Search results for "merit"
showing 10 items of 135 documents
Effects of Masking on Open-Circuit Voltage and Fill Factor in Solar Cells
2019
Guidelines for the correct measurement protocol of novel photovoltaic technologies such as perovskites are becoming more frequent in literature. This because, as will be confirmed in this perspective, it is not straightforward to correctly measure the efficiency parameters of these and many other novel solar cells. This is particularly the case for small area research devices which are prone to overestimate the short circuit current density, due to edge effects of various types. To reduce the inaccuracy of current density determination, the common recommended practice is to utilize masks with well‐defined apertures, often smaller than the device active area. Herein we show both experimental…
Towards higher zT in early transition metal oxides: optimizing the charge carrier concentration of the WO3-x compounds
2018
Abstract Thermoelectric devices are believed to play an important role in the energy research for the next decades. Thanks to their low costs coupled with high stability and sustainability, metal oxides are very promising materials even if their efficiencies still need improvements to ensure a wide applicability. Slightly reduced early transition metal oxides show intrinsic defects in the crystal structure which guarantee very low values of the thermal conductivity. The challenge to fulfil the “phonon-glass electron-crystal” concept is to decouple the optimization of the electronic properties from the thermal transport properties. In this contribution we report the optimization of the charg…
Enhanced thermoelectric properties of lightly Nb doped SrTiO3 thin films
2021
Novel thermoelectric materials developed for operation at room temperature must have similar or better performance along with being as ecofriendly as those commercially used, e.g., BiTe, in terms of their toxicity and cost. In this work, we present an in-depth study of the thermoelectric properties of epitaxial Nb-doped strontium titanate (SrTiNbO) thin films as a function of (i) doping concentration, (ii) film thickness and (iii) substrate type. The excellent crystal quality was confirmed by high resolution transmission electron microscopy and X-ray diffraction analysis. The thermoelectric properties were measured by the three-omega method (thermal conductivity) and van der Pauw method (el…
Thermoelectric properties of Sr_3GaSb_3 – a chain-forming Zintl compound
2012
Inspired by the promising thermoelectric properties in the Zintl compounds Ca_3AlSb_3 and Ca_5Al_2Sb_6, we investigate here the closely related compound Sr_3GaSb_3. Although the crystal structure of Sr_3GaSb_3 contains infinite chains of corner-linked tetrahedra, in common with Ca_3AlSb_3 and Ca_5Al_2Sb_6, it has twice as many atoms per unit cell (N = 56). This contributes to the exceptionally low lattice thermal conductivity (κ_L = 0.45 W m^(−1) K^(−1) at 1000 K) observed in Sr_3GaSb_3 samples synthesized for this study by ball milling followed by hot pressing. High temperature transport measurements reveal that Sr_3GaSb_3 is a nondegenerate semiconductor (consistent with Zintl charge-coun…
Tailoring of the electrical and thermal properties using ultra-short period non-symmetric superlattices
2016
Thermoelectric modules based on half-Heusler compounds offer a cheap and clean way to create eco-friendly electrical energy from waste heat. Here we study the impact of the period composition on the electrical and thermal properties in non-symmetric superlattices, where the ratio of components varies according to (TiNiSn)���:(HfNiSn)���������, and 0 ��� n ��� 6 unit cells. The thermal conductivity (��) showed a strong dependence on the material content achieving a minimum value for n = 3, whereas the highest value of the figure of merit ZT was achieved for n = 4. The measured �� can be well modeled using non-symmetric strain relaxation applied to the model of the series of thermal resistanc…
Optimization of the carrier concentration in phase-separated half-Heusler compounds
2014
Inspired by the promising thermoelectric properties of phase-separated half-Heusler materials, we investigated the influence of electron doping in the n-type Ti_(0.3−x)Zr_(0.35)Hf_(0.35)NiSn compound. The addition of Nb to this compound led to a significant increase in its electrical conductivity, and shifted the maximum Seebeck coefficient to higher temperatures owing to the suppression of intrinsic carriers. This resulted in an enhancement of both the power factor α^2σ and figure of merit, zT. The applicability of an average effective mass model revealed the optimized electron properties for samples containing Nb. There is evidence in the literature that the average effective mass model i…
Novel plasmonic sensor design using plasmon-induced transparency
2010
We introduce a novel sensor concept in the field of plasmonics, namely plasmon-induced transparency sensors. These sensors combine localized particle plasmon resonances with extremely small sensing volume with excellent sharp spectral resonances that show a good respose to refractive index changes of the surrounding environment. The principle is based on the plasmonic analog of electromagnetically induced transparency (EIT) between a radiative dipole and a nonradiative quadrupole antenna. This effect yields a spectrally narrow resonance within a broad localized particle plasmon resonance in the near-infrared spectral region [1, 2]. Using deposition of biotin and streptavidin, we demonstrate…
Charge carrier concentration optimization of thermoelectric p-type half-Heusler compounds
2015
The carrier concentration in the p-type half-Heusler compound Ti0.3Zr0.35Hf0.35CoSb1−xSnx was optimized, which is a fundamental approach to enhance the performance of thermoelectric materials. The optimum carrier concentration is reached with a substitution level x = 0.15 of Sn, which yields the maximum power factor, 2.69 × 10−3 W m−1 K−2, and the maximum ZT = 0.8. This is an enhancement of about 40% in the power factor and the figure of merit compared to samples with x = 0.2. To achieve low thermal conductivities in half-Heusler compounds, intrinsic phase separation is an important key point. The present work addresses the influence of different preparation procedures on the quality and re…
Engineering the crack path in lattice cellular materials through bio-inspired micro-structural alterations
2019
Abstract A computational study on the fracture behaviour of bio-inspired finite-size lattice configurations is performed in this work. The study draws inspiration from recent investigations aimed at increasing the fracture energy of some materials through small modifications of their microstructure. The main question here is whether it is possible, to some extent, to engineer the crack path in metallic cellular materials through such small micro-structural modifications and how to quantify the effect of alternative strategies. Nature provides several examples of strategies used to delay or arrest damage and crack propagation. One striking example is given by the micro-architecture of severa…
Thermoelectric properties of p-type Bi2Sr2Co2O9 glass-ceramics
2014
In the oxide system of Bi–Sr–Co glass melts have been prepared by adding a small amount of glass formers. A crystallization leads to crystalline phases of Bi8Sr8Co4O25, BiSrCo2Ox and Bi2Sr2Co2O9 (BC-222) densely embedded into a residual glass phase. This work shows the possibility of obtaining microstructured bulk material with low thermal conductivity and relatively high electrical conductivity via such a glass ceramic approach. Furthermore the stability of these materials under thermal cycling for temperatures up to 700 °C is shown. A characterization of the thermoelectric properties leads to a figure of merit (ZT) between 0.008 and 0.018.