Promising N-type Semiconductor Research Articles

Titanium-coated high-density Fe2O3 single crystal nanowire array for solar water splitting

Fe2O3 holds promising n-type semiconductor material in the field of solar water splitting due to its excellent photocatalytic properties. However, the photoelectrochemical performance of Fe2O3 is limited by its inherent properties such as poor conductivity, and charge separation efficiency owing to its recombination rate. Therefore, researchers are more focused on nanostructuring, doping, and surface coating to overcome these issues of Fe2O3. In this study, we have investigated a low-cost way to fabricate a Ti coating layer on a high-density Fe2O3 single-crystal nanowire array for solar water splitting. Firstly, we have prepared a high-density single-crystal Fe2O3 nanowire array at lower temperatures by a new approach stress-induced atomic diffusion method. Thereafter, the prepared nanowire array was coated by Ti film using RF sputtering. The optimal film thickness of 13 nm titanium coatings layer into Fe2O3 single crystal nanowire array exhibited a high photocurrent density of 1.36 mA/cm2 at 1.23 V versus RHE and solar to hydrogen conversion efficiency (STH) of 1.67%, which could be resulting from adjusted optoelectronic properties of the nanowires.

Insights into the Photoelectrocatalytic Behavior of gCN-Based Anode Materials Supported on Ni Foams.

Graphitic carbon nitride (gCN) is a promising n-type semiconductor widely investigated for photo-assisted water splitting, but less studied for the (photo)electrochemical degradation of aqueous organic pollutants. In these fields, attractive perspectives for advancements are offered by a proper engineering of the material properties, e.g., by depositing gCN onto conductive and porous scaffolds, tailoring its nanoscale morphology, and functionalizing it with suitable cocatalysts. The present study reports on a simple and easily controllable synthesis of gCN flakes on Ni foam substrates by electrophoretic deposition (EPD), and on their eventual decoration with Co-based cocatalysts [CoO, CoFe2O4, cobalt phosphate (CoPi)] via radio frequency (RF)-sputtering or electrodeposition. After examining the influence of processing conditions on the material characteristics, the developed systems are comparatively investigated as (photo)anodes for water splitting and photoelectrocatalysts for the degradation of a recalcitrant water pollutant [potassium hydrogen phthalate (KHP)]. The obtained results highlight that while gCN decoration with Co-based cocatalysts boosts water splitting performances, bare gCN as such is more efficient in KHP abatement, due to the occurrence of a different reaction mechanism. The related insights, provided by a multi-technique characterization, may provide valuable guidelines for the implementation of active nanomaterials in environmental remediation and sustainable solar-to-chemical energy conversion.

Liquid phase sintering of Nb doped SrTiO3-δ ceramics with enhanced thermoelectric figure of merit

SrTiO3 (STO) based ceramics are a promising n-type semiconductor oxide for high-temperature thermoelectric application. In the present work, the results of liquid-phase sintering (LPS) aid incorporating various concentrations of Al2O3, CuO and ZnOin Nb-doped STO (STN) is presented. With the inclusion of sintering aid, densities comparable to those obtained by conventional sintering (greater than 97%) were achieved for samples sintered as low as 1623 K. We also report the effect of various sintering aid (Al2O3, CuO, and ZnO) with different concentrations (1–5 wt %) on the thermoelectric figure of merit ZT of Nb-doped SrTiO3 (STN) ceramics. SEM images provided evidence of the presence of the low-temperature liquid phase around the grain boundaries of STN ceramics. The dislocations caused by liquid phase formation remove densification issues and enhances thermoelectric properties. A simultaneous increase in both electrical conductivity and the Seebeck coefficient was observed when the sintering aid concentration increased. The maximum electrical conductivity value of 390 Scm−1 at 420 K was obtained for the 5 wt % CuO added STN (STNCu5) ceramics, which was about two orders higher than the pristine STN sample sintered at that temperature. The highest PF value of 1040 Wm−2K−2 resulted in a remarkable ZT value of ≈0.4 (0.38) at 573 K for 5 wt % Al2O3 added STN (STNAl5) ceramics at a very low sintering temperature. To our knowledge, the LPS strategy is a completely novel approach in STO-based ceramics for thermoelectric applications.

P-n heterojunction constructed by γ-Fe2O3 covering CuO with CuFe2O4 interface for visible-light-driven photoelectrochemical water oxidation

Fe2O3 is a promising n-type semiconductor as the photoanode of photoelectrochemical water-splitting method due to its abundance, low cost, environment-friendly, and high chemical stability. However, the recombination of photogenerated holes and electrons leads to low solar-to-hydrogen efficiency. In this work, to overcome the recombination issue, a p-type semiconductor, CuO, is introduced underneath the γ-Fe2O3 to synthesize γ-Fe2O3/CuO on the FTO substrate. Along with the formation of p-n heterojunction, CuFe2O4 is in situ generated at the interface of γ-Fe2O3 and CuO. The existence of Cu2O in CuO and CuFe2O4 promotes the charge transfer from CuO to γ-Fe2O3 and within CuFe2O4, respectively, resulting in creating an internal electric field in γ-Fe2O3/CuO and leading to the conduction band of CuO bending up and γ-Fe2O3 bending down. Additionally, Cu(II) in CuFe2O4 contributes to fast electron capture. Consequently, the charge transfer efficiency and charge separation efficiency of photo-generated holes are promoted. Hence, γ-Fe2O3/CuO exhibits an enhanced photocurrent density of 13.40 mA cm−2 (1.9 times higher than γ-Fe2O3). The photo corrosion resistance of CuO is dramatically increased with the protection of CuFe2O4, resulting in superior high chemical stability, i.e. 85% of the initial activity remains after a long-term test.

Chlorine‐Substituted N‐Heteroacene Analogues Acting as Organic Semiconductors for Solution‐Processed n‐type Organic Field‐Effect Transistors

High performance solution processable n-type organic semiconductor is an essential element to realize low-cost, all organic and flexible composite logic circuits. In the design of n-type semiconducting materials, tuning the LUMO level of compounds is a key point. As a strong electron withdrawing unit, the introduction of chlorine atom into the chemical structure can increase the electron affinity of the material and reduce the LUMO energy level. Here, a series chlorine substituted N-heteroacene analogues of 6,7,8,9-tetrachloro-4,11-bis(4-((2-ethylhexyl)oxy)phenyl)-[1,2,5]thiadiazolo[3,4-b]phenazine (O4Cl), 6,7,8,9-tetrachloro-4,11-bis(4-((2-ethylhexyl)thio)phenyl)-[1,2,5]thiadiazolo[3,4-b]phenazine (S4Cl), 1,2,3,4,8,9,10,11-octachloro-6,13-bis(4-((2-ethylhexyl)oxy)phenyl)quinoxalino[2,3-b]phenazine (8Cl) and 12Cl have been synthesized and characterized. Solution-processed organic field-effect transistors (OFETs) based on these four compounds exhibit good electron mobilities of 0.04 cm2 V-1 s-1 , 0.01 cm2 V-1 s-1 , 2×10-3 cm2 V-1 s-1 and 3×10-3 cm2 V-1 s-1 , respectively, under ambient conditions. The results suggest that these chlorine substituted π-conjugated N-heteroacene analogues are promising n-type semiconductors in OFET applications.

Thermoelectric properties of CaMnO3 ceramics produced by using powder synthesized by modified Pechini method

Calcium manganate (CMO) is a promising n-type semiconductor for thermoelectric applications due to its intrinsic properties. Still, these properties are highly dependent on the processing route used to produce these materials. In this work, properties of the polycrystalline CMO ceramics are reported by studying samples obtained from powders synthesized by a modified Pechini method and sintered at 1543K for 1, 3, 6, 12 and 24 h. Crystallographic parameters of the resulting phases were determined from X-ray diffraction patterns. The ceramics sintered for 6 h has the highest density (94.8%TD), while the CMO-1h sample (sintered only 1 h) presented the lowest density (77.2%TD) due to a large amount of secondary phase and short sintering time. The crystallite sizes of the CMO particles reached 49.2 nm; meanwhile, the grain sizes were in the range from 1.04 to 4.85 ?m. Seebeck coefficient has a negative value, characterizing an n-type material, and its value approached ?350 ?V/K at 873K. The sample sintered for 1 h has the lowest value of thermal conductivity (3.3W/mK), while the ceramics sintered for 3 h reached maximum electrical conductivity value (1830 S/m), both at 873K. In addition, this high conductivity of the ceramics sintered for 3 h contributed to it having the highest ZT value of about 0.039.

Defective Metal–Organic Framework Assisted with Nitrogen Doping Enhances the Photoelectrochemical Performance of BiVO4

BiVO4 is a promising n-type semiconductor for photoelectrochemical (PEC) water splitting, which can serve as a photoanode. However, severe surface recombination and slow water oxidation kinetics hinder the realization of its highly theoretical PEC performance. Single-atom catalyst-like metal–organic frameworks (MOFs) and their derived metal oxides have been broadly investigated to enhance the kinetics of BiVO4 photoanodes. According to the principle of catalysis, only coordinatively unsaturated atoms can participate in the catalytic reaction. Herein, a defective cobalt-based MOF (d-CoMOF) with missing linker defects is modified onto the surface of N-doped BiVO4 (N:BVO) photoanodes. The photocurrent density of d-CoMOF/N:BVO is 3.59 times higher than that of pristine BVO (0.56 mA/cm2) at 1.23 VRHE. The onset potential of d-CoMOF/N:BVO shows a cathodic shift of 300 mV relative to BVO. The roles of the d-CoMOF overlayer and N doping are experimentally revealed. The d-CoMOF modification and N doping could increase the electron density, passivate the surface states, and promote the catalysis kinetics of BVO. Thus, the kinetic parameters, such as the charge separation/injection efficiency, onset potential, and photocurrent density, are significantly enhanced. This work provides a way to use MOFs for PEC water splitting by the introduction of defects.

Dianthracenylazatrioxa[8]circulene: Synthesis, Characterization and Application in OLEDs.

A soluble, green-blue fluorescent, π-extended azatrioxa[8]circulene was synthesized by oxidative condensation of a 3,6-dihydroxycarbazole and 1,4-anthraquinone by using benzofuran scaffolding. This is the first circulene to incorporate anthracene within its carbon framework. Solvent-dependent fluorescence and bright green electroluminescence accompanied by excimer emission are the key optical properties of this material. The presence of sliding π-stacked columns in the single crystal of dianthracenylazatrioxa[8]circulene is found to cause a very high electron-hopping rate, thus making this material a promising n-type organic semiconductor with an electron mobility predicted to be around 2.26 cm2 V-1 s-1 . The best organic light-emitting diode (OLED) device based on the dianthracenylazatrioxa[8]circulene fluorescent emitter has a brightness of around 16 000 Cd m-2 and an external quantum efficiency of 3.3 %. Quantum dot-based OLEDs were fabricated by using dianthracenylazatrioxa[8]circulene as a host matrix material.

Isomeric anthracene diimide polymers.

N-type semiconducting polymers are attractive for organic electronics, but desirable electron-deficient units for synthesizing such polymers are still lacking. As a cousin of rylene diimides such as naphthalene diimide (NDI) and perylene diimide (PDI), anthracene diimide (ADI) is a promising candidate; its polymers, however, have not been achieved yet because of synthetic challenges for its polymerizable monomers. Herein, we present ingenious synthesis of two dibromide ADI monomers with dibromination at differently symmetrical positions of the ADI core, which are further employed to construct ADI polymers. More interestingly, the two obtained ADI polymers possess the same main-chain and alkyl-chain structures but different backbone conformations owing to varied linking positions between repeating units. This feature enables their different optoelectronic properties and film-state packing behavior. The ADI polymers offer first examples of conjugated polymer conformational isomers and are highly promising as a new class of n-type semiconductors for various organic electronics applications.

ELECTROCHEMICAL REDUCTION OF SELENIUM IONS FROM ORGANIC SOLUTION

Due to the unique properties of metal dichalcogenides, they are wide used in various fields of nano- and optoelectronics. Bi2Se3 is one of the promising n-type semiconductor materials belonging to the Av – Bvı group, with a band gap of 0.3 eV. To obtain these compounds by co-electrodeposition, we study the electroreduction of the initial components separately. Therefore, the study is devoted to the electrochemical reduction of selenite ions from the ethylene glycol solution. By drawing cyclic and linear polarization curves on Pt electrodes, the kinetics, the mechanism of the process, and the influence of various factors on the electroreduction of selenite ions are studied. Using the obtained data on the influence of temperature, the effective activation energy was calculated by the Gorbachov method. The calculation results show that the electroreduction of selenite ions from ethylene glycol is accompanied by electrochemical kinetics closer to diffusion

Ecofriendly Highly Robust Ag8SiSe6-Based Thermoelectric Composites with Excellent Performance Near Room Temperature.

Bi2(TeSe)3 is a dominant n-type thermoelectric material used in commercial applications. However, its toxicity and rarity hamper further large-scale industrial applications. Herein, we develop a Ag8SiSe6-based composite as a promising n-type semiconductor with the advantages of nontoxicity and elemental abundance. Ag8SiSe6 composites with Ag2Se and Si nanoprecipitation are fabricated by a unique precipitation reaction sensitive to the hot pressing process. The energy-filtering effect between these phases optimizes electrical resistivity (∼14.59 μΩ·m) and the Seebeck coefficient (above -150 μV·K-1) of the composites, resulting in a maximum power factor of ∼1772 μW·m-1·K-2(@125 °C), which is the highest value in an argyrodite system near room temperature. Nanoprecipitation of Ag2Se and Si can also scatter more phonons and further reduce the lattice thermal conductivity to 0.20 W·m-1·K-1. As a result, a maximum ZT value of ∼0.9 (@125 °C) and an average ZT value of ∼0.7 (25-200 °C) are obtained in the composite with 12 vol % Ag2Se and 0.23 vol % Si, which is sintered at 525 °C. These thermoelectric properties are comparable to those of a commercial n-type Bi2Te3 compound. In addition, the Ag8SiSe6 composite has robust mechanical properties (Vickers hardness of >110 HV and bending strength of 70.6 MPa), much better than those of other thermoelectric compounds, because of which Ag8SiSe6 has great commercial application as an alternative to Bi2Te3-based compounds.

Analysis of Electrical Characteristics of Pd/n-Nanocarbon/p-Si Heterojunction Diodes: By C-V-f and G/w-V-f

Diamond films are candidate for a wide range of applications, due to their wide band gap, high thermal conductivity, and chemical stability. In this report, diamond-based heterojunction diodes (HJDs) were fabricated by growing n-type nanocarbon composite in the form of nitrogen-doped ultrananocrystalline diamond/amorphous carbon (UNCD/a-C:H:N) films onto p-type Si substrates. X-ray photoemission and the Fourier transform infrared spectroscopies were employed to examine the contribution of nitrogen atoms from the gas phase into the deposited films. The results indicate the incorporation of nitrogen atoms into the grain boundaries of UNCD/a-C:H film by replacing hydrogen atoms. The capacitance- (C-V-f), conductance- (G/ω-V-f), and series resistance-voltage characteristics of the fabricated Pd/n-(UNCD/a-C:H:N)/p-Si HJDs were studied in the frequency range of 40 kHz-2 MHz. The existence of interface states (Nss) and series resistance (Rs) were attributed to the interruption of the periodic lattice structure at the surface of the fabricated junction as well as the defects on the (UNCD/a-C:H:N)/Si interface. By increasing the frequency (≥500 kHz), the Nss reveals an almost frequency-independent behavior, which indicates that the charges at the interface states cannot follow ac signal at higher frequency. The obtained results demonstrated that the UNCD/a-C:H:N is a promising n-type semiconductor for diamond-based heterostructure diodes.

On the conversion of amorphous In2S3 thin films to polycrystalline In2S3 and to In2O3 through thermal oxidation process

Indium sulfide (In2S3) and Indium oxide (In2O3) are promising n-type semiconductors that have been used in optoelectronic applications owing to their unique optical and electrical properties. In this work, amorphous In2S3 thin films were grown by co-evaporation technique. The as-deposited films are subjected to air annealing process in the temperature range of 300–550 °C. In2O3 thin films were obtained through the oxidation process of the as-prepared In2S3 thin films. X-ray diffraction patterns reveal that as-deposited films are amorphous in nature and are systematically converted into polycrystalline In2S3 and then to In2O3. The energy dispersive X-ray spectroscopy results also confirm the transformation of In2S3 films into In2O3. The obtained direct energy band gap of In2S3 films is in the range of 2.47–2.85 eV and the direct energy band gap of In2O3 film found to be 3.48 eV. The resistivity of as-deposited film is 2.04 × 102 Ωcm and it decreases to 8.17 × 10-2 Ωcm for the films annealed at 550 °C. The obtained results show that the In2S3 and In2O3 thin films could be a right choice for buffer layer and transparent conducting oxide layer respectively for thin film solar cell applications.

Molybdenum defect complexes in bismuth vanadate.

Monoclinic bismuth vanadate (BiVO4) is a promising n-type semiconductor for applications in sunlight-driven water splitting. Several studies have shown that its photocatalytic activity is greatly enhanced by high concentrations of Mo and W dopants. In the present work, we performed ab initio calculations to assess the most favorable relative position between pairs of Mo dopants in BiVO4. Surprisingly, we verify that the lowest energy configuration for MoV pairwise defects in BiVO4 occurs on nearest-neighbor sites, despite the higher electrostatic repulsion and larger strain on the crystal lattice. Similar results were observed for WV defect pairs in W-doped BiVO4. We show that the origin of this effect lies in a favorable hybridization between the atomic orbitals of the impurities that is only verified when they are closest to each other, resulting in an enthalpy gain that overcomes the repulsive components of the pair formation energy. As a consequence, Mo and/or W doped BiVO4 are likely to present donor-donor defect complexes, which is an outcome that can be applied in experimental approaches for improving the photocatalytic activity of these metal oxides.

An ultra-thin NiOOH layer loading on BiVO4 photoanode for highly efficient photoelectrochemical water oxidation

Monoclinic bismuth vanadate has been widely used as a promising n-type semiconductor for photoelectrochemical (PEC) water decomposition due to its high reserves, good stability in neutral solutions, and relatively narrow band gap. Here, we developed a simple method to prepare a thin NiOOH layer on the surface of BiVO4 nanorod arrays. The heterostructured photoanode shows great enhancement for the photocurrent density of 2.7 mA cm−2 at 1.23 V vs. RHE, which is ~2.3 times higher than that of pristine BiVO4 electrode, due to NiOOH as an efficient oxygen-releasing catalyst with abundant oxygen vacancies. The NiOOH/BiVO4 photoanodes are systematically studied with X-ray diffraction, Raman, X-ray photoelectron spectra, scanning electron microscopy, transmission electron microscopy, and UV–vis diffuse-reflectance spectrum. The heterostructured photoanode shows excellent PEC activity, which can provide a promising and easy strategy to prepare such photoanode with high-efficient oxygen evolution co-catalysts.

N-Type conjugated polymers based on 3,3′-dicyano-2,2′-bithiophene: synthesis and semiconducting properties

Polymers based on bithiophene containing two CN groups are promising n-type semiconductors.

A thiadiazole-capped nanoribbon with 18 linearly fused rings.

Polycyclic aromatic hydrocarbons that extend over 2 nm in one dimension are seen as monodisperse graphene nanoribbons, which have attracted significant attention for a broad range of applications in organic electronics and photonics. Herein we report the synthesis of a stable bisthiadiazole-capped pyrene-containing nanoribbon with 18 linearly fused rings (NR-18-TD). Thanks to the presence of alternating tert-butyl and tri-iso-butylsilyl groups, NR-18-TD is highly soluble in organic solvents and therefore its structure and fundamental optoelectronic, redox and electrical properties could be unambiguously established. This work illustrates that NR-18-TD is a promising soluble NR-based n-type semiconductor for applications in organic electronics.

Mo6+ Doped BiVO4 with improved Charge Separation and Oxidation Kinetics for Photoelectrochemical Water Splitting

Monoclinic bismuth vanadate (BiVO4) has been widely applied as a promising n-type semiconductor for photoelectrochemical (PEC) water splitting because of its low cost, environmentally friendly, and relatively narrow band gap of ∼2.4eV. Here, we developed a facile fabrication of Mo doped BiVO4 photoanode on the fluorine-doped tin oxide substrate by electrodeposition method and used these samples to better understand the doping effect for charge separation and charge oxidation kinetics. Compared with the undoped BiVO4 photoanode, the optimized Mo doped BiVO4 (3AMo:BV) produced a much higher photocurrent of 1.91mA/cm2 at 1.23V vs. RHE under AM 1.5G illumination for water oxidation. The results of the photoelectric conversion kinetics for various samples revealed that the charge separation and oxidation kinetics efficiencies for 3AMo:BV sample are 74.42% and 49.25% at 1.23V vs. RHE, while the values for undoped BiVO4 are 48.04% and 32.98%, respectively. The improved PEC performance for Mo doped BiVO4 is mainly ascribed to the crystal deformation caused by larger tetrahedral ionic VO4 and higher photovoltage generated by the interface of photoanode and electrolyte.

Structural study of TiO2hierarchical microflowers grown by aerosol-assisted MOCVD

TiO2 is a promising n-type semiconductor for optoelectronic devices, in particular dye sensitized and hybrid solar cells, and more recently for hybrid perovskite-based solar cells, as well as for lithium batteries. For these applications, TiO2 structures offering a high mesoporosity and surface area are especially interesting as these increase the efficiency of phenomena taking place at the interfaces. We have used aerosol-assisted metal–organic chemical vapor deposition (AA-MOCVD) to deposit TiO2 films containing hierarchical TiO2 microflowers. Both the film and the microflowers crystallize in the anatase structure. The microflowers have diameters of around 2–3 microns while the petals are only several nanometers thick. The density of the microflowers and of the petals in each flower can be controlled by adjusting the deposition parameters. These microstructures are stable under high temperature annealing (950 °C). In this communication, we describe the synthesis of the microflowers and present the detailed study of their structural and morphological properties.

Cyclobuteno[60]fullerenes as Efficient n-Type Organic Semiconductors.

Cyclobuteno[3,4:1,2][60]fullerenes have been prepared in a straightforward manner by a simple reaction between [60]fullerene and readily available allenoates or alkynoates as organic reagents under basic and mild conditions. The chemical structure of the new modified fullerenes has been determined by standard spectroscopic techniques and confirmed by X-ray diffraction analysis. Some of these new fullerene derivatives exhibit a remarkable intrinsic electron mobility (determined by using flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements), which surpasses that of the well-known phenyl-C61-butyric acid methyl ester, thus behaving as promising n-type organic semiconductors.