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1156 KiB

Open AccessArticle

Effect of Spark Plasma Sintering on the Structure and Properties of Ti_1−xZr_xNiSn Half-Heusler Alloys

by Ruth A. Downie, Srinivas R. Popuri, Huanpo Ning, Mike J. Reece and Jan-Willem G. Bos

Materials 2014, 7(10), 7093-7104; https://doi.org/10.3390/ma7107093 - 20 Oct 2014

Cited by 23 | Viewed by 7023

Abstract

XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This [...] Read more.

XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This manuscript describes the impact of spark plasma sintering (SPS) on the phase distributions and thermoelectric properties of Ti_0.5Zr_0.5NiSn based half-Heuslers. Rietveld analysis reveals small changes in composition, while measurement of the Seebeck coefficient and electrical resistivities reveals that all SPS treated samples are electron doped compared to the as-prepared samples. The lattice thermal conductivities fall between 4 W·m⁻¹·K⁻¹ at 350 K and 3 W·m⁻¹·K⁻¹ at 740 K. A maximum ZT = 0.7 at 740 K is observed in a sample with nominal Ti_0.5Zr_0.5NiSn composition. Full article

(This article belongs to the Special Issue New Energy Materials)

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3836 KiB

Open AccessArticle

Preparation and Characterization of Li-Ion Graphite Anodes Using Synchrotron Tomography

by Tim Mitsch, Yvonne Krämer, Julian Feinauer, Gerd Gaiselmann, Henning Markötter, Ingo Manke, Andreas Hintennach and Volker Schmidt

Materials 2014, 7(6), 4455-4472; https://doi.org/10.3390/ma7064455 - 12 Jun 2014

Cited by 22 | Viewed by 8244

Abstract

We present an approach for multi-layer preparation to perform microstructure analysis of a Li-ion cell anode active material using synchrotron tomography. All necessary steps, from the disassembly of differently-housed cells (pouch and cylindrical), via selection of interesting layer regions, to the separation of [...] Read more.

We present an approach for multi-layer preparation to perform microstructure analysis of a Li-ion cell anode active material using synchrotron tomography. All necessary steps, from the disassembly of differently-housed cells (pouch and cylindrical), via selection of interesting layer regions, to the separation of the graphite-compound and current collector, are described in detail. The proposed stacking method improves the efficiency of synchrotron tomography by measuring up to ten layers in parallel, without the loss of image resolution nor quality, resulting in a maximization of acquired data. Additionally, we perform an analysis of the obtained 3D volumes by calculating microstructural characteristics, like porosity, tortuosity and specific surface area. Due to a large amount of measurable layers within one stacked sample, differences between aged and pristine material (e.g., significant differences in tortuosity and specific surface area, while porosity remains constant), as well as the homogeneity of the material within one cell could be recognized. Full article

(This article belongs to the Special Issue New Energy Materials)

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527 KiB

Open AccessArticle

Characteristics of the Dye-Sensitized Solar Cells Using TiO₂ Nanotubes Treated with TiCl₄

by Jun Hyuk Yang, Chung Wung Bark, Kyung Hwan Kim and Hyung Wook Choi

Materials 2014, 7(5), 3522-3532; https://doi.org/10.3390/ma7053522 - 5 May 2014

Cited by 66 | Viewed by 9135

Abstract

The replacement of oxide semiconducting TiO₂ nano particles with one dimensional TiO₂ nanotubes (TNTs) has been used for improving the electron transport in the dye-sensitized solar cells (DSSCs). Although use of one dimensional structure provides the enhanced photoelectrical performance, it tends [...] Read more.

The replacement of oxide semiconducting TiO₂ nano particles with one dimensional TiO₂ nanotubes (TNTs) has been used for improving the electron transport in the dye-sensitized solar cells (DSSCs). Although use of one dimensional structure provides the enhanced photoelectrical performance, it tends to reduce the adsorption of dye on the TiO₂ surface due to decrease of surface area. To overcome this problem, we investigate the effects of TiCl₄ treatment on DSSCs which were constructed with composite films made of TiO₂ nanoparticles and TNTs. To find optimum condition of TNTs concentration in TiO₂ composites film, series of DSSCs with different TNTs concentration were made. In this optimum condition (DSSCs with 10 wt% of TNT), the effects of post treatment are compared for different TiCl₄ concentrations. The results show that the DSSCs using a TiCl₄ (90 mM) post treatment shows a maximum conversion efficiency of 7.83% due to effective electron transport and enhanced adsorption of dye on TiO₂ surface. Full article

(This article belongs to the Special Issue New Energy Materials)

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1286 KiB

Open AccessArticle

Structural Properties of Zinc Oxide Nanorods Grown on Al-Doped Zinc Oxide Seed Layer and Their Applications in Dye-Sensitized Solar Cells

by Kyung Ho Kim, Kazuomi Utashiro, Yoshio Abe and Midori Kawamura

Materials 2014, 7(4), 2522-2533; https://doi.org/10.3390/ma7042522 - 28 Mar 2014

Cited by 50 | Viewed by 9895

Abstract

We fabricated zinc oxide (ZnO) nanorods (NRs) with Al-doped ZnO (AZO) seed layers and dye-sensitized solar cells (DSSCs) employed the ZnO NRs between a TiO₂ photoelectrode and a fluorine-doped SnO₂ (FTO) electrode. The growth rate of the NRs was strongly dependent [...] Read more.

We fabricated zinc oxide (ZnO) nanorods (NRs) with Al-doped ZnO (AZO) seed layers and dye-sensitized solar cells (DSSCs) employed the ZnO NRs between a TiO₂ photoelectrode and a fluorine-doped SnO₂ (FTO) electrode. The growth rate of the NRs was strongly dependent on the seed layer conditions, i.e., thickness, Al dopant and annealing temperature. Attaining a large particle size with a high crystallinity of the seed layer was vital to the well-aligned growth of the NRs. However, the growth was less related to the substrate material (glass and FTO coated glass). With optimized ZnO NRs, the DSSCs exhibited remarkably enhanced photovoltaic performance, because of the increase of dye absorption and fast carrier transfer, which, in turn, led to improved efficiency. The cell with the ZnO NRs grown on an AZO seed layer annealed at 350 °C showed a short-circuit current density (J_SC) of 12.56 mA/cm², an open-circuit voltage (V_OC) of 0.70 V, a fill factor (FF) of 0.59 and a power conversion efficiency (PCE, η) of 5.20% under air mass 1.5 global (AM 1.5G) illumination of 100 mW/cm². Full article

(This article belongs to the Special Issue New Energy Materials)

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761 KiB

Open AccessArticle

Effect of the Cu Source on Optical Properties of CuZnO Films Deposited by Ultrasonic Spraying

by Chih-Hung Hsu, Lung-Chien Chen and Xiuyu Zhang

Materials 2014, 7(2), 1261-1270; https://doi.org/10.3390/ma7021261 - 18 Feb 2014

Cited by 29 | Viewed by 7788

Abstract

CuZnO (CZO) films have received considerable attention, owing to their potential applications in semiconductor devices, including gas sensors or solar cells. However, exactly how these films affect the properties of CZO films by using different Cu sources has seldom been investigated. This study [...] Read more.

CuZnO (CZO) films have received considerable attention, owing to their potential applications in semiconductor devices, including gas sensors or solar cells. However, exactly how these films affect the properties of CZO films by using different Cu sources has seldom been investigated. This study demonstrates the feasibility of preparing CZO films by using different Cu sources via a simple ultrasonic spray method, in which copper nitrate and copper acetate were used as copper sources. Optical properties of CZO films prepared by copper nitrate and copper acetate were also investigated, based on transmittance and photoluminescence measurements. Additionally, the composition and the morphology of the films were investigated using the X-ray diffraction analysis and field emission scanning electron microscopy. The results of this study demonstrate that the CZO films prepared by using copper acetate exhibit better optical properties. Full article

(This article belongs to the Special Issue New Energy Materials)

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Review

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3268 KiB

Open AccessReview

Review on Polymers for Thermoelectric Applications

by Mario Culebras, Clara M. Gómez and Andrés Cantarero

Materials 2014, 7(9), 6701-6732; https://doi.org/10.3390/ma7096701 - 18 Sep 2014

Cited by 192 | Viewed by 18580

Abstract

In this review, we report the state-of-the-art of polymers in thermoelectricity. Classically, a number of inorganic compounds have been considered as the best thermoelectric materials. Since the prediction of the improvement of the figure of merit by means of electronic confinement in 1993, [...] Read more.

In this review, we report the state-of-the-art of polymers in thermoelectricity. Classically, a number of inorganic compounds have been considered as the best thermoelectric materials. Since the prediction of the improvement of the figure of merit by means of electronic confinement in 1993, it has been improved by a factor of 3–4. In the mean time, organic materials, in particular intrinsically conducting polymers, had been considered as competitors of classical thermoelectrics, since their figure of merit has been improved several orders of magnitude in the last few years. We review here the evolution of the figure of merit or the power factor during the last years, and the best candidates to compete with inorganic materials. We also outline the best polymers to substitute classical thermoelectric materials and the advantages they present in comparison with inorganic systems. Full article

(This article belongs to the Special Issue New Energy Materials)

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1020 KiB

Open AccessReview

Donor-Acceptor Block Copolymers: Synthesis and Solar Cell Applications

by Kazuhiro Nakabayashi and Hideharu Mori

Materials 2014, 7(4), 3274-3290; https://doi.org/10.3390/ma7043274 - 22 Apr 2014

Cited by 38 | Viewed by 10689

Abstract

Fullerene derivatives have been widely used for conventional acceptor materials in organic photovoltaics (OPVs) because of their high electron mobility. However, there are also considerable drawbacks for use in OPVs, such as negligible light absorption in the visible-near-IR regions, less compatibility with donor [...] Read more.

Fullerene derivatives have been widely used for conventional acceptor materials in organic photovoltaics (OPVs) because of their high electron mobility. However, there are also considerable drawbacks for use in OPVs, such as negligible light absorption in the visible-near-IR regions, less compatibility with donor polymeric materials and high cost for synthesis and purification. Therefore, the investigation of non-fullerene acceptor materials that can potentially replace fullerene derivatives in OPVs is increasingly necessary, which gives rise to the possibility of fabricating all-polymer (polymer/polymer) solar cells that can deliver higher performance and that are potentially cheaper than fullerene-based OPVs. Recently, considerable attention has been paid to donor-acceptor (D-A) block copolymers, because of their promising applications as fullerene alternative materials in all-polymer solar cells. However, the synthesis of D-A block copolymers is still a challenge, and therefore, the establishment of an efficient synthetic method is now essential. This review highlights the recent advances in D-A block copolymers synthesis and their applications in all-polymer solar cells. Full article

(This article belongs to the Special Issue New Energy Materials)

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480 KiB

Open AccessReview

Bismuth Telluride and Its Alloys as Materials for Thermoelectric Generation

by H. Julian Goldsmid

Materials 2014, 7(4), 2577-2592; https://doi.org/10.3390/ma7042577 - 28 Mar 2014

Cited by 466 | Viewed by 21643

Abstract

Bismuth telluride and its alloys are widely used as materials for thermoelectric refrigeration. They are also the best materials for use in thermoelectric generators when the temperature of the heat source is moderate. The dimensionless figure of merit, ZT, usually rises with [...] Read more.

Bismuth telluride and its alloys are widely used as materials for thermoelectric refrigeration. They are also the best materials for use in thermoelectric generators when the temperature of the heat source is moderate. The dimensionless figure of merit, ZT, usually rises with temperature, as long as there is only one type of charge carrier. Eventually, though, minority carrier conduction becomes significant and ZT decreases above a certain temperature. There is also the possibility of chemical decomposition due to the vaporization of tellurium. Here we discuss the likely temperature dependence of the thermoelectric parameters and the means by which the composition may be optimized for applications above room temperature. The results of these theoretical predictions are compared with the observed properties of bismuth telluride-based thermoelements at elevated temperatures. Compositional changes are suggested for materials that are destined for generator modules. Full article

(This article belongs to the Special Issue New Energy Materials)

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