bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Fluid Flow Dispersion in Electrodes By Means of Computed Tomography and Lattice-Boltzmann Simulations
Authors: Maggiolo Dario , Trovo' Andrea , Picano Francesco , Carmignato Simone , Guarnieri Massimo
Published: February 2020

Lattice-Boltzmann simulations of fluid flow in fully reconstructed porous materials are performed in order to characterized the macroscopic behavior of fluid flow and dispersion in porous media for flow batteries applications [1]. The material quantitative reconstruction has been performed by means of X-ray microtomography and the obtained data have been used as input geometry in the Lattice-Boltzmann algorithm. The Lattice-Boltzmann model is coupled with a Lagrangian Particle Tracking algorithm in order to better understand the complex dispersion behavior of species induced by the medium microstructure that conforms a superdiffusive behavior [2].

Different materials have been investigated, including typical carbon felt used as electrodes in redox flow batteries and innovative carbonized rigid materials. The anisotropic behavior due to the fiber orientation has been taken into account and its effects have been investigated (Fig. 1).

For each material and microstructure, the flow behavior and particle trajectories have been computed extracting the flow resistance and dispersion features (Fig 2). These analyses have allowed identifying the optimal material and its arrangement, which involve minimal drag and maximized mixing. These conditions ensure an increase of the performance of the redox flow cell, in terms of reduced diffusion losses in the electrochemical reaction as well as reduced pressure drop and pumping needs of the electrolyte solutions and of the overall efficiency of flow batteries.

References

[1] Wang B., Kuo J., Bae S.C. and Granick S., Nature Materials, 2012, 11(6): 481-5.

[2] Maggiolo D., Picano F., Marion A., Guarneri M., “Application of the Lattice-Boltzmann Method for Modeling All-Vanadium Redox Flow Batteries”, Proc.
IV International Conference on Particle-based Methods – Fundamentals and Applications - Particle 2015, pp. 579-589, Barcelona, Spain, Sept. 28-30, 2015.

Figure 1
Investigation of LiMn2O4 Thin-Film Electrode Using Redox Reaction of Ferrocene
Authors: Inamoto Jun-ichi , Miyazaki Kohei , Fukutsuka Tomokazu , Abe Takeshi
Published: February 2020

Introduction

Lithium-ion batteries (LIBs) have been expected as the power supplies of electric vehicles (EVs). LiMn2O4 is widely desired as the positive active materials for EVs-use, However, LiMn2O4 suffer from severe degradation at elevated temperature, leading to poor cycleability of LIBs. One of the factors of degradation is formation of surface film. The surface film might bring passivation of the electrode, however, detailed properties of the surface film were not fully understood. In this study, we investigated passivation behavior of LiMn2O4using redox reaction of ferrocene.

Experimental

LiMn2O4 thin-film electrode was prepared by pulsed laser deposition. Three-electrode cell was used for electrochemical measurements of LiMn2O4 thin-film electrode. Lithium-ion de-intercalation/intercalation was conducted in 1 mol dm-3 LiPF6/propylene carbonate (PC) by cyclic voltammetry (0.1 mV s-1, 3.5 – 4.2 V vs. Li+/Li.). Before and after the lithium-ion de-intercalation/intercalation process, redox reaction of ferrocene was measured in 1 mol dm-3 LiClO4/PC containing 1 mmol dm-3 ferrocene by cyclic voltammetry (10 mV s-1, 3.0 – 3.6 V vs. Li+/Li.).

Results and discussion

Figure 1 shows cyclic voltammograms (CVs) of LiMn2O4 thin-film electrode at room temperature. Around 4.0 and 4.2 V, reversible peaks of lithium-ion de-intercalation/intercalation, which are characteristic of LiMn2O4, were observed. As the cycle number increased, peak currents gradually decreased. It indicated degradation of LiMn2O4 proceeded during cycling test. Figure 2 shows the CVs of redox reaction of ferrocene on LiMn2O4 thin-film electrode before and after the cycling process of lithium-ion de-intercalation/intercalation. Reversible redox peaks of ferrocene were observed before the initial cycle. However, these peaks disappeared after the initial cycle, indicating passivation of LiMn2O4thin-film electrode. X-ray photoelectron spectroscopy revealed that LiF was formed on the surface, and it should be the cause of the passivation. The influence of electrolyte, elevated temperature and additive on the passivation behavior will be discussed in the meeting.

Acknowledgment

This work was partially supported by CREST, JST.

Figure 1
New Redox Polymer Hybrids: Bridging the Gap Between Li-Ion Batteries and Supercapacitors
Authors: Gohy Jean Francois
Published: February 2020

A rational management of the energy resources and consumption is at the center of the preoccupations of a world in constant development. In this context, a sustainable development and exploitation of the energetic resources is asked, necessitating practical and quick solutions to direct the economy towards an energetic autonomy. This presentation is centered on the development of novel energy storage systems with enhanced performances through original organic electroactive material chemistry and engineering approaches. Deciphering the fundamental flaws and building better organic batteries is the primary target, the long-term goal of this research being the development of sustainable all-carbon-based batteries. Based on this, we focus on three complementary yet, distinct directions with specific goals: improve and develop new organic radical materials for pseudo-capacitive energy storage by engineering high energy density nitroxide radical containing block copolymer architectures [1,2]; design and synthesize hybrid macromolecular architectures displaying both, electroactive and electron conductive properties [3-5]; and develop hybrid organic-inorganic electrochemical energy storage materials and technologies that combine best-of-both worlds characteristics [6]. Accordingly, this research aims the design and development of novel electroactive organic materials and architectures and, by doing so, develop faster, safer & longer-lasting organic batteries, capacitors and their hybrids.

References

[1] Hauffman, G.; Vlad, A.; Janoschka, T.; Schubert,

U. S.; Gohy, J.-F. J. Mater. Chem. A
2015, 3, 19575

[2] Winsberg, J.; Janoschka, T.; Morgenstern, S.; Hageman, T.; Muench, S.; Hauffman, G.; Gohy, J.-F.;  Hager, M. D.; Schubert,

U. S. Adv. Mater.
2016, DOI: 10.1002/adma.201505000

[3] Ernould, B.; Devos,

M.; Bourgeois, J.-P.; Rolland, J.;

Vlad, A.;

Gohy, J.-F. J. Mater. Chem.
A
2015, 3, 8832.

[4] Vlad
, A.; Arnould, K.; Ernould, B.; Sieuw
, L; Rolland, J.; Gohy J
.-F. J. Mater.
Chem. A
2015
, 3, 11189.

[5] Vlad, A.; Rolland, J.; Hauffman, G.; Ernould, B.; Gohy, J.-F. ChemSusChem.
2015, 8, 1692.

[6] Vlad, A.; Singh, N.; Rolland, J.; Melinte, S.; Ajayan, P.M.; Gohy, J.-F. Sci. Rep.
2014, 4, 4315.
Tandem Cell-Based Vanadium Redox Flow Battery Stack
Authors: Jin Chang-Soo , Park Se-Kook
Published: February 2020

Today about two-thirds of the world’s total electric power is generated from fossil fuels and nuclear based energy. Globally accelerating concerns regarding environmental pollution from the burning fossil fuels in combination with increasing energy shortages have provoked great interest in the generation of electrical energy from renewable sources such as wind and solar [1-3]. However, the random and intermittent nature of these power sources induces low-quality output in electricity, which affects the stability of the grid. Given that energy storage system (ESSs) can be efficiently balanced between power generation and the consumption of renewable energy sources through load-leveling and peak-shaving strategies, they have emerged as a key technological challenge [4-5].

Among various types of ESSs, the all-vanadium redox flow battery (VRFBs) is a promising technology for large scale electrical energy storage systems. These batteries utilize the reduction and oxidation reaction of two active species in the electrolytes for charge and discharge processes. VRFBs can independently be the scalable application which shows power and energy capacity component of the system [6,7].

In this study, we report in detail our investigation of Tandem electrode structure for VRFB system and its effect on long-term stability and electrochemical performance.

[1] Z. Yang, J. Zhang, M.C. Kintner-Meyer, X. Lu, D. Choi, J.P. Lemmon, J. Liu, Chem. Rev., 111 (2011) 3577-3613.

[2] B. Dunn, H. Kamath, J.-M. Tarascon, Science, 334 (2011) 928-935.

[3] C. Koroneos, T. Spachos, N. Moussiopoulos, Renewable energy, 28 (2003) 295-310.

[4] D. Wang, Z. Geng, B. Li, C. Zhang, Electrochim. Acta, 173 (2015) 377-384.

[5] H. Chen, T. N. Cong, W. Yang, C. Tan, Y. Li, Y. Ding, Progress in Natural Science, 19 (2009) 291-312.

[6] H. Kaneko, K. Nozaki, Y. Wada, T. Aoki, A. Negishi, M. Kamimoto, Electrochim. Acta , 36 (1991) 1191-1196.

[7] M. Skyllas‐Kazacos, C. Menictas, M. Kazacos, J. Electrochem. Soc., 143 (1996) L86-L88.
(Invited) Effect of Heat Treatment Conditions on Crystallization of Anodic Alumina Membrane Formed in Phosphoric Acid
Authors: Asoh Hidetaka , Shigehara Yoshihito , Hashimoto Hideki , Ono Sachiko
Published: February 2020

Porous-type anodic aluminum oxide films have attracted considerable attention as a key material in the fabrication of several types of devices owing to their potential technological applications. However, conventional anodic alumina films have low chemical resistance because the anodic oxide films obtained by typical anodizing processes are amorphous. Expanding the application of alumina films necessitates enhancement of the chemical resistance of alumina.

Previously, we identified the optimized anodizing conditions and the detachment method for suppressing thermal deformation, such as curving and cracking, during heat treatment of the alumina membrane (1-4). In our previous study, anodizing was conducted under an applied voltage of 25 V–185 V, which resulted in the formation of an anodic porous alumina film with pore diameters tunable over a wide range of approximately 30-350 nm. When oxalic acid was used as an electrolyte, the fabrication of a crack-free and flat α-alumina membrane with a diameter of 25 mm, a thickness of 50 μm and a pore diameter of approximately 60 nm was fabricated using the optimized anodizing conditions in oxalic acid at 40 V, followed by subsequent detachment from the substrate and heat treatment (2). In the case of phosphoric acid, the fabrication of α-alumina membrane with a pore diameter of 350 nm was achieved through optimization of various conditions (3).

In the present study, the chemical composition and morphological changes of the alumina membrane formed in phosphoric acid during heat treatment were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA). The results of analyses clearly showed that the alumina membrane formed in phosphoric acid has unique characteristics such as coexistence of crystalline alumina and aluminum phosphate at high temperature region above around 1100 oC. Therefore, we focused on the effect of heat treatment conditions (e.g., temperature, heating rate and holding time) on the morphological changes of alumina cell wall in comparison with alumina films formed in sulfuric acid and oxalic acid. By controlling of heating conditions, alumina membrane with hierarchically porous structures consisted of main macropores and smaller textural mesopores in the cell walls could be fabricated. Through-hole structure of heated alumina membrane was maintained even at high temperature, and additional mesopores were formed by the selective removal of aluminum phosphate from alumina cell wall.

[1] F. Rashidi, T. Masuda, H. Asoh, S. Ono, Surface and Interface Analysis, 45, 1490-1496 (2013)

[2] T. Masuda, H. Asoh, S. Haraguchi, S. Ono, Electrochemistry, 82, 448-455 (2014)

[3] T. Masuda, H. Asoh, S. Haraguchi, S. Ono, Materials, 8, 1350-1368 (2015)

[4] H. Asoh, T. Masuda, S. Ono, ECS Transactions, 69, 225-233 (2015)
Contribution of Hydrogen to the Intergranular Corrosion Damage in a 2024 T351 Aluminum Alloy
Authors: de Bonfils-Lahovary Marie-Laetitia , Lafouresse Manon , Laffont Lydia , Blanc Christine
Published: February 2020

In aeronautic industry, lifetime prediction of structural elements is a capital issue, in particular for the parts exposed to atmospheric corrosion processes. Tests exist to detect corrosion defects but only a few predictive tests allowing the corrosion defects propagation kinetics to be determined are developed and they need to be optimized. In this framework, tensile tests on pre-corroded samples are assumed to be useful. First results were obtained for AA 2024 samples pre-corroded by continuous immersion in a 1M NaCl solution for times ranging from 6h to 1200h. Results from tensile tests evidenced a decrease of the mechanical properties with the exposure time. Propagation depths of the corrosion defects were then derived from the results of mechanical tests. However, depending on the exposure conditions, a volume damage related to the corrosion-induced hydrogen absorption seemed to contribute to the loss of mechanical properties of the pre-corroded samples. To better understand, hydrogen content of pre-corroded samples was measured using an Instrumental Gas Analysis on a Horiba EMGA-621 W analyzer. Moreover, AA-2024 samples were hydrogenated by cathodic polarization in H2SO4solution to model the corrosion defect tip. Samples were then corroded by continuous immersion in 1 M NaCl solution. First, observations using optical microscope and scanning electron microscope allowed the morphology of the corrosion defects to be studied for the hydrogenated samples. Then, electrochemical characterizations of the hydrogenated samples were performed in order to determine the influence of hydrogen on the corrosion defect propagation kinetics.

This work is supported by ANR-14-CE07-0027-01 – M-SCOT: Multi Scale COrrosion Testing.
Novel Approaches for Characterizing the Delamination Resistance of Organic Coatings
Authors: Rohwerder Michael , Dandapani Vijayshankar
Published: February 2020

Based on the results of the pioneering work by Stratmann et al. [1, 2, 3, 4], it may be assumed that corrosion driven delamination of an organic coating should be mainly determined by a few key properties, such as its barrier properties against water, ions and oxygen, its resistance against cation diffusion/migration along its interface to the metal, its resistance against oxygen reduction at this interface and its resistance against radicals produced as side products of this oxygen reduction reaction. Especially the two last properties should define highly delamination resistant coatings. However, so far it was not possible to obtain information about the correlated reaction rates at the buried interface between the organic coating and the metal. Recently, we have developed a novel experimental approach that direct provides information about the oxygen reduction rate at the buried interface as well as on the interfacial degradation resistance [5]. The potential of this technique will be discussed for the case of selected examples.

[1] A. Leng, H. Streckel, M. Stratmann, Corros. Sci. 41 (1999) 547-578

[2] A. Leng, H. Streckel, M. Stratmann, Corros. Sci. 41 (1999) 579-597

[3] A. Leng, H. Streckel, K. Hofmann, M. Stratmann, Corros. Sci. 41 (1999) 599-620

[4] M. Rohwerder, M. Stratmann, MRS Bulletin 24 (1999) 43-47

[5] V. Dandapani, T.H.Tran, A. Bashir, S. Evers. M. Rohwerder, Electrochim. Acta 189 (2016) 111-117
Microstructure and EIS Characterization of Multi-Layered Coatings on Metals
Authors: Tang Shawei , Hu Jin
Published: February 2020

Surface coating is powerful for corrosion protection of metals, and electrochemical impedance spectroscopy is widely used when the corrosion behavior of coating is studied. Equivalent circuits (ECs) method are commonly used for analysis of the EIS data, however, the establishment of ECs is difficult sometimes. The reason is the coating structure is actually complicated and the physical model of the coating is not properly understood. In this study, different coating, such as metals, oxides and polymers were prepared on the surface of aluminum alloy and steel. The coatings designed are multi-layered, and contain some controllable artificial defects. So the relationship between the coating structures and the constructions of the equivalent circuits can be studied in detail. The coating structures were characterized by SEM and TEM. The ECs were established according to the coating structure and the defect character, and the fitting results will be evaluated. The relationship between the coating structure and the ECs was established.

Figure 1
Fundamental Investigation of E-Coat Systems for Next Generation Corrosion Control
Authors: Padash Fardin , Harb John N.
Published: February 2020

Electrodeposition of coatings is widely used in the auto industry to protect against corrosion. Increased fundamental understanding is needed to enhance the effectiveness of coatings while decreasing the environmental risks associated with surface treatments and coatings, as well as the processes used to form them. In addition, the incorporation of fundamental understanding into modeling tools will help to improve the quality of predictions and ensure that the desired level of corrosion protection is achieved. Fundamentally based models can also provide insight to guide the development and use of new types of environmentally friendly surface pretreatments. Key parameters of interest to the present study include the coulombic efficiency (mass deposited per charge), the coating resistivity, bath conductivity, the degree of neutralization and the extent of amine substitution. The influence of operating conditions such as temperature and flow on these parameters is also critical. In this study, experiments are performed to investigate the influence of factors such as the degree of neutralization and the extent of amine substitution on the size of resin particles in solution and on the processes that render the resin insoluble, leading to deposition. Models are used to describe and quantify critical mechanisms. The impact of key parameters on the local deposition rate and on the coulombic efficiency is demonstrated. The ability to determine the local deposition rate is critical to the performance of large-scale systems and to our ability to predict that performance for a variety of bath compositions, operating conditions, and surface pretreatments.
Zinc Diffusion Coatings on Aluminium for Improved Pitting Resistance
Authors: Lunder Otto , Nordlien Jan Halvor , Lein John Erik
Published: February 2020

The automotive industry has replaced copper tube based heat exchangers with all-aluminium solutions during the past years in order to reduce weight, material costs and environmental impact. Conversely, the use of aluminium tubing in the HVAC&R (Heat, Ventilation, Air Conditioning and Refrigeration) heat exchanger market is limited due to the much more demanding lifetime requirements. One way of obtaining the required level of safety against failure of aluminium tubing in such applications is corrosion protection by surface modification. This work investigates the effect of surface alloying with zinc on the pitting resistance of heat exchanger tubes.

Pure zinc was applied on flat, thin-walled (≈ 400 µm) multi-port extruded Al-Mn alloy tubes by thermal arc spraying immediately after extrusion, resulting in a sub-micron thick metallic Zn layer on the surface. The tubes were subsequently heat treated to obtain various Zn-rich diffusion layers ranging up to about 70 µm into the alloy substrate. Zn depth profiles were determined by glow discharge optical emission spectroscopy (GD-OES). Corrosion testing was performed by exposure to a cyclic acidified (pH 3) synthetic seawater fog test (ASTM G85 annex A3), normally referred to as the SWAAT test. Open circuit potentials were measured on separate samples as a function of time during immersion in the SWAAT solution at 25 °C. The extent of corrosion as a function of time was determined by weight loss on samples retrieved from the salt spray cabinet at predetermined time intervals for a period of up to eight weeks. The maximum pit depth on each sample was measured by use of a light microscope with a micrometre focusing dial. Ten replicate samples (each 25 mm x 100 mm in size) for each substrate/coating combination were tested, allowing analysis of the maximum pit depth data from extreme value probability plots.

The open circuit potential of the Zn diffusion coated samples in artificial seawater solution was about -0.95 V (SCE), shifting only 10 mV in positive direction during 24 h of immersion. The corrosion potential of the Al-Mn alloy substrate remained constant at -0.74 V (SCE) under similar conditions. The cathodic protection provided by the Zn-rich diffusion layers effectively protected the Al-Mn alloy tubes against formation of deep pits during SWAAT testing. No pits deeper than about 50 µm had formed on the Zn diffusion coated samples after eight weeks of exposure, whereas pit depths exceeding 200 µm was observed on uncoated reference samples already after two weeks. However, weight loss measurements showed that the (uniform) corrosion rate of the anodic Zn-rich diffusion layer was nearly two orders of magnitude higher than that of the Al-Mn alloy substrate under the aggressive low pH conditions prevailing during SWAAT exposure. The results suggest that a lower Zn load than that realizable by thermal arc spraying is required to obtain optimal Zn diffusion profiles in terms of service life of the heat exchanger tubing.
Effectiveness of a TCP Conversion Coating at Inhibitiung Corrosion on AA2024-T3 during so2 Atmospheric Testing
Authors: Swain Greg M , Whitman Brandon
Published: February 2020

Trivalent chromium process conversion coatings are being investigated as alternates for commonly used chromate conversion coatings on aerospace aluminum allloys. In our studies, the TCP coating is formed by immersion on a polished, degreased and deoxidized specimen. The ca. 100 nm-thick biphasic coating consists of a hydrated ZrO2 layer that is about 50 nm thick with an Al-O-F interfacial layer that is also approximately 50 nm thick. Cr(OH)3 is co-deposited within the hydrated ZrO2 layer at less than 5 at. %. There is a need to better understand the mechanisms by which these coatings inhibit corrosion on these alloys and how well the coatings perform during different accelerated degradation tests. In this presentation, we will report on the formation, chemical composition and electrochemical properties of one commercial TCP coating (Bonderite T5900) on AA2024-T3. The corrosion inhibition provided by the coating depends on the coating bath formulation as well as the physicochemical properties (roughness and elemental composition) of the aluminum alloy after degreasing and deoxidation. The coating provides both anodic and cathodic protection by serving as a barrier layer. In terms of the cathodic inhibition, the kinetics of the oxygen reduction reaction are reduced because the coating functions as a diffusional barrier and coating species chemisorb on Cu intermetallic sites to block O2 chemisorption.  In this presentation, we will report on the electrochemical characterization of coated and uncoated AA2024-T3 before and after exposure to a 14-day SO2 atmospheric corrosion test (ASTM G87). SEM and EDXS, optical and stylus surface profilometry and weight loss measurements were used to assess the coating peformance. The results show that the TCP coating is stable on the alloy surface during exposure to the SO2/H2O environment and significantly reduces the corrosion damage and metal loss as compared to the uncoated controls.
(Invited) Terawatt Solar Photovoltaics: Roadblocks and Our Approaches
Authors: Tao Meng , Sun Wen-Cheng , Huang Wen-Hsi , Wang Laidong , Azzolini Joseph A , Tracy Clarence J
Published: February 2020

The global energy demands are predicted to reach 46 terawatts by 2100. Solar photovoltaics has to be deployed at a scale of tens of peak terawatts in order to meet a meaningful portion of the demands. The enormous scale required creates a number of roadblocks for photovoltaic technologies, which are unprecedented in other semiconductor technologies. Some of the roadblocks include scarce raw materials in today’s solar cells, high energy input for silicon cells, recyclability of solar cells/modules, storage of intermittent solar electricity, and high production/installation costs for solar cells/modules. In this talk, we will present an analysis, as quantitative as possible, on some of these roadblocks under the best scenarios, i.e. the maximum possible wattage from each of the current commercial cell technologies. Without significant technological breakthroughs, these cell technologies combined would not be able to make a noticeable impact on our energy mix or carbon emission. Several strategic R&D directions are identified for a scalable and sustainable solar photovoltaic technology.

The second part of the talk will provide an overview of the research portfolio in the Laboratory for Terawatt Photovoltaics at Arizona State University. Several current research projects are highlighted including a zinc/zinc oxide loop for terawatt-scale storage of solar electricity, silver-free all-aluminum terawatt-capable silicon solar cells, electrorefining of metallurgical-grade silicon for solar-grade silicon, value-added recycling of silicon cells/modules, module standardization through cell efficiency uniformization, and smart load management in solar photovoltaic systems.
Efficiency Potential of Future Generation Solar Cells
Authors: Yamaguchi Masafumi , Lee Kan-Hua , Araki Kenji , Nakamura Kyotaro , Kojima Nobuaki , Ohshita Yoshio
Published: February 2020

Various solar cells and materials have great potential as future generation solar cells and materials including crystalline Si. Si tandem solar cells such as III-V/Si tandem, II-VI/Si tandem, Chalcopyrite/Si tandem and Perovskite/Si tandem solar cells are expected to have great potential of space and terrestrial application because of high efficiency, light weight and low cost potential. Quantum and Nano structures such as MQWs ‘(Multi Quantum Wells) and QDs (Quantum Dots) are also expected as high-efficiency solar cells. However, there are some problems to be solved. Because point defects in crystalline Si, high density of dislocations and interface recombination in Si tandem solar cell materials and interface recombination in MQWs and QDs affect on solar cell properties, understanding and controlling those defects are very important for realizing higher efficiency. This paper presents analytical results for high efficiency potential of single crystalline Si solar cells, Si tandem solar cells, and MQW and QD solar cells. Although 25.6% efficiency has been attained with hetero-junction and back contact structure and by using bulk minority-carrier lifetime of around 10 msec, high efficiency of more than 27.5% is expected to be realized by increasing bulk lifetime of more than 100 msec Si. Really, high bulk lifetime of around 100 msec has been obtained by the MCZ (Magnetic-field-applied Czochralski) method and decreasing carbon concentration to less than 1014 cm-3 in Si. Understanding behavior of point defects such as Cs-Oi and so forth in Si and decreasing those defects density are suggested for realizing higher bulk lifetime and higher efficiency Si solar cells of more than 27.5%. High efficiency potential of Si tandem solar cells such as III-V/Si tandem, II-VI/Si tandem, Chalcopyrite/Si tandem and Perovskite/Si tandem solar cells is also analyzed by using measure of external radiative efficiency: 43% for III-V/Si 3-J(Junction) tandem, 38% for III-V/Si 2-J tandem, 33% for II-V/Si 2-J tandem, 32% for Chalcopyrite/Si tandem, and 32% for Perovskite/Si tandem solar cells. Effects of dislocations upon minority-carrier lifetime in III-V/Si tandem solar cells are also presented. Our recent result for mechanically stacked InGaP/GaAs//Si 3-junction tandem solar cell with efficiency of 27.4% is shown. Although MQW and QD solar cells are expected as high efficiency solar cells, one of big problems is higher interface recombination near MQWs and QDs because of their lattice mismatching. Lattice mismatch (Δa/a0) dependence of interface recombination velocity (SI) in MQW and QD solar cells is analyzed. Open-circuit voltage drop by interface recombination in

MQWs and QDs and their efficiency potential is discussed.
High-Efficiency Dye-Sensitized Solar Cells with Molecular Copper Phenanthroline As Solid Hole Conductor
Authors: Freitag Marina , Pazoki Meysam , Sveinbjörnsson Kári , Zhang Jinbao , Daniel Quentin , Sun Licheng , Boschloo Gerrit , Hagfeldt Anders
Published: February 2020

Until recently, there have been no viable alternatives for Spiro-OMeTAD as a hole-transport material (HTM) for dye-sensitized solar cells (DSSC).1 In this study we show that copper phenanthroline complexes in the solid phase can act as efficient molecular hole conductors in DSSCs. Normally, DSSCs utilize a liquid redox electrolyte, but there are significant advantages in replacing it by a solid state hole transport material (HTM): The use of an HTM prevents dye desorption, electrolyte leakage and evaporation problems, as well as making series connection between cells much easier.2 The photovoltaic performance of solid state-DSSCs is, however, usually much lower than its liquid counterparts.3 Here we present a new HTM alternative: bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) (Cu(dmp)2). This copper complex has a straightforward synthetic route from low cost starting materials.

We prepared solid-state DSSCs with the organic dye LEG44 and Cu(dmp)2 as HTM with a power conversion efficiency of 8.2% under 1000 W m-2AM1.5G illumination, having an open-circuit potential higher than 1.0 V. The successful application of a copper complex-based HTM paves the way for low-cost and efficient hybrid solar cells, as well as other optoelectronic devices. This type of material is anticipated to have large impact on current DSC and MSC research.

(1) Bach, U.; Lupo, D.; Comte, P.; Moser, J. E.; Weissortel, F.; Salbeck, J.; Spreitzer, H.; Gratzel, M. Nature
1998, 395, 583.

(2) Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H. Chem. Rev.
2010, 110, 6595.

(3) Bai, Y.; Yu, Q.; Cai, N.; Wang, Y.; Zhang, M.; Wang, P. Chem. Commun.
2011, 47, 4376.

(4) Yang, L.; Xu, B.; Bi, D.; Tian, H.; Boschloo, G.; Sun, L.; Hagfeldt, A.; Johansson, E. M. J. J. Am. Chem. Soc.
2013, 135, 7378.

Figure 1
Feasible Strategy Towards Low Temperature Fabrication of Flexible Perovskite Solar Cells
Authors: MA Tingli , Wang Kai
Published: February 2020

Recent years, organic-inorganic halide perovskite is an increasingly popular and promising candidate as a photovoltaic material for third-generation solar cells.Due to their low cost and considerable charge mobility, inorganic n-type semiconductors such as TiO2, ZnO,and SnO2 are strong ESL candidates and have been used extensively to fabricate highly efficient PSCs. Usually, the compact inorganic ESL films are typically prepared in two steps. The first step involves the spin-coating of the precursor colloidal sol on a conductive substrate, and the second step uses high-temperature annealing to eliminate organic components and to achieve comparable crystallinity. Nevertheless, high-temperature annealing increases production cost and energy payback time significantly; more importantly, such a process is unsuitable for the fabrication of flexible PSCs based on plastic substrate. Hence, it is of great significance to exploit some advanced materials or new technologies for the low-temperature fabrication of inorganic Tungsten oxides (WOx) are common oxide semiconductors with high electron mobility and other special electronic properties. In our previous work, we prepared amorphous WOx at 150 °C as ESL material for PSCs.Nevertheless, when pure WOx was used, the inherent charge recombination and Fermi level (which is lower than that of TiO2) prevents the realization of high photovoltage and PCE. In the present study, we report one facile solution route to successfully fabricate inorganic, amorphous, and WOx-based composite ESLs at the extremely low temperature of 70 °C (or even at room temperature) for efficient planar PSCs. Our sample preparation method requires only two processes: the spin-coating of a precursor solution and drying at low temperature. We will present our latest photoelectrochemical performace of these perovskite solar cells.
Direct Observation of Ferroelectricity and Charge Separation Process in CH3NH3PbI3 Perovskite Solar Cell
Authors: Wang Peiqi
Published: February 2020

In recent years, organometallic trihalide perovskites has attracted more and more attention for the application of solar cells. In particular, methylammonium (MA) lead triiodide (CH3NH3PbI3 or MAPbI3) has attracted the most attention and undergoes rapid development since it was first applied as light absorber in mesoscopic solar cells. Up to now, it has been demonstrated that the power conversion efficiency of MAPbI3 based solar cells can reach 20%, which is directly related to the favorable direct band gap, high carrier mobilities and long carrier diffusion length. To further improve the performance of MAPbI3 based solar cell, researchers have been focused on studying the otpical, electronic, and optoelectronic properties of MAPbI3 perovskites extensively. However, there is not a systematic study of its ferroelectric properties and the correlation between its ferroelectricity and its optoelectronic properties.

Here, we report our direct observation of the ferroelectric domain structure in MAPbI3 thin film using piezoresponse force microscope (PFM). A strong evidence of the intrinsic ferroelectricity is that the ferroelectric domain structure has no correlation to its crystal domain structure, as shown in figure 1. Besides, we also observed the characteristic butterfly loop and hysteresis loop from pointwise experiment, to further verify the ferroelectricity. In addition to using PFM, we also directly observed the charge separation process by measuring the surface potential with Kelvin probe force microscope (KPFM). Under laser illumination when the charge carriers are generated, the surface potential will either decrease or increase depending on the device structure (p-i-n or n-i-p), which can be probed with KPFM and correlated with the surface topography as well. Our preliminary study shows that with AFM’s capability of localized probing, both the ferroelectric property and the optoelectronic properties can be measured and correlated to the structure, which can help us better understand the role of ferroelectricity in the high performance of organometallic trihalide perovskites.

Figure 1
Temperature-Dependent Device Characterization of Perovskite Solar Cells Prepared By Different Synthesis Methods
Authors: Kim Daehan , Pae Seongryul , Lee YunSeog , Gunawan Oki , Shin Byungha
Published: February 2020

While a number of synthesis methods have been reported to prepare perovskite solar cells with good device performance, it has not been well studied how they affect the properties of perovskite layers and devices. Here we report on temperature-dependent device characterizations of perovksite solar cells prepared by different synthesis methods. Solar cells with perovkiste absorbers with compact thin film-like morphology are prepared by both one-step and two-step processes, which exhibit comparable efficiencies at room temperature. However, temperature-dependence of device parameters is markedly different between the devices prepared by one-step and two-step processes. The two-step processed sample exhibits the significant collapse of efficiency as temperature is reduced below 300K because of diverging series resistance of the device, but the efficiency recovers as temperature is raised back to 300K. Once the device is heated to 340K, the device suffers from irreversible degradation. By contrast, the one-step processed sample shows a much milder degradation of efficiency at low temperatures and does not experience the irreversible damage at ~340K. We will discuss possible reasons behind the different temperature-dependence of the perovskite devices. Additionally, comparison of different device architectures—standard vs. inverted—focusing on electrical characterization is studied and it reveals that transport of electrons, but not holes, is what limits a total collected photocurrent. Details of the comparison will be presented.
First-Principles Study of Ion Diffusions in CH3NH3PbI3 and (NH2)2CHPbI3 for Perovskite Solar Cells
Authors: Haruyama Jun , Sodeyama Keitaro , Han Liyuan , Tateyama Yoshitaka
Published: February 2020

Perovskite solar cells (PSCs), which photo-absorbing layer consists of organometal halide perovskites, have gotten much attention because of their rapidly increasing power conversion efficiencies (3.8% in 2009, but nowadays over 22% cell has appeared). [1, 2] Especially, lead halide perovskites such as CH3NH3PbI3 (MAPbI3) and (NH2)2CHPbI3 (FAPbI3) show remarkable properties for solar cell applications, e.g. high optical absorption coefficients and long diffusion lengths of both charge carriers. However, the current−voltage (J−V) curve of PSCs often depends on voltage sweep rates and sweep directions, [3, 4] which make the evaluation of conversion efficiency difficult. Recently, the rate-dependent J−V hysteresis, which is due to a slow process continued about seconds, was attributed to ionic diffusions in MAPbI3. [5]

In this study, we calculated activation barriers of ion diffusions in tetragonal MAPbI3 and trigonal FAPbI3 by first-principles calculations. The vacancy migrations of I− anions in both perovskites show low barriers of 0.3 to 0.45 eV, which values indicate that MAPbI3 and FAPbI3 are ion conductors. Furthermore, MA+ and FA+ cations have rather low barriers c.a. 0.6 eV. The results strongly suggest that the not only anions but also molecular cations can migrate in the perovskites when a bias voltage is applied. Based on the dilute diffusion theory, we can expect that small vacancy concentrations suppress these ion conductions. In addition, we suggest that replacement of MA molecule with larger one is also able to reduce MA migrations and to prevent the degradation of PSC photo absorbers. [6]

[1] A. Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, J. Am. Chem. Soc., 131, 6050 (2009).

[2] Best Research-Cell Efficiencies, National Renewable Energy Laboratory. http://www.nrel.gov/ncpv/images/efficiency_chart.jpg

[3] A. Dualeh, T. Moehl, N. Tétreault, J. Teuscher, P. Gao, M. K. Nazeeruddin, M. Grätzel, ACS Nano, 8, 362 (2014).

[4] H. J. Snaith, A. Abate, J. M. Ball, G. E. Eperon, T. Leijtens, N. K. Noel, S. D. Stranks, J. T.-W. Wang, K. Wojciechowski, W. Zhang, J. Phys. Chem. Lett., 5, 1511 (2014).

[5] W. Tress, N. Marinova, T. Moehl, S. M. Zakeeruddin, M. K. Nazeeruddin, M. Grätzel, Energy Environ. Sci., 8, 995 (2015).

[6] J. Haruyama, K. Sodeyama, L. Han, and Y. Tateyama, J. Am. Chem. Soc., 137, 10048 (2015).
(Invited) Resistive Switching in Mott Insulators: From Fundamentals to Mott Memories
Authors: Tranchant Julien , Janod Etienne , Corraze Benoit , Querré Madec , Besland Marie-Paule , Cario Laurent
Published: February 2020

The application of short electrical pulses on narrow gap Mott insulators gives rise to a new phenomenon of resistive switching. This transition is volatile above threshold electric fields of a few kV/cm and stabilizes into a non-volatile RS for higher electric fields. Our works have shown that this phenomenon is driven by the electric field, which triggers an electronic avalanche [1]. This avalanche provokes the collapse of the Mott insulating state at the nanoscale [2] and generates the formation of granular conductive filaments. The resulting non-volatile transition is reversible and these materials have the ability to switch back and forth between two resistance states with possible intermediate levels. This phenomenology was first evidenced on the family of chalcogenide compounds AM4Q8 (A=Ga,Ge; M=V,Nb,Ta,Mo; Q=S,Se), either on single crystals or on thin films [3]. We have recently demonstrated that these properties are actually universal to all canonical Mott insulators such as (V1-xCrx)2O3 or NiS2-xSex [4]. In the V2O3:Cr system, these new results indicate that, beyond temperature for V2O3 and pressure for (V1-xCrx)2O3, a third tuning parameter, electric field E, is prone to induce an reversible Insulator to Metal transition. This is particularly interesting since these E-induced transitions can occur at room temperature and are hence suitable for applications. Our last results demonstrate that (V1-xCrx)2O3 thin films can be deposited by reactive magnetron co-sputtering [5]. We show that this deposition technique allows controlling the Cr content, oxidation degree and crystallinity after ex-situ annealing. Our last results demonstrate that (V1-xCrx)2O3 thin films can be deposited by reactive magnetron co-sputtering [5]. We show that this deposition technique allows controlling the Cr content, oxidation degree and crystallinity after ex-situ annealing. Our first results on metal-insulator-metal (MIM) devices show that we retrieve the electric-field-induced resistive switching on these TiN/(V1-xCrx)2O3/TiN symmetric ReRAM cells. The characterization of these Mott memory single cells demonstrate very competitive performances which place narrow gap Mott insulators as promising candidates for ReRAM and memristor applications [6].

[1] V. Guiot et al., Nat. Commun.
2013, 4, 1722

[2] V. Dubost et al., Nano Lett.
2013,13, 3648

[3] V. Ta Phuoc et al., Phys. Rev. Lett.
2013, 110, 037401 ; A. Camjayi et al., Phys. Rev. Lett.
2014, 113, 086404 ; E. Souchier et al., Phys. Stat. solidi-RRL 2011, 5, 53 ; J. Tranchant et al., Thin Solid Films
2013, 533, 61

[4] P. Stoliar et al., Adv. Mater.
2013, 25, 3222 ; E. Janod et al., Adv. Funct. Mater. 2015, 25(40), 6287

[5] M. Querré et al., Thin Solid Films 2015, doi: 10.1016/j.tsf.2015.12.043

[6] L. Cario et al. – Patent PCT/EP2008/052968 ; M.P. Besland et al. – Patent PCT/EP2010/053442; L. Cario et al. – Patent PCT/EP2013/057500.
Evaluating Resistive Memory Devices for Neuromorphic Computing Using Ultrashort Voltage Pulses
Authors: Jacobs-Gedrim Robin Bay , Hughart David R. , Agarwal Sapan , Finnegan Patrick Sean , Goeke Ronald S. , Van Heukelom Michael , Nowlin Joshua , Wagner Jamison , James Conrad D. , Marinella Matthew J.
Published: February 2020

A special purpose neural algorithm accelerator based on resistive memory could potentially reduce the energy requirements of neural algorithm implementation by six orders of magnitude over conventional general purpose GPU/CPU hardware (1). The device requirements for such a neural algorithm accelerator depend on attributes including write variability, write linearity, and read noise, as described in reference (2). Devices with multiple resistance states accessible via symmetric voltage pulses of constant magnitude are highly desired for neuromorphic hardware implementations. Tantalum oxide resistive memory devices have been previously shown to have low energy requirements and better control of conductivity during switching in the ultrashort time domain (3). We will report on how employing voltage pulses with ultrashort pulse widths allow for finer control of tantalum oxide based device conductance change per pulse (ΔG/G) unlocking additional neuromorphic states. A parameter space of pulse voltage and time is used to elucidate switching kinetics and switching energy expenditure during device operation. Lastly, the performance of several different resistive memory device structures will be comparatively evaluated for suitability in implementing a neural algorithm accelerator.

This work was supported by Sandia National Laboratories’ Laboratory Directed Research and Development (LDRD) Program under the Hardware Acceleration of Adaptive Neural Algorithms Grand Challenge. Sandia National Laboratories is a multi-program 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.

REFERENCES:

1. Kadetotad, Deepak, et al. "Parallel architecture with resistive crosspoint array for dictionary learning acceleration." IEEE Journal on Emerging and Selected Topics in Circuits and Systems, 5.2 (2015): 194-204.

2. S. Agarwal, et. al. “Resistive Memory Device Requirements for a Neural Algorithm Accelerator,” International Joint Conference on Neural Networks, (2016)

3. Strachan, John Paul, et al. “Measuring the switching dynamics and energy efficiency of tantalum oxide memristors” Nanotechnology22.50 (2011): 505402.

Figure 1
(Invited) The Challenges and Opportunities in Plasma Etching of Functionally Enhanced Complex Material Systems
Authors: Chen Jack Kun-Chieh , Kim Taeseung , Chang Jane P.
Published: February 2020

The introduction of new and functionally improved materials into silicon based integrated circuits is a major driver to enable the continued down-scaling of circuit density and performance enhancement in analog, logic, and memory devices. Many new materials, such as multiferroics, magnetic materials and phase change materials, are much harder to pattern, thereby posing significant challenges to the design and selection of plasma etching chemistries. While ion milling is effective in patterning some of these functionally improved materials, such as complex magnetic material stacks used in magnetic tunnel junctions, it limits the scalability and integration of devices. These challenges point to the growing needs of identifying and developing viable etch chemicals and processes that are more effective in patterning complex materials and material systems.

In this talk, a generalized approach based on combined thermodynamic assessment and kinetic validation is presented to identify and validate the efficacy of various plasma chemsitries. Specifically, potential reactions between the dominant vapor phase/condensed species at the surface are considered at various temperatures and reactant partial pressures. The volatility of etch product was determined to aid the selection of viable etch chemistry leading to improved etch rate of reactive ion etching process. Based on the thermodynamic screening, viable chemistries are tested experimentally to corroborate the theoretical prediction. Some of the above mentioned material systems such as magnetic materials used in magnetic tunnel junctions are used as examples to demonstrate the broad applicability of this approach.
Self-Aligned Contact Etch Process Optimization with Pulsing Plasma Technology
Authors: Zheng Er-Hu , Zhang Yi-Ying , Zhang Hai-Yang
Published: February 2020

The self-aligned contact (SAC) is a key process in developing the next generation ultra-large scale integrated (ULSI) devices because its advantage on providing an efficient reduction of active array areas, decreasing the transistor gate features, and alignment margin improvements in photolithography. [1-2] With the transistor gate feature size continuously scaled down, pattern density and aspect ratios continuously increase, conversely. It requires a robust etch process to solve the multiple issues such as nitride hard mask loss loading between trench/hole, nitride shoulder profile, free necking profile. [3] In this work, we examined the impact of various pulsing technologies on the extremely high aspect ratio SAC etch process, including source pulsing/bias pulsing/synchronous pulsing and the hybrid method. Results indicate the introduction of pulsing function could significantly reduce the nitride loss while avoid the contact open. The synchronous pulsing scheme shows its superior capability on improving the trade-off between nitride loss and profile control. Finally we achieved a manufacturable SAC process without any side effect.

References

S. Kim, J. Vac. Sci. Technol. A 23(4), 7(2005).

J. Kim, J.Vac.Scl. Technol. B 20(5), 9(2002)

E.H. Zheng, A study of self-aligned contact etch of NOR flash, China Semiconductor Technology International Conference (2015).