Modulation in Electric Conduction of PVK and Ferrocene-Doped PVK Thin Films

In this article, the dielectric properties of poly (9-vinylcarbazole) (PVK) and ferrocene-doped PVK thin films are studied. The thin films were grown by the isothermal solution casting technique. Dielectric properties of grown films were studied as function of ferrocene concentration, frequency, and temperature. The relative permittivity (ε′) is increased with increasing ferrocene percentage (~1%) due to the free charge carriers. The relative permittivity decreases for higher ferrocene percentage (~2%). However, the relative permittivity of PVK and ferrocene-doped PVK samples remains almost constant for studied temperature range (313–413 K). The frequency dependence of tan δ for all samples is studied. The frequency dependence of dielectric parameter exhibits frequency dispersion behavior, which suggests all types of polarization present in the lower frequency range. The loss tangent (tanδ) values are larger at higher temperatures in the low frequency region. However, the tan δ values at different temperatures are almost similar in the high frequency region. It is observed that the relative permittivity is maximum, dielectric loss is minimum, and AC conductivity is minimum for 1% ferrocene doped PVK as compared to pure PVK and 2% ferrocene doped PVK samples.

Synthesis and Physical Properties of Iridium-Based Sulfide Ca1−xIr4S6(S2) [x = 0.23–0.33]

We present the synthesis and characterization of the iridium-based sulfide Ca1−xIr4S6(S2). Quality and phase analysis were conducted by means of energy-dispersive X-ray spectroscopy (EDXS) and powder X-ray diffraction (XRD) techniques. Structure analysis reveals a monoclinic symmetry with the space group C 1 2/m 1 (No. 12), with the lattice constants a = 15.030 (3) Å, b = 3.5747 (5) Å and c = 10.4572 (18) Å. Both X-ray diffraction and EDXS suggest an off-stoichiometry of calcium, leading to the empirical composition Ca1−xIr4.0S6(S2) [x = 0.23–0.33]. Transport measurements show metallic behavior of the compound in the whole range of measured temperatures. Magnetic measurements down to 1.8 K show no long range order, and Curie–Weiss analysis yields θCW = −31.4 K, suggesting that the compound undergoes a magnetic state with short range magnetic correlations. We supplement our study with calculations of the band structure in the framework of the density functional theory.

Defect- and H-Free Stoichiometric Silicon Carbide by Thermal CVD from the Single Source Precursor Trisilacyclohexane

Stoichiometric silicon carbide (SiC) thin films were grown using thermal chemical vapor deposition (TCVD) from the single source precursor 1,3,5-trisilacyclohexane (TSCH) on c-Si (100) substrates within an optimized substrate temperature window ranging from 650 to 850 °C. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analyses revealed that the as-deposited films consisted of a Si-C matrix with a Si:C ratio of ~1:1. FTIR and photoluminescence (PL) spectrometry studies showed that films deposited ≥ 750 °C were defect- and H-free within the detection limit of the techniques used, while ellipsometry measurements yielded an as-grown SiC average refractive index of ~2.7, consistent with the reference value for the 3C-SiC phase. The exceptional quality of the films appears sufficient to overcome limitations associated with structural defects ranging from failure in high voltage, high temperature electronics to 2-D film growth. TSCH, a liquid at room temperature with good structural stability during transport and handling as well as high vapor pressure (~10 torr at 25 °C), provides a viable single source precursor for the growth of stoichiometric SiC without the need for post-deposition thermal treatment.

p-Type Iodine-Doping of Cu3N and Its Conversion to γ-CuI for the Fabrication of γ-CuI/Cu3N p-n Heterojunctions

Cu3N with a cubic crystal structure is obtained in this paper by the sputtering of Cu under N2 followed by annealing under NH3: H2 at 400 °C, after which it was doped with iodine at room temperature resulting into p-type Cu3N with hole densities between 1016 and 1017 cm−3. The Cu3N exhibited distinct maxima in differential transmission at ~2.01 eV and 1.87 eV as shown by ultrafast pump-probe spectroscopy, corresponding to the M and R direct energy band gaps in excellent agreement with density functional theory calculations, suggesting that the band gap is clean and free of mid-gap states. The Cu3N was gradually converted into optically transparent γ-CuI that had a hole density of 4 × 1017 cm−3, mobility of 12 cm2/Vs and room temperature photoluminescence at 3.1 eV corresponding to its direct energy band gap. We describe the fabrication and properties of γ-CuI/TiO2/Cu3N and γ-CuI/Cu3N p-n heterojunctions that exhibited rectifying current-voltage characteristics, but no photogenerated current attributed to indirect recombination via shallow states in Cu3N and/or deep states in the γ-CuI consistent with the short (ps) lifetimes of the photoexcited electrons-holes determined from transient absorption–transmission spectroscopy.

Attaining Low Lattice Thermal Conductivity in Half-Heusler Sublattice Solid Solutions: Which Substitution Site Is Most Effective?

Low thermal conductivity is an important materials property for thermoelectricity. The lattice thermal conductivity (LTC) can be reduced by introducing sublattice disorder through partial isovalent substitution. Yet, large-scale screening of materials has seldom taken this opportunity into account. The present study aims to investigate the effect of partial sublattice substitution on the LTC. The study relies on the temperature-dependent effective potential method based on forces obtained from density functional theory. Solid solutions are simulated within a virtual crystal approximation, and the effect of grain-boundary scattering is also included. This is done to systematically probe the effect of sublattice substitution on the LTC of 122 half-Heusler compounds. It is found that substitution on the three different crystallographic sites leads to a reduction of the LTC that varies significantly both between the sites and between the different compounds. Nevertheless, some common criteria are identified as most efficient for reduction of the LTC: The mass contrast should be large within the parent compound, and substitution should be performed on the heaviest atoms. It is also found that the combined effect of sublattice substitution and grain-boundary scattering can lead to a drastic reduction of the LTC. The lowest LTC of the current set of half-Heusler compounds is around 2 W/Km at 300 K for two of the parent compounds. Four additional compounds can reach similarly low LTC with the combined effect of sublattice disorder and grain boundaries. Two of these four compounds have an intrinsic LTC above ∼15 W/Km, underlining that materials with high intrinsic LTC could still be viable for thermoelectric applications.

Self-Absorption Analysis of Perovskite-Based Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) are considered promising in their application as building-integrated photovoltaics (BIPVs). However, they suffer from low performance, especially in large-area devices. One of the key issues is the self-absorption of the luminophores. In this report, we focus on the study of self-absorption in perovskite-based LSCs. Perovskite nanocrystals (NCs) are emerging luminophores for LSCs. Studying the self-absorption of perovskite NCs is beneficial to understanding fundamental photon transport properties in perovskite-based LSCs. We analyzed and quantified self-absorption properties of perovskite NCs in an LSC with the dimensions of 6 in × 6 in × 1/4 in (152.4 mm × 152.4 mm × 6.35 mm) using three approaches (i.e., limited illumination, laser excitation, and regional measurements). The results showed that a significant number of self-absorption events occurred within a distance of 2 in (50.8 mm), and the photo surface escape due to the repeated self-absorption was the dominant energy loss mechanism.

Effect of Surfactant Addition on Organic Transparent Conductive Films Fabricated by Inkjet Printing Method

Recently, active research has been conducted on the development of flexible electronic devices. Hence, the transparent conductive film (TCF), an essential component of the device, must also be flexible. However, the commonly used indium tin oxide (ITO) TCF lacks flexibility and contains rare metal, making resource depletion an issue. Therefore, we focused on poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS), which has high flexibility and conductivity. Flexible TCFs have been fabricated by coating PEDOT:PSS on polyethylene naphthalate substrates using an inkjet printer. However, the current issue in such fabrication is the effect of the interface state on the transparency and conductivity of the thin film. In this study, we investigated the effect of surfactant in addition to polar solvents on the properties of thin films fabricated with PEDOT:PSS ink. Although the electrical conductivity was reduced, the transmittance remained above 90%. Thus, these results are comparable to those of ITO TCFs for practical use in terms of optical properties.

Batteryless Electronic System Printed on Glass Substrate

Batteryless hybrid printed electronic systems manufactured on glass substrates are reported. The electronic system contains a sensor capable of detecting water, an electrochromic display, conductors, a silicon chip providing the power supply through energy harvesting of electromagnetic radiation, and a silicon-based microcontroller responsible for monitoring the sensor status and the subsequent update of the corresponding display segment. The silicon-based components were assembled on the glass substrate by using a pick and place equipment, while the remainder of the system was manufactured by screen printing. Many printed electronic components, often relying on organic materials, are sensitive to variations in environmental conditions, and the reported system paves the way for the creation of electronic sensor platforms on glass substrates for utilization in see-through applications in harsh conditions. Additionally, this generic hybrid printed electronic sensor system also demonstrates the ability to enable autonomous operation through energy harvesting in future smart window applications.

A Novel Method to Significantly Improve the Mechanical Properties of n-Type Bi(1−x)Sbx Thermoelectrics Due to Plastic Deformation

A unique method was developed to significantly improve the strength of Bi(1−x)Sbx single crystals, the most effective thermoelectric (TE) materials in the temperature range from 100 to 200 K due to their plastic deformation by extrusion. After plastic deformation at room temperature under all-round hydrostatic compression in a liquid medium, n-type Bi–Sb polycrystalline solid solutions show a significant increase in mechanical strength compared to Bi–Sb single crystals in the temperature range from 300 to 80 K. The significantly higher strength of extruded alloys in comparison with Bi–Sb single crystals is associated with the development of numerous grains with a high boundary surface as well as structural defects, such as dislocations, that accumulate at grain boundaries. Significant stability of the structure of extruded samples is achieved due to the uniformity of crystal plastic deformation under all-round hydrostatic compression and the formation of the polycrystalline structure consisting of grains with the orientation of the main crystallographic directions close to the original single crystal. The strengthening of Bi–Sb single crystals after plastic deformation allows for the first time to create workable TE devices that cannot be created on the basis of single crystals that have excellent TE properties, but low strength.

Structural, Electronic, and Optical Properties of p-Type Semiconductors Cu2O and ZnRh2O4: A Self-Consistent Hybrid Functional Investigation

The p-type semiconductors Cu2O and ZnRh2O4 have been under investigation for potential applications as transparent conducting oxides. Here, we re-evaluate their structural, electronic, and optical properties by means of first-principles calculations employing density functional theory and a recently introduced self-consistent hybrid functional approach. Therein, the predefined fraction α of Hartree–Fock exact exchange is determined self-consistently via the inverse of the dielectric constant ε∞. The structural, electronic, and optical properties will be discussed alongside experimental results, with a focus on possible technological applications.