Jerry D. Harris

Optical and structural characterization of copper indium disulfide thin films

Thin films of copper indium disulfide (CuInS2) were synthesized by spray chemical vapor deposition. Rutherford backscattering measurements were used to determine the composition and thickness of the films. The elemental ratios were found to be within 2% of stoichiometrically correct CuInS2. The thickness of the films was found to be approximately 1.0 μm. An optical band-gap of approximately 1.44 eV for this material was determined by optical transmission spectroscopy. Reflectance spectroscopy identified phonon bands centered at 225, 291 and 317 cm−1.

Wet-Chemical Synthesis of Thin-Film Solar Cells

We have been working on the development of wet-chemical processing methods that can be used to create thin film photovoltaic solar cells. Electrochemically deposition methods have been used to produce copper indium diselenide (CIS) thin films on molybdenum coated polymer substrates. CIS has an extremely high optical absorption coefficient, excellent radiation resistance, and good electrical conductivity and thus has proved to be an ideal absorber material for thin film solar cells. A series of compositionally different p-type CIS films were produced by using different electrochemical deposition potentials. Cadmium sulfide (CdS) window layers were deposited directly on these CIS films using a chemical bath process. CdS is a naturally ntype wide-bandgap semiconductor which has good transparency and is well lattice-matched to CIS. Zinc oxide thin films were grown by electrochemical deposition directly on the CdS films. ZnO is a transparent and conductive thin film that serves as the top contact of the cells. The structural and elemental properties of the individual ZnO, CdS and CIS films were characterized by x-ray diffraction and energy dispersive spectroscopy. The electrical behavior of the CdS on CIS junctions was determined using current versus voltage measurements. We will discuss the performance of these devices based on the physical properties of the component films and the processing methods employed in their fabrication.

Thin film CuInS/sub 2/ prepared by spray pyrolysis with single-source precursors

Both horizontal hot-wall and vertical cold-wall atmospheric chemical spray pyrolysis processes deposited near single-phase stoichiometric CuInS/sub 2/ thin films. Single-source precursors developed for ternary chalcopyrite materials were used for this study, and a new liquid phase single-source precursor was tested with a vertical cold-wall reactor. The depositions were carried out under an argon atmosphere, and the substrate temperature was kept at 400/spl deg/C. Columnar grain structure was obtained with vapor deposition, and the granular structure was obtained with (liquid) droplet deposition. Conductive films were deposited with planar electrical resistivities ranging from 1 to 30/spl Omega//spl middot/cm.

Thin-film organic-based solar cells for space power

Recent advances in dye-sensitized and organic polymer solar cells have lead NASA to investigate the potential of these devices for space power generation. Dye-sensitized solar cells were exposed to simulated low-earth orbit conditions and their performance evaluated. All cells were characterized under simulated air mass zero (AM0) illumination. Complete cells were exposed to pressures less than 1/spl times/10/sup -7/ torr for over a month, with no sign of sealant failure or electrolyte leakage. Cells from Solaronix SA were rapid thermal cycled under simulated low-earth orbit conditions. The cells were cycled 100 times from -80 C to 80 C, which is equivalent to 6 days in orbit. The best cell had a 4.6% loss in efficiency as a result of the thermal cycling. In a separate project, novel -Bridge-Donor-Bridge-Acceptor- (-BDBA-) type conjugated block copolymer systems have been synthesized and characterized by photoluminescence (PL). In comparison to pristine donor or acceptor, the PL emissions of final -B-D-B-A- block copolymer films were quenched over 99%. Effective and efficient photo induced electron transfer and charge separation occurs due to the interfaces of micro phase separated donor and acceptor blocks. The system is very promising for a variety high efficiency light harvesting applications. Under an SBIR contract, fullerene-doped polymer-based photovoltaic devices were fabricated and characterized. The best devices showed overall power efficiencies of -0.14% under white light. Devices fabricated from 2% solids content solutions in chlorobenzene gave the best results. Presently, device lifetimes are too short to be practical for space applications.

CCDC 972792: Experimental Crystal Structure Determination

Related Article: Jesse S. Hyslop, Amanda R. Boydstun, Theron R. Fereday, Joanna R. Rusch, Jennifer L. Strunk, Christian T. Wall, Cecelia C. Pena, Nicholas L. McKibben, Jerry D. Harris, Aaron Thurber, Alex Punnoose, Jason Brotherton, Pamela Walker, Lloyd Lowe, Blake Rapp, Shem Purnell, William B. Knowlton, Seth M. Hubbard, Brian J. Frost|2015|Mat.Sci.Semicond.Proc.|38|278|doi:10.1016/j.mssp.2015.04.001

Crystallite Size Evaluation of ZnO Nanoparticles via Transmission Electron Microscopy and X-ray Powder Diffraction

Zinc Oxide has received a considerable amount of attention over the past decades due to its unique electronic and optical properties. The material is readily available, inexpensive, and environmentally friendly compared to other semiconducting materials1. These properties make ZnO an excellent candidate material for applications such as: photovoltaic devices2, gas sensors3, transparent conductive oxides (TCO)4, biomedical devices5, and photocatalysis6 among many others. Zinc oxide was synthesized by alkali precipitation using aqueous solutions of zinc acetate, various amines, and precipitated with the addition of NaOH. The resulting materials were characterized with Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), and the Brunauer–Emmett–Teller (BET) method. The optical band gap of the material was determined with Ultraviolet-visible reflectance spectroscopy.

Injection CVD Grown MWNTs for PEM Fuel Cells

Synthesis of multi -walled carbon nanotubes (MWNTs) by the injection chemical vapor deposition (CVD) process has been investigated with characterization performed by scanning electron microscopy, transmission electron microscopy, surface area analysis, and thermogravimetric analysis. The results show highly crystalline materials with low metal catalyst and carbon impurities and a specific surface area of 1252 m 2 /g. As-produced MWNTs were dispersed in a 5% w/w Nafion solution to produce composite membrane electrodes for testing in a proton-exchange-membrane (PEM) fuel cell. The device performance was measured in a side-by-side comparison for a control membrane containing 100% w/w E-TEK (Vulcan XC-72) and the test membrane which was 25% w/w MWNTs and 75% w/w E-TEK. Even with the reduction in platin um loading in the cell membrane electrodes by replacement with MWNTs, the results showed an increase in the output power as well as a significant decrease in cell resistance.

Chemical vapor deposition for ultralightweight thin-film solar arrays

The development of thin-film solar cells on flexible, lightweight, space-qualified substrates provides an attractive cost solution to fabricating solar arrays with high specific power, (W/kg). The use of a polycrystalline chalcopyrite absorber layer for thin film solar cells is considered as the next generation photovoltaic devices. A key technical issues outlined in the 2001 US Photovoltaic Roadmap, is the need to develop low cost, high throughput manufacturing for high-efficiency thin film solar cells. At NASA GRC we have focused on the development of new single-source-precursors (SSPs) and their utility to deposit the chalcopyrite semiconducting layer (CIS) onto flexible substrates for solar cell fabrication. The syntheses and thermal modulation of SSPs via molecular engineering is described. Thin-film fabrication studies demonstrate the SSPs can be used in a spray CVD process, for depositing CIS at reduced temperatures, which display good electrical properties, suitable for PV devices.