Moderate Doping Research Articles

Performance Evaluation of Modified Zinc-Phthalocyanine Groups as an Active Material in Dye-Sensitized Solar Cells

The increasing demand for energy and electricity and the depletion of fossil fuels are global problems. In recent years, dye-sensitized solar cell (DSSC) technologies have gained notoriety for their application in solar energy. DSSCs are considered a promising alternative renewable energy source to both inorganic and organic photovoltaic (PV) cells. Many types of dyes are being investigated to enhance the light-harvesting properties of DSSCs, but the actual realization of these absorbers in cell structure requires optimum parameters. The main aim of this study was to simulate proposed zinc phthalocyanine (ZnPC)-based structures to validate their design, assess their performance for commercial implementation, and optimize the cell parameters for optimum efficiency. To that end, Scaps-1D was employed to evaluate the performance of DSSCs to determine their optimum parameters. We found that ZnPC and isopropoxy ZnPC molecules outperform others molecules because of better optoelectronic properties. Several other parametric effects, such as photoactive layer thicknesses, doping densities, trap densities, and charge carrier mobilities, were also evaluated to observe their impact on device performance. The results show that moderate thickness, low defect density, moderate doping, and charge carrier mobility are favorable for better device performance due to low recombination losses, electrical losses, and better transport of charge carriers. The utmost power conversion efficiency values found for ZnPC- and ZnPC: PC70BM-based DSSCs after optimization were 9.50% and 9.81%. This paper also suggests a practical method for efficiently using DSSC cells by modifying factors that are significantly reliant on DSSC performance and output.

Study of anode doping and avalanche in foundry compatible 1.2 kV vertical GaN PiN diodes

Foundry compatible vertical GaN PiN diodes were fabricated. The devices investigated in this work are based on 8 um drift layer thickness to achieve ∼1.2 kV of voltage blocking. Three different anode doping levels were fabricated on three wafers with the same p-layer thickness, and planar hybrid edge termination. The moderate anode doping level of 1 × 1018 cm−3 has achieved the highest breakdown voltage of 1.2 kV and its temperature-dependent breakdown behavior proved an avalanche behavior. Furthermore, our electroluminescence displayed the breakdown at the edge of the anode. Our simulation results imply an improvement in the field management with moderate anode doping.

Effect of moderate Fe doping and heat treatment on the microstructure of Ni-Mn-Ga melt-spun ribbons

The present work investigates the effects of Mn substitution with additions of Fe (0.5, 1, 2, and 3 at%) on the crystal structure, phase transformation temperatures, and magnetic properties of casted and heat-treated Ni49.8Mn28.5−xGa21.7Fex magnetic shape memory (MSM) alloys. The alloys doped with 0.5 and 1 at% Fe exhibited single-phase seven-layered modulated (14 M) and five-layered modulated (10 M) martensite structures at ambient temperature, whereas the alloys doped with 2 and 3 at% Fe exhibited L21 Heusler austenite structures at ambient temperature. The Ni49.8Mn27.5Ga21.7Fe1 alloy exhibiting the 10 M crystal structure at ambient temperature was selected for making ribbons using the melt-spinning process. The effects of heat treatment on grain growth, crystal structure, and other functional properties of the melt-spun ribbons were studied. The ribbons heat-treated at 1273 K exhibited a 10 M martensite structure and an average grain size of 220 µm along the ribbon plane. The results show that Ni49.8Mn27.5Ga21.7Fe1 is a particularly promising composition for designing and manufacturing functional MSM micro-actuators.

Nonlinear Plasmonics in Nanostructured Phosphorene.

Phosphorene has emerged as an atomically thin platform for optoelectronics and nanophotonics due to its excellent optical properties and the possibility of actively tuning light-matter interactions through electrical doping. While phosphorene is a two-dimensional semiconductor, plasmon resonances characterized by pronounced anisotropy and strong optical confinement are anticipated to emerge in highly doped samples. Here we show that the localized plasmons supported by phosphorene nanoribbons (PNRs) exhibit high tunability in relation to both edge termination and doping charge polarity and can trigger an intense nonlinear optical response at moderate doping levels. Our explorations are based on a second-principles theoretical framework, employing maximally localized Wannier functions constructed from ab initio electronic structure calculations, which we introduce here to describe the linear and nonlinear optical response of PNRs on mesoscopic length scales. Atomistic simulations reveal the high tunability of plasmons in doped PNRs at near-infrared frequencies, which can facilitate the synergy between the electronic band structure and plasmonic field confinement to drive efficient high-harmonic generation. Our findings establish nanostructured phosphorene as a versatile atomically thin material candidate for nonlinear plasmonics.

Low temperature and rapid synthesis of nitrogen-doped carbon-based catalysts via atmospheric pressure plasma

Nitrogen-doped carbon materials have attracted significant attention as promising non-metal electrochemical catalysts for oxygen reduction reaction. The commonly used chemical synthesis methods which usually necessitate prolonged elevated-temperature sintering are unsuitable for thermally sensitive catalysts. Generally, these methods require a long duration of gas infiltration and the involvement of toxic chemical reagents. These factors make it difficult to maintain sample consistency during the preparation process. In this paper, a low-temperature synthesis approach is introduced to prepare nitrogen-doped carbon-based catalysts using Ar surface dielectric barrier discharge to treat a mixed precursor of Ketjen Black and ammonium carbonate at atmospheric pressure. The obtained catalysts exhibit moderate defects and successful nitrogen doping. Compared with catalysts prepared using traditional chemical methods, they show superior electrochemical performance. The limiting current density has exhibited performance superior to commercial Pt/C catalysts, as well as higher stability and methanol tolerance. Furthermore, the mechanism of nitrogen doping achieved through plasma treat chemical bonds is explained. This work proposes a feasible strategy for synthesizing nitrogen-doped carbon materials and tuning catalyst performance, and provides deep insights into the plasma regulation of catalysts.

Nanocrystalline silicon-oxygen based tunneling recombination junctions in perovskite/silicon heterojunction tandem solar cells

The tunneling recombination junction (TRJ) of efficient perovskite/silicon heterojunction tandem cells should possess excellent optoelectronic characteristics to minimize light parasitic absorption and carrier transport/recombination losses. One effective approach is the utilization of hydrogenated nanocrystalline silicon-oxygen (nc-SiOx: H) materials, which characteristics can be controlled by adjusting the flow rate of CO2 and doped gas during the fabrication process. By carefully screening the material properties, the suitable n/p-doped nc-SiOx: H materials can be identified. For n-nc-SiOx: H, it is necessary to use a lower CO2 flux and perform moderate doping, while for p-nc-SiOx: H, strict control of CO2 and Trimethylboron (TMB) fluxes at lower levels is essential to preserve the electrical properties. Compared to the TRJ based on nc-Si: H, the TRJ based on nc-SiOx: H exhibits notable improvements in the open-circuit voltage (VOC) and short-circuit current density (JSC) of the tandem cell. The VOC increases by 38 mV (from 1.822 V to 1.864 V), and the JSC gains 0.82 mA/cm2 (from 19.00 mA/cm2 to 19.82 mA/cm2). Consequently, the conversion efficiency of the tandem cell, with an aperture area of 0.5091 cm2, is enhanced from 25.70% to 27.16%. Additionally, by considering the distinct lateral and vertical growth characteristics of nc-SiOx: H, the fill factor (FF) experiences a significant enhancement when applied to the TRJ of large-area tandem cells. Specifically, the FF increases from 55.21% to 69.68%. As a result, for a tandem cell with an aperture area of 12.5 cm2, the conversion efficiency improves from 17.87% to 23.39%.

Phosphonic acid-imidazolium containing polymer ionomeric membranes derived from poly (phenylene oxide) towards boosting the performance of HT-PEM fuel cells

Phosphoric acid (PA)-dependent proton conductivity and polymer-offered mechanical properties are contradictory in high-temperature proton exchange membranes (HT-PEMs). Microphase separation strategy contributes to achieve a tradeoff between proton conductivity and mechanical properties. Herein, a kind of phosphonic acid-imidazolium containing polymer (PICP) ionomeric membranes, in which acidophilic (imidazolium) and acidophobic groups (-PO3H2) can be induced to form a microphase separation structure by PA, are firstly prepared. The acidophilic phase with adsorbed PA plays the role of proton conduction and the acidophobic phase can not only provides -PO3H2 group synergistically conduct protons but also largely maintains the intrinsic mechanical properties. As a result, the PICP ionomeric membranes with microphase separation structure possess high proton conductivity (48 mS cm−1, 160 °C) and satisfying mechanical strength (16.5 MPa) simultaneously at a moderate PA doping level (130 wt%). The fuel cell based on such HT-PEMs demonstrates a peak power density of 493 mW cm−2 and high voltage stability. This is the first report of phosphonic acid-imidazolium containing ionomeric membranes with satisfactory fuel cell performance and durability, representing a meaningful step towards practical HT-PEM fuel cells.

Synthesis and Hydrogenation of the Ti45−xVxZr38Ni17 (5 ≤ x ≤ 40) Mechanically Alloyed Materials

The mechanically alloyed amorphous alloys of the Ti45Zr38Ni17 composition are known for their ability to form a quasicrystalline state after thermal treatment. It is also known that the amorphous and quasicrystal alloys belonging to the Ti45Zr38Ni17 family are able to store hydrogen and yield gravimetric densities above 2 wt.%. In this contribution, we report the results of research on the Ti45Zr38Ni17 system with vanadium doped instead of titanium. We found that the amorphous samples with moderate doping (x < 20) show the ability to absorb hydrogen while maintaining the amorphous state and they transform into the novel glassy-quasicrystal phase during annealing. Those materials with higher vanadium concentrations do not form entirely amorphous structures. However, they still can absorb hydrogen easily. It was also confirmed that the in situ hydrogenation of the amorphous alloys is a straightforward process without decomposition of the alloy. In this process, hydrogen does not attach to any particular constituent of the alloy, which would lead to the formation of simple hydrides or nanoclusters. Therefore, we were able to confirm the fully amorphous nature of the deuterides/hydrides of the Ti45−xVxZr38Ni17 with moderate V doping.

Realizing metallicity in Sr2IrO4 thin films by high-pressure oxygen annealing

Perovskite iridates are a promising material platform for hosting unconventional superconductivity. Transport measurements of Sr2IrO4 thin-film field-effect transistors are expected to provide irrefutable evidence for the existence of superconductivity. However, these experiments have revealed a remarkably robust insulating state over wide electron and hole doping ranges; this finding is in contrast to the case of the bulk material, in which metallicity appears upon moderate electron doping by substituting cations in place of Sr. The nature of this robust insulating state and whether any metallic state can be realized in the Sr2IrO4 thin film are two remaining challenges that preclude further progress in the search for superconductivity in this system. Here, we show that this insulating state is enhanced in Sr2IrO4 thin films by thermal annealing under vacuum conditions, while it can be destroyed upon annealing in an oxygen atmosphere within restricted ranges of oxygen pressure, annealing temperature and ion substitution levels. The resulting films exhibit metallic transport behavior near room temperature and a metal–insulator crossover at ~200 K. Our results point to the potentially important roles of the oxygen vacancies at different atomic sites in the formation of the robust insulating state and the new metallic state and to their interplay in the Sr2IrO4 thin film. This finding opens new possibilities in the search for unconventional superconductivity by further tailoring the as-found metallic state in properly oxygen-annealed Sr2IrO4 thin films.

Influence of La3+ doping on nebulizer spray pyrolysed In2S3 thin film for enhanced photodetector performance

In recent years, the photodetectors gained much attention due to their wide range of applications and fabrication of high-performance, cost-effective devices using environmentally friendly material is always challenging. In this work we report the fabrication of Lanthanum -doped indium sulfide thin films (In2S3:La) using a low-cost nebulizer spray pyrolysis method. La-doping concentration is varied from 0 to 5 wt% and the effect of doping on the properties of In2S3 thin films are investigated using X-ray diffraction (XRD), energy dispersive x-ray analysis (EDX), field emission scanning electron microscope (FESEM), UV–Vis spectroscopy, photoluminescence spectra. Incorporation of 3 wt% of La3+ in In2S3 lattice has substantially improved the crystallinity, surface morphology and optical properties of the thin films suitable for the device fabrication. Moderate doping of La3+ in the crystal lattice of β-In2S3 led to a red-shift in the absorption edge, which benefited utilization of wider light spectrum. Photodetectors are fabricated using In2S3:La (0–5 wt%) films and photodetector performance parameters are evaluated using I-V characteristics and current–time characterization. The In2S3 film with 3% La dopant concentration showed high photodetector performance with estimated detectivity (D*), photoresponsivity (R), and external quantum efficiency (EQE) of 1.11 × 1011 Jones, 5.05 × 10-1 AW−1, 118% respectively. For the same sample, the rise and fall time calculated from transient photo-response analysis is found to be 0.4 s and 0.3 s respectively. These optimally doped In2S3:La 3wt% thin film samples could be useful for the fabrication of photosensor based optoelectronic devices.

Facile synthesis of nitrogen-doped porous graphene for efficient adsorption of tetracycline: Behavior and mechanism

Developing economic and efficient adsorbents is critically important for antibiotic residual removal from contaminated water. Here, Nitrogen-doped porous graphene-like carbon (NPGC) adsorbents were successfully synthesized by self-blowing and doping method, where glucose was used as the carbon source, zinc nitrate was acted as the nitrogen source and the derived ZnO was as the porogen. The obtained NPGC possessed a graphene-like porous structure with moderate nitrogen doping. The removal capacity of NPGC was as high as 451.2 mg g−1 in 50 mg L−1 TC solution, which is much higher than graphene, carbon nanotubes, and activated carbon, due to the larger specific surface area and micro/mesopores on graphene sheets. The adsorption isotherms and kinetics for TC onto NPGC were well-fitted with Langmuir model and pseudo-second-order model. The adsorptive ability of NPGC increased linearly with the increasing graphitic N content due to the enhanced π-π interaction and hydrophobic effect between TC and NPGC. The NPGC also showed potential environmental application as revealed by anti-interference capacity in the interference (coexisting ions and humic acid) and reusability. This work not only provides a facile strategy to develop economic and scalable N-doped graphene, but also systematically studies the adsorption mechanism of TC onto N-doped carbon adsorbents.

Design and simulation investigations on electron transport layer-free in tin-based p-n homojunction perovskite solar cells

Inverted tin-based perovskite solar cell (PSC) devices with the electron transport layer-free (ETL-free) have drawn tremendous attention. Nonetheless, the photovoltaic performance of the device still lags behind that of conventional structural devices. In this context, a novel ETL-free inverted PSC with p-type MASnI3/n-type MASnI3 all-perovskite homojunction as light-harvester has been modeled and investigated by using wxAMPS software. This innovative PSC configuration not only promotes carrier separation and oriented transmission but also reduces carrier recombination losses. The simulation results reveal that NiO stands out as the best alternative. To enhance the device's overall efficiency, the optimal hole transport layer and perovskite layer thickness should be 30 nm and 200 nm, respectively. Lower defect densities in the perovskite layer and interface layers can favor the reduction of carrier recombination losses and efficient carrier transfer. Additionally, superior-performance photovoltaic devices can be further realized with a moderate perovskite layer acceptor doping density of 1E14 cm−3. With these optimized values, the optimal power conversion efficiency (PCE) of 20.5609 % has been obtained for the PSC devices. This work indicates that the proposed inverted homojunction PSC with ETL-free will be a valuable reference for future research in optoelectronic and electro-optical devices.

Optimization of activated phosphorus concentration in recrystallized polysilicon layers for the n-TOPCon solar cell application

The pivotal structure of n-TOPCon (tunnel oxide passivating contact) solar cells is the passivating contact structure composed of a heavily doped polysilicon (poly-Si) layer and an ultrathin silicon oxide (SiOx), which can provide excellent selectively carrier transport. The activated phosphorus concentration in the passivating contact structure plays a crucial role in the passivation quality and contact resistivity performance. By adjusting PH3 flow rate, SiOx thickness and activation temperature, three different activated phosphorus concentrations in poly-Si were achieved in this work, the phosphorus concentration from SiOx to silicon bulk decreased at the same rate. It can be found that the passivation quality decreases with increasing concentration and the contact resistivity decreases significantly. With the aid of ellipsometry, we successfully extracted the refractive index n and extinction coefficient k of three poly-Si with different activated phosphorus concentrations. The extracted n and k values can well feedback the influence of concentration change on short-circuit current density in the simulation. Due to the high concentration led to the decrease of the open circuit voltage and short circuit current of the final TOPCon solar cell, but the obvious filling factor benefit can be obtained, only moderate doping concentration can obtain the best efficiency performance. Finally, the activated phosphorus concentration of about 3 × 1020 cm−1 can obtain the best efficiency, >24.8% on average.

Enhanced Tribological Performance of Low-Friction Nanocomposite WSexSy/NP-W Coatings Prepared by Reactive PLD

A novel laser-based method for producing nanocomposite coatings consisting of a tungsten sulfoselenide (WSexSy) matrix and W nanoparticles (NP-W) was developed. Pulsed laser ablation of WSe2 was carried out in H2S gas under appropriate laser fluence and reactive gas pressure. It was found that moderate sulfur doping (S/Se ~0.2-0.3) leads to significant improvement in the tribological properties of WSexSy/NP-W coatings at room temperature. Changes in the coatings during tribotesting depended on the load on the counter body. The lowest coefficient of friction (~0.02) with a high wear resistance was observed in a N2 environment at an increased load (5 N), resulting from certain structural and chemical changes in the coatings. A tribofilm with a layered atomic packing was observed in the surface layer of the coating. The incorporation of nanoparticles into the coating increased its hardness, which may have influenced the formation of the tribofilm. The initial matrix composition, which had a higher content of chalcogen atoms ((Se + S)/W~2.6-3.5), was altered in the tribofilm to a composition close to the stoichiometric one ((Se + S)/W~1.9). W nanoparticles were ground and retained under the tribofilm, which impacted the effective contact area with the counter body. Changes in the tribotesting conditions-lowering the temperature in a N2 environment-resulted in considerable deterioration of the tribological properties of these coatings. Only coating with a higher S content that was obtained at increased H2S pressure exhibited remarkable wear resistance and a low coefficient of friction, measuring 0.06, even under complicated conditions.

Improved Thermal Stability and Film Uniformity of Halide Perovskite by Confinement Effect brought by Polymer Chains of Polyvinyl Pyrrolidone.

Polyvinyl pyrrolidone (PVP) is doped to PbI2 and organic salt during two-step growth of halideperovskite. It is observed that PVP molecules can interact with both PbI2 and organic salt, reduce the aggregation and crystallization of the two, and then slow down the coarsening rate of perovskite. As doping concentration increases from 0 to 1mM in organic salt, average crystallite size of perovskite decreases monotonously from 90 to 34nm; Surface fluctuation reduces from 259.9 to 179.8nm at first, and then increases; Similarly, surface roughness decreases from 45.55 to 26.64nm at first, and then rises. Accordingly, a kind of "confinement effect" is resolved to crystallite growth and surface fluctuation/roughness, which helps to build compact and uniform perovskite film. Density of trap states (t-DOS) is cut down by ≈60% at moderate doping (0.2mM). Due to the "confinement effect", power conversion efficiencyof perovskite solar cellsis improved from 19.46 (±2.80) % to 21.50 (±0.99) %, and further improved to 24.11% after surface modification. Meanwhile, "confinement effect" strengthens crystallite/grain boundaries and improves thermal stability of both film and device. T80 of device increases to 120h, compared to 50h for reference ones.

Ab Initio Study of the Electronic Properties of a Silicene Anode Subjected to Transmutation Doping.

In the present work, the electronic properties of doped silicene located on graphite and nickel substrates were investigated by first-principles calculations method. The results of this modeling indicate that the use of silicene as an anode material instead of bulk silicon significantly improves the characteristics of the electrode, increasing its resistance to cycling and significantly reducing the volume expansion during lithiation. Doping of silicene with phosphorus, in most cases, increases the electrical conductivity of the anode active material, creating conditions for increasing the rate of battery charging. In addition, moderate doping with phosphorus increases the strength of silicene. The behavior of the electronic properties of doped one- and two-layer silicene on a graphite substrate was studied depending on its number and arrangement of phosphorus atoms. The influence of the degree of doping with silicene/Ni heterostructure on its band gap was investigated. We considered the single adsorption of Li, Na, K, and Mg atoms and the polyatomic adsorption of lithium on free-standing silicene.

Metal borohydrides as ambient-pressure high-Tcsuperconductors

The extreme pressures required to stabilize the recently discovered superhydrides represent a major obstacle to their practical application. In this paper, we propose a novel route to attain high-temperature superconductivity in hydrides at ambient pressure, by doping commercial metal borohydrides. Using first-principles calculations based on Density Functional Theory and Migdal-Eliashberg theory, we demonstrate that in Ca(BH$_4$)$_2$ a moderate hole doping of 0.03 holes per formula unit, obtained through a partial replacement of Ca with monovalent K, is sufficient to achieve $T_c$'s as high as 110 K. The high-$T_c$ arises because of the strong electron-phonon coupling between the B-H $\sigma$ molecular orbitals and bond-stretching phonons. Using a random sampling of large supercells to estimate the local effects of doping, we show that the required doping can be achieved without significant disruption of the electronic structure and at moderate energetic cost. Given the wide commercial availability of metal borohydrides, the ideas presented here can find prompt experimental confirmation. If successful, the synthesis of high-$T_c$ doped borohydrides will represent a formidable advancement towards technological exploitation of conventional superconductors.

Spectroelectrochemistry of CdSe/CdxZn1-xS Nanoplatelets.

We report an unexpected enhancement of photoluminescence (PL) in CdSe-based core/shell nanoplatelets (NPLs) upon electrochemical hole injection. Moderate hole doping densities induce an enhancement of more than 50% in PL intensity. This is accompanied by a narrowing and blue-shift of the PL spectrum. Simultaneous, time-resolved PL experiments reveal a slower luminescence decay. Such hole-induced PL brightening in NPLs is in stark contrast to the usual observation of PL quenching of CdSe-based quantum dots following hole injection. We propose that hole injection removes surface traps responsible for the formation of negative trions, thereby blocking nonradiative Auger processes. Continuous photoexcitation causes the enhanced PL intensity to decrease back to its initial level, indicating that photocharging is a key step leading to loss of PL luminescence during normal aging. Modulating the potential can be used to reversibly enhance or quench the PL, which enables electro-optical switching.

Synthesis and characterisation of Ga- and In-doped CdS by solventless thermolysis of single source precursors.

We report a facile and low temperature synthesis of Ga- and In-doped CdS nanoparticles from molecular precursors. Diethyldithiocarbamate complexes of Cd(II), Ga(III), and In(III), were synthesised and decomposed in tandem through solventless thermolysis, producing Ga- or In-doped CdS. The resultant MxCd1-xS1+0.5x (where M = Ga/In at x values of 0, 0.02, 0.04, 0.06, 0.08 and 0.1) particulate powder was analysed by powder X-ray diffraction, which showed that both Ga (through all doping levels) and In (at doping levels <8 mol%) were successfully incorporated into the hexagonal CdS lattice without any impurities. Raman spectroscopy also showed no significant change from CdS. Scanning electron microscopy and energy dispersive X-ray spectroscopy were used to investigate the morphology and elemental dispersion through the doped CdS materials, showing homogenous incorporation of dopant. The optical and luminescent properties of the doped MxCd1-xS1+0.5x materials were examined by UV-Vis absorption and photoluminescence spectroscopies respectively. All materials were found to exhibit excitonic emission, corresponding to band gap energies between 2.7 and 2.9 eV and surface defect induced emission which is more prominent for Ga than for In doping. Additionally, moderate doping slows down charge carrier recombination by increasing the lifetimes of excitonic and surface state emissions, but particularly for the latter process.

Superconductivity and density-wave fluctuations in an extended triangular Hubbard model: an application to SnSe2

We employ the fluctuation-exchange approximation to study the relation of superconducting pairing symmetries and density-wave fluctuations based on the extended triangular Hubbard model upon electron doping and interactions, with an possible application to the layered metal dichalcogenide SnSe2. For the case where the interactions between electrons contain only the on-site Hubbard term, the superconducting pairings are mainly mediated by spin fluctuations, and the spin-singlet pairing with the d-wave symmetry robustly dominates in the low and moderate doping levels, and a d-wave to extended s-wave transition is observed as the electron doping reaches n = 1. When the near-neighbor site Coulomb interactions are also included, the charge fluctuations are enhanced, and the spin-triplet pairings with the p-wave and f-wave symmetries can be realized in the high and low doping levels, respectively.