Symposium Organizers
Ramon Escobar-Galindo, Abengoa Research
Ibon Azkona, Metal Estalki
Jose Luis Endrino, Cranfield University
Matthias Krause, Helmholtz-Zentrum Dresden-Rossendorf
Symposium Support
IK4-TEKNIKER
FOM Technologies
METAL ESTALKI
ES9.1: Boosting the Efficiency of Solar Collectors Using Nitride Films
Session Chairs
Ramon Escobar-Galindo
Andreas Schuler
Wednesday PM, April 19, 2017
PCC North, 200 Level, Room 226 C
9:45 AM - *ES9.1.02
On the Search of New Solar Absorbers for High Temperature Solar Selective Coatings—Molybdenum Short-Range Order in Mo–Si–N Systems
Carlos Prieto 1 , Adrian Rodriguez-Palomo 1 , Eva Cespedes 2
1 , Instituto de Ciencia de Materiales de Madrid (CSIC), MADRID Spain, 2 , IMDEA NanoScience, Madrid Spain
Show AbstractThe design of solar selective coatings (SSC) for concentrated solar power (CSP) applications requires a precise knowledge and control of the whole stack optical behaviour. Moreover, the study of its chemical stability becomes essential for their use at high temperatures. In this communication, we report on the promising properties of SSCs prepared with absorbers based on novel composites from the Mo–Si–N system.
As required from an adequate balance between cost and efficiency, the studied SSC stacks are formed by: (i) an IR-mirror metal, (ii) a double cermet layer and (iii) an antireflective dielectric cover. Besides the experimental characterization, the optical reflectance in the whole visible – infrared range is simulated from the complex dielectric permittivity of the components. Those simulations allow the optimization of the optical characteristics by changing parameters such as the double cermet and the antireflective dielectric layers thickness, and the metallic volume fraction in the cermet (cermet filling factor).
It has been shown that the precise control of thickness and composition of sputtering–deposited SSC stacks based on Mo–Si–N, either Mo-Si3N4 cermets or MoSi2-Si3N4 composites absorbers, leads to high solar absorptivity and low thermal emissivity values [1,2]. On the other hand, its thermal stability points towards its practical use at temperatures near 600 °C. The key point of the high temperature performance of these SSCs without degradation in vacuum or air makes particularly interesting the fundamental research of the chemistry taking place in the coating.
In this report, the promising SSC optical stability at high temperatures is correlated with the specific study of the short-range order around Mo by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies.
[1] E. Céspedes, M.Wirz, J.A. Sánchez-García, L. Alvarez-Fraga, R. Escobar-Galindo, C. Prieto, Novel Mo–Si3N4 based selective coating for high temperature concentrating solar power applications, Sol. Energy Mater. Sol. Cells 122 (2014) 217.
[2] D. Hernández-Pinilla, A. Rodríguez-Palomo, L. Álvarez-Fraga, E. Céspedes, J. E. Prieto, A. Muñoz-Martín and C. Prieto, “MoSi2-Si3N4 Absorber for High Temperature Solar Selective Coating” Sol. Energy Mater Sol. Cells, 152 (2016) 141.
10:15 AM - ES9.1.03
Design of Solar Selective Coatings Based on Aluminium Titanium AlTi(OxN1-x) Oxynitrides for High-Temperature CSP Applications
Irene Heras 1 , Matthias Krause 2 , Frank Lungwitz 2 , Rincon Gonzalo 1 , Mercedes Alcon-Camas 1 , Ibon Azkona 3 , Cristina Guillen 1 , Ramon Escobar-Galindo 1
1 , Abengoa Research S.L., Seville Spain, 2 , Helmholtz-Zentrum Dresden-Rossendorf, Dresden Germany, 3 , Metal Estalki, Derio Spain
Show AbstractAluminium titanium oxynitrides were selected as candidate materials for solar selective coatings (SSC) on the basis of the state of the art. A set of individual AlTi(OxN1-x) layers deposited by cathodic vacuum arc (CVA) with different oxygen content were prepared by cathodic vacuum arc deposition. The composition, morphology and microstructure of the films were characterized by ion beam analysis, scanning and transmission electron microscopy and X-ray diffraction. The optical properties were determined by ellipsometry and spectrophotometry (UV-Vis-NIR, FTIR). The microstructural and morphological characterization shows the evolution of the AlTiN ternary phases when the oxygen concentration was increased. After the analysis of the ellipsometry data, it can be concluded that there is a transition from metallic to dielectric by increasing the oxygen content. The optical properties of these AlTi(OxN1-x) films can be controlled in a wide range from metallic to the dielectric character by choosing the oxygen concentration. Once single AlTi(OxN1-x) thin films were fully characterized, complete SSC were designed with optical simulations, based on measured optical constants of each of the individual layers, providing excellent selective optical selective properties (α=94.7% and εRT=5.6%). The selected multilayers stacks were CVA deposited, obtaining excellent agreement between simulated and experimental reflectance spectra. Finally, the thermal stability in air of the complete deposited SSC was analyzed by cyclic heating tests, showing no degradation after 750h of cycles in air at 600oC.
10:30 AM - ES9.1.04
Optical and Thermal Characterizations of an Ultrathin Metafilm Selective Solar Thermal Absorber with Excellent High Temperature Stability
Hassan Alshehri 1 , Qing Ni 1 2 , Hao Wang 1 , Liping Wang 1
1 School for Engineering of Matter, Transport & Energy, Arizona State University, Tempe, Arizona, United States, 2 , University of Science and Technology of China, Hefei, Anhui, China
Show AbstractA novel sub-micron multilayer metafilm selective solar thermal absorber has been fabricated and its temperature-dependent optical properties as well as thermal performance are characterized in this study. The absorber, which is made of tungsten, SiO2, and Si3N4 thin films, has near normal, angle insensitive, absorptance greater than 95% in the solar spectrum and less than 10% in the mid-infrared. Fiber optics based temperature-dependent spectroscopic characterization shows that the absorber exhibits stable optical properties when heated up to 600°C in ambient conditions. Thermal testing in a furnace reveals excellent thermal stability at 400°C in ambient conditions for 72 hrs. Solar thermal experiments, which consist of a xenon lamp, an AM1.5 filter, a vacuum chamber, and optical and thermal parts, are conducted to experimentally measure the stagnation temperature (i.e. highest surface temperature with zero solar-to-thermal efficiency) as well as the solar-to-thermal efficiency of the fabricated metafilm selective solar absorber in both ambient and vacuum conditions. The solar-thermal measurement setup utilizes thin pins to hold the absorber to minimize thermal conduction losses, while the absorber temperature is measured by a thermocouple inserted into a copper heat spreader, which the absorber rests on. A heat sink changes the absorber temperature by varying the flowrate of cooling water, while the thermal energy harvested by the water is measured by a calibrated heat flux meter placed between the copper heat spreader and the heat sink. The incident optical power from the lamp, which is measured by an optical power meter, along with the heat flux, could then be used to experimentally obtain the solar-to-thermal efficiency. A heat transfer model will also be developed to estimate the thermal losses and validate the experimentally measured stagnation temperature and solar-to-thermal efficiency. In order to demonstrate the optical and thermal performance of the novel metafilm coating, black absorbers and some commercial selective coatings like TiNOX will be characterized in-house for comparison. Finally, a cost analysis of the metafilm absorber will be performed. As a future application, this highly efficient selective metafilm could be used to possibly improve the performance of solar thermophotovotalic energy conversion by pairing with a cell separated by microscale vacuum gaps.
ES9.2: New Trends to Optimize Energy Conversion in Concentrated Photovoltaics
Session Chairs
Javier Barriga
Sungho Jin
Wednesday PM, April 19, 2017
PCC North, 200 Level, Room 226 C
11:15 AM - *ES9.2.01
Coupled Thermo-Mechanical and Photo-Chemical Degradation in Materials and Interfaces for Concentrated Solar Energy Applications
Reinhold Dauskardt 1
1 , Stanford University, Stanford, California, United States
Show AbstractWe describe research to identify and characterize the coupled thermo-mechanical and photo-chemical degradation mechanisms that determine the adhesion and reliability of materials and interfaces in concentrated photovoltaic (CPV) solar technologies. Three specific interfaces and adjacent materials identified by a survey of CPV module manufacturers as the most critical for reliability will be described. These include the silicone adhesive associated with the light collection and concentration optics to the antireflection (AR) coating on high-performance multi-junction solar cells, and the others involve the adhesion of the AR coating to the solar cell itself, along with cell damage caused by the metallization following thermal cycling. CPV provides an ideal vehicle for solar degradation studies due to the elevated levels of “stressing” parameters, and the examples, characterization methods and models described are relevant broadly to other solar technologies.
We describe quantitative adhesion characterization techniques we have developed to measure the synergistic effect of mechanical stresses, temperature, environmental species and the presence of simulated solar UV light on inherent thermo-mechanical properties including interface debonding kinetics and cohesive failure of layers. Further, we developed the capability to age specimens in an outdoor concentrator in excess of 1100x the AM1.5 direct irradiance and in indoor environmental chambers with broadband UV irradiation with controlled temperature and humidity. We characterized changes in mechanical properties and chemical structures to understand the fundamental connection between mechanical properties and defect evolution in the material layers.
We developed mechanics, physics and photo-chemical rate models to explain the change in adhesion along with damage processes following thermal cycling as a basis for predicting operational lifetimes of the materials and interfaces. We include results from both the indoor and field exposures. Using models of the degradation process, we show how short term accelerated testing can be correlated with degradation in the field. Implications to optimize materials, develop accelerated test methods and provide the fundamental basis for realistic science-based lifetime predictions are described.
11:45 AM - ES9.2.02
A Tool to Characterize the Electrical Influence of the Thermal and Mechanical Behaviors of Materials of Optics for CPV Applications
Arnaud Ritou 2 , Philippe Voarino 2 , Olivier Raccurt 1 , Mathieu Baudrit 2 , Pierre Besson 3
2 LCPV, CEA INES, Le-Bourget-du-Lac France, 1 LITEN-LSHT, CEA INES, Le-Bourget-du-Lac France, 3 , Fraunhofer, Santiago Chile
Show AbstractThe price of Photovoltaic (PV) energy is now competitive with other technologies. However Silicon PV cells are reaching their theoretical limit of efficiency while integrated in the common flat PV panels. Because the efficiency of a module is led by the efficiency of the cell, it is interesting to use better semi-conductor materials with several pn junctions per cell and to concentrate light on cells [1]. In concentrated photovoltaic (CPV) modules, commonly used III-V materials are more efficient but more expensive than Silicon one. For example, the efficiency record for a Four-junction III-V cell under concentrated light count 46% rather than 25.8% for a non-concentrated Si one [2]. Concentrating light on PV cell takes 2 advantages. It reduces costs by reducing cell area for the same output power and increases cell efficiency while concentrating light power [1]. On another hand, integrating concentrating optics in a CPV module induce different losses. Fresnel reflection or bulk absorption are unavoidable but other losses in the cell led by non-uniform irradiance or bad spectral management must be quantified to attest a reliable module assembly [3]. A test method that measures spectrally resolved irradiance distribution for concentrator photovoltaic (CPV) optical systems is presented [4]. In conjunction with electrical I-V curves it is a means to visualize and characterize the effects of chromatic aberration and non-uniform flux profiles under controllable testing conditions putting in relief the role of thermal expansion for material constituting the optics. The indoor characterization test bench, METHOD (Measurement of Electrical, Thermal and Optical Devices) decouples the temperatures of the primary optical element (POE) and the cell. It allows analysis of their respective effects on optical and electrical performances. In varying the temperature of the POE, the effects on electrical efficiency, focal distance, spectral sensitivity, acceptance angle and multi-junction current matching profiles can be quantified.
References:
[1] A. Fedoseyev, T. Bald, A. Raman, S. Hubbard, D. Forbes, and A. Freundlich, “Detailed physics based modeling of triple-junction InGaP/GaAs/Ge solar cell,” 2014, vol. 8981, pp. 898119-898119–10.
[2] NREL, “Best Research-Cell Efficiencies,” 12-Aug-2016. [Online]. Available: http://www.nrel.gov/ncpv/images/efficiency_chart.jpg. [Accessed: 11-Oct-2016].
[3] R. Herrero, M. Victoria, C. Domínguez, S. Askins, I. Antón, and G. Sala, “Understanding causes and effects of non-uniform light distributions on multi-junction solar cells: Procedures for estimating efficiency losses,” in AIP Conference Proceedings, 2015, vol. 1679, p. 50006.
[4] P. Besson et al., “Spectrally-resolved measurement of concentrated light distributions for Fresnel lens concentrators,” Opt. Express, vol. 24, no. 2, p. A397, Jan. 2016.
12:00 PM - ES9.2.03
Efficient Luminescent Solar Concentrators Based on Indirect Band Gap Silicon Quantum Dots
Samantha Ehrenberg 2 , Francesco Meinardi 1 , Lorena Dhamo 1 , Francesco Carulli 1 , Michele Mauri 1 , Francesco Bruni 1 , Roberto Simonutti 1 , Uwe Kortshagen 2 , Sergio Brovelli 1
2 Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 1 Dipartimento di Scienza dei Materiali, Universita degli Studi di Milano-Bicocca, Milano, Milano, Italy
Show AbstractLuminescent solar concentrators (LSCs) are a promising renewable energy technology which may enable the integration of concentrated solar photovoltaics (PV) into point-of-use applications. Particularly in urban environments, where buildings grow predominantly in height and rooftop surfaces become less and less sufficient for collecting all of the energy required for local operations, LSCs as semitransparent PV windows are one strategy for achieving nearly zero net energy buildings. Composed simply of a transparent waveguide embedded with a luminescent species, LSCs have yet to be commercially realized due to a lack of suitable emitters. Here, we demonstrate for the first time the use of silicon quantum dots (Si QDs) as the luminescent species in LSCs. Synthesized via nonthermal plasma, these indirect band gap nanocrystals exhibit efficient photoluminescence which negligibly overlaps with their absorbance spectra. As a result, reabsorption losses within the waveguide are drastically suppressed. The low scattering and reabsorption losses of our experimental devices have resulted in nearly ideal LSCs with optical efficiencies of 2.85%, matching state-of-the-art semitransparent LSCs of similar, large areas. Furthermore, Monte Carlo simulations show that optimized Si QD LSCs can expect efficiencies in excess of 5% for 1 m2 devices. As Si QDs are also elementally nontoxic, low cost, and extremely earth abundant, this work holds high promise for industrial scaling.
S. Ehrenberg and U. Kortshagen thank the Center for Advanced Solar Photophysics, an Energy Frontier Research Center funded by Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy for financial support of this work. S.Brovelli thanks the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement N. 324603 (EDONHIST) for financial support of this work.
12:15 PM - ES9.2.04
Optical and Luminescence Properties of Ultranocrystalline Diamond (UNCD) Grown by Hot Filament Chemical Vapor Deposition Like a Principal Top Layer for “Photo-Enhanced Thermionic Emission Cells”
Jorge Montes 1 2 , Jesus Alcantar-Pena 3 2 , Rafael Garcia 3 , Orlando Auciello 2
1 Departamento de Física, Universidad de Sonora, Hermosillo, Sonora, Mexico, 2 Material Science and Engineering, University of Texas at Dallas, Richardson, Texas, United States, 3 Departamento de Investigación en Física, Universidad de Sonora, Hermosillo, Sonora, Mexico
Show AbstractUltrananocrystalline diamond (UNCD) films exhibit a unique combination of properties such as highest hardness (similar to single crystal diamond) of any material other than diamond, corrosion resistant to any corrosive environment, high surface carrier mobility when terminated in hydrogen, chemical inertness, nontoxicity, extreme biocompatibility and radiation hardness. An advance on characterizing other properties of UNCD films is provided in this research for use in Photo-voltaic Cells. These studies are focused on understanding the optical properties of UNCD films studying afterglow (AG), thermoluminescence (TL), optically stimulated luminescence (OSL) and their relationship to Photo-Enhanced Thermionic Emission (PETE). Also the different quantities of Trans-Polly Acetylene (TPA) molecules in the films and thickness of the films are compared between the different samples. The films were grown using the hot filament chemical vapour deposition (HFCVD) method involves gas flows of 1.9% of CH4 diluted in a) 9.8% H2, b) 49% H2 and c) 73.5 % H2 and Ar gas to reach a total pressure of 10 Torr in the reactor and a substrate temperature of ~550 C and temperature filament of ~2200 C. The Raman spectra of all films showed the typical signal of diamond at ~1332 cm-1 wavenumber, correlated with good sp3 characteristic diamond chemical bond of carbon atoms in the films, and a peak at 1150 cm-1 corresponding to TPA molecules in the films, which increased as the H2 concentration in the Ar/CH4/H2 gas mixture, used in the HFCVD growth process, increased. The UNCD films with different TPA concentration exhibit improved optical and luminescence properties as a function of increasing TPA content in the films.
12:30 PM - *ES9.2.05
Hybrid PV/CSP and Micro-Concentrated Solar PV Programs at ARPA-E
Michael Haney 1
1 , Advanced Research Projects Agency - Energy, Washington, District of Columbia, United States
Show AbstractOver the past few years, the Advanced Research Projects Agency-Energy (ARPA-E) has established two solar energy R&D programs – which share the overall objective of exploiting novel methods for combining/integrating distinct harvesting concepts in a manner that boosts the overall level of collected energy, while also enhancing the economic viability. These programs are: the “Full-Spectrum Optimized Conversion and Utilization of Sunlight” (FOCUS) program, launched in 2014; and the “Microscale Optimized Solar-cell Arrays with Integrated Concentration” (MOSAIC) program, initiated in 2015.
In the FOCUS program, new ideas for combining Photovoltaic (PV) harvesting and dispatchable concentrated solar thermal energy harvesting are being explored. Novel ways of splitting and directing the received solar spectrum between PV and/or Concentrated PV (CPV) components and thermal harvesting elements are being developed. Key challenges center on efficient solar spectrum management and the optimization of high-temperature PV cell performance.
The goal of the MOSAIC program is to combine the enhanced harvesting efficiency of CPV with the low cost and flat form factor of flat panel 1-sun PV. To do this, concepts that concentrate the solar energy in an array of micro-optical elements are being investigated. Various micro-optical concentrating architectures are under development. Techniques for embedding actuation elements for solar tracking within the array are being evaluated, as well as techniques for potentially harvesting the direct and diffuse elements of the solar resource within the common planar structure.
This talk reviews the technical approaches and challenges for the various projects of the FOCUS and MOSAIC programs. The discussion includes potential future steps needed to enhance the ability of the new solar harvesting technologies to be transitioned into the marketplace.
ES9.3: Are Perovkistes the Future in PV Technology?
Session Chairs
Reinhold Dauskardt
Xavier Tonnellier
Wednesday PM, April 19, 2017
PCC North, 200 Level, Room 226 C
2:30 PM - ES9.3.01
Graphene Oxide/Perovskite Interfaces for Hybrid Lead Halide Perovskite/Graphene Solar Cells—An In Situ Spectroscopic Evaluation
Muge Acik 1 , Richard Rosenberg 1 , Saw-Wai Hla 1 2 , Seth Darling 1 3
1 , Argonne National Laboratory, Lemont, Illinois, United States, 2 , Ohio University, Athens, Ohio, United States, 3 , University of Chicago, Chicago, Illinois, United States
Show AbstractHigh power conversion efficiency of perovskite-based solar cells offers promise for low-cost and scalable production of renewable energy. The need to identify key factors varying PCE at ~0.62-18% motivated us to study graphene/perovskite hybrid interfaces since GO/RGO recently emerged as an ETL/HTL. Hybrid organic-inorganic methylammonium lead halides, MAPbX3 (X=I, Br, Cl)/mixed-halides (I3-xClx, I3-xBrx) have been reported as light harvesting layers with their superior optoelectronic properties: tunable bandgap, long electron-hole diffusion lengths and high electron/hole mobility. Nevertheless, halide-based perovskites require in situ investigation for film growth, degradation and perovskite formation mechanisms to overcome detrimental effects of inconsistent crystallite formation and weak cation-anion-solvent coordination. Understanding growth/degradation mechanisms of these perovskites on GO surfaces and the origin of interfacial chemical reactions at the interfaces is lacking due to limited materials characterization. Moreover, effect of film thickness, lead content, stoichiometry control, overlayer/underlayer morphology/composition, and cation-anion electrostatic interactions ought to be examined for better charge transport at the graphene/perovskite interfaces.
To address scalability/stability issues, we examined degradation, nucleation and growth mechanisms in reduced graphene/graphite oxide (RGO) upon halide-based perovskite (CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3) deposition, derived from DMF and followed by a hot-plate annealing at 130°C. Chemical interactions were interpreted at perovskite/RGO interfaces for the grain size, orientation, boundaries, and surface/bulk effects using variable-temperature (≤400°C, Ar(g)) in situ spectroscopy (infrared absorption, micro-Raman, and XPS). GO thin films (3-5 layers) were deposited by a vacuum filtration method, followed by a perovskite formation via controlled spin-coating, and further annealed on GO. CH3NH3PbI3 growth on GO indicated Pb-I formation upon deposition and Pb-O formed at GO/perovskite interfaces after annealing, modifying point defects in perovskites by removal of iodide vacancy and unsaturated Pb states. Bromide/chloride-based perovskites resulted in improved chemical stability with heat as a result of crystal reorientation via perovskite deposition on GO, indicating a crystal nucleation via symmetry disorder. Overall, perovskite decomposition was observed at ~150°C for all perovskites. Oxygen-induced chemical reactions occurred at ≤150°C that eliminated epoxides and hydroxyls. Carboxyls were maintained at CH3NH3PbBr3/GO interfaces, while ketones were removed via CH3NH3PbCl3 growth on GO. Film morphology was explored by characterization techniques such as SEM, XRD, XPS, and AFM. (1) M. Acik et al. (2016), in preparation. (2) M. Acik et al. J. Mater. Chem. (2016) A 4 (17), 6185. (3) Gong et al. Energy Environ. Sci. (2015) 8, 1953. (4) M. Acik et al. Nature Mater. (2010) 9, 840 .
ACKNOWLEDGMENT
Use of the Center for Nanoscale Materials was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The abstract has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. Office of Science User Facility under Contract No. DE-AC02-06CH11357. M.A. also acknowledges support from the Joseph Katz Named Fellowship at Argonne National Laboratory.
2:45 PM - ES9.3.02
Flux Coating Growth of (10-1)-Oriented Epitaxial NaTaO3 Crystals on SrTiO3 Single Crystal Substrates
Sayaka Suzuki 1 , Kunio Yubuta 2 , Katsuya Teshima 1 3
1 Faculty of Engineering, Shinshu University, Nagano Japan, 2 Institute for Materials Research, Tohoku University, Sendai Japan, 3 Center for Energy and Environmental Science, Shinshu University, Nagano Japan
Show AbstractEpitaxial thin films can provide an ideal surface with very flat surfaces with roughnesses of ∼1 nm. They have been used for clarifying the surface reaction mechanism and dependences of crystal face on the material performance. With respect to TiO2 rutile, the photochemical properties have been shown to be dependent on the crystal surface orientation. Sodium tantalate (NaTaO3) is one of the ABO3 perovskite-type compounds. It crystallizes in the orthorhombic system. NaTaO3 is especially known as a semiconductor photocatalyst for overall water splitting under ultraviolet light irradiation. Its band gap is 4.0 eV. Here, we report the epitaxial growth of NaTaO3 crystals on single-crystalline SrTiO3 substrate using flux coating.
First, tantalum-metal or -oxide thin film was deposited on the SrTiO3 (100) substrate by sputtering with a tantalum target. These films were used as a tantalum source for NaTaO3. Aqueous solution of NaNO3, Na2CO3, and/or NaCl was coated on the TaOx/SrTiO3 or Ta/SrTiO3 as a sodium source and the flux for the growth of NaTaO3. The substrates were heated at 500-800 °C for 0-1 h in the electric furnace. After cooling, the products were immersed in warm water to remove any residual flux.
When NaNO3-coated TaOx/SrTiO3 (100) was heated, a number of well-ordered, cube-like NaTaO3 crystals were epitaxially grown. The grown NaTaO3 consisted of island-shaped crystals. The electron diffraction pattern produced from the NaTaO3/SrTiO3 interface clearly showed good overlap regardless of the diffraction spots corresponding to the two phases, that is, NaTaO3 and SrTiO3. In addition, the diffraction spots were confirmed to correspond with an orthorhombic NaTaO3 structure. By changing the tantalum source and flux, NaTaO3 crystal layers having thin film structures were successfully fabricated by flux coating.
Acknowledgements: This research was partially supported by JSPS Grant-in-Aid for Scientific Research (A) 25249089.
3:00 PM - ES9.3.03
Synthesis and Characterization of Ammonium-Terminated Alkyl Monolayers on Si(111) Surfaces
Alexander Carl 1 , Ronald Grimm 1
1 , Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractAs interest in heterojunction solar cells increases, particularly perovskite/silicon, continuing efforts address a robust interface that maintains maximum electronic efficiency, minimum surface recombination, and synthetic simplicity. We have explored synthetic strategies to functionalize Si(111) surfaces with organic species containing a terminal ammonium group that could be employed to “glue” perovskites to silicon surfaces. A mixed monolayer (MM) of allyl and methyl groups was attached to the Si(111) face utilizing techniques that yield high electronic quality silicon surfaces. Secondary reactions of the allyl groups with bromine and ammonia yielded the desired ammonium functionality. X-ray photoelectron spectroscopy (XPS) quantifies the extent of alkyl coverage and amine attachment. Trap-state densities and surface recombination velocities (SRV) were measured by Time-Resolved Microwave Photoconductivity. Amine terminated alkyl groups demonstrated surface coverages of >20% on the Si (111) face. The secondary reaction chemistry did not significantly alter the carrier recombination or trap state density of the Si(111) surfaces, and amine functionalized surfaces also proved resistant against analogous conditions required to grow perovskite crystals.
3:15 PM - ES9.3.04
3D Si-SiO2 Nano-Networks Formed by Diode Laser-Induced Liquid- and Solid-State Decomposition of SiOx
Erik Schumann 1 , R. Huebner 1 , Veronica Carcelen 2 , Joerg Grenzer 1 , K. Heinig 1 , Sibylle Gemming 1 3 , Matthias Krause 1
1 Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden - Rossendorf, Dresden Germany, 2 , Abengoa Research, Sevilla Spain, 3 Institute of Physics, Technische Universität Chemnitz, Chemnitz Germany
Show AbstractThin films of nano-structured crystalline silicon (nc-Si) are potential absorber and supporting layers for next-generation Si solar cells. As one candidate, Si-SiO2 nanocomposites with percolated nc-Si have been fabricated by rapid thermal annealing (RTA) of sputter-deposited SiOx films (x≈1). A percolated silicon network has been formed by solid state phase separation into nc-Si and SiO2 [1, 2].
In the present study, SiO0.6 layers of ~500nm thickness are grown on quartz by ion beam sputter (IBS) as well as by reactive magnetron sputter (RMS) deposition. Formation of percolated Si-SiO2 nanocomposites is achieved by two different modes of thermal treatment: (i) Furnace annealing at 950°C and (ii) scanning laser processing. In case (ii), a diode laser with dwell times in the ms range, power densities of ~30 kW/cm2, a wavelength of λ= 808nm and a line focus of 100µm x 11mm is applied. This process is ~106 times faster than isothermal treatment and ~103 times faster than RTA. Another advantage of this method is the usability of temperature sensitive substrates and maintaining homogeneous processing.
Rutherford backscattering spectra of as-deposited and processed SiO0.6 reveals a compositional change in thin surface and interface layers, but no significant change in the bulk composition. Raman spectroscopy and X-ray diffraction show that the crystallinity of the nc-Si is higher for the laser-treated sample.
High resolution- and energy-filtered transmission electron microscopy (HTEM, EFTEM) show additionally, that in both cases the as-deposited SiO0.6 is transformed into a percolated nanocomposite consisting of amorphous SiO2 and nc-Si.
In more detail, laser processing of IBS-deposited layers leads to isotropic morphologies self-similar to furnace-annealed samples, but scaled up by a factor of ~5. This is explained by a phase separation in the liquid state and the solid state, respectively, which cause diffusion coefficients differing by several orders of magnitude.
During the deposition by RMS, phase separated filament-like morphologies form. Here, furnace annealing leads to enhanced phase separation accompanied by crystallization. In contrast laser processing erases the as-deposited filaments and produces isotropic morphologies similar to IBS-deposited and laser-processed samples
[1] Friedrich, D. et al. Sponge-like Si-SiO2 nanocomposite - Morphology studies of spinodally decomposed silicon-rich oxide. Appl. Phys. Lett. 103, 131911 (2013).
[2] Ilday, S. et al. Multiscale Self-Assembly of Silicon Quantum Dots into an Anisotropic Three-Dimensional Random Network. Nano Lett. 16, 1942–1948 (2016).
ES9.4: Advanced Tools for Modeling and In Situ Characterization of CSP Materials
Session Chairs
Andrea Ambrosini
Matthias Krause
Wednesday PM, April 19, 2017
PCC North, 200 Level, Room 226 C
4:30 PM - *ES9.4.01
Performances and Durability of Solar Absorber for CSP—Toward the Qualification Procedure
Olivier Raccurt 1
1 CEA, LITEN/DTBH, High Temperature Solar Thermal Systems Laboratory, Univ. Grenoble Alpes, Le Bourget du Lac France
Show AbstractThe CSP (Concentrated Solar Power Plant) technologies concentrate the solar energy by means of mirrors on an absorber tube where it is collected as thermal energy. The absorber is one of the main parts of the system, and the characterization of its optical properties must be accurate in order to evaluate the performances of the whole system, especially since these properties may evolve through the use of the absorber, due to all the environmental constraints [1, 2]. Durability of solar components for CSP (Concentrated Solar Power Plant) technologies is a key point to improve their cost and to ensure their large deployment [1]. The absorbers are submitted to strong environmental constraints and degradation of their optical properties (emittance and solar absorbance) have a direct impact on the performances [2, 3]. Unlike in others field like PV or solar thermal [4], there is no standard for durability test of solar absorber for CSP. In the first part we will presented the advanced optical characterization tools developed for measuring the optical performance of solar absorber in temperature [5]. In a second part we will presented the methodology to establish the accelerated ageing tests for qualify the durability of solar absorbers. Each part will be illustrated by experimental results.
References
[1] C. Kennedy, H. Price, Progress in Development of High-Temperature Solar-Selective Coating, Proceedings of ISEC2005, International Solar Energy Conference, August 6-12, 2005, Orlando, Florida USA.
[2] C. Kennedy, Review of Mid- to High- Temperature Solar Selective Absorber Materials, Technical report, NREL (NREL/TP-520-31267), 2002.
[3] O. Raccurt, A. Disdier, D. Bourdon, S. Donnola, A. Stollo and A. Gioconia, Study of the stability of a selective solar absorber coating under air and high temperature conditions, International Conference on Concentrating Solar Power and Chemical Energy Systems, SolarPACES 2014.
[5] P. Giraud, J. Braillon, C. Delord and O. Raccurt, Development of Optical Tools for the Characterization of Selective Solar Absorber at Elevated Temperature. SolarPACES 2015.
[4] NF EN ISO 22975-3, Solar energy - collector components and materials - Part 3: Absorber surface durability (2014)
5:00 PM - ES9.4.02
In Situ RBS, Raman, and Ellipsometry Studies of Layered Material Systems at High Temperatures in a Cluster Tool
Robert Wenisch 1 , Daniel Janke 1 , Irene Heras 2 , Frank Lungwitz 1 , Elena Guillen 2 , Rene Heller 1 , Sibylle Gemming 1 3 , Ramon Escobar-Galindo 2 , Matthias Krause 1
1 , Helmholtz-Zentrum Dresden-Rossendorf, Dresden Germany, 2 , Abengoa Research S.L., Sevilla Spain, 3 , Technische Universität Chemnitz, Chemnitz Germany
Show AbstractThe detailed knowledge of composition and microstructure is essential for the understanding of processes and properties of new materials for applications at high temperatures. To ensure materials functionality under in operando conditions, new concepts for analysis and process monitoring are necessary. In this contribution, selected PVD deposited thin film material systems were studied in situ at temperatures up to 830°C by Rutherford backscattering spectrometry (RBS), Raman spectroscopy, and spectroscopic ellipsometry (SE) within a cluster tool.
Metal-induced crystallization with and without layer exchange (MIC w/o LE) is an emerging technique for processing of amorphous group IV elements below their isothermal crystallization temperatures. In this study, a bilayer system of 60 nm amorphous Si covered by 30 nm Ag (a-Si/Ag) was annealed at temperatures of 380 to 700°C by the combination of the above mentioned in situ techniques. The process comprised a relatively long-term incubation period followed by a fast MIC w/o LE step. More than 90% of the initial a-Si could be crystallized on top of the Ag-layer for optimized process conditions with temperatures of about 550°C. The as-formed Si consisted of up to 95% crystalline Si.
As an example for high-temperature solar selective coatings for thermo-solar applications, AlTiN and AlTiN1-xOx (x = 0 - 0.2) thin films were investigated in order to understand the influence of the oxygen/nitrogen ratio on the optical properties and failure mechanisms at high temperatures. The elemental depth profiles and the phase structure of both coatings do not change during annealing in high vacuum at temperatures up to of 750°C, as revealed by unchanged RBS and Raman spectra, respectively. SE and RBS results showed the influence of the initial oxygen content on high temperature stability of AlTiN and AlTiN1-xOx thin films. The low emittance of AlTiN1-xOx, allowed performing in situ RBS analysis at temperatures up to 830°C for the first time.
Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged.
5:15 PM - ES9.4.03
Surface Chemistry for the Atomic Layer Deposition of Solar Selective Nanocomposite Coatings
Anil Mane 1 , J. Avila 1 , Jian Liu 2 , Angel Yanguas-Gil 1 , Joseph Libera 1 , Mohammad Mushfiq 3 , Kevin Yu 3 , Uma Sampathkumaran 3 , Jeffrey Elam 1
1 , Argonne National Laboratory, Lemont, Illinois, United States, 2 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 3 , InnoSense, LLC, Torrance, Illinois, United States
Show AbstractConcentrated solar power tower plants use an array of mirrors to concentrate sunlight onto a central receiver tower. The receiver surface heats up, and this heat is used drive turbines that generate electricity. To improve the efficiency of solar power tower facilities, the receiver must be enhanced to operate at higher temperatures and this requires developing high performance solar absorbing coatings. These coatings must be spectrally selective in order to absorb essentially all of the visible light (high absorptivity) while emitting as little infrared radiation as possible (low emissivity). In addition, these coatings must be refractory to endure extended high temperature operation under ambient conditions.
We are developing a novel strategy to grow refractory solar selective coatings using atomic layer deposition (ALD). Our approach uses thin film nanocomposites composed of conducting metallic nanoparticles in an amorphous dielectric matrix. These films are prepared by combining the ALD processes for a metal (e.g. W using Si2H6/WF6) with that of an oxide (e.g. Al2O3 using TMA/H2O). In this presentation I will focus on in situ measurements performed to elucidate the surface chemistry responsible for the nucleation and growth of these unique materials. I will discuss a range of solar selective coating materials combining different metallic (W, Nb, Mo, Co) and dielectric (Al2O3, ZrO2, MgO, TiO2) components. We use in situ gravimetric, spectroscopic, and mass spectrometric measurements to gain a detailed understanding of how the ALD precursors behave on the growing surface, and this knowledge is used to identify candidate processes for further study and eventual scale up.
5:30 PM - ES9.4.04
Refractory Solar Selective Nanocomposite Coatings for Concentrated Solar Power Receivers
Jeffrey Elam 1 , Anil Mane 1 , J. Avila 1 , Angel Yanguas-Gil 1 , Joseph Libera 1 , Joseph Hupp 2 , Jian Liu 2 , Uma Sampathkumaran 3 , Kevin Yu 3 , Reiner Buck 4 , Florian Sutter 4
1 , Argonne National Laboratory, Argonne, Illinois, United States, 2 , Northwestern University, Evanston, Illinois, United States, 3 , InnoSense, LLC, Torrance, California, United States, 4 , DLR, Stuttgart Germany
Show AbstractWe are developing a new strategy for fabricating high-performance selective receiver coatings for concentrated solar power. These coatings are engineered at multiple length scales. In the 0.1-1 μm regime, the coatings have a photonic crystal structure composed of a periodic mesoporous array. This structure alters the photonic density of states to improve spectral selectivity while also mitigating thermal stress for improved lifetime. At the 1-10 nm scale, the coatings are composed of optically absorbing nanoparticles in a transparent matrix where the size, spacing, and composition of the nanoparticles are tailored to tune the optical properties for high visible absorption and low IR emittance - similar to a cermet, but with greater thermal stability. The mesoporous photonic structure is fabricated by self-assembly from a nanoparticle suspension to form a porous matrix. The nanophase composite is created by infiltrating this scaffold using atomic layer deposition (ALD) films composed of metallic and dielectric components. We are evaluating a range of processing methods for the mesoporos scaffold and targeting sturctures guided by finite difference time domain (FDTD) modeling. In addition, we have undertaken a design of experiments (DOE) study of ALD nanocomposite films to establish the effects of composition, metal:dielectric ratio, and thickness on the optical efficiency. These studies have yielded simple design rules to predict the optical properties of the solar selective coatings, allowing us to focus on optimizing the high temperature stability and manufacturability of the materials. We have identified coatings that maintain a high selective solar absorption efficiency of ηsel > 0.91 after isothermal treatment and temperature cycling at 650°C with no delamination. We are using technoeconomic modeling and levelized cost of energy (LCOE) metrics to gauge the cost competitiveness of our coatings compared to existing coatings such as Pyromark 2500.
5:45 PM - ES9.4.05
The Role of Microstructure on Absorber Efficiency and Selectivity in Concentrating Solar Power—An FDTD Approach
Angel Yanguas-Gil 1 , J. Avila 1 , Jian Liu 2 , Anil Mane 1 , Joseph Libera 1 , Mohammad Mushfiq 3 , Kevin Yu 3 , Uma Sampathkumaran 3 , Jeffrey Elam 1
1 , Argonne National Laboratory, Lemont, Illinois, United States, 2 , Northwestern University, Evanston, Illinois, United States, 3 , InnoSense LLC, Torrance, California, United States
Show AbstractFrom black silicon to photonic crystals, microstructure has long been used to control the absorptivity and the optical properties of materials. In this work we focus on understanding the interplay between optical properties and microstructure to design selective absorbers for concentrating solar power applications. Using an approach based on finite difference time domain simulations, we have developed a model that allows us to generate and calculate the absorptivity and emissivity of a wide range of possible microstructures, ranging from periodic opals and inverse opals to disordered materials with variable porosity and particle distribution function. Our model also allows us to import experimental optical properties derived from techniques such as spectroscopic ellipsometry and reflectivity data.
In this work we focus on three key variables: the interplay between microstructure and the attenuation coefficient of simulated materials, the comparison between macroscopically homogeneous materials and core-shell structures, and the influence of local and medium range order in materials microstructure. Understanding the impact of these variables on the overall efficiency is crucial in order to develop rational design principles for absorber materials that take advantage of the structuring of the coating. In this work The structures are supported on a Haynes metal alloy substrate.
In order to validate our simulations, we have compared the model results with experimental reflectivity data obtained on selective absorber coatings synthesized on porous scaffolds using atomic layer deposition. The results show excellent agreement between the simulations and the experiments under normal incidence conditions. However, further work is needed in order to verify the dependence of reflectivity with the angle of incidence and the diffuse scattering under non-normal conditions.
Symposium Organizers
Ramon Escobar-Galindo, Abengoa Research
Ibon Azkona, Metal Estalki
Jose Luis Endrino, Cranfield University
Matthias Krause, Helmholtz-Zentrum Dresden-Rossendorf
Symposium Support
IK4-TEKNIKER
FOM Technologies
METAL ESTALKI
ES9.5: Scaling Up Challenges of Solar Collectors
Session Chairs
Carlos Prieto
Olga Sanchez Garrido
Thursday AM, April 20, 2017
PCC North, 200 Level, Room 226 C
10:00 AM - *ES9.5.01
Sol Gel Coating of Solar Receiver Tubes—Machine Design Criteria
Christopher Sansom 1 , Xavier Tonnellier 1
1 , Cranfield University, Cranfield United Kingdom
Show AbstractCoating of absorber tubes for concentrating solar power applications requires the deposition of sub-micron multi-layers on both glass and metal surfaces. For glass tube AR coatings this includes both inner and outer surface coatings. These two concentric tubes form the solar receiver, usually to be located along the line focus of a parabolic mirror or a linear Fresnel. In current state-of-the-art these multi-layer films are deposited in large, custom-built PVD chambers. We describe the design of a flexible production-scale sol gel system for cleaning, coating, and curing of these multi-layer films, including the evolution of the design as the processes are ramped up the accommodate absorber tubes of up to 4m in length. The work involved the development and selection of the sol gels, plus the building of two experimental rigs to evaluate a number of coating configurations. The evolution of these designs are outlined and the route to design a full-scale prototype is discussed in detail. In addition to meeting a challenging specification for film thicknesses and refractive index, considerations for throughput, coating uniformity, ATEX and other safety considerations, tube handling, and control systems, are all shown to influence the final system design. Chemical, mechanical, and temperature considerations also influenced materials selection. Manufacturing simulations were performed in order to determine the throughput of the design in a number of high-volume batch-production scenarios. Finally, an estimated cost to manufacture a prototype system based on the selected design was derived.
10:30 AM - ES9.5.02
Development and Characterisation of Spectrally Selective Coatings to Work at 550C under Inert Gas Atmosphere
Javier Barriga 1
1 , IK4-TEKNIKER, Eibar Spain
Show AbstractThe CSP technology based on parabolic trough solar collector for large electricity generation purposes is currently the most mature of all CSP designs in terms of previous operation experience and scientific and technical research and development. The current parabolic trough design deals with a typical operating temperature around 400C in the absorber collector tube but some designs are planned to increase the working temperature up to 600C increasing the performance by 5-10% to attain the improved productivity that the market demands .These systems are expected to be working during 20-25 years. However, nowadays there are recent designs to work at higher temperature but changing the overall concept of the receiver, avoiding evacuated tubes, and using inert gases instead. For instance, Argon is quite a common noble gas, with a low thermal conductivity (to avoid thermal losses by convection), easy to get and cheap.
One of the key points of the receiver is the stack of layers forming the selective absorber coating. Typical optical values for this coating are 96% of absorbance and <10% of emittance at 400C. In the present work a stable stack has been developed on real 4 meter long tubes with 96% of absorbance and 7% of emittance. The stack has been tested under accelerated ageing conditions in vacuum to check its stability. Moreover, characterisation has been carried out in the presence of 1 atm of Argon. Different qualities of Ar have been used to analyse the effect of impurities in the degradation of the coating and, as a consequence, the reduction in the optical efficiency of the stack. With high purity Ar there is no degradation of the coatings. However, higher amount of oxygen impurities produces oxidation of the infrared reflector (pure metal layer).
10:45 AM - ES9.5.03
Spectrally-Selective Copper-Oxide Spinel Absorber Coatings for High-Temperature Concentrated Solar Power Systems
Dale Karas 1 , Cilla Jose 2 , Samuel Tam 3 , Jaeyun Moon 1
1 Department of Mechanical Engineering, University of Nevada, Las Vegas, Las Vegas, Nevada, United States, 2 Department of Chemistry, University of Nevada, Las Vegas, Las Vegas, Nevada, United States, 3 Dept. of Electrical Engineering, University of Nevada, Las Vegas, Las Vegas, Nevada, United States
Show AbstractConcentrated Solar Power (CSP), in comparison to photovoltaic solar panels, involve methods to concentrate the sun’s energy onto receiver systems that generate steam, activate turbines, and consequently generate electrical power. To achieve cost-effective power generation, CSP implementation in solar-favorable geographic areas provides a competitive avenue in the market for energy production; additionally, the technology features storable energy at times of limited or null solar irradiance, higher energy conversion potential, and the ability to retrofit older nonrenewable-based power plant installations for a reduced environmental footprint. One significant technology for reliable high-temperature operation has been the application of durable spectrally-selective solar absorber coatings on CSP receiver systems, using materials that favor ultraviolet, visible, and near-infrared solar irradiation responsivity while limiting spontaneous thermal radiation from emittance at higher wavelengths, correlating to a reduction of undesirable energy loss through waste heat. In this work, black metal-oxide nanoparticles comprising copper cobalt oxides (Cu[x]Co[3-x]O4) and copper manganese oxides (Cu[x]Mn[3-x]O4) are synthesized for solar absorber coating potential by hydrothermal syntheses, selected for low-cost, energy-efficient fabrication capable for bulk manufacturability in contrast to sol-gel and dip-coating methods. The material is deposited onto high-temperature, durable Inconel substrates by a flexible spray-coating method, and characterization is performed by SEM, EDS, and XRD analyses, as well as measurements to gauge thermal performance. The solar receiver performance and high temperature stability are accessed by comparing spectral reflectance and the figure of merit (FOM) before and after high temperature exposure. To extend spectrally-selective absorbance capability, the coating surfaces are geometrically-textured using sacrificial polymer beads that are jointly implemented in the spray-coating process. In addition to extending metrological and materials analyses, computational routines for optical simulations are discussed, regarding the feasibility for the energy-efficient solar absorber coaters presented in this work. This study ultimately showcases produced materials with high figure-of-merit conversion efficiency, demonstrating solar absorber coatings capable of interfacing with CSP receiver systems.
ES9.6: Smart Concepts for Improving Perfomance of CSP Components
Session Chairs
Jeffrey Elam
Olivier Raccurt
Thursday PM, April 20, 2017
PCC North, 200 Level, Room 226 C
11:30 AM - ES9.6.01
Nickel-Aluminium Based Anticorrosion Coatings Prepared by Plasma Spray for CSP Applications
Sarah Yasir 1 , Elena Guillen 2 , Simon Gray 1 , Ramon Escobar-Galindo 2 , Barbara Shollock 3 , Jose Luis Endrino 1
1 , Cranfield University, Cranfield United Kingdom, 2 , Abengoa Research S.L., Seville Spain, 3 , University of Warvick, Coventry United Kingdom
Show AbstractA number of technologies have been developed to use solar energy for power generation. Among them, concentrating solar power (CSP) is one of the most promising technologies due to high efficiency and the capability for thermal storage. The capability to store heat using molten salts permits CSP plants to produce electricity during the periods of cloud cover and low solar radiations. Despite the clear advantages of using molten salts as heat transfer fluid in solar power plants with thermal storage, they prone corrosion in component systems at high temperature. The resulting corrosion is due to oxidation of the base metal and from solubility-driven dissolution reactions. Several strategies to prevent hot corrosion have been described such as the use of high alloy steels and the use of high purity molten salts, both contributing to a significant increase of production costs.
In this work we propose the use of coatings to make the increment of the storage temperature possible and less expensive. Nickel aluminium coatings with different compositions are deposited to enhance the corrosion resistance against molten salts at temperatures up to 600oC. An air plasma spray system is employed to deposit intermetallic nickel aluminum alloys with different deposition parameters to obtain a variety of stoichiometries and crystalline structures. Regarding process parameters, three different input power levels and two different torch to substrate distances have been studied to correlate with the coating thickness, porosity, and corrosion resistance. The as deposited coatings were thoroughly characterized using EDX, SEM and XRD. An optimum value of porosity is desirable for corrosion resistance and it was found that porosity increases with increasing the torch to substrate distance. The number of unmelt-particles decreased with increasing input power level, affecting mechanical properties of the coating; minimum unmelt-particles are sought. In conclusion, maximum input power and minimum distance to substrate has shown to provide the finest lamellar coating among all the parameters used.
Optimized coatings deposited on austenitic SS (AISI 347H) were introduced in a mixture of low impurities NaNO3 / KNO3 molten salts (60:40% in weight) at 600oC for 1000 hours. Bare substrates were also included in the test for comparison. After the test the samples were characterized by SEM and XRD to evaluate their corrosion resistance. First experimental results pointed out the great potential of nickel aluminide coatings to fight hot corrosion by molten salts in concentrating solar power plants.
11:45 AM - ES9.6.02
High Accuracy Infrared Directional Emission Spectroscopy between 100 and 1000 Degrees Celsius
Telmo Echaniz 1 , Gabriel Lopez 1 , Raquel Fuente 1 , Inigo Gonzalez de Arrieta 1 , Atasi Dan 2 , Bikramjit Basu 2 , Harish Barshilia 2 , Manuel Tello 1
1 , Basque Country University, Leioa Spain, 2 , CSIR-National Aerospace Laboratories, Bangalore India
Show AbstractThe total hemispherical emissivity of the absorbing surfaces is a critical parameter in the calculation of the radiative thermal losses in solar thermal collectors. This is because the radiative heat losses have a significant economic impact on the final cost of the electricity produced in a solar thermal plant. Our laboratory in the Basque Country University in Spain is the first to have published infrared spectral emissivity measurements in Solar Absorber Surfaces at working temperature. The laboratory allows measuring between 100 and 1000 degrees Celsius in the 0.83-25 μm range and is also able capable of doing directional measurements at different angles between 0 and 80 degrees. In this presentation we show the specifications of our laboratory, results of spectral emissivity measurements in selective stacks and we demonstrate the necessity of measuring at working temperature in order to have reliable data.
12:00 PM - ES9.6.03
Degradation of Solar Mirrors in Accelerated Aging Test for Simulation of Costal Area Exposure
Coralie Avenel 1 , Olivier Raccurt 1 , Jean-Luc Gardette 2 3 , Sandrine Therias 2 3 , Angela Disdier 1
1 , University of Grenoble Alpes, Grenoble France, 2 Institut de Chimie de Clermont-Ferrand, Clermont Université, Université Blaise Pascal, Aubière France, 3 Institut de Chimie de Clermont-Ferrand, CNRS, UMR 6296, Aubière France
Show AbstractBecause the locations that match all the criteria required by CSP technologies are mostly deserts and costal zones, these technologies are exposed to severe environmental constraints. [1] To be profitable, mirrors must have a 25 years lifetime. Their degradation has then to be studied to point weaknesses of mirror technologies [2] and to select the best candidates.
Degradation studies in saline environment have been performed on first generations of glass mirrors with lead paints and copper layer, using NSS (neutral salt spray) test [3,4]. It is, however, difficult to transpose the obtained results to new technologies: glass mirror with free lead paints, aluminum and polymer mirror, which means that new studies using outdoor exposure and accelerated aging tests are required. [5]
Durability of these new mirrors under NSS test was compared in this study, according to ISO 9227. Specular reflectivity and surface of corrosion were monitored. To evaluate the protection provided by coating, a scratch was performed on paints for glass mirrors and on the topcoat for aluminum and polymer mirrors, following the usual methods. [6]
Different modes of degradation were identified for each technology: corrosion of the reflective layer from the edges or through the topcoat and degradation of the topcoat. Focus was made on paint degradation: blistering and delamination were observed, and hypothesis proposed about conditions that favored the degradation. Modifications of binder and pigments of the top paint were characterized by FTIR-ATR spectroscopy. NSS test is currently used to simulate saline environment but its relevance is criticized [6,7]. A new test has then been performed to simulate natural aging, consisting in an alternation between saline exposure and dry environment with UV irradiation. The results and the limits of this aging test are discussed.
[1] F. Trieb, C. Schillings, M. O’Sullivan, T. Pregger, and C. Hoyer-Klick. Proceeding of SolarPACES 2009, September 2009.
[2] A. Garcia-Segura, A. Fernandez-Garcia, M.J. Ariza, F. Sutter, and L. Valenzuela. Renewable and Sustainable Energy Reviews, 62:453 – 467, 2016.
[3] E. Schutz, F. Berger, O. Dirckx, and A. Chambaudet. Polymer Degradation and Stability, 65(1):123 – 130, 1999.
[4] E. Schütz, F. Berger, R. Barillon, P. Audebert, and A. Chambaudet. Applied Surface Science, 120(1-2):106–118, April 1997.
[5] T. Kaltenbach, E. Klimm, T. Meier, M. Koehl, and K.-A.Weiss. Energy Procedia, 2013.
[6] T. Bos. PhD thesis, Technische Universiteit Delf, 2008.
[7] J. Wette, F. Sutter, and A. Fernández-García. EuroMat, 2013.
12:15 PM - ES9.6.04
Bismuth-Based Thin Films for Solar Concentrator Water Treatment—Relationship between Synthesis Conditions, Optical Properties and Photocatalytic Efficiency
Maeve O'Brien 1 , Laura Gomez-Velazquez 2 3 , Monserrat Bizarro 2 , Valerie Leppert 4
1 School of Natural Sciences, University of California, Merced, Merced, California, United States, 2 Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Mexico City, D.F., Mexico, 3 Posgrado en Ciencia e Ingeniería de Materiales, Universidad Nacional Autónoma de México, Mexcio City, D.F., Mexico, 4 School of Engineering, University of California, Merced, California, United States
Show AbstractSemiconductor photocatalysis is a promising route for the use of solar energy for the cost-effective treatment of water for the decomposition of contaminants and other applications, including H2 production, organic chemical synthesis and the conversion of CO2 to fuel. Bismuth oxides are promising for this application due to the wide availability of bismuth from other industrial processes and its relatively benign impact on the environment; while spray pyrolysis is an efficient and cost effective method of producing thin films. Here, we discuss the spray pyrolysis synthesis of bismuth oxide based thin films (e.g. Bi2O3 and BiOX, where X = Cl, Br, F) for photocatalysis for water treatment in solar concentrator photoreactors. The thin film compositions and morphologies obtained using different precursors and processing conditions, and their relationship to solar optical properties and photocatalytic efficiency are discussed. Specifically, it is found that precursor composition and deposition conditions can be tailored to achieve an enhancement in photocatalytic efficiency through increasing light absorption and increasing surface area via the introduction of 100-200 nm nanoscale morphologies. Implications for deployment of the resulting thin films in solar concentrator photoreactor configurations for water treatment are discussed.
12:30 PM - ES9.6.05
Solar-Selective and Temperature-Stable SnO2-Based TCO for Solar Thermal Applications
Frank Lungwitz 1 , Erik Schumann 1 , Daniel Janke 1 , Elena Guillen 2 , Ramon Escobar-Galindo 2 , Sibylle Gemming 1 3 , Matthias Krause 1
1 , Helmholtz-Zentrum Dresden-Rossendorf, Dresden Germany, 2 , Abengoa Research S.L., Sevilla Spain, 3 Physics, Chemnitz University of Technology, Chemnitz Germany
Show AbstractIn solar-thermal power plants the receiver tubes are one of the key components for increasing the efficiency of concentrated solar power (CSP) technology. Absorber materials of those tubes have to exhibit high-temperature and air stability, high optical absorption in the solar region and low thermal emittance. Temperatures of up to 400 °C and up to 550 °C are reached in currently operated parabolic trough and central receiver plants, respectively. The CSP efficiency could be increased by 15 to 20% applying operation temperatures of around 800 °C. In state of the art central tower plants black paints are used as absorber material. Due to limited stability they have to be periodically replaced. Furthermore the high emissivity of those paints leads to high radiative energy losses. Most of the R&D approaches for high-temperature solar receiver materials are focused on complex multilayer coatings.
Here, an alternative concept for high-temperature stable solar-selective coatings is presented. It consists of a transparent conductive oxide (TCO) deposited as solar-selective transmitter on a black body absorber. The latter is responsible for high absorption in the solar spectral range (300 nm – 2000 nm), the former ensures low emissivity in the infrared range (> 2000 nm) and oxidation resistance. The concept is easily implementable and combines significant improvements of CSP technology performance and cost competiveness.
This study is focused on the solar-selective transmitter component of the concept. For this purpose, SnO2:Ta thin films are reactively magnetron co-sputtered from tantalum doped and undoped tin targets at high temperatures on fused quartz, silicon and carbon substrates. Their optical properties are tailored to meet the specific requirements of a solar-selective transmitter coating. The correlation between structural, optical, and electrical properties is analyzed by Raman spectroscopy, spectroscopic ellipsometry (SE) and Rutherford backscattering spectrometry (RBS). All the techniques are applied in situ at high- temperatures in a cluster tool. In order to simulate real operating conditions, cyclic heating tests and heating in reactive atmospheres are conducted. Additionally, X-ray Diffraction (XRD), UV-VIS spectrometry, and Hall Effect measurements are performed. It is shown that structural parameters like e.g. grain sizes and dopant concentration result in different electrical properties and as a result determine the optical behavior like spectral selectivity of the TCO.
Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged.
12:45 PM - ES9.6.06
Semiconductor-Dielectric Selective Absorbers for Solar Thermal Energy Conversion
Nate Thomas 1 , Austin Minnich 1
1 , California Inst of Technology, Pasadena, California, United States
Show AbstractSpectrally selective absorbers that absorb visible light yet do not emit infrared light are key to achieving high efficiency in solar thermal applications. However, available selective absorbers achieve at best around 200°C under unconcentrated sunlight due to high thermal losses via infrared (IR) emission, limiting the applications of solar thermal energy conversion. Here, we report photonic structures composed of thin films of semiconductors and dielectrics for high temperature, unconcentrated solar thermal applications. Our selective surface exhibits hemispherical IR emittance of 4% and average solar absorptance of 85% for an unprecedented absorption-to-emission ratio of 21, and in vacuum without concentration it reaches temperatures in excess of 200°C. Such low IR emittance is critical for reaching the high temperatures relevant for industrial processes under single sun illumination.
ES9.7: Emerging Materials for Non-Conventional PV
Session Chairs
Samantha Ehrenberg
Matthias Krause
Thursday PM, April 20, 2017
PCC North, 200 Level, Room 226 C
2:30 PM - ES9.7.01
Monolithic Glass-Based Antireflective and Superhydrophobic Coatings—Broadband/Omnidirectional Light Harvesting and Self-Cleaning Characteristics
Tolga Aytug 1 , Andrew Lupini 1 , Ilia Ivanov 1 , Gerald Jellison 1 , Edgar Lara-Curzio 1 , Rajesh Menon 2
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , The University of Utah, Salt Lake City, Utah, United States
Show AbstractNatural biological structures, in particular, moth’s eye and lotus leaf were the inspirations for the formation of low-refractive index antireflective glass film that embody omni-directional optical properties over a wide range of wavelengths, while also possessing water-repelling, or superhydrophobic, capability that holds significant potential for solar panels, architectural windows, and optical components used in many other products. The coatings comprise an interconnected network of nanoscale pores surrounded by a nanostructured silica framework. These structures result from a novel fabrication method that utilizes metastable spinodal phase separation in low-alkali borosilicate glass materials. The approach not only enables design of surface microstructures with graded-index antireflection characteristics, where the surface reflection is suppressed through optical impedance matching between interfaces, but also facilitates self-cleaning ability through modification of the surface chemistry. Based on near complete elimination of Fresnel reflections through a single-side coated glass and corresponding increase in broadband transmission, the fabricated nanostructured surfaces are found to promote a general and an invaluable ~ 3-7% relative increase in current output of multiple direct/indirect bandgap photovoltaic cells, while preventing dust/pollution accumulation. Moreover, these antireflective, self-cleaning surfaces demonstrate superior resistance against mechanical wear and abrasion. With demonstrated scalable and manufacturable formulations, providing an all-in-one combination of multiple salient and unique performance enhancers (i.e., antireflectivity, self-cleanability, mechanical durability), our approach will benefit a variety of applications, especially those exposed to humid conditions and/or dust prone environments.
2:45 PM - ES9.7.02
Efficiency Enhancement of ZnO Based Inverted BHJ Solar Cells via Interface Engineering Using Organic Interfacial Modifiers
Sujit Kumar 1 , Debdatta Panigrahi 1 , Achintya Dhar 1
1 , IIT Kharagpur, Kharagpur India
Show AbstractThe interface quality of ZnO and the photoactive polymer blend is critically important in the performance of organic-inorganic hybrid photovoltaic devices. The chemically prepared ZnO electron transporting layer often produce surfaces unacceptable for efficient electron extraction and understate the photovoltaic performance. Herein, we propose a facile interfacial modification technique to enhance the charge collection efficiency of ZnO cathode electrode by efficiently bridging the superficial troughs and ridges of ZnO with the photoactive PCDTBT: PC71BM polymer blend. The investigations show that vacuum sublimated organic interfacial modifier interlayers (OIMs) efficiently fills the gaps between ZnO and the polymer blend reducing accumulation of the charges at the interface and thus minimizing the recombination probability. They also play a very crucial role in passivating ZnO electrode against interfacial traps due to adsorbed chemical species. The inclusion of OIMs interlayer into the devices led to a substantial increase in device performance with PCE reaching close to 4%, an increment by a factor of 2 compared to the control devices. Two different OIMs were thoroughly investigated for their application as a ZnO modifier layer and their feasibility was established. Our investigations aim towards showing the efficacy of OIMs small molecule in significantly enhancing the PCE of ZnO based BHJ solar cells fabricated and measured in ambient conditions rather than setting benchmark efficiency for the configured device. However, better performances for the devices are conceivable by performing the fabrication and measurement in controlled inert atmosphere.
3:00 PM - ES9.7.03
Comparative Study of Annealed and High Temperature Grown ITO and AZO Films for Solar Energy Applications
Diego Alonso Alvarez 1 , Lourdes Ferre Llin 2 , Alexander Mellor 1 , Douglas Paul 2 , N.J. Ekins-Daukes 1
1 , Imperial College London, London United Kingdom, 2 , University of Glasgow, Glasgow United Kingdom
Show AbstractTransparent conductive oxides (TCO) are at the heart of modern electronic devices. They are an essential component of displays and touchscreens in tablets and mobile phones. They are also key in photovoltaics as the front electrode in many solar cell technologies. For this application the required properties of the TCOs are quite rigid: they must have very high transparency over a broad spectral range at the same time they possess excellent electrical transport properties. A more recent application is their use as low emissivity coatings for hybrid PV-thermal solar systems to keep the heat inside the solar cell and rise its temperature. In this work we study the two most common TCOs, indium tin oxide (ITO) and aluminium zinc oxide (AZO) with this latter application in mind.
Two sets of films deposited on silicon were studied for each of the materials: grown at different temperatures from room temperature to 350C, and grown at room temperature and then annealed up to 800C. The second method has the advantage of being faster and having a lower thermal budget that growing at high temperatures, but it has the caveat that many materials might not withstand such extreme thermal treatments.
Ellipsometry measurements taken from 300 nm to 30 µm and Hall measurements both show that ITO films grown at 250C and those annealed at 600C have comparable mobilities (30 cm2 V-1 s-1), carrier densities (9x1020 cm3), and optical properties. These samples show also the highest transparency in the UV-VIS region and the highest reflectance in the MIR which is desirable for the photovoltaic performance and as low emissivity coating. The other annealed ITO films are generally less reflective in the MIR and have poorer electrical properties possibly suggesting a different distribution of the dopants. The crystalline structure is very different, too, with the annealed samples made of large poly-crystals extending the whole thickness of the film, compared with the much smaller grains with preferential crystal orientation found in the samples grown at high temperature. In all cases, the films are inhomogeneous, being more conductive near the substrate that towards the surface. All AZO films are more transparent that those of ITO at all wavelengths, showing much higher resistivity, lower carrier densities and mobilities (about one order of magnitude), in contrast with some of the existing literature. The electrical measurements and the conclusions from the modelling of the ellipsometry differ significantly, though. In particular, the latter reveals the presence of a strong oscillator at around 6 µm, rather than a smooth Drude-like behaviour, that increases in strength with the annealing temperature and might have the explanation of the unexpected performance of these films.
Ongoing work and analysis of the results is expected to shed more light into the properties of these films and their actual impact as multi-functional coatings for PV-thermal applications.
3:15 PM - ES9.7.04
High Device-Specific Haacke Figure of Merit in Transparent Composite Electrodes as a Promising Replacement of ITO in Organic Solar Cell Applications
Zhao Zhao 1 , Terry Alford 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractFor indium-free, transparent composite electrodes (TCEs) used in organic solar cell and light emitting diodes, optimization of the average transmittance over the entire visible light spectrum might not always be a viable means to satisfy the specific needs of the devices. For example, the light absorption peak of the active layer in P3HT:PC61BM organic solar cell is between 450 nm to 600 nm. As a result, maximizing the average transmittance of TCE across 450 nm to 600 nm of the visible spectrum can specifically increase the light absorbed by the organic solar cell. In our study, the layer thicknesses of TCE are theoretically simulated and optimized, such that the optical transmittances are maximized across the wavelength range where the light absorption of P3HT:PC61BM is highest. The deposition rate of metal layer can also play a significant role on the electrical and optical properties of this TCE. As a result, the deposition rate of the layer was optimized in order to ensure relatively high transmittance and low sheet resistance. Results show that the metal films deposited with high deposition rate tend to have lower voids density. The low voids density in the metal layer gives rise to higher transmittance and lower sheet resistance of the corresponding TCE structure. For example, the optimized TiO2/Ag/TiO2 electrode has a device-specific Haacke figure of merit (FOM) about two times higher than ITO electrodes. The conventional bulk heterojunction OSC Anode/MoO3/P3HT:PC61BM/LiF-Al fabricated on optimized TiO2/Ag/TiO2 electrode shows high power conversion efficiency (PCE) that is almost twice that of OSC fabricated on ITO. Our finding indicates that TCEs can be integrated into organic solar cells and have considerable potential to replace ITO in solar cell applications. Most importantly, TCEs can be specifically tailored to additional applications.
3:30 PM - ES9.7.05
Effect of Ambient Microwave Annealing on Electrical and Optical Properties of Indium Tin Oxide
Sharvanti Pinglay 1 , Aditya Yerramilli 1 , Terry Alford 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractTransparent conductive oxide (TCO) layers are a significant part of semiconductors in various electronic devices like light emitting diode (LEDs), organic light emitting diodes (OLEDs), touch screens and solar cells. Indium tin oxide (ITO) is the most widely utilized TCO material owing to its high electrical conductivity and high optical transparency. Layers of indium tin oxide are deposited onto glass substrates using RF magnetron sputtering. These films are subjected to microwave annealing between 50°C - 100 °C for times up to 120 sec, with an interval of 30 seconds. Sheet resistance measurements determined using the 4-point-probe technique, from which the conductivity of the material was obtained. UV-Visible spectrophotometry measurements are used to determine the transmittance percentage. The results reveal a decrease in the sheet resistance with an increase in annealing time. We also obtain a transmittance percentage close to 90% in the visible region. The figure of merit reached a peak of 40x10-3Ω-1/sq for an annealed time of 90 seconds and later decreased with further increase in annealing time.
ES9.8: Revisiting Oxide Surfaces for Competitive CSP Plants
Session Chairs
Jose Luis Endrino
Ramon Escobar-Galindo
Thursday PM, April 20, 2017
PCC North, 200 Level, Room 226 C
4:15 PM - *ES9.8.01
Thermal Sprayed Oxide Coatings for Concentrating Solar Power Receivers
Andrea Ambrosini 1 , Aaron Hall 1 , David Adams 1 , Antoine Boubault 2
1 , Sandia National Laboratory, Albuquerque, New Mexico, United States, 2 Center for Applied Mathematics, MINES ParisTech, Sophia Antipolis Cedex France
Show AbstractConcentrating solar power (CSP) receivers utilize solar absorptant coatings to more effectively absorb sunlight to heat a working fluid for electric power generation. The efficiency of a power tower plant can be increased if the energy absorbed by the receiver is maximized while the heat loss from the receiver to the environment is minimized. One mechanism of heat loss is by thermal radiation from the hot receiver surface to the environment. Thermal radiation losses in the receiver can be significant at higher temperatures, which is a challenge facing next-generation power towers that aim to operate above 650 °C. Pyromark 2500™, the current industry standard, has a very high solar absorptance (α > 0.95), but also high emittance (ε ~0.87) at the temperatures of interest. In addition, it has been reported to physically degrade over time on-sun. Improved selective absorber coatings for receivers must maintain such high absorptance in the solar spectrum but exhibit lower emittance in the infrared spectrum. Any selective absorber material developed for next-generation receivers must also be stable in air at high temperature, easily applied at large scales in the field, cost effective, and survive thousands of heating and cooling cycles.
To meet this challenge, a thermal spray process was utilized to deposit metal oxide coatings onto Haynes and Inconel Ni-alloy substrates. The absorptance measurements of the as-prepared coatings were promising, but lower than what is necessary for CSP applications. To improve the optical properties, a laser treatment was utilized to modify the surface texture of the coatings, resulting in increased solar absorptivity competitive with that of Pyromark. The materials were characterized by x-ray diffraction and electron microscopy, which showed that the laser treatment induced surface changes on the nano- and micro-scales. The coatings were subjected to isothermal aging between 600 – 800 °C for up to 480 hours. Additionally, selected coatings were tested on-sun on the solar furnace and solar simulator at Sandia National Labs. The results of aging on the optical, structural, and morphological properties of these novel coatings will be discussed.
Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
4:45 PM - *ES9.8.02
Nano Black-Oxide Coating as a High Efficiency Solar Absorber for Concentrating Solar Power
Sungho Jin 2 1 , Renkun Chen 1 , David Wait 2
2 , Solar Reserve, LLC, Santa Monica, California, United States, 1 , University of California, San Diego, San Diego, California, United States
Show AbstractSolar absorber coating is one of the key enabling technologies to achieve higher-temperature higher-efficiency concentrating solar power (CSP) operation. A desirable solar absorbing material must simultaneously meet all the stringent requirements of high thermal efficiency (usually measured by figure of merit, FOM), high-temperature durability of optical, thermal and mechanical properties, as well as oxidation resistance during the long service period. This talk will review some recent new progress related to black oxide nanoparticle materials that can be applied onto the metallic receiver tubes that carry the heat transfer fluid. Preliminary evaluations of optical and thermal properties indicate that a high solar-to-thermal efficiency greater than 90% is possible with the absorber coating, while maintaining high temperature durability of optical, thermal and mechanical behavior on long-time exposure at a temperature higher than 750oC. The repairability of previously applied absorber coating has also been shown to be feasible. Therefore, this technology seems promising for commercial applications in the next-generation high-temperature concentrating solar power (CSP) plants. The preparation of solar absorber coatings and the implications of the observed optical and thermal behavior will also be discussed.
5:15 PM - *ES9.8.03
Selective Solar Absorber Coatings on Receiver Tubes for CSP—From Vacuum-Deposited Carbon Based Coatings to Wet-Chemical Derived Mixed Oxide Coatings
Andreas Schuler 1
1 , EPFL, Lausanne Switzerland
Show Abstract
In previous work, we have developed selective solar absorber coatings based on titanium containing amorphous hydrogenated carbon a-C:H/Ti, produced by a combined physical vapor deposition / plasma enhanced chemical vapor deposition process (PVD/PECVD). By introducing Si into these films, their ageing stability at elevated temperatures in air has been strongly increased. Carbon-based coatings are still a topic of current research. Recently,
I. Heras, R. Escobar-Galindo and coworkers designed selective solar absorber coatings based on carbon / transition metal carbide nanocomposites (a-C:MeC, Me = V, Mo). Such coatings are deposited by pulsed filtered cathodic arc and exhibit a maximum solar absorptance of 96% and a low thermal emittance of 5% and 15% at 25 and 600 °C, respectively.
In order to overcome the barrier of initial investment cost, wet-chemical derived solar absorber coatings might be an interesting alternative. By sol-gel dip-coating and subsequent thermal annealing, multilayered mixed Cu-Co-Mn-Si oxide coatings have been produced. The optical and morphological properties of these multilayers have been characterized by spectrophotometry, transmission electron microscopy (TEM), time-of-flight secondary ion mass spectroscopy (ToFSIMS) and X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) yields evidence for crystalline grains with 5-20 nm in diameter.
After optimization of the multilayer design, a solar absorptance of 0.95 and a thermal emissivity of 0.12 at 100°C have been achieved. For the energy-efficient thermal annealing of 2 m long receiver tubes, a special induction heating process has been developed.
The excellent stability at elevated temperatures in air makes such sol-gel derived black oxide coatings an interesting candidate for solar applications involving concentrated solar radiation, such as the generation of solar electricity (concentrated solar power), industrial process heating and solar cooling.
ES9.9: Poster Session
Session Chairs
Jose Luis Endrino
Erik Schumann
Friday AM, April 21, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ES9.9.01
Solution-Processed Copper Nanoparticles for Selective Solar Absorption
Derek Wang 1 , Jyotirmoy Mandal 2 , Yuan Yang 2
1 , Stanford University, Stanford, California, United States, 2 Applied Physics and Applied Mathematics, Columbia University, New York City, New York, United States
Show AbstractSelective solar absorbers can improve the efficiency of solar thermal converters by absorbing visible and near-infrared sunlight and retaining thermal energy, which is typically emitted as near- to mid-infrared radiation. Deposition of current selective solar absorbers, however, requires costly or toxic raw materials and techniques. In the present study, we investigated the suitability of solution-processed plasmonic copper nanoparticles deposited on a zinc substrate for selective solar absorption. The copper particles are in the order of hundreds of nanometers in size, which enhances plasmonic absorption of solar light, especially in the visible regime. The bulk zinc substrate underneath is highly reflective to infrared radiation, indicating that thermal emittance εt is low. This novel coating is prepared by submerging the zinc substrate in aqueous copper ion solution, a green synthesis that requires only readily available chemicals. We studied the effects of washing procedures, chelating agents, length of time submerged, temperature of solution, and concentration of copper ion on the nanoparticle growth. By controlling nanoparticle size and distribution, we created a selective solar absorber with αs = 0.88 and εt = 0.05. We then investigated the robustness of the copper plasmonic nanoparticles on zinc substrate under accelerated degradation conditions. While bare, low-density polyethylene-coated, and polydimethylsiloxane-coated copper plasmonic nanoparticles experienced rapid degradation under both humid and hot atmospheric conditions, the material’s performance was unchanged after 84 hours at 120C in inert argon gas. We also demonstrated a 25% increase in distillation efficiency with a simple solar distillation device. Given the high speed of synthesis, low cost and toxicity of materials, and level of control over particle formation of the plasmonic copper nanoparticles, this material has exciting potential to serve as a selective solar absorber in solar thermal converters, but further work is needed to protect the surface from degradation.
9:00 PM - ES9.9.02
Nickel Electrodeposition on Anodized Aluminum Oxide Films as Selective Absorbing Coating Made by AC Voltage with Variable Frequency
Samuel Santiago Cruz 1 2 , Arturo Fernandez Madrigal 2 , Esther Santiago Cruz 1
1 , Universidad Tecnológica de Huejotzingo, Huejotzingo Puebla Mexico, 2 Materiales Solares, Universidad Nacional Autonoma de Mexico, Temixco, Morelos, Mexico
Show AbstractAnodized aluminum oxide films (Al2O3) on aluminum substrates 1050 (99.5% w Al) was impregnated with nickel (Al2O3-Ni) by electrodeposition technique with alternating current (AC) voltage with variable frequency. In this paper, we report the synthesis of Ni using the galvanostat mode, as well as some experimental variations in the frequency and intensity of AC voltage in order to optimize the amount of nickel in the oxide aluminum substrates. EDS, XRD, SEM and UV-VIS spectrophotometry techniques was used to analyses the atomic composition, structural morphology and optical properties of the samples. Additionally, an emissometer was used to measure the hemispherical thermal emissivity. Data values of the total reflectance for the visible solar spectrum (VIS) and near infrared (NIR) as a function of voltage and frequency for fixed times nickel impregnation were analyzed, several experiments were performed with in order to correlate these parameters with the nickel content in the bottom of the pores of the films and their optical properties. Absorptance values between 0.09 to 0,15 and emittance values of 0.09 to 0.15 were obtained, the pores of the films developed to 11 Vrms and 60 Hz are filled with nickel 30% by volume pore and optical properties αs= 0.83, emmitance(80oC) = 0.11 that make them good prospects for application in solar collectors.
9:00 PM - ES9.9.03
Effect of Pyramids Size Obtained by KOH Texturing on Silicon Solar Cell Performance
Rameshwari Ghimire 1 3 , Som Dahal 2 , Stuart Bowden 2 , Raymond Tsui 2 , Trevor Thornton 2
1 Physics, Arizona State University, Tempe, Arizona, United States, 3 Solar Power Lab, Arizona State University, Tempe, Arizona, United States, 2 Electrical Computer and Energy Engineering, Arizona State University, Tempe, Arizona, United States
Show AbstractIt is well known that surface texturing in silicon by anisotropic etching of KOH or NaOH reduces the reflection down to 10% and enhances the path length of light in solar cells. Surface texturing with potassium hydroxide is widely used in the solar cell industry. In this work, we present the effect of pyramid size in solar cell performance by: (1) studying the minority carrier lifetime of passivated wafers with the pyramid size from less than 1 µm to 5 µm and (2) studying the device parameters such as Voc, Jsc , series resistance, fill factor and efficiency. The size and uniformity of these pyramids can be tuned with texturing chemistry and texturing time. In this work, we were able to tune the pyramid size from 1 µm to 6 µm with a very good uniformity. A detailed characterization of pyramid size has been performed together with a reflectance study. It is observed that the small pyramid (1 µm) samples have the same reflectance as their counterparts with bigger pyramids (5 µm). For both texturing conditions, double side diffused samples were prepared and surfaces were passivated with silicon dioxide and silicon nitride stacks. Photoconductance decay measurements showed that the small pyramids samples have higher minority carrier lifetimes and implied Voc than their larger pyramid counterparts. The devices are made on 156 mm CZ , boron doped solar wafers with different texturing conditions resulting in different pyramid size and the effect of pyramid size on light IV parameter were studied and will be presented.
9:00 PM - ES9.9.04
Polarization Resolved Grazing Angle Scatterometry for In Situ Monitoring of Roughness for Silicon and Compound Solar Cells, Light Emitting Devices and other Structured Surfaces
Wojciech Walecki 1 , Peter Walecki 2 3 , Eve Walecki 2 4 , Abigail Walecki 2 5
1 R&D, Frontier Semiconductor, San Jose, California, United States, 2 , Sunrise Optical LLC, Sunrise, Florida, United States, 3 Engineering, Brown University, Providence, Rhode Island, United States, 4 , University of Florida, Gainsville, Florida, United States, 5 , Florida Atlantic University, Boca Raton, Florida, United States
Show AbstractNovel metrology tool for in-situ characterization of surfaces semiconductor solar cells (both silicon and compound), and Light Emitting Device diffusers is presented. The tool measures the total integrated scattering when measuring forward, or back-reflection at very large angles of incidence. The tool is insensitive to vibrations and stray light. We discuss polarization resolved data and characterize our technique using NIST traceable standards. We discuss it's applications to semiconductor manufacturing.
The grazing angle reflection measurements were subject of radar [1], semiconductor [2], machine vision [3], space [4], traffic materials [5], and theoretical research [6]. The grazing angle forward reflection metrology was reported by us earlier [7], however, we are not aware of the fully polarization resolved grazing angle back-reflection metrology of roughness of Silicon nor Compound Sollar Cells or Light Emitting Device diffusers.
[1] Billingsley, J. Barrie. Low-angle radar land clutter: measurements and empirical models. IET, 2002.
[2] Stover, John C. Optical scattering: measurement and analysis. Vol. 2. Bellingham: SPIE optical engineering press, 1995.
[3] Ngan, Addy et al. "Experimental Analysis of BRDF Models." Rendering Techniques 2005.16th (2005): 2.
[4] Speicher, Andy. Identification of geostationary satellites using polarization data from unresolved images. Diss. UNIVERSITY OF DENVER, 2015.
[5] Belcour, Laurent, et al. "Bidirectional reflectance distribution function measurements and analysis of retroreflective materials." JOSA A 31.12 (2014): 2561-2572.
[6] Elfouhaily, Tanos Mikhael, et al. "A critical survey of approximate scattering wave theories from random rough surfaces." Waves in Random Media 14.4 (2004): R1-R40.
[7] Walecki, Wojciech, et al. "Robust diffuser and roughness metrology tool for LED manufacturing." SPIE OPTO. International Society for Optics and Photonics, 2015.
9:00 PM - ES9.9.05
Large-Area of High Uniform CdS Thin Film Grown by Special Technique Chemical Bath Deposition
Sheng Wen Chan 1
1 , Industrial Technology Research Institute, Taiwan Taiwan
Show AbstractCIGS thin film solar cells have shown the conversion efficiency beyond 22.6% [1] and it was well-known the n-type buffer layer grown by chemical bath deposition (CBD). However, it is difficult to grow large-area of high uniform CdS thin film by traditional CBD process. In this study, a special technique chemical bath deposition to grow large-area of high uniform CdS thin film had been developed, and the large-area of CdS thin film quality are characterized by employing scanning electronic microscopy (SEM) and UV–visible–NIR spectrophotometer. In the result, we got the large-area and high quality CdS thin film, which could be suitable to mass production of CdS buffer layer for large-area CIGS thin film solar cells.
9:00 PM - ES9.9.06
Fabrication of Zn(S, O) Buffer Layer for CIGS Solar Cells by Highly Deposited Rate Chemical Bath Deposition Process
Sheng Wen Chan 1
1 , Industrial Technology Research Institute, Taiwan Taiwan
Show AbstractCIGS solar cells have shown the conversion efficiency beyond 21% [1], but the toxic material “CdS” was still used as a n-type buffer layer in the solar cell. Recently, ZnS/CIGS solar cells were developed rapidly and it could also show efficiency as high as 20.7%, which was comparable to the CdS/CIGS solar cells [2]. But the zinc-based buffer layer has two drawbacks such as low deposition rate and insufficient coverage, which must be met for large mass production. In this paper, Zn(S, O) buffer layers for CIGS solar cells were prepared by a “high rate” chemical bath deposition process. In this new process, 30 nm Zn(S,O) thin film could be prepared within 5 minutes. Scanning electronic microscopy and UV–visible–NIR spectrophotometer were employed to characterize the thin film quality. The Zn(S, O) thin films showed good uniformity, good coverage and high transmittance. The optical bandgap of the as-grown Zn(S,O) thin films were measured to be 3.6eV. Besides, the efficiencies of ZnS/CIGS solar cells were also measured under standard condition. The efficiencies of ZnS/CIGS solar cells could reach 12.6%, which was close to a reference CdS/CIGS solar cell(12.8%). The results hinted that the new ZnS process showed promising potential to get good film quality and high throughput, which could be suitable to mass production for CIGS thin film solar cells.
9:00 PM - ES9.9.07
ZnO 1-xTex Thin Films Deposited by Reactive Magnetron Co-Sputtering—Compositional, Structural and Optical Properties
Olga Sanchez Garrido 1 , Monica Fernandez Barcia 1 , Oscar Garcia 2 , Aurelio Climent 3 , Manuel Hernandez Velez 3
1 , Instituto de Ciencia de Materiales de Madrid (CSIC), Madrid Spain, 2 UGdS-Optronlab Group, Dpto. Física Materia Condensada, Universidad de Valladolid, Valladolid Spain, 3 Física Aplicada , Universidad Autónoma de Madrid, Madrid Spain
Show AbstractIn recent years there is growing interest in the study of ZnO1-xTex thin films because their potential use in a variety of applications in solar conversion technology including its application as transparent conductor oxide (TCO) and their expected use in multiband, single junction, high-efficiency photovoltaic devices. In this work, ZnO1-xTex thin films were deposited by DC reactive magnetron co-sputtering using pure Zn and Te targets. Te atomic concentration in the films was ranged from x=0 to 0.33 by adjusting the power applied on the targets and also varying the cathode-substrate distance. Chemical composition and Crystalline structure were determined by RBS experiments and X-ray Diffraction, respectively. These studies revealed that for low Te atomic concentrations (x≤0.04) the deposited ZnO1-xTex films showed a well-defined crystalline structure like ZnO wurtzite hexagonal phase, however as the Te concentration increases the peaks positions shifted to lower 2θ with decreasing intensities and broadening compared to pure ZnO films. For higher x values the main peak characteristic of wurtzite phase disappears and different ZnO crystalline orientations appeared. For x=0.33 a broad band associated to TeO2 can be observed suggesting the presence of this compound in the samples. In all deposited films, FTIR studies showed absorption bands in transmittance spectra located in the 200-600 cm-1 range which have been related to bending vibrations of Te-O-Te or Te-O-Zn linkages. The crystalline and optical properties were also investigated by Raman and Photoluminescence (PL) spectroscopies. PL results showed transition bands at lower energies than that corresponding to the pure ZnO band gap; the lowest energy transition was identified for x=0.04 around 2.3 eV in the low temperature PL experiments.
9:00 PM - ES9.9.08
Stress-Induced Surface Characterization by Wavelet and Fractal Analysis in Ga-Doped ZnO Thin Films
Chenlei Jing 1 , Wu Tang 1
1 , University of Electronic Science and Technology of China, Chengdu, Sichuan, China
Show AbstractFractal geometry and multi-resolution signal decomposition (MRSD) based on wavelet transform were applied to process surface profiles of various thicknesses Ga-doped ZnO (GZO) deposited by magnetron reactive sputtering on glass substrates at room temperature. The atomic force microscopy (AFM) images release that the root-mean-square (RMS) roughness is observed to shift linearly with the deposited time while the fractal dimension of each profile shows an opposite trend as compared with the roughness, and the roughness of analyzed profile by MRSD only depends on the height information that cannot expresses the surface morphology. Also, it is found that fractal dimension is closely connected to the underside diameter (grain size) and the distance between adjacent grains that affect the change rate of surface and the increase of the defects such as abrupt changes lead to a larger value of fractal dimension. What’s more, the in-plane compressive stress of highly c-axis oriented GZO thin film decreases with the deposited time that could conclude the in-plane stress affects the surface morphology to a certain extent and that there is a relationship between fractal dimension and in-plane stress.
9:00 PM - ES9.9.09
Photocurrent Enhancements from Biomimetic Reconstructs of Photosystem I-Proteoliposomes Supported on Electrode
Hanieh Niroomand 1 2 , Ravi Pamu 3 , Dibyendu Mukherjee 1 2 3 , Bamin Khomami 1 2 3
1 Sustainable Energy Education and Research Center (SEERC), University of Tennessee, Knoxville, Knoxville, Tennessee, United States, 2 Chemical & Biomolecular Engineering Department, University of Tennessee, Knoxville, Knoxville, Tennessee, United States, 3 Mechanical, Aerospace & Biomedical Engineering Department, University of Tennessee, Knoxville, Knoxville, Tennessee, United States
Show AbstractThe robust structural and photoactive electrochemical properties of Photosystem I (PSI), a transmembrane photosynthetic protein complex, make it an ideal candidate for incorporation into solid state bioelectronic or hybrid photovoltaic devices. However, the first step towards the successful fabrication of such devices requires systematic assembly of oriented and functional PSI onto desired bio-abio interfaces via suitable protein scaffoldings. To this end, in this study the effect of systematic incorporation of PSI complexes into synthetic membrane-bound structures that mimic the natural thylakoid membrane housing of PSI quantifies via its performance and photocurrent response is demonstrated. A facile yet elegant method for detergent-mediated reconstitution of proteoliposomes is introduced. The efficacy of this method is demonstrated via absorption and fluorescence spectroscopy measurements as well as direct visualization using atomic force microscopy. The current work also provides direct evidence that PSI confinements in synthetic lipid scaffolds can be used for tuning the photoexcitation characteristics of PSI. Finally, detailed chronoamperometry measurements were conducted on PSI-proteoliposomes made from PSI incorporated within biomimetic membrane scaffolds and supported on suitable SAM substrates to investigate the enhancement in photocurrent responses arising from such confinement. The significant observation here is the enhanced photo current generation from PSI complexes under liposome confinements as compared to that produced from dense monolayer of individual PSI on SAM substrates using an equivalent concentration of PSI. In turn, the aforementioned studies provide valuable insight into easy incorporation of membrane protein-lipid complexes into novel bio-hybrid devices.