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Effects of light on the resistivity of chemical vapor deposited graphene films

Description: This article reports that the resistance of a chemical vapor deposition (CVD) grown graphene film transferred onto an SiO₂ substrate increases to higher saturation values upon exposure to light of decreasing wavelength from the visible to ultraviolet.
Date: October 24, 2016
Creator: Mo, Yudong; Pérez, José M.; Ye, Zhou; Zhao, Lei; Yang, Shizhong; Tan, Liuxi et al.
Partner: UNT College of Arts and Sciences

Liquid-Phase Deposition of CIS Thin Layers: Final Report, February 2003--July 2005

Description: The goal of this project was to fabricate single-phase CIS (a-Cu-In-Se, stoichiometric composition: CuInSe2) thin films for photovoltaic applications from a liquid phase - a Cu-In-Se melt of appropriate composition. This approach of liquid-phase deposition (LPD) is based on the new phase diagram we have established for Cu-In-Se, the first complete equilibrium phase diagram of this system. The liquidus projection exhibits four composition fields in which the primary solid phase, i.e., the first solid material that forms on cooling down from an entirely liquid state, is a-CuInSe2. Remarkably, none of the four composition fields is anywhere near the stoichiometric composition (CuInSe2) of a-CuInSe2. The results demonstrate that the proposed technique is indeed capable of producing films with a particularly large grain size and a correspondingly low density of grain boundaries. To obtain films sufficiently thin for solar cell applications and with a sufficiently smooth surface, it is advantageous to employ a sliding boat mechanism. Future work on liquid-phase deposition of CIS should focus on the interaction between the melt and the substrate surface, the resulting CIS interfaces, the surface morphology of the LPD-grown films, and, of course, the electronic properties of the material.
Date: February 1, 2006
Creator: Ernst, F. & Pirouz, P.
Partner: UNT Libraries Government Documents Department

Small-angle x-ray scattering studies of microvoids in amorphous-silicon-based semiconductors. Annual subcontract report, February 1, 1992--January 31, 1993

Description: Our general objectives are to provide new details of the microstructure for the size scale from about 1 to 30 nm in high-quality a-Si:H and related alloys prepared by current state-of-the-art deposition methods as well as by new and emerging deposition technologies and thereby help determine the role of microvoids and other density fluctuations in controlling the opto-electronic properties. More specifically, the objectives are to determine whether the presence of microstructure as detected by small-angle x-ray scattering (SAXS) (1) limits the photovoltaic properties of device-quality a-Si:H, (2) plays a role in determining the photo-stability of a-Si:H, and (3) is responsible for degradation of the photovoltaic properties due to alloying with Ge, C and other constituents. The approach involves collaboration with several groups that can supply relevant systematic sets of samples and the associated opto-electronic data to help address these issues. Since the SAXS technique has not been a standard characterization technique for thin-film materials, and was recently set up at CSM with support by NREL, the project involves considerable development of the method with regard to standardizing the procedures, minimizing substrate influences and implementing improved data reduction and modeling methodology. Precise, highly reproducible, and accurate results are being sought in order to allow useful, reliable, and sensitive comparisons of materials deposited under different conditions, by different methods, and by different systems that represent the same nominal method.
Date: May 1, 1994
Creator: Williamson, D L; Jones, S J & Chen, Y
Partner: UNT Libraries Government Documents Department

Comparison of Composite Transparent Conducting Oxides Based on the Binary Compounds CdO and SnO2: Preprint

Description: Presented at the 2001 NCPV Program Review Meeting: Properties of CVD-formed SnO2 and CdO thin films and composite CdySnxO2x+y are discussed, then electronic and optical properties of CdySnxO2x+y are compared to those of SnO2 and CdO.
Date: October 1, 2001
Creator: Li, X.; Gessert, T.; DeHart, C.; Barnes, T.; Moutinho, H.; Yan, Y. et al.
Partner: UNT Libraries Government Documents Department

Identifying Electronic Properties Relevant to Improving the Performance and Stability of Amorphous Silicon Based Photovoltaic Cells: Final Subcontract Report, 27 November 2002--31 March 2005

Description: A major effort during this subcontract period has been to evaluate the microcrystalline Si material under development at United Solar Ovonics Corporation (USOC). This material is actually a hydrogenated nanocrystalline form of Si and it will be denoted in this report as nc-Si:H. Second, we continued our studies of the BP Solar high-growth samples. Third, we evaluated amorphous silicon-germanium alloys produced by the hot-wire chemical vapor deposition growth process. This method holds some potential for higher deposition rate Ge alloy materials with good electronic properties. In addition to these three major focus areas, we examined a couple of amorphous germanium (a-Ge:H) samples produced by the ECR method at Iowa State University. Our studies of the electron cyclotron resonance a-Ge:H indicated that the Iowa State a Ge:H material had quite superior electronic properties, both in terms of the drive-level capacitance profiling deduced defect densities, and the transient photocapacitance deduced Urbach energies. Also, we characterized several United Solar a Si:H samples deposited very close to the microcrystalline phase transition. These samples exhibited good electronic properties, with midgap defect densities slightly less than 1 x 1016 cm-3 in the fully light-degraded state.
Date: November 1, 2005
Creator: Cohen, J. D.
Partner: UNT Libraries Government Documents Department

Identifying the Electronic Properties Relevant to Improving the Performance of High Band-Gap Copper Based I-III-VI2 Chalcopyrite Thin Film Photovoltaic Devices: Final Subcontract Report, 27 April 2004-15 September 2007

Description: This report summarizes the development and evaluation of higher-bandgap absorbers in the CIS alloy system. The major effort focused on exploring suitable absorbers with significant sulfur alloying in collaboration with Shafarman's group at the Institute of Energy Conversion. Three series of samples were examined; first, a series of quaternary CuIn(SeS)2-based devices without Ga; second, a series of devices with pentenary Cu(InGa)(SeS)2 absorbers in which the Se-to-S and In-to-Ga ratios were chosen to keep the bandgap nearly constant, near 1.52 eV. Third, based on the most-promising samples in those two series, we examined a series of devices with pentenary Cu(InGa)(SeS)2 absorbers with roughly 25 at.% S/(Se+S) ratios and varying Ga fractions. We also characterized electronic properties of several wide-bandgap CuGaSe2 devices from both IEC and NREL. The electronic properties of these absorbers were examined using admittance spectroscopy, drive-level capacitance profiling, transient photocapacitance, and transient photocurrent optical spectroscopies. The sample devices whose absorbers had Ga fraction below 40 at.% and S fractions above 20 at.% but below 40% exhibited the best electronic properties and device performance.
Date: August 1, 2008
Creator: Cohen, J. D.
Partner: UNT Libraries Government Documents Department

Nanostructure of a-Si:H and Related Alloys by Small-Angle Scattering of Neutrons and X-Rays; Annual Technical Progress Report, May 22, 1999 to August 21, 2000

Description: This report describes work being performed to provide details of the microstructure in high-quality hydrogenated amorphous and microcrystalline silicon and related alloys on the nanometer size scale. The materials under study are being prepared by current state-of-the-art deposition methods, as well as by new and emerging deposition techniques. The purpose is to establish the role of nanostructural features in controlling the opto-electronic and photovoltaic properties. The approach centers around the use of the uncommon technique of small-angle scattering of both X-rays (SAXS) and neutrons (SANS). SAXS has already been established as highly sensitive to microvoids and columnar-like microstructure. A major goal of this research is to establish how sensitive SANS is to the hydrogen nanostructure. Conventional X-ray diffraction techniques are being used to examine medium-range order and microcrystallinity, particularly near the boundary between amorphous and microcrystalline material.
Date: October 30, 2000
Creator: Williamson, D.
Partner: UNT Libraries Government Documents Department