Showing papers on "Doping published in 2016"

Formation of oxygen vacancies and Ti 3+ state in TiO 2 thin film and enhanced optical properties by air plasma treatment

Abstract: This is the first time we report that simply air plasma treatment can also enhances the optical absorbance and absorption region of titanium oxide (TiO2) films, while keeping them transparent. TiO2 thin films having moderate doping of Fe and Co exhibit significant enhancement in the aforementioned optical properties upon air plasma treatment. The moderate doping could facilitate the formation of charge trap centers or avoid the formation of charge recombination centers. Variation in surface species viz. Ti3+, Ti4+, O2−, oxygen vacancies, OH group and optical properties was studied using X-ray photon spectroscopy (XPS) and UV-Vis spectroscopy. The air plasma treatment caused enhanced optical absorbance and optical absorption region as revealed by the formation of Ti3+ and oxygen vacancies in the band gap of TiO2 films. The samples were treated in plasma with varying treatment time from 0 to 60 seconds. With the increasing treatment time, Ti3+ and oxygen vacancies increased in the Fe and Co doped TiO2 films leading to increased absorbance; however, the increase in optical absorption region/red shift (from 3.22 to 3.00 eV) was observed in Fe doped TiO2 films, on the contrary Co doped TiO2 films exhibited blue shift (from 3.36 to 3.62 eV) due to Burstein Moss shift.

Mn2+-Doped Lead Halide Perovskite Nanocrystals with Dual-Color Emission Controlled by Halide Content

Abstract: Impurity doping has been widely used to endow semiconductor nanocrystals with novel optical, electronic, and magnetic functionalities. Here, we introduce a new family of doped NCs offering unique insights into the chemical mechanism of doping, as well as into the fundamental interactions between the dopant and the semiconductor host. Specifically, by elucidating the role of relative bond strengths within the precursor and the host lattice, we develop an effective approach for incorporating manganese (Mn) ions into nanocrystals of lead-halide perovskites (CsPbX3, where X = Cl, Br, or I). In a key enabling step not possible in, for example, II–VI nanocrystals, we use gentle chemical means to finely and reversibly tune the nanocrystal band gap over a wide range of energies (1.8–3.1 eV) via postsynthetic anion exchange. We observe a dramatic effect of halide identity on relative intensities of intrinsic band-edge and Mn emission bands, which we ascribe to the influence of the energy difference between the cor...

High-quality β-Ga2O3 single crystals grown by edge-defined film-fed growth

Abstract: β-Ga2O3 bulk crystals were grown by the edge-defined film-fed growth (EFG) process and the floating zone process. Semiconductor substrates containing no twin boundaries with sizes up to 4 in. in diameter were fabricated. It was found that Si was the main residual impurity in the EFG-grown crystals and that the effective donor concentration (N d − N a) of unintentionally doped crystals was governed by the Si concentration. Intentional n-type doping was shown to be possible. An etch pit observation revealed that the dislocation density was on the order of 103 cm−3. N d − N a for the samples annealed in nitrogen ambient was almost the same as the Si concentration, while for the samples annealed in oxygen ambient, it was around 1 × 1017 cm−3 and independent of the Si concentration.

Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals

Abstract: We report the one-pot synthesis of colloidal Mn-doped cesium lead halide (CsPbX3) perovskite nanocrystals and efficient intraparticle energy transfer between the exciton and dopant ions resulting in intense sensitized Mn luminescence Mn-doped CsPbCl3 and CsPb(Cl/Br)3 nanocrystals maintained the same lattice structure and crystallinity as their undoped counterparts with nearly identical lattice parameters at ∼02% doping concentrations and no signature of phase separation The strong sensitized luminescence from d–d transition of Mn2+ ions upon band-edge excitation of the CsPbX3 host is indicative of sufficiently strong exchange coupling between the charge carriers of the host and dopant d electrons mediating the energy transfer, essential for obtaining unique properties of magnetically doped quantum dots Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX3 nanocrystals and well-defined electron paramagnetic resonance spectra of Mn2+ in host CsPbX3 nanocrysta

Molecular Electrical Doping of Organic Semiconductors: Fundamental Mechanisms and Emerging Dopant Design Rules

Abstract: ConspectusToday’s information society depends on our ability to controllably dope inorganic semiconductors, such as silicon, thereby tuning their electrical properties to application-specific demands. For optoelectronic devices, organic semiconductors, that is, conjugated polymers and molecules, have emerged as superior alternative owing to the ease of tuning their optical gap through chemical variability and their potential for low-cost, large-area processing on flexible substrates. There, the potential of molecular electrical doping for improving the performance of, for example, organic light-emitting devices or organic solar cells has only recently been established. The doping efficiency, however, remains conspicuously low, highlighting the fact that the underlying mechanisms of molecular doping in organic semiconductors are only little understood compared with their inorganic counterparts.Here, we review the broad range of phenomena observed upon molecularly doping organic semiconductors and identify ...

New insight into the enhanced photocatalytic activity of N-, C- and S-doped ZnO photocatalysts

Abstract: In general, N-, C- and S-doped ZnO exhibit much higher phototcatalytic activity than the pure ZnO. However, the essential factors and underlying mechanism regarding the enhancement of photocatalytic activity are still unclear. In this work, the electronic structures, optical properties and effective masses of charge carriers are investigated by first-principle density functional theory calculation. Due to the nature of p-type doping, N and C doping can generate vacant states above the Fermi level and shift the conduction band into lower energy region, resulting in narrowing of band gap. Thus, N- and C-doped ZnO demonstrate much stronger light absorption in both visible and ultraviolet region. In contrast, because of the absence of vacant states, only limited enhancement of light absorption is observed for S-doped ZnO whose improved photocatalytic performance can only be attributed to the direct reduction of band gap. The calculation of the effective masses show that ZnO typically possess light electrons and heavy holes, confirming its intrinsic character of n-type semiconductor, while N, C and S doping can generally render electrons lighter and holes heavier, resulting in slower recombination rate of photogenerated electron–hole pairs. Noticeably, C doping can discourage such recombination to the greatest extent and separate electron–hole pairs most efficiently compared with N and S doping, serving as a potentially promising pathway to increase the quantum efficiency of ZnO-based photocatalysts. This work will provide some new insights into the understanding of doping effect over the enhancement of photocatalytic activity of N-, C- and S-doped ZnO.

Efficient silicon solar cells with dopant-free asymmetric heterocontacts

Abstract: A salient characteristic of solar cells is their ability to subject photo-generated electrons and holes to pathways of asymmetrical conductivity—‘assisting’ them towards their respective contacts. All commercially available crystalline silicon (c-Si) solar cells achieve this by making use of doping in either near-surface regions or overlying silicon-based films. Despite being commonplace, this approach is hindered by several optoelectronic losses and technological limitations specific to doped silicon. A progressive approach to circumvent these issues involves the replacement of doped-silicon contacts with alternative materials which can also form ‘carrier-selective’ interfaces on c-Si. Here we successfully develop and implement dopant-free electron and hole carrier-selective heterocontacts using alkali metal fluorides and metal oxides, respectively, in combination with passivating intrinsic amorphous silicon interlayers, resulting in power conversion efficiencies approaching 20%. Furthermore, the simplified architectures inherent to this approach allow cell fabrication in only seven low-temperature (≤200 ∘C), lithography-free steps. This is a marked improvement on conventional doped-silicon high-efficiency processes, and highlights potential improvements on both sides of the cost-to-performance ratio for c-Si photovoltaics. The use of doped-silicon contacts in silicon solar cells adds cost and complexity to the fabrication process. These issues can now be circumvented by using dopant-free carrier-selective interfaces on silicon, realized by alkali metal fluorides and metal oxides.

A facile synthesis of Br-modified g-C3N4 semiconductors for photoredox water splitting

Abstract: Hydrogen production by semiconductor photocatalysis using abundant sunlight and water is an ideal method to address the globe energy and environment issues. Here, we present a facile synthesis of bromine doped graphitic carbon nitride (g-C 3 N 4 ) photocatalysts for hydrogen evolution with visible light irradiation. Bromine modification is shown to enhance the optical, conductive and photocatalytic properties of g-C 3 N 4 , while still keeping the poly-tri-s(triazine) core structure as the main building blocks of the materials. This modification method can be generally applicable to several precursors of g-C 3 N 4 , including urea, dicyandiamide, ammonium thiocyanide, and thiourea. The optimal sample CNU-Br 0.1 shows more than two times higher H 2 evolution rates than pure CNU sample under visible light irradiation, with high stability during the prolonged photocatalytic operation. Results also found that the photocatalytic O 2 evolution activity of CNU-Br 0.1 was promoted when the sample was subjected to surface kinetic promotion by loading with cobalt oxide as a cocatalyst. This study affords us a feasible modification pathway to rationally design and synthesize g-C 3 N 4 based photocatalysts for a variety of advanced applications, including CO 2 photofixation, organic photosynthesis and environmental remediation.

Cobalt‐Doping in Molybdenum‐Carbide Nanowires Toward Efficient Electrocatalytic Hydrogen Evolution

Abstract: Efficient hydrogen evolution reaction (HER) over noble-metal-free electrocatalysts provides one of the most promising pathways to face the energy crisis Herein, facile cobalt-doping based on Co-modified MoOx–amine precursors is developed to optimize the electrochemical HER over Mo2C nanowires The effective Co-doping into Mo2C crystal structure increases the electron density around Fermi level, resulting in the reduced strength of Mo–H for facilitated HER kinetics As expected, the Co-Mo2C nanowires with an optimal Co/Mo ratio of 0020 display a low overpotential (η10 = 140 and 118 mV for reaching a current density of –10 mA cm−2; η100 = 200 and 195 mV for reaching a current density of –100 mA cm−2), a small Tafel slope (39 and 44 mV dec−1), and a low onset overpotential (40 and 25 mV) in 05 m H2SO4 and 10 m KOH, respectively This work highlights a feasible strategy to explore efficient electrocatalysts via engineering on composition and nanostructure

Field-Plated Ga 2 O 3 MOSFETs With a Breakdown Voltage of Over 750 V

Abstract: Depletion-mode field-plated Ga2O3 metal–oxide–semiconductor field-effect transistors were demonstrated for the first time. Substantial enhancement in breakdown voltage was achieved with a gate-connected field plate. The device channels, formed by selective-area Si ion implantation doping of an undoped Ga2O3 epilayer, were electrically isolated by the highly resistive epilayer without mesa etching. Effective surface passivation and high Ga2O3 material quality contributed to the absence of drain current collapse. The transistors exhibited an off-state breakdown voltage of 755 V, a high drain current on/off ratio of over $10^{9}$ , and stable high temperature operation against 300°C thermal stress.

Efficient perovskite solar cells by metal ion doping

Abstract: Realizing the theoretical limiting power conversion efficiency (PCE) in perovskite solar cells requires a better understanding and control over the fundamental loss processes occurring in the bulk of the perovskite layer and at the internal semiconductor interfaces in devices. One of the main challenges is to eliminate the presence of charge recombination centres throughout the film which have been observed to be most densely located at regions near the grain boundaries. Here, we introduce aluminium acetylacetonate to the perovskite precursor solution, which improves the crystal quality by reducing the microstrain in the polycrystalline film. At the same time, we achieve a reduction in the non-radiative recombination rate, a remarkable improvement in the photoluminescence quantum efficiency (PLQE) and a reduction in the electronic disorder deduced from an Urbach energy of only 12.6 meV in complete devices. As a result, we demonstrate a PCE of 19.1% with negligible hysteresis in planar heterojunction solar cells comprising all organic p and n-type charge collection layers. Our work shows that an additional level of control of perovskite thin film quality is possible via impurity cation doping, and further demonstrates the continuing importance of improving the electronic quality of the perovskite absorber and the nature of the heterojunctions to further improve the solar cell performance.

2D coherent charge transport in highly ordered conducting polymers doped by solid state diffusion

Abstract: Doping is one of the most important methods to control charge carrier concentration in semiconductors. Ideally, the introduction of dopants should not perturb the ordered microstructure of the semiconducting host. In some systems, such as modulation-doped inorganic semiconductors or molecular charge transfer crystals, this can be achieved by spatially separating the dopants from the charge transport pathways. However, in conducting polymers, dopants tend to be randomly distributed within the conjugated polymer, and as a result the transport properties are strongly affected by the resulting structural and electronic disorder. Here, we show that in the highly ordered lamellar microstructure of a regioregular thiophene-based conjugated polymer, a small-molecule p-type dopant can be incorporated by solid state diffusion into the layers of solubilizing side chains without disrupting the conjugated layers. In contrast to more disordered systems, this allows us to observe coherent, free-electron-like charge transport properties, including a nearly ideal Hall effect in a wide temperature range, a positive magnetoconductance due to weak localization and the Pauli paramagnetic spin susceptibility.

Few-Layer MoS2 p-Type Devices Enabled by Selective Doping Using Low Energy Phosphorus Implantation

Abstract: P-type doping of MoS2 has proved to be a significant bottleneck in the realization of fundamental devices such as p-n junction diodes and p-type transistors due to its intrinsic n-type behavior. We report a CMOS compatible, controllable and area selective phosphorus plasma immersion ion implantation (PIII) process for p-type doping of MoS2. Physical characterization using SIMS, AFM, XRD and Raman techniques was used to identify process conditions with reduced lattice defects as well as low surface damage and etching, 4X lower than previous plasma based doping reports for MoS2. A wide range of nondegenerate to degenerate p-type doping is demonstrated in MoS2 field effect transistors exhibiting dominant hole transport. Nearly ideal and air stable, lateral homogeneous p-n junction diodes with a gate-tunable rectification ratio as high as 2 × 104 are demonstrated using area selective doping. Comparison of XPS data from unimplanted and implanted MoS2 layers shows a shift of 0.67 eV toward lower binding energie...

Covalent Nitrogen Doping and Compressive Strain in MoS2 by Remote N2 Plasma Exposure.

Abstract: Controllable doping of two-dimensional materials is highly desired for ideal device performance in both hetero- and p-n homojunctions. Herein, we propose an effective strategy for doping of MoS2 with nitrogen through a remote N2 plasma surface treatment. By monitoring the surface chemistry of MoS2 upon N2 plasma exposure using in situ X-ray photoelectron spectroscopy, we identified the presence of covalently bonded nitrogen in MoS2, where substitution of the chalcogen sulfur by nitrogen is determined as the doping mechanism. Furthermore, the electrical characterization demonstrates that p-type doping of MoS2 is achieved by nitrogen doping, which is in agreement with theoretical predictions. Notably, we found that the presence of nitrogen can induce compressive strain in the MoS2 structure, which represents the first evidence of strain induced by substitutional doping in a transition metal dichalcogenide material. Finally, our first principle calculations support the experimental demonstration of such stra...

An ultra-thin, un-doped NiO hole transporting layer of highly efficient (16.4%) organic–inorganic hybrid perovskite solar cells

Abstract: NiO is a wide band gap p-type oxide semiconductor and has potential for applications in solar energy conversion as a hole-transporting layer (HTL). It also has good optical transparency and high chemical stability, and the capability of aligning the band edges to the perovskite (CH3NH3PbI3) layers. Ultra-thin and un-doped NiO films with much less absorption loss were prepared by atomic layer deposition (ALD) with highly precise control over thickness without any pinholes. Thin enough (5–7.5 nm in thickness) NiO films with the thickness of few time the Debye length (LD = 1–2 nm for NiO) show enough conductivities achieved by overlapping space charge regions. The inverted planar perovskite solar cells with NiO films as HTLs exhibited the highest energy conversion efficiency of 16.40% with high open circuit voltage (1.04 V) and fill factor (0.72) with negligible current–voltage hysteresis.

MOF-derived C-doped ZnO prepared via a two-step calcination for efficient photocatalysis

Abstract: ZnO is an important semiconductor that has been widely applied in solar cell, photocatalysis, environmental remediation. Doping and morphology control are important approaches to improve its photocatalytic performance. Herein, a facile two-step calcination method was developed to fabricate carbon(C)-doped cubic ZnO with porous structure from zeolite imidazolate frameworks (ZIF-8). Compared with one-step pyrolysis, the approach of two-step calcination not only retains the cubic morphology with inter-connected ZnO nanoparticles and porous structure but also introduces C doping in ZnO lattice effectively. This morphology has advantage in charge transfer, optical absorption and mass transfer during the photoreaction, and C doping results in high charge-separation efficiency. The sample C350-400 (C-doped ZnO, firstly calcined at 350 °C for 2 h from ZIF-8, then 400 °C for 1 h) shows the maximum photoactivity, which is ca . 3-fold and 4-fold higher than ZnO (C450) in photodegradation and PEC water splitting (under UV–vis irradiation), respectively. It is expected that the preparation of metal oxide from MOF is a very promising way to fabricate highly efficient photocatalyst.

Distinct Impact of Alkali-Ion Doping on Electrical Transport Properties of Thermoelectric p-Type Polycrystalline SnSe.

Abstract: Recent findings about ultrahigh thermoelectric performance in SnSe single crystals have stimulated related research on this simple binary compound, which is focused mostly on its polycrystalline counterparts, and particularly on electrical property enhancement by effective doping. This work systematically investigated the thermoelectric properties of polycrystalline SnSe doped with three alkali metals (Li, Na, and K). It is found that Na has the best doping efficiency, leading to an increase in hole concentration from 3.2 × 10(17) to 4.4 × 10(19) cm(-3) at room temperature, accompanied by a drop in Seebeck coefficient from 480 to 142 μV/K. An equivalent single parabolic band model was found adequate to capture the variation tendency of Seebeck coefficient with doping levels within a wide range. A mixed scattering of carriers by acoustic phonons and grain boundaries is suitable for numerically understanding the temperature-dependence of carrier mobility. A maximum ZT of ∼0.8 was achieved in 1% Na- or K-doped SnSe at 800 K. Possible strategies to improve the mobility and ZT of polycrystals were also proposed.

Elemental superdoping of graphene and carbon nanotubes

Abstract: Doping of low-dimensional graphitic materials, including graphene, graphene quantum dots and single-wall carbon nanotubes with nitrogen, sulfur or boron can significantly change their properties. We report that simple fluorination followed by annealing in a dopant source can superdope low-dimensional graphitic materials with a high level of N, S or B. The superdoping results in the following doping levels: (i) for graphene, 29.82, 17.55 and 10.79 at% for N-, S- and B-doping, respectively; (ii) for graphene quantum dots, 36.38 at% for N-doping; and (iii) for single-wall carbon nanotubes, 7.79 and 10.66 at% for N- and S-doping, respectively. As an example, the N-superdoping of graphene can greatly increase the capacitive energy storage, increase the efficiency of the oxygen reduction reaction and induce ferromagnetism. Furthermore, by changing the degree of fluorination, the doping level can be tuned over a wide range, which is important for optimizing the performance of doped low-dimensional graphitic materials.

Stabilizing nickel-rich layered cathode materials by a high-charge cation doping strategy: zirconium-doped LiNi0.6Co0.2Mn0.2O2

Abstract: Ni-rich layered lithiated transition metal oxides Li[NixCoyMnz]O2 (x + y + z = 1) are the most promising materials for positive electrodes for advanced Li-ion batteries. However, one of the drawbacks of these materials is their low intrinsic stability during prolonged cycling. In this work, we present lattice doping as a strategy to improve the structural stability and voltage fade on prolonged cycling of LiNi0.6Co0.2Mn0.2O2 (NCM-622) doped with zirconium (+4). It was found that LiNi0.56Zr0.04Co0.2Mn0.2O2 is stable upon galvanostatic cycling, in contrast to the undoped material, which undergoes partial structural layered-to-spinel transformation during cycling. The current study provides sub-nanoscale insight into the role of Zr4+ doping on such a transformation in Ni-rich Li[NixCoyMnz]O2 materials by adopting a combined experimental and first-principles theory approach. A possible mechanism for a Ni-mediated layered-to-spinel transformation in Ni-rich NCMs is also proposed.

Graphitic Carbon Nitride Doped with Biphenyl Diimide: Efficient Photocatalyst for Hydrogen Peroxide Production from Water and Molecular Oxygen by Sunlight

Abstract: Photocatalytic hydrogen peroxide (H2O2) production from water and molecular oxygen (O2) by sunlight is a promising strategy for green, safe, and sustainable H2O2 synthesis. We prepared graphitic carbon nitride (g-C3N4) doped with electron-deficient biphenyl diimide (BDI) units by a simple calcination procedure. The g-C3N4/BDI catalyst, when photoirradiated by visible light (λ >420 nm) in pure water with O2, successfully promotes water oxidation by the photogenerated valence band holes and selective two-electron reduction of O2 by the conduction band electrons, resulting in successful production of millimolar levels of H2O2. Electrochemical analysis, Raman spectroscopy, and ab initio calculation results revealed that, upon photoexcitation of the catalyst, the photogenerated positive holes are localized on the BDI unit while the conduction band electrons are localized on the melem unit. This spatial charge separation suppresses rapid recombination of the hole–electron pairs and facilitates efficient H2O2 pr...

Co-doping Strategy for Developing Perovskite Oxides as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

Abstract: A synergistic co-doping strategy is proposed to identify a series of BaCo0.9-x Fe x Sn0.1O3-δ perovskites with tunable electrocatalytic activity for the oxygen evolution reaction (OER). Simply through tailoring the relative concentrations of less OER-active tin and iron dopants, a cubic perovskite structure (BaCo0.7Fe0.2Sn0.1O3-δ) is stabilized, showing intrinsic OER activity >1 order of magnitude larger than IrO2 and a Tafel slope of 69 mV dec-1.

Comparison of solution-mixed and sequentially processed P3HT:F4TCNQ films: effect of doping-induced aggregation on film morphology

Abstract: Doping polymeric semiconductors often drastically reduces the solubility of the polymer, leading to difficulties in processing doped films. Here, we compare optical, electrical, and morphological properties of P3HT films doped with F4TCNQ, both from mixed solutions and using sequential solution processing with orthogonal solvents. We demonstrate that sequential doping occurs rapidly (<1 s), and that the film doping level can be precisely controlled by varying the concentration of the doping solution. Furthermore, the choice of sequential doping solvent controls whether dopant anions are included or excluded from polymer crystallites. Atomic force microscopy (AFM) reveals that sequential doping produces significantly more uniform films on the nanoscale than the mixed-solution method. In addition, we show that mixed-solution doping induces the formation of aggregates even at low doping levels, resulting in drastic changes to film morphology. Sequentially coated films show 3–15 times higher conductivities at a given doping level than solution-doped films, with sequentially doped films processed to exclude dopant anions from polymer crystallites showing the highest conductivities. We propose a mechanism for doping induced aggregation in which the shift of the polymer HOMO level upon aggregation couples ionization and solvation energies. To show that the methodology is widely applicable, we demonstrate that several different polymer:dopant systems can be prepared by sequential doping.

Structurally stable Mg-doped P2-Na2/3Mn1−yMgyO2 sodium-ion battery cathodes with high rate performance: insights from electrochemical, NMR and diffraction studies

Abstract: Sodium-ion batteries are a more sustainable alternative to the existing lithium-ion technology and could alleviate some of the stress on the global lithium market as a result of the growing electric car and portable electronics industries. Fundamental research focused on understanding the structural and electronic processes occurring on electrochemical cycling is key to devising rechargeable batteries with improved performance. We present an in-depth investigation of the effect of Mg doping on the electrochemical performance and structural stability of Na2/3MnO2 with a P2 layer stacking by comparing three compositions: Na2/3Mn1−yMgyO2 (y = 0.0, 0.05, 0.1). We show that Mg substitution leads to smoother electrochemistry, with fewer distinct electrochemical processes, improved rate performance and better capacity retention. These observations are attributed to the more gradual structural changes upon charge and discharge, as observed with synchrotron, powder X-ray, and neutron diffraction. Mg doping reduces the number of Mn3+ Jahn–Teller centers and delays the high voltage phase transition occurring in P2-Na2/3MnO2. The local structure is investigated using 23Na solid-state nuclear magnetic resonance (ssNMR) spectroscopy. The ssNMR data provide direct evidence for fewer oxygen layer shearing events, leading to a stabilized P2 phase, and an enhanced Na-ion mobility up to 3.8 V vs. Na+/Na upon Mg doping. The 5% Mg-doped phase exhibits one of the best rate performances reported to date for sodium-ion cathodes with a P2 structure, with a reversible capacity of 106 mA h g−1 at the very high discharge rate of 5000 mA g−1. In addition, its structure is highly reversible and stable cycling is obtained between 1.5 and 4.0 V vs. Na+/Na, with a capacity of approximately 140 mA h g−1 retained after 50 cycles at a rate of 1000 mA g−1.

Te-Doped Black Phosphorus Field-Effect Transistors.

Abstract: Element doping allows manipulation of the electronic properties of 2D materials. Enhanced transport performances and ambient stability of black-phosphorus devices by Te doping are presented. This provides a facile route for achieving airstable black-phosphorus devices.

Carrier Diffusion Lengths of over 500 nm in Lead-Free Perovskite CH3NH3SnI3 Films

Abstract: The dynamics of photoexcited lead-free perovskite films, CH3NH3SnI3, were studied using broadband transient absorption and time-resolved fluorescence spectroscopy. Similar to its lead analogue CH3NH3PbI3, we show that free carrier (electrons and holes) recombination is also the dominant relaxation pathway in CH3NH3SnI3 films. The slow hot carrier relaxation time is 0.5 ps. Long carrier diffusion lengths for electrons (279 ± 88 nm) and holes (193 ± 46 nm) were obtained from fluorescence quenching measurements. We also show that SnF2 doping in the CH3NH3SnI3 film effectively increases the fluorescence lifetime up to 10 times and gives diffusion lengths exceeding 500 nm. These results suggest that the photophysics of CH3NH3SnI3 perovskite are as favorable as those of CH3NH3PbI3, demonstrating that it is a promising nontoxic lead-free replacement for lead iodide perovskite-based solar cells.

Doping effect of phosphate in Bi2WO6 and universal improved photocatalytic activity for removing various pollutants in water

Abstract: Ionic group doping into the semiconductor photocatalyst is a new concept to improve photocatalytic performance, which always is a difficult challenge. In this paper, PO 4 -doped Bi 2 WO 6 photocatalyst is prepared by the urea-precipitation way in the hydrothermal process for the first time. The as-prepared sample presents the universal enhanced photocatalytic activity for removing various contaminants in water compared with the pristine Bi 2 WO 6 under visible-light irradiation, such as heavy metal Cr (VI), colored dye RhB, colorless phenol and different kind antibiotics. It attributes to the doping effect of PO 4 group in Bi 2 WO 6 influencing on energy band structure, light absorption property and separation efficiency of the charge carriers. This work provides a new insight into anionic group doping effects and takes an important step toward the development of improving Bi-based photocatalyst activity.