Double Heterojunction Research Articles

Achieving high energy storage performance in BiFeO3@TiO2 filled PVDF-based composites with opposite double heterojunction via electric field tailoring

Polymer-based dielectric capacitors are well recognized for high energy density and efficiency. However, the energy density is restricted by the deterioration of breakdown strength with excessive addition of inorganic fillers. Herein, an innovative design of the lamellar-structured BiFeO3@TiO2 (BFO@TO) fillers is proposed and a small amount of BFO@TO is added into P(VDF-HFP)/PMMA blended polymer to fabricate BFO@TO-P(VDF-HFP)/PMMA composites, which delivers an outstanding energy density of 19.3 J cm−3 at 549.2 kV mm−1. The filler possesses a BFO/TO/BFO triple-layered structure. Due to the different Fermi level, electrons are injected from TO into BFO to form electron accumulation layer and construct the heterojunction electric fields between TO and BFO layers. Heterojunction electric fields at two interfaces produced by the triple-layered structure are opposite. The opposite double heterojunction can withstand larger external electric field and improve the breakdown strength. Besides, BFO, as a narrow bandgap semiconductor, is easier for electrons and holes to separate, which further widens the width of the built-in electric field and reduces the dielectric breakdown. Electric field distribution simulations intuitively confirm the enhancement of the breakdown strength. The results provide an effective strategy to address the critical issue of improving the breakdown strength for high energy storage capability.

Fabrication and characteristics of double heterojunction bipolar transistor based on p-CuO/n-Si heterojunction

Fabrication and characteristics of double heterojunction bipolar transistor based on p-CuO/n-Si heterojunction

Vertically Stacked vdW Double Heterojunction Photodiode with Ultrawide Bandgap Gallium Oxide Electron Reservoir

AbstractCo‐integration of visible and infrared (IR) photodetection into a simple configuration is of essential importance for broadband multispectral imaging, and various heterostructures based on group IV, III–V, and recent 2D semiconductors have been studied in efforts to circumvent limits on photoresponsivity and response speed in IR ranges. In this work, a vertically stacked double heterojunction (DHJ) photodiode (PD) with ultrawide‐bandgap gallium oxide (Ga2O3) is reported on, and the performance is compared with p‐WSe2/n‐Ge PD. The fabricated n‐Ga2O3/p‐WSe2/n‐Ge PD responds to a broad spectral range from vis to shortwave IR (SWIR) (1550 nm) with a response time of ≈2.6 µs and responsivity of 17.2 A W−1. The superior performance is attributed to amplified photocurrent gains, and the additional n‐Ga2O3 has a high electron carrier density with negligible hole density at room temperature and thus, can play a role as an electron reservoir while being transparent to the spectral ranges. vScanning photocurrent microscopy analysis is performed to provide the mechanism. The demonstrated SWIR imaging shows that the proposed DHJ provides a potential pathway for high‐speed multispectral vision applications.

Double Heterojunction Crystalline Silicon Solar Cells: From Doped Silicon to Dopant-Free Passivating Contacts

Carrier-selective passivating contacts for effective electron and hole extraction are crucial to the attainment of high efficiency in crystalline silicon (Si) solar cells. In this comprehensive review, the principle of carrier extraction and recombination mechanisms in conventional industrial Si solar cells are discussed first. Passivating contacts based on (i) amorphous hydrogenated Si and (ii) polysilicon/silicon oxide are next reviewed, with emphasis on carrier selectivity mechanisms including contact layer band alignment with silicon, and localized carrier transport in ultrathin oxides. More recent developments in dopant-free passivating contacts deposited by lower-cost fabrication processes with lower thermal budget are then described. This third category of non-Si based electron- and hole-selective passivating contacts include transition metal oxides, alkali/alkali earth metal fluorides and organic conjugated polymers. The photovoltaic performance of asymmetric double heterojunction Si solar cells fabricated using these non-Si passivating contacts and their stability in damp heat conditions are discussed and compared with Si based passivating contacts.

High-detectivity organic photodetectors with double bulk heterojunction enabled by water transfer printing

Suppressing the dark current is an effective strategy to boost the detection capability of organic photodetectors (OPDs). In this Letter, the water transfer printing method is demonstrated in double bulk heterojunction (BHJ) OPDs, which is solvent-independent rather than the traditional sequential spin-coating method, enabling the elimination of the negative effects of solvents on the underlying film and the suppressing of the dark current. As a result, a photo detectivity up to 1012 Jones was obtained in the wide spectral range of 400-900 nm with a small working area of 3 mm2.

In situ self-assembly of mesoporous Zn-Cd-Mo-S quaternary metal sulfides with double heterojunction synergistic charge transfer for boosting photocatalytic hydrogen production

The construction of semiconductor heterojunctions is regarded as an efficient strategy for promoting photogenerated carrier transfer and enhancing photocatalytic performance. [1] Moreover, the in-situ self-assembly method of the main catalyst and the cocatalyst is believed to overcome the shortcomings of the traditional surface loading method and provide a more efficient hydrogen evolution reaction capability. In this work, Zn-Cd-Mo-S quaternary metal sulfide mesoporous nanospheres were generated by in-situ self-assembly via a one-step mild hydrothermal method. A photocatalyst with a double-heterojunction synergistic structure and a large specific surface area was constructed to form a high-speed charge transfer channel as a mechanism to promote photocatalytic hydrogen production. The best quaternary catalyst ZCM5S has a hydrogen evolution yield of 23.32 mmol h−1 g−1, which is 53 times and 11 times that of the corresponding binary (CdS) and ternary (ZnCdS) metal sulfides, respectively, and still has high stability within 20 h. Furthermore, the ZCM5S gets an apparent quantum efficiency (AQE) of 6.9 % at 420 nm. Through further analysis, such as photoluminescence (PL) and photoelectrochemical, etc., the enhanced photocatalytic performance of ZCM5S can be attributed to the synergistic effect of the heterojunction between ZnS and CdS and the heterojunction between ZnCdS and MoS2. In addition, the Pt-like structure of molybdenum sulfide cocatalyst can lead to efficient photoinduced charge separation and transfer. Meanwhile, the mesoporous structure endows the material with abundant reactive sites and increases the catalytic reaction efficiency. The unique in situ construction method of this work also provides a reference for the design and synthesis of heterojunction quaternary catalysts for green energy conversion.

One-Step Coating of a ZnS Nanoparticle/MoS2 Nanosheet Composite on Supported ZnO Nanorods as Anodes for Photoelectrochemical Water Splitting

ZnO-based photoanodes absorb a limited spectrum of light, and their photogenerated electrons and holes combine easily. Such features limit their photoelectrochemical activity. Herein, we report the synthesis of ternary heterostructures comprising ZnO nanorods (NRs) and ZnS nanoparticles wrapped in MoS2 nanosheets (ZnO/ZnS/MoS2, ZSM) directly grown on a substrate by a low-cost hydrothermal route and their performance as anodes for photoelectrochemical water splitting. The ZSM heterostructures exhibit a sixfold photocurrent density of 0.72 mA cm–2, a fourfold maximum applied bias photon-to-current efficiency of 0.28% compared to bare ZnO NRs, and excellent photostability. These improvements in the overall photoelectrochemical activity are due to enhanced light absorption in the visible light range, higher surface active sites, and efficient charge separation enabled by the introduction of a ZnS/MOS2 coating. Our study demonstrates an alternative architecture design of ternary heterostructures with increased photoelectrochemical activity. In general, this approach of constructing a double heterojunction can also be extended to other materials with similar architectures.

Improving the Performance of Direct Bonded Five-Junction Solar Cells by Optimization of AlInP Window Layer

It is well-known that the quantum efficiency (QE) of inverted AlGaInP solar cells is less than that of upright ones, and the mechanism has not been well-explained. In this paper, a Si-doped AlInP window layer, compared with an emitter layer, is revealed to be one more important factor that decreases QE. It is noted that the quality of a heavily Si-doped AlInP window layer would decrease and further deteriorate subsequent active layers. An optimization strategy of a Si-doped AlInP window layer is proposed, which proves effective through time-resolved photoluminescence measurements (TRPL) of double heterojunctions. Inverted 2.1 eV AlGaInP solar cells with an improved AlInP window layer are fabricated. A 60 mV Voc increment is achieved with a remarkable enhancement of the fill factor from 0.789 to 0.827. An enhanced QE of 10% to 20% is achieved at short-wavelength and the peak IQE rises from 83.3% to 88.2%, which presents a nearly identical IQE compared with the upright reference. Further optimization in GaAs homojunction sub-cells is performed by introducing an n-GaInP/p-GaAs heterojunction structure, which decreases the recombination loss in the emitter caused by a poor AlInP window layer. The optimized structure significantly improves the Voc of the inverted GaAs-based T-3J solar cells to 3830 mV, boosting the efficiency of SBT five-junction solar cells to 35.61% under AM0 illumination.

Temperature-dependent DC and small signal performance of InGaAs/InP DHBT

Temperature-dependent DC and small-signal analysis have been carried out on 0.7 μm × 15 μm InGaAs/InP double heterojunction bipolar transistors over a temperature range of 25 °C–125 °C by on-wafer S-parameter measurements up to 50 GHz. The thermal behavior of DC and equivalent circuit parameters along with their temperature coefficients were analyzed and reported for the first time using the same InP-based DHBT. Most of the DC parameters show a negative with temperature, for example the temperature coefficients of the VBE,on and VBC,on are −1.4 and −1.48 mV/°C, respectively. And the peak current gain declined from 44.04 to 36.09 with the temperature increased from 25 °C to 125 °C. On the other hand, most of the small-signal parameters show a positive trend with temperature, except for the intrinsic base resistance Rbi, intrinsic base–collector capacitance Cbc, intrinsic base–emitter capacitance Cbe, and common-base current transport factor α0. The results will provide valuable references and insights for future design optimizations of temperature susceptible circuits.

Double-defect-induced polarization enhanced OV-BiOBr/Cu2−xS high-low junction for boosted photoelectrochemical hydrogen evolution

In order to improve the carrier transfer driving force and separation efficiency, OV-BiOBr/Cu2−xS high-low junction with double defects (Oxygen vacancy and Copper vacancy) was successfully prepared by a facile two-step solvothermal in situ growth technique. OV-BiOBr/Cu2−xS-0.2 showed the highest hydrogen evolution rate (509.75 μmol·cm−2·h−1), which was 12.45, 6.94 and 3.44 times that of pure BiOBr, OV-BiOBr and BiOBr/Cu2−xS composite, respectively. Obvious free radicals (·OH and ·O2-) were observed in the dark state for the first time. Theoretical and experimental results demonstrate that the charge imbalance within OV-BiOBr/Cu2−xS intensifies after the introduction of the double defects, resulting in enhanced interfacial polarization phenomena. Boosted photoelectrochemical hydrogen evolution activities were achieved with the synergistic effect of the internal electric field and polarization electric field. This study will lay a scientific and experimental foundation for the preparation of high-performance photoelectrochemical anode materials with double defect heterojunction.

Double-Layered NiO/SnO2 Sensor for Improved SO2 Gas Sensing with MEMS Microheater Device

Micro Electro mechanical systems (MEMS) sensor is fabricated for testing low concentration gas sensing of sulphur dioxide (SO2) with sensing layers of single layer tin oxide (SnO2) and double layered heterojunction structure of nickel oxide and tin oxide (NiO/SnO2). NiO and SnO2 structures are deposited with RF sputtering and the elemental composition were identified with structural properties such as X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy Dispersive X-ray Analysis (EDX) analysis. Sensing results proved that NiO/SnO2 double layered sensor had better sensing characteristics than single layered SnO2 sensor due to the formation of p-n junctions. At 400 ppb of SO2 gas concentration, NiO/SnO2 sensor has maximum sensing response of 20% is recorded and at 2000 ppb, 30% sensing response is recoded. The optimal temperature of the sensor is 250 °C (∼63 mW). Selectivity of the sensor is tested with 5 different gases such as VOC, pyruvate, CO, NH3, SO2 and the sensor has high and better response with SO2 gas.

Synergistic effect of double heterojunction in CNNS/Co3O4@CoP ternary composite for enhancing photocatalytic performance

In recently year, constructing heterojunction has been proved to be an important method to improve the efficiency of medical pollution degradation and photocatalytic hydrogen production. However, as we known that the single heterojunction cannot get the satisfactory photocatalytic efficiency. Herein, a new double heterojunction photocatalyst was prepared by phosphating Co3O4 on g-C3N4 nanosheets (CNNS/Co3O4@CoP). The as-prepared CNNS/4%Co3O4@7%CoP exhibit excellent catalytic activity, which degradation rate of TC under visible–light irradiation could reach to 92% within 3 h, and the H2 production could reach to 1677.38 μmol g−1 h−1. Photoelectrochemical tests and density functional theory (DFT) analysis show that the synergistic effect between p-n junction (CNNS/Co3O4) and Ohmic junction (Co3O4@CoP) can significantly facilitate charge transfer, prolong the lifetime of photogenerated carriers, and improve the photocatalytic degradation and hydrogen production activity. This work provides an evidential proof of rational designing double heterojunction, and confirms the synergistic effect of double heterojunction can drive charge transfer and separation effectively, which promoting photocatalytic performances.

Enhanced room-temperature NO2 sensing performance of SnO2/Ti3C2 composite with double heterojunctions by controlling co-exposed {221} and {110} facets of SnO2

Here, we firstly synthesized SnO2/Ti3C2 composites with Schottky and surface heterojunctions via a hydrothermal oxidation process to lower the operation temperature of SnO2-based gas sensors and increase the response of Ti3C2-based gas sensors simultaneously. The SnO2 nanoparticles are mainly surrounded by {221} and {110} facets by controlling the HCl content, and a surface heterojunction is formed inside SnO2 due to the difference in energy band structure between {221} and {110} facets. The synergistic effect of the SnO2/Ti3C2 Schottky heterojunction and SnO2 {221}/{110} surface heterojunction can accelerate electron transport and thus enhance sensitivity to NO2. Under a moderate pulse heating (100 °C) during desorption process, the optimal SnO2/Ti3C2 composite presents the outstanding responses (ΔR/Ra) of 0.02, 0.83 and 1.57 to 0.05, 5 and 10 ppm NO2 at room temperature, respectively. Moreover, the optimal SnO2/Ti3C2 composite exhibits the excellent linear response (R2 = 0.99729) and good recycling performance and selectivity to NO2. This work provides an idea for synergistically improving the gas-sensing performance of MXene by in-situ constructing double heterojunctions.

Long-wavelength InAs/GaSb superlattice double heterojunction infrared detectors using InPSb/InAs superlattice hole barrier

We demonstrate two double heterojunction long-wavelength infrared detectors based on InAs/GaSb superlattice on InAs substrates grown by metal-organic chemical vapor deposition. In the two structures, the hole barrier employs a novel InPSb/InAs superlattice to achieve conduction-band alignment, while the electron barrier is InAs/GaSb superlattice to achieve valence-band alignment. Two devices with n-type absorber layer and p-type absorber layer exhibit cut-off wavelengths of ∼10.4 μm and ∼12.2 μm, dark current densities of 9 × 10−4 A cm−2 and 2 × 10−2 A cm−2, and specific detectivities of ∼1.7 × 1010 cm Hz1/2 W−1 and ∼1.5 × 1010 cm Hz1/2 W−1, respectively. The device with n-type absorber has a lower dark current due to the natural valence-band alignment, but it has a low quantum efficiency (QE) resulting from the use of n-type absorber layer. In contrast, the device with p-type absorber has a higher dark current that can be possibly attributed to the conduction-band misalignment, but it achieves a higher QE due to the benefits from the p-type absorber.

Enhanced photocatalytic activity of 3D hierarchical RP/BP/BiOCOOH via oxygen vacancies and double heterojunctions

A 3D hierarchical RP/BP/BiOCOOH double heterostructures with abundant oxygen vacancies (OVs) was obtained by hydrothermal process and its photocatalytic activity was investigated by degradation of TC-HCl with different light sources and various natural water. The physicochemical characteristics of RP/BP/BiOCOOH heterojunctions were systematically characterized via TEM, XPS, EPR, EIS et al. Compared with BiOCOOH, the photocatalytic activity of RP/BP/BiOCOOH was obviously enhanced. Under simulated solar light irradiation, 60.5% of TC-HCl was removed by 3%RP/BP/BiOCOOH. And the rate constant of 3%RP/BP/BiOCOOH was 2.95 times than that of BiOCOOH. Traces of small molecular organics were beneficial to improve photocatalytic efficiency. The process of photocatalytic degradation and the cytotoxicity of intermedia products of TC-HCl were discussed via HPLC-MS, 3D-EEM, and antibacterial properties test. Based on the results of trapping experiments and ESR tests, •OH and •O2− were the most significant reactive oxygen species. The enhanced photocatalytic activity was ascribed to two reasons: 1 double heterojunctions structure enhanced the separation efficiency of carriers, 2 the introduction of OVs and BP/RP expanded the response range of light. This work provides a feasible strategy that non-metallic element semiconductor is used to modify the wide band gap semiconductor to enhance the photocatalytic efficiency.

Growth of 2D-layered double hydroxide nanorods heterojunction with 2D tungsten carbide nanocomposite: Improving the electrochemical sensing of norfloxacin

The potential impact of antibiotics in water environments affects aquatic organisms, microbial community structure, and resistance genes. In this work, we report the hydrothermal synthesis of two-dimensional (2D) tungsten carbide (WC) nanoparticles on CO32- anion intercalated three-dimensional (3D) self-assembled nickel–cobalt layered double hydroxide (NiCo-LDH) nanorods, for the electrochemical determination of norfloxacin (NRF). The synergistic impact between the dual active components of the prepared electrode offered increased active surface area, high electrical conductivity, and prompt mass and ion diffusion, resulting in improved electrochemical performance for NRF monitoring. In ideal conditions, WC@NiCo-LDH modified electrode exhibited enhanced electrochemical characteristics, wide linear response (DPV = 0.02–83.4 µM and in i-t = 0.002–346 µM), and lowdetection limit (LOD) (DPV = 0.005 µM and i-t = 0.002 µM). Furthermore, good reproducibility, virtuous operational and cycle stabilities, were obtained. The practical applications in real-world samples with acceptable recovery ranges were verified the interference-free sensing of NRF.

High temperature and trap sates characterization of Al0.35Ga0.65N/GaN/Al0.25Ga0.75N double heterojunction

In this work, the high temperature and trap sates characteristics have been investigated for Al0.35Ga0.65N/GaN/Al0.25Ga0.75N double heterojunction. By using high-Al AlGaN barrier and back barrier layers, the maximum current at 200 ℃ is reduced by 35%, which is much lower than 58% reduction for conventional double heterojunction. The ION/IOFF ratio is as high as 4.6 × 107 at 200 ℃, demonstrating the excellent high-temperature characteristics of high-Al AlGaN barrier layer. For Al0.35Ga0.65N/GaN/Al0.25Ga0.75N double heterojunction, the shallow trap state density DT of 3.57 × 1011–1.37 × 1013 cm−2eV−1 is located at energy ET in the range of 0.259–0.322 eV, and the deep DT of 0.237–2.19 × 1013 cm−2eV−1 is located at energy ET in the range of 0.388–0.441 eV. The trap densities for heterojunction with high-Al AlGaN barrier and back barrier are lower than those for heterojunction with low-Al AlGaN back barrier.

Graphdiyne based GDY/CuI/NiO parallel double S-scheme heterojunction for efficient photocatalytic hydrogen evolution

As a new kind of two-dimensional (2D) layered carbon allotrope, graphdiyne (GDY) is rarely studied in the application field of photocatalytic hydrogen production. In addition, the efficient construction of photocatalyst heterostructure is a promising strategy to improve the yield of hydrogen production from photocatalytic split of water. Therefore, it is an excellent method to construct heterostructure photocatalytic system by introducing GDY into semiconductor photocatalytic materials. Herein, it is an excellent method to construct heterostructure photocatalytic system by introducing the cuprous iodide based 2D layered carbon allotrope (GDY) into metallic oxide semiconductor (NiO). Thus, a ternary hybrid photocatalyst (GDY/CuI/NiO) was prepared by in situ ultrasonic agitation method. X-ray diffraction, SEM, transmission electron microscope and x-ray photoelectron spectroscopy results showed that NiO nanosheets were successfully adsorbed by GDY/CuI. In addition, the composite catalyst (GDY/CuI/NiO) showed excellent photocatalytic performance, which performed a high hydrogen production activity of 5955 μmol g−1 and good stability in the 20 h hydrogen production experiment. Amorphous GDY provides more active sites for the process of hydrogen evolution in this photocatalytic system. Most importantly, the construction of S-scheme heterojunction promotes electron transfer and plays an important role in enhancing the hydrogen production activity. These findings provide new ideas for realizing efficient solar hydrogen production system.

Construction of layered embedding dual Z-Scheme Bi2O2CO3/g-C3N4/Bi2O3: Tetracycline degradation pathway, toxicity analysis and mechanism insight

• Bi 2 O 2 CO 3 /g-C 3 N 4 /Bi 2 O 3 dual Z-scheme heterostructure was easily prepared by precipitation-calcination method. • The matching band gap of heterostructure greatly promotes the transfer of the carrier, which makes full use of the reducibility of the conduction band and the oxidation of the valence band. • The possible pathways of TC degradation intermediates were reasonably deduced by LC-MS. • The toxicity analysis were evaluated based on quantitative structure activity relationship QSAR and structure of warning. In this study, a floral and lamellar interlaced double Z-scheme ternary heterojunction Bi 2 O 2 CO 3 /g-C 3 N 4 /Bi 2 O 3 was prepared by a simple precipitation and acalcination methods. TEM images demonstrated the flower-like layered structures of 3D Bi 2 O 2 CO 3 and Bi 2 O 3 were interwoven with the 2D g-C 3 N 4 block structures. The synthesized heterostructure indicated the enhanced photocatalytic performance in tetracycline (TC) degradation compared with single Bi 2 O 2 CO 3 , Bi 2 O 3 and g-C 3 N 4 under simulated solar irradiation. Besides, organic pollutants including ciprofloxacin (CIP), methylene blue (MB), and rhodamine B (Rh B) were further used to evaluate the photocatalytic activity of Bi 2 O 2 CO 3 /g-C 3 N 4 /Bi 2 O 3 . The effects of pH, supporting electrolyte on photocatalytic performance were also investigated. Furthermore, the possible pathways of TC degradation intermediates were reasonably deduced by liquid mass spectrometry (LC-MS), and the toxicity analysis were evaluated based on quantitative structure activity relationship (QSAR) and structure of warning. Finally, according to free radical trapping experiments a double Z-scheme photocatalysis mechanism was proposed.

A magnetically recyclable dual Z-scheme GCNQDs-CoTiO3/CoFe2O4 composite photocatalyst for efficient photocatalytic degradation of oxytetracycline

g-C3N4 exhibits excellent performance in photocatalytic degradation of organic pollutants, but the high recombination rate of photogenerated electron-hole pairs limits its application. Herein, a dual Z-scheme g-C3N4 QDs-CoTiO3/CoFe2O4 (GCC) composite photocatalyst was synthesized by in-situ growth method and ultrasonic impregnation method, which effectively increased the separation rate of photogenerated electron-hole pairs and significantly improved the photocatalytic degradation performance. The degradation efficiency of oxytetracycline can reach up to 88% and shows good stability and reusability. At the same time, the GCC composite photocatalyst can be quickly recovered by applying an external magnetic field after the photocatalytic reaction, which reflecting its good magnetic controllability. Furthermore, this work also proposed the possible degradation pathways and degradation mechanisms of the GCC composite photocatalyst to degrade oxytetracycline, which provides efficient way to prepare a low-cost and high-efficiency double Z-scheme heterojunctions.