bykov, G. Contreras-Puente, R.G. Bohn, and A.D. Compaan, “Radio-frequency-magnetron-sputtered CdS/CdTe solar cells on soda-lime glass,” Appl. Phys. Lett. 69, 3045-3047 (1996).
A. Fischer, L. Anthony and A.D. Compaan, "Raman Analysis of Short-Range Clustering in Laser-Deposited CdSxTe1-x Films," Appl. Phys. Lett. 72, 2559, (1998).
Y.L. Soo, S. Huang, Y.H. Kao, and A.D. Compaan, "Investigation of interface morphology and composition mixing in CdTe/CdS heterojunction photovoltaic materials using synchrotron radiation," J. Appl. Phys. 83, 4173 (1998).
S. Huang, Y.L. Soo, Y.H. Kao, and A.D. Compaan, "Annealing effects and Te mixing in CdTe/CdS heterojunctions," Appl. Phys. Lett., 74, 218-220 (1999).
R. Wendt, A. Fischer, D. Grecu and A.D. Compaan, "Improvement of CdTe solar cell performance with discharge control during film deposition by magnetron sputtering," J. Appl. Phys. 84, 2920-2925 (1998).
J.R. Gottschalk, A. Shvidky, A.D. Compaan, C.E. Theodosiou, and W. Williamson, Jr., “Time-Resolved Electrical and Optical Measurements in a Plasma Display Panel,” IEEE Transactions on Plasma Science, 27, 772-777 (1999).
K. Wei, F.H. Pollak, J.L. Freeouf, D. Shvydka, and A.D. Compaan, “Optical Properties of CdTe1-xSx (0 £ x £ 1): Experiment and Modeling,” J. Appl. Phys. 85, 7418-7425 (1999).
D. Grecu and A.D. Compaan, "Photoluminescence Study of Cu Diffusion and Electromigration in CdTe, Appl. Phys. Lett. 75, 361-363 (1999).
A.D. Compaan, J.R. Sites, R.W. Birkmire, C.S. Ferekides, and A.L. Fahrenbruch, "Critical Issues and Research Needs for CdTe-Based Solar Cells," Photovoltaics for the 21st Century Electrochemical Society Symposium Proceedings, ECS99-11, edited by
V.J. Kapur, R.D. McConnell, D. Carlson, G.P. Ceasar, and A. Rohatgi (1999) pp.241-251.
D. Grecu, A.D. Compaan, D. Young, U. Jayamaha, and D.H. Rose, “Photoluminescence of Cu-doped CdTe and related stability issues in CdS/CdTe solar cells,” J. Appl. Phys. 88, 2490 (2000).
Y.L. Soo, S. Huang, S. Kim, G. Kioseoglou, Y.H. Kao, A.D. Compaan, D. Grecu, and D. Albin, “Effects of heat treatment on diffusion of Cu atoms into CdTe single crystals,” Appl. Phys. Letts. 76, 3729 (2000).
A.D. Compaan, I Matulionis, and S. Nakade, "Laser scribing of polycrystalline thin films," Optics and Lasers in Engineering 34 15-45 (2000).
K. Makhratchev, K.J. Price, X. Ma, D.A. Simmons, J. Drayton, K. Ludwig, A. Gupta, R.G. Bohn, & A.D. Compaan, "ZnTe:N Back Contacts to CdS/CdTe Solar Cells," 28th IEEE Photovoltaic Specialists Conference—2000, pp. 475-478 (IEEE, Piscataway, N.J.)
K.J. Price, D. Grecu, D. Shvydka, & A.D. Compaan, "Photoluminescence of CdTe:Cu and CdS/Cu," 28th IEEE Photovoltaic Specialists Conference—2000, pp. 658-661 (IEEE, Piscataway, N.J.).
J. Drayton, A. Gupta, K. Makhratchev, K.J. Price, R.G. Bohn, and A.D. Compaan, "Properties of RF Sputtered ZnTe:N for Back Contact to CdS/CdTe Solar Cells," Mat. Res. Soc. Symp. Proc. 668, H5.9.1, 2001
Matulionis, S. Han, J.A. Drayton, K.J. Price, and A.D. Compaan, "CdTe Solar Cells on Molybdenum Substrates," Mat. Res. Soc. Symp. Proc. 668, H8.23.1, 2001
D. Shvydka, A.D. Compaan, and K. J. Price, "Absorption and photoluminescence studies of lightly alloyed CdTe(S) and CdS(Te)," Mat. Res. Soc. Symp. Proc. 668, H6.2.1, 2001
A. Gupta, I Matulionis, J. Drayton, and A.D. Compaan, “Effect of CdTe thickness reduction in high efficiency CdS/CdTe solar cells,” II-VI Compound Semiconductor Photovoltaic Materials edited by R. Noufi, D. Lincot, and H.W. Schock [Mat. Res. Soc. Symp. Proc. 668, H6.4.1, (2001)].