P-type Charge Carriers Research Articles

Theoretical insight into physical characteristics of lead-free perovskites Rb2TlSbX6 (X = Cl, Br, I) for optoelectronic devices.

Novel optoelectronic and thermoelectric properties with broad compositional range, non-toxic nature and structural stability make halide-based double perovskites fascinating for flexible optoelectronic devices. In this work, the structural electronic, optical and transport properties of Rb2TlSbX6 (X = Cl, Br, I) were studied using density functional theory for optoelectronic devices. The elastic analysis demonstrates ductile nature, mechanical stability, anisotropic behaviour and feasibility for flexible optoelectronic devices. The band structure study using Tran-Blaha-modified Becke-Johnson (TB-mBJ) potential shows that all studied materials have direct bandgap. In addition, the bandgap of Rb2TlSbCl6 is more appropriate for optoelectronic devices. The small loss and maximum absorption in visible regions make these materials prime candidates for optoelectronic devices. The transport features indicate that all the studied double perovskites reflect p-type semiconducting behaviour as highlighted by positive Seebeck coefficient values. Furthermore, the high power factor values of Rb2TlSbX6 (X = Cl, Br, I) double perovskites make them suitable for thermoelectric device applications at high temperatures. Based on electronic optical and thermoelectric properties Rb2TlSbCl6 is the best candidate for flexible optoelectronic devices. In this paper, structural optimization of Rb2TlSbX6 (X = Cl, Br, I) double perovskites was conducted utilizing the Wien2k software based on first principle calculations with Perdew-Burke-Ernzerhof's generalized-gradient approximation (PBE-sol approximation). The TB-mBJ potential was employed to compute the accurate band gap of studied materials. The thermoelectric properties are evaluated with BoltzTraP code, showing a predominance of P-type charge carriers in all studied perovskites. This methodological strategy verifies the material's remarkable stability and optical properties and offers a solid framework for examining its potential in optoelectronic devices.

Study of structural, elastic, electronic, optical, magnetic and thermoelectric characteristics of Hexafluoromanganets A2MnF6 (A = Cs, Rb, K) cubic double perovskites

We analyse a detailed investigation of structure, electronic, optical, magnetic and thermoelectric properties of (Cs, Rb, K)2MnF6 double perovskites with cubic Fm3¯m space group. The calculation method was the augmented plane-wave functions plus local orbitals as implemented in the WIEN2k code and the GGA followed by the most accurate GGA-mBJ as exchange potentials. The precision of our K2MnF6, Rb2MnF6 and Cs2MnF6 lattice constant compared with their available experimental data is in the range 1.2 % to 3.6 %. The calculated band gap of K2MnF6, Rb2MnF6 and Cs2MnF6 materials advantages them for use in light-emitting diode technology. These materials exhibit ferromagnetic behavior. The negative formation energy, free Helmholtz energy and the dispersion of phonons confirm their thermal, thermodynamic and dynamic stability. The calculated band gap of K2MnF6, Rb2MnF6 and Cs2MnF6 materials advantages them for use in light-emitting diode technology. The p-type charge carriers, direct band gap, and flat conduction and valence bands make them as good thermoelectric materials. The major contribution to the magnetization comes from the unfilled Mn-3d orbital. The high static dielectric constant reduces the recombination rate of charge carriers and the presence of absorption peaks in the ultraviolet region are advantageous in the exploitation in the optoelectronic field. The flat valence and conduction bands, high p-type conductivity, good thermoelectric parameters, as well as non-toxicity make these compounds mainly attractive in the thermoelectric application.

Facile Doping of 2,2,2-Trifluoroethanol to Single-Walled Carbon Nanotubes Electrodes for Durable Perovskite Solar Cells

Perovskite solar cells with an indium tin oxide (ITO)/SnO2/CH3NH3PbI3/Spiro-OMeTAD/2,2,2-trifluoroethanol (TFE) doped single-walled carbon nanotube (SWCNT) structure were developed by dropping TFE onto SWCNTs, which replaced the metal back electrode, and a conversion efficiency of 14.1% was achieved. Traditionally, acidic doping of the back electrode, SWCNT, has been challenging due to the potential damage it may cause to the perovskite layer. However, TFE has facilitated easy doping of SWCNT as the back electrode. The sheet resistance of the SWCNTs decreased and their ionization potential shifted to deeper levels, resulting in improved hole transport properties with a lower barrier to carrier transport. Furthermore, the Seebeck coefficient (S) increased from 34.5 μV/K to 73.1 μV/K when TFE was dropped instead of EtOH, indicating an enhancement in the behavior of p-type charge carriers. It was observed that hydrophilic substances adhered less to the SWCNT surface, and the formation of PbI2 was suppressed. These effects resulted in higher conversion efficiency and improved solar cell performance. Furthermore, the decrease in conversion efficiency after 260 days was suppressed, showing improved durability. The study suggests that combining SWCNTs and TFEs improves solar cell performance and stability.

Unravelling the structural, electronic, mechanical and thermoelectric properties of half-Heusler alloys NaYX (X = C, Si, Ge, Sn)

We investigate the structural, electronic, and thermoelectric properties of the newly designed half-Heusler (hH) alloys NaYX (X = C, Si, Ge, Sn) using first-principles methods combined with Boltzmann transport theory. Our results indicate that the hH alloys are chemically, mechanically, as well as dynamically stable. The electronic calculations suggest that all the alloys are direct bandgap semiconductor with a bandgap of NaYC (0.52 eV), NaYSi (0.56 eV), NaYGe (0.57 eV) and NaYSn (0.65 eV). The lattice thermal conductivities of the hH alloys are quite low (12-24 W m−1 K−1) at room temperature. The computed figure of merit (ZT) for p-type charge carrier concentration show higher value for NaYC alloy (ZT = 0.57) as compared to NaYSi (ZT = 0.07),NaYGe (ZT = 0.27) and NaYSn (ZT = 0.42) at 1200 K, respectively. Altogether, our results indicate the potential of hH alloys for the high-temperature thermoelectric applications.

Comprehensive first principles to investigate optoelectronic and transport phenomenon of lead-free double perovskites Ba2AsBO6 (B[dbnd]Nb, Ta) compounds

In the current work we studied the structural, elastics, electrical, optical, thermoelectric, as well as spectroscopic limited maximum efficiency (SLME) of oxide based Ba2AsBO6 (BNb, Ta) materials. All the calculations were performed using first-principles calculation by employing the WIEN2k code. We checked the stability in diverse forms such as optimization, phonon dispersion, mechanical, formation energy, cohesive energy, and thermal stability is computed. The semiconducting nature of these Ba2AsBO6 (BNb, Ta) systems is revealed by calculating the direct band gap values are 1.97 eV and 1.49 eV respectively. Additionally, we determined the optical properties which analyze the utmost absorption and transition of carriers versus photon energy (eV). Moreover, Ba2AsNbO6 has an estimated SLME of 32 %, making it an encouraging alternative for single-junction solar cells. Lastly, we studied the transport properties against temperature, the chemical potential for p-type and n-type charge carriers at various temperatures. At 300 K, the zT values are found to be 0.757 and 0.751 for Ba2AsBO6 (BNb, Ta) compounds respectively. Both materials were examined as having strong absorption patterns and an excellent figure of merit (ZT), indicating that materials are appropriate for daily life applications.

Enhanced Thermoelectric Performance in Ca-doped AgSbTe2

Thermoelectric materials play a crucial role in applications such as recovering waste heat and refrigeration. We report a thermoelectric figure of merit (zT) of 1.17 at 623 K for AgSb1-xCaxTe2, representing a 31% enhancement compared to pristine AgSbTe2. The improved thermoelectric performance arises from enhancements in both the power factor and lattice thermal conductivity. Dopant substitution of element Ca at the Sb site in AgSbTe2 suppresses the formation of Ag2Te and increases the concentration of p-type charge carriers, leading to enhanced electrical transport properties. Additionally, Ca doping introduces solid solution point defects that enhance phonon scattering, consequently reducing the lattice thermal conductivity of the sample. This work demonstrates that a doping effectively modulates the electrical and thermal transport properties of AgSbTe2, thereby realizing improvements in thermoelectric performance.

Investigating the physical and optoelectronic characteristics of Co2ZrZ compounds: findings from computational analysis and thermoelectric evaluation.

The study examines the physical characteristics of Co2ZrZ compounds using the Wien2k code and the Anisimov and Gunnarsson approach. Results show metallic attributes in Co2ZrBi and Co2ZrAs, while Co2ZrPb exhibits semi-metallic tendencies. Energy gap evaluations reveal significant infrared transitions, indicating altered electron mobility compensated by increased ultraviolet absorption. These compounds have potential in space solar energy applications due to UV light absorption capabilities, especially in Co2ZrPb. The study also identifies optical phenomena like "super-luminescence" and plasmatic oscillations. The study uses computational techniques like Wien2k calculation code and Hubbard parameter calculations to investigate Co2ZrPb, a compound with potential for space energy applications. Energy gap assessments are conducted using GGA and mBJ-GGA methods. The study also analyzes the optical behavior of the compounds, including infrared and ultraviolet absorption. The BoltzTraP code is used for thermoelectric investigations, revealing a P-type charge carrier predominance in Co2ZrPb. This comprehensive approach provides valuable insights into electrical conductivity and thermoelectric properties.

Vapor growth of V-doped MoS2 monolayers with enhanced B-exciton emission and broad spectral response

Dynamically engineering the optical and electrical properties in two-dimensional (2D) materials is of great significance for designing the related functions and applications. The introduction of foreign-atoms has previously been proven to be a feasible way to tune the band structure and related properties of 3D materials; however, this approach still remains to be explored in 2D materials. Here, we systematically demonstrate the growth of vanadium-doped molybdenum disulfide (V-doped MoS2) monolayers via an alkali metal-assisted chemical vapor deposition method. Scanning transmission electron microscopy demonstrated that V atoms substituted the Mo atoms and became uniformly distributed in the MoS2 monolayers. This was also confirmed by Raman and X-ray photoelectron spectroscopy. Power-dependent photoluminescence spectra clearly revealed the enhanced B-exciton emission characteristics in the V-doped MoS2 monolayers (with low doping concentration). Most importantly, through temperature-dependent study, we observed efficient valley scattering of the B-exciton, greatly enhancing its emission intensity. Carrier transport experiments indicated that typical p-type conduction gradually arisen and was enhanced with increasing V composition in the V-doped MoS2, where a clear n-type behavior transited first to ambipolar and then to lightly p-type charge carrier transport. In addition, visible to infrared wide-band photodetectors based on V-doped MoS2 monolayers (with low doping concentration) were demonstrated. The V-doped MoS2 monolayers with distinct B-exciton emission, enhanced p-type conduction and broad spectral response can provide new platforms for probing new physics and offer novel materials for optoelectronic applications.Graphical abstract

Magnetic and electrical transport properties of Cu0.5Ni0.5Fe2O4 ferrite synthesized by plasma arc discharge process

In this study, the plasma arc discharge process was employed to synthesize nanocrystalline Cu0.5Ni0.5Fe2O4 ferrite powders. A spinel-type ferrite structure has been formed successfully, exhibiting a saturation magnetization of 87 emu g−1 and a coercivity of 26 Oe. The investigation involved studying the frequency and temperature dependence of dielectric permittivity, dielectric loss, and DC/AC conductivity over a broad frequency range (1 kHz–1 MHz) in a temperature range of 298 K–403 K. The highest value of the dielectric contestant (4746) is observed at a frequency of 1 kHz and temperature of 313 K. A maximum in the DC conductivity is observed at 403 K, which can be ascribed to the combined effects of thermally activated hopping and an increase in the concentration of both n-type and p-type charge carriers at higher temperatures.

Thermoelectric behavior of Bi2Te2.55Se0.45 with a tunable seebeck coefficient: A comparison between coarse needle-like structure and bulk nanostructured alloys

In this study, we compare the thermoelectric properties of coarse-grained n-type Bi2Te2.55Se0.45 alloy prepared by induction melting with the bulk-nanostructured prepared by ball milling and hot-pressing techniques. The corresponding thermoelectric properties showed different behavior for each material processed using different routes. The most striking result of the study is observing a p-type behavior and charge carrier transition from p-to n-type for the coarse-grained alloy. These observed phenomena are related mainly to the unique needle-like microstructure accompanied by high lattice strain. Lastly, the obtained figure-of-merit values for the coarse needle-like structure and bulk nanostructured Bi2Te2.55Se0.45 alloys are 0.20 and 0.80 at their optimum temperatures of 60 and 120 °C, respectively.

Crossover from n- to p-Type Charge Carriers in Cr-Substituted Bi2Te3 Single Crystal

Crossover from n- to p-Type Charge Carriers in Cr-Substituted Bi2Te3 Single Crystal

Aharonov-Bohm Interference and Phase-Coherent Surface-State Transport in Topological Insulator Rings.

We present low-temperature magnetotransport measurements on selectively grown Sb2Te3-based topological insulator ring structures. These devices display clear Aharonov-Bohm oscillations in the conductance originating from phase-coherent transport around the ring. The temperature dependence of the oscillation amplitude indicates that the Aharonov-Bohm oscillations originate from ballistic transport along the ring arms. We attribute these oscillations to the topological surface states. Further insight into the phase coherence is gained by comparing with similar Aharonov-Bohm-type oscillations in topological insulator nanoribbons exposed to an axial magnetic field. Here, quasi-ballistic phase-coherent transport is confirmed for closed-loop topological surface states in the transverse direction enclosing the nanoribbon. In contrast, the appearance of universal conductance fluctuations indicates phase-coherent transport in the diffusive regime, which is attributed to bulk carrier transport. Thus, it appears that even in the presence of diffusive p-type charge carriers in Aharonov-Bohm ring structures, phase-coherent quasi-ballistic transport of topological surface states is maintained over long distances.

Effect of Sr-doping on electronic and thermal properties of Pr2-xSrxFeCrO6 (0≤x≤1) oxide materials synthesized by using sol-gel technique

ABSTRACT The thermoelectric properties of a new type of Pr2-xSrxFeCrO6 double perovskite were investigated at higher temperature after its sol-gel synthesis. The XRD results validate the single-phase orthorhombic structure, and the crystallite sizes meet the morphological measurements. XPS examination, which formed the defect sites in these oxides, confirmed the varied oxidation states of constituents. The temperature-dependent electrical conductivity (σ) was poor in the original Pr2FeCrO6 composition, but after substituting Sr on the Pr-site, a significant rise in σ with two semiconductors and one metal transition was observed. A positive Seebeck coefficient confirmed the presence of a p-type charge carrier in the entire composition, and the charge transport mechanism was driven by the SPH model. Thermal conductivity increases in all doped samples, while it decreases in pristine compounds over the broad analyzed temperature range. Thermal expansion coefficient increased after doping in oxygen-deficient compound. The PrSrFeCrO6 compound had the maximum ZT (0.105), which was 3.9 times higher than that of the pristine compound.

Quantum effects in silicon-germanium p-type heterostructures with quantum wells of different widths

The magneto-quantum and quantum interference effects in a two-dimensional gas of p-type charge carriers are studied for three quantum wells made of practically pure germanium in a Si0.6Ge0.4/Si0.2Ge0.8/Si0.6Ge0.4 heterostructure. The quantum well widths were 8 nm for sample I, 19.5 nm for sample II, and 25.6 nm for sample III. The dependences of resistance on the magnetic field for all samples exhibit Shubnikov–de Haas oscillations. Their analysis made it possible to calculate the kinetic characteristics of charge carriers for the cases of one (sample I) and two occupied subbands (samples II and III). In the region of weak magnetic fields (B < 0.1 T), the effect of weak localization of holes was revealed, which determines the negative magnetoresistance and the increase in resistance with decreasing temperature. The manifestation of the charge carriers interaction effect at various temperatures and magnetic fields is discovered and analyzed. A transition from the diffusion mode of manifestation of the quantum correction to the intermediate, and then to the ballistic mode is observed. In all regions, the behavior of the quantum correction due to the charge carriers interaction effect is in good agreement with modern theoretical predictions. The temperature dependences of the hole-phonon relaxation time are calculated. In weak magnetic fields, with an increase in the temperature of the 2D system, a transition from the “partial inelasticity” mode, characterized by the dependence τhph−1∝T2, to the small-angle scattering mode, described by the relation τhph−1∝T5, takes place. In stronger magnetic fields for samples with two occupied subbands, the dependence τhph−1∝T3was observed. Possible explanations for this dependence are presented.

Effect of Ce and Sm doping on optoelectronic and thermoelectric properties of Bi2Te3 alloy

Metallic materials attracted much attention in the field of optoelectronics for several applications such as infrared radiation detection. In present study, electronic, optical and thermoelectric spectra of Sm and Ce co doped Bi2Te3 materials have been studied using density functional theory (DFT) calculations. Electronic study of the studied material indicates metallic and good optical and thermoelectric properties. Optical spectra of the doped Bi2Te3 show that absorption lies in visible and near UV region of the radiation. Thus, it seems to have potential applications in optoelectronics. Thermoelectric properties favor the semiconducting nature with high Seebeck coefficient and dominant character of p-type charge carriers.

Effect of A-site doping on electrical properties of La2-xPrxFeCoO6 double perovskite prepared by sol-gel technique

The present work deals with the synthesis, characterization, and thermoelectric properties of La2-xPrxFeCoO6 (x ​= ​0.0, 0.25, 0.50, 0.75, and 1.0) ceramics. The crystal structure, microstructural characteristics, electrical properties, and thermal transport characteristics of the sintered samples were studied. The samples prepared by sol-gel technique resulted in the presence of nanocrystalline single phase material after 6 ​h of sintering, and the increased crystallite size with increasing Pr concentration alongwith the occurrences of multivalent oxidation states of La, Pr, Fe, Co and O. The conductivity investigation revealed the presence of a nearest neighbor hopping charge carrier conduction mechanism in the entire samples, i.e., an increasing Pr-content result in enhanced conductivity at every examined temperature. For the entire composition range (x), conductivity increases with increasing temperature up to maximum value at a transition temperature followed by a downward trend, indicating the metallic behavior (reduction in semiconducting behavior) due to the presence of oxygen deficiency at higher temperature. Positive S values indicate the presence of p-type charge carrier in La2-xPrxFeCoO6 double perovskite and intrinsic behavior was conserved with increasing doping concentration (x). Temperature dependent power factor increases with increasing Pr-content and the maximum values were observed at their transition temperatures. Within recorded temperature, the highest Figure of Merit (ZT ​= ​∼0.87) was observed at x ​= ​1.0 in La2-xPrxFeCoO6 compound, which was 5.4 times more as compare to x ​= ​0.0.

Investigations of structural, electronic, magnetic, and thermoelectric properties of laves phase intermetallic XZn2(X=Zr/Hf) compound: DFT study

Thermoelectric materials are a good source of sustainable energy. XZn2 (X = Zr/Hf) intermetallic compounds for the utilization of high temperature thermoelectric applications were examined using the Density functional theory (DFT) method. The good source of free electrons present in thelaves phase intermetallic compound are greatly enhanced the electrical conductivity and thermo-power. The first-principles calculation-based density functional theory is used to investigate the structural, electronic, magnetic, and thermoelectric properties of XZn2 (X = Zr/Hf) crystallizes with a face-centered cubic structure and it's a d-band itinerant ferromagnetic compound. High electronic density near the Fermi level in the both compounds confirms the metallic nature of the compounds. Positive Seebeck coefficients for ZrZn2 (∼84 μV/K) and HfZn2 (∼15 μV/K) confirm the presence of P-type charge carriers in the compounds. The power factor for the HfZn2(∼2.16×1010w/mK2s ) compound is relatively high compared to ZrZn2(∼1.22×1010w/mK2s ) at the order of 1200 K.

Exploring the defect equilibrium and charge transport in electrode material La0.5Sr0.5Fe0.9Mo0.1O3-δ.

Perovskite-type La0.5Sr0.5Fe0.9Mo0.1O3-δ synthesized via glycine nitrate combustion and sintered at 1350 °C was found to have an orthorhombic lattice, which transforms upon heating into a rhombohedral and then a cubic one. The oxygen content and electrical conductivity in this oxide were measured in the range of oxygen partial pressures from 10-20 to 0.5 atm at 750-950 °C by coulometric titration and four-probe dc techniques, respectively. The oxygen content data were used to model the defect equilibrium in the oxide. Oxidation, charge disproportionation and electron exchange reactions between iron and molybdenum were assumed by the model to be involved in the formation of defects. The experimental data were well approximated with the model and the concentrations of charge carriers in La0.5Sr0.5Fe0.9Mo0.1O3-δ were determined to be used for the electrical conductivity analysis. The average mobility of oxygen ions and n- and p-type charge carriers was determined to be about 10-5, 0.007, and 0.07 cm2 V-1 s-1 with an activation energy of 0.80 ± 0.02, 0.34 ± 0.01, and 0.23 ± 0.01 eV, respectively. Comparison with La0.5Sr0.5FeO3-δ shows that 10% Mo substitution provides a substantial increase in both the concentration and mobility of n-type carriers, which results in an almost threefold increase in electron conductivity under reducing conditions, while maintaining a high level of ionic conductivity.

Ab-initio investigations for structural, mechanical, optoelectronic, and thermoelectric properties of Ba2SbXO6 (X[dbnd]Nb, Ta) compounds

We report the structural, mechanical, electronic, optical, thermoelectric properties and spectroscopic limited maximum efficiency (SLME) of oxide double perovskite structure Ba2SbNbO6 and Ba2SbTaO6 compounds. All the investigations were performed through the first-principles density functional theory (DFT). The results obtained for the elastic constants affirms the mechanical stability of the studied double perovskite compounds. The calculated data of bulk modulus (B), shear modulus (G), and Young's modulus (E) for Ba2SbTaO6 are found to be greater than those of Ba2SbNbO6. The obtained ratio of Bulk to shear modulus (B/G) shows that Ba2SbNbO6 and Ba2SbTaO6 are ductile in nature and are suitable for the device fabrications. The electronic properties of studied compounds are explained in terms of their energy bands, total and partial density of states. The computed electronic band structure reveals the direct band gap semiconducting nature of both compounds. The energy dependent optical properties such as, dielectric tensor, optical conductivity, absorption, reflectivity, refraction and energy loss for both the studied compounds are investigated and are explained in order to highlight the potential of studied compounds for the photovoltaic applications. In addition to electronic and optical properties, we have also studied the electron relaxation time-dependent thermoelectric properties, such as Seebeck coefficient, electronic thermal conductivity, electrical conductivity, thermoelectric power factor, and the thermoelectric figure of merit as a function of chemical potential at various temperatures for p-type and n-type charge carriers. The high absorption spectra and good thermoelectric figure of merit reveal that both the studied compounds, Ba2SbXO6 (X = Nb, Ta) are promising materials for photovoltaic and thermoelectric applications. The calculated SLME of 26.8% reveals that Ba2SbNbO6 is an appealing candidate for single-junction solar cells.

First-principles calculations of structural, electronic, magnetic, thermoelectric, and thermodynamic properties of BaMn2P2 in the Anti and ferromagnetic phase

The materials that possessing narrow band-gap had got great attention in the field of thermoelectric especially in the field of optoelectronics for a number of applications like as in infrared radiation detection. In this study, thermodynamical, optoelectronic and thermoelectric properties of BaMn2P2 have been studied using density functional theory (DFT) calculations. We did different sides e.g., for the nonmagnetic, antiferromagnetic, and ferromagnetic phase. The antiferromagnetic study directs narrow bandgap (less than 1 ​eV, closed results with the literature value) and upright optoelectronic and thermoelectric properties. Optical spectra display that absorption lies in visible as well as in UV region of the radiation. As a result, it looks to have probable applications in optoelectronics. Thermoelectric properties indulged the semiconducting nature with high Seebeck coefficient and dominant character of p-type charge carriers. Furthermore, we have computed both pressure and temperature-dependent thermodynamic parameters for this compound using quasi-harmonic Debye approximation.