Research into Thin-Film photovoltaic cells had been present at USF since the early 1990s, focusing on improvements in the conversion efficiency of homojunction and heterojunction CdTe, CdSe, and CIGS PV Cells, as well as additional variations of those materials.
Investigations have included:
1. Impact of variations in stoichiometric ratios of polycrystalline films, including dimethyl-cadmium, isopropyl-tellurium, and respective deposition temperatures during Metalorganic Chemical Vapor Deposition (MOCVD) [1-3]
2. Formation of CdS films via Chemical Bath Deposition versus Close-Spaced Sublimation on CdTe thin-film PV cells [4-8]
3. Addition of Zn-Sn-O2 buffer layers, varying stoichiometric ratios and processing temperatures, as well as observing changes in the electrical properties of the developed films [10,11]
4. Analysis of the mechanisms associated with CdCl2 heat-treatment techniques utilized during the deposition process [9,15]
5. Presence of Cu chemically deposited or introduced as a back-contact material during deposition process [12-14]
6. New junction arrangements in PV cells in order to improve their conversion efficiency [16]
7. Exploration of other types of materials to serve as front and back contacts, including glass and foil [17, 18]
8. Review and analysis of shortcomings that still need to be addressed to make CdTe PV cells competitive with conventional solar technologies [19, 20]
9. Application of thin-film PV cells to space exploration [21, 22]
10. Development of CdSe/CIGS Thin-Film PV Cells[23]
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Major Contributions to CdTe Cell Performance
1. 1991: Achievement of CdS/CdTe Thin-Film PV cells with 13.4% Efficiency under laboratory specifications[25]
2. 1992: Development of CdS/CdTe Thin-Film PV cells with 14.6% conversion efficiency[26]
3. 1993: Achievement of CdS/CdTe Thin-Film PV cells with 15.8% conversion efficiency[27]
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Work Cited
[1] T. L. Chu, et al., “Cadmium telluride films by metalorganic chemical vapor deposition,” J. Appl. Phys., vol. 69, pp. 7651-5, 1991.
[2] T. L. Chu, et al., “Cadmium zinc telluride films by metalorganic chemical vapor deposition,” Int. SAMPE Electron. Conf., vol. 5, pp. 499-510, 1991.
[3] T. L. Chu, et al., “Thin-film junctions of cadmium telluride by metalorganic chemical vapor deposition,” J. Appl. Phys., vol. 71, pp. 3870-6, 1992.
[4] T. L. Chu, et al., “High efficiency cadmium sulfide/cadmium telluride solar cells from solution-grown cadmium sulfide films,” Conf. Rec. IEEE Photovoltaic Spec. Conf., vol. 22nd, pp. 952-6, 1991.
[5] C. S. Ferekides, et al., “The effects of CdS processing and glass substrates on the performance of CdTe solar cells,” Conf. Rec. IEEE Photovoltaic Spec. Conf., vol. 24th, pp. 99-102, 1994.
[6] C. S. Ferekides, et al., “CdS films prepared by the close-spaced sublimation and their influence on CdTe/CdS solar cell performance,” Conf. Rec. IEEE Photovoltaic Spec. Conf., vol. 25th, pp. 751-756, 1996.
[7] C. Ferekides, et al., “CdS: characterization and recent advances in CdTe solar cell performance,” Conf. Rec. IEEE Photovoltaic Spec. Conf., vol. 26th, pp. 339-342, 1997.
[8] D. M. Oman, et al., “Device performance characterization and junction mechanisms in CdTe/CdS solar cells,” Sol. Energy Mater. Sol. Cells, vol. 58, pp. 361-373, 1999.
[9] H. Zhao, et al., “Vapor chloride treatment studies of CdTe/CdS solar cells,” Conf. Rec. IEEE Photovoltaic Spec. Conf., vol. 29th, pp. 668-671, 2002.
[10] R. Bhatt, et al., “The dependence of reactively sputtered ZnO electronic properties on growth parameters for use as buffer layers in CuInxGa1-xSe2 solar cells,” Conf. Rec. IEEE Photovoltaic Spec. Conf., vol. 26th, pp. 383-386, 1997.
[11] S. Gayam, et al., “The structural and electrical properties of Zn-Sn-O buffer layers and their effect on CdTe solar cell performance,” Thin Solid Films, vol. 515, pp. 6060-6063, 2007.
[12] K. Barri, et al., “Introduction of Cu in CdS and its effect on CdTe solar cells,” Conf. Rec. IEEE Photovoltaic Spec. Conf., vol. 31st, pp. 287-290, 2005.
[13] S. Erra, et al., “An effective method of Cu incorporation in CdTe solar cells for improved stability,” Thin Solid Films, vol. 515, pp. 5833-5836, 2007.
[14] H. Zhao, et al., “The effect of Cu and annealing treatments on CdS/CdTe heterostructures studied with QE and photocurrent relaxation techniques,” Conf. Rec. IEEE Photovoltaic Spec. Conf., vol. 33rd, pp. 817-821, 2008.
[15] V. Komin, et al., “The effect of the CdCl2 treatment on CdTe/CdS thin film solar cells studied using deep level transient spectroscopy,” Thin Solid Films, vol. 431-432, pp. 143-147, 2003.
[16] S. Vakkalanka, et al., “Development of ZnSexTe1-x p-type contacts for high efficiency tandem structures,” Thin Solid Films, vol. 515, pp. 6132-6135, 2007.
[17] D. R. Hodges, et al., “Mechanical properties and adhesion of CdTe/CdS thin film solar cells deposited on flexible foil substrates,” Mater. Res. Soc. Symp. Proc., vol. 1165, pp. No pp given, Paper #: 1165-M02-09, 2009.
[18] D. Hodges, et al., “Development of back contacts for CdTe thin film solar cells deposited on flexible foil substrates,” IEEE Photovoltaic Spec. Conf., 34th, pp. 1347-1351, 2009.
[19] A. D. Compaan, et al., “Critical issues and research needs for CdTe-based solar cells,” Proc. – Electrochem. Soc., vol. 99-11, pp. 241-251, 1999.
[20] C. S. Ferekides, et al., “CdTe thin film solar cells: device and technology issues,” Sol. Energy, vol. 77, pp. 823-830, 2004.
[21] A. F. Hepp, et al., “Multi-junction thin-film solar cells on flexible substrates for space power,” National Aeronautics and Space Administration,Glenn Research Center,Cleveland,OH,USA.2002.
[22] J. E. Dickman, et al., “Utility of thin-film solar cells on flexible substrates for space power,” Glenn Research Center,National Aeronautics and Space Administration,Cleveland,OH,USA.2004.
[23] P. Mahawala, et al., “Transparent contact development for CdSe top cells in high efficiency tandem structures,” Conf. Rec. IEEE Photovoltaic Spec. Conf., vol. 31st, pp. 418-421, 2005.
[24] United States Department of Energy NREL, “Best Research-Cell Efficiencies,” 2nd Edition ed: National Renewable Energy Laboratory, 2010.
[25] T. L. Chu, et al., “The 13.4% efficient thin-film cadmium sulfide/cadmium telluride solar cells,” J. Appl. Phys., vol. 70, pp. 7608-12, 1991.
[26] T. L. Chu, et al., “14.6% efficient thin-film cadmium telluride heterojunction solar cells,” IEEE Electron Device Lett., vol. 13, pp. 303-4, 1992.
[27] J. Britt and C. Ferekides, “Thin-film cadmium sulfide/cadmium telluride solar cell with 15.8% efficiency,” Appl. Phys. Lett., vol. 62, pp. 2851-2, 1993.