High Efficiency Thin Film CdTe and a-Si Based Solar Cells: Annual Technical Report, March 4, 1998 - March 3, 1999

Research output: NRELSubcontract Report


This report describes work done by the University of Toledo during the first year of this subcontract. During this time, the CdTe group constructed a second dual magnetron sputter deposition facility; optimized reactive sputtering for ZnTe:N films to achieve 10 ohm-cm resistivity and~9% efficiency cells with a copper-free ZnTe:N/Ni contact; identified Cu-related photoluminescence features andstudied their correlation with cell performance including their dependence on temperature and E-fields; studied band-tail absorption in CdSxTe1-x films at 10 K and 300 K; collaborated with the National CdTe PV Team on 1) studies of high-resistivity tin oxide (HRT) layers from ITN Energy Systems, 2) fabrication of cells on the HRT layers with 0, 300, and 800-nm CdS, and 3) preparation ofZnTe:N-based contacts on First Solar materials for stress testing; and collaborated with Brooklyn College for ellipsometry studies of CdSxTe1-x alloy films, and with the University of Buffalo/Brookhaven NSLS for synchrotron X-ray fluorescence studies of interdiffusion in CdS/CdTe bilayers. The a-Si group established a baseline for fabricating a-Si-based solar cells with single, tandem, andtriple-junction structures; fabricated a-Si/a-SiGe/a-SiGe triple-junction solar cells with an initial efficiency of 9.7% during the second quarter, and 10.6% during the fourth quarter (after 1166 hours of light-soaking under 1-sun light intensity at 50 deg C, the 10.6% solar cells stabilized at about 9%); fabricated wide-bandgap a-Si top cells, the highest Voc achieved for the single-junction topcell was 1.02 V, and top cells with high FF (up to 74%) were fabricated routinely; fabricated high-quality narrow-bandgap a-SiGe solar cells with 8.3% efficiency; found that bandgap-graded buffer layers improve the performance (Voc and FF) of the narrow-bandgap a-SiGe bottom cells; and found that a small amount of oxygen partial pressure (~2 X10 -5 torr) was beneficial for growing high-qualityfilms from ITO targets.
Original languageAmerican English
Number of pages68
StatePublished - 1999

Bibliographical note

Work performed by University of Toledo, Toledo, Ohio

NREL Publication Number

  • NREL/SR-520-27666


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