Triple Heterojunction Research Articles

EFFECTIVE MgO /ALUMINA / ITO NANO HETEROSTRUCTURE AS SMART MATERIAL FOR LIGHT-EMITTING DIODE

Transparent conducting oxides (TCO) offer the uncommon functional combination of being both transparent and electrically conductive. For this reason, this study is concerned with the preparation of the triple heterojunction consisting of magnesium oxide, alumina, and ITO using a pulsed laser deposition method with a laser intensity of 3 J. Alumina bulk pellets in propanol were irradiated (Nd:YAG) at a wavelength of 1064 nm. Laser ablation was performed at a laser intensity of 3 J and deposited on ITO, which was then left to dry for 24 hours. The same method was used to attain magnesium nanoparticles, which were spin-coated on the previous sample and dried in a 500 °C oven for 4 hours. Then the properties of nanoparticles were investigated using X-ray diffraction, UV spectroscopy, and scanning electron microscopy (SEM). The results were obtained by UV and XRD analyses. From SEM images, the average size of the synthesized nanoparticles was determined to be about 25–35 nm. Aluminum oxide, MgO, and ITO are 1-D nanostructured semiconductors that function as transparent conducting oxide thin film while also increasing absorption in the visible spectrum. ITO is identified as an appropriate electrode material for infrared photoelectric devices.

Constructing Bi2O3/BiOIO3 triple heterojunction doped with Yb3+ ions as accelerating charge carriers transfer channel to enhance photocatalytic activity

Yb3+- Bi2O3/BiOIO3 heterojunction photocatalyst was successfully prepared by EG assisted hydrothermal method and calcination method. Bi2O3 has a variety of crystal structure. Doped different proportion of Yb3+ will lead to lattice phase transition of Bi2O3. When the amount of Yb3+ doped in the complex is 1 mol%, the two crystal phases of Bi2O3 coexist. α-Bi2O3, β-Bi2O3 and BiOIO3 are compounded in pairs to form a triple heterostructure, which constructs a unique electron transmission channel and promotes the separation of photogenerated carriers. At the same time, Yb3+ has unique electronic transition characteristics, effectively broadening the spectral response range of Yb3+- Bi2O3/BiOIO3 photocatalyst, which can respond to 850–1100 nm near-infrared light. The photocatalytic activity is greatly improved. Due to its optimized performance, the best efficiency of Yb3+-Bi2O3/BiOIO3 triple heterojunction photocatalyst to remove gaseous Hg0 under visible light can reach 76.73%, which is much higher than its pure component. Finally, the possible mechanism of photocatalysis is proposed, which provides a new idea for the construction of high-performance photocatalysts.

BiVO4/Fe2O3/ZnFe2O4; triple heterojunction for an enhanced PEC performance for hydrogen generation.

n/n/n triple heterojunction photoanodes made up of Zr:W-BiVO4, Fe2O3, and ZnFe2O4 metal oxides are fabricated through a simplistic spray pyrolysis method. Use of Zr and W as dopants in BiVO4 plays an important role as Zr increases the carrier density and W reduces the charge recombination. Further, Fe2O3 and ZnFe2O4 serve as a protective layer for Zr:W-BiVO4, which augmented the photoelectrochemical performance and achieved a 1.90% conversion efficiency in the triple heterojunction. XRD measurements display the crystalline nature and reduction in particle size due to strain in the sample, UV-vis absorbance shows an extended absorption towards the visible region and the FE-SEM imaging confirms the successful deposition of ZnFe2O4 over BiVO4/Fe2O3. By analyzing the band edge position, it was observed that on formation, the triple heterojunction not only suppresses the charge carrier recombination but also utilizes the band edge offset for the water splitting reaction using solar energy.

Doping Profile Engineered Triple Heterojunction TFETs With 12-nm Body Thickness

Triple heterojunction (THJ) TFETs have been proposed to resolve the low ON-current challenge of TFETs. However, the design space for THJ-TFETs is limited by fabrication challenges with respect to device dimensions and material interfaces. This work shows that the original THJ-TFET design with 12 nm body thickness has poor performance, because its sub-threshold swing is 50 mV/dec and the ON-current is only 6 $\mu A/\mu m$. To improve the performance, the doping profile of THJ-TFET is engineered to boost the resonant tunneling efficiency. The proposed THJ-TFET design shows a sub-threshold swing of 40 mV/dec over four orders of drain current and an ON-current of 325 uA/um with VGS = 0.3 V. Since THJ-TFETs have multiple quantum wells and material interfaces in the tunneling junction, quantum transport simulations in such devices are complicated. State-of-the-art mode-space quantum transport simulation, including the effect of thermalization and scattering, is employed in this work to optimize THJ-TFET design.

Impact of Body Thickness and Scattering on III–V Triple Heterojunction TFET Modeled With Atomistic Mode-Space Approximation

The triple heterojunction TFET has been originally proposed to resolve TFET's low ON-current challenge. The carrier transport in such devices is complicated due to the presence of quantum wells and strong scattering. Hence, the full band atomistic NEGF approach, including scattering, is required to model the carrier transport accurately. However, such simulations for devices with realistic dimensions are computationally unfeasible. To mitigate this issue, we have employed the empirical tight-binding mode space approximation to simulate triple heterojunction TFETs with the body thickness up to 12 nm. The triple heterojunction TFET design is optimized using the model to achieve a sub-60mV/dec transfer characteristic under realistic scattering conditions.

Signal amplified photoelectrochemical assay based on Polypyrrole/g-C3N4/WO3 inverse opal photonic crystals triple heterojunction assembled through sandwich-type recognition model

A novel photoelectrochemical (PEC) sensing strategy with an amplified signal was proposed based on polypyrrole/g-C3N4/WO3 inverse opal photonic crystals triple heterojunction. The sandwich-type detection model was applied to increase the sensitivity and favor the assembly of heterojunction structure. The heterojunction among PPy, g-C3N4 and WO3 highly improved the separation of photo-generated charges. Meanwhile, WO3 IOPCs with good optical performance were employed to enhance the light absorption of PEC detection electrode. With the simultaneous combination of these amplification techniques, the designed PEC sensor achieved high sensitivity with low limit of detection (LOD) as 0.004 nM (≈ 1.99 ng L−1) and admirable selectivity in the detection of oxytetracycline under visible light irradiation.

Triple Layer Heterojunction WO3/BiVO4/BiFeO3 Porous Photoanode for Efficient Photoelectrochemical Water Splitting

Storing sunlight into chemical bonds for further use as a photoelectrochemical (PEC) water splitting is one of the most promising methods to fulfill the human interminable energy desire. In this research, a triple heterojunction WO3/BiVO4 (BVO)/BiFeO3 (BFO) porous photoanode is synthesized through a sol–gel method and its PEC performance is compared to those of WO3/BVO as well as pristine films. The triple layer heterojunction photoanode is comprised of three interdiffused layers of each component with interconnected pores, thickness of 340 nm, and absorption edge slightly red-shifted compared to pristine layers. Although WO3/BVO junction demonstrates enhanced PEC performance, introduction of BFO on WO3/BVO dramatically improves the overpotential and charge transfer resistance. Not only the appropriate band alignment between WO3 and BVO but also the self-polarization behavior as well as p–n junction formation by BFO top layer entirely improves the PEC performance of the triple layer heterojunction photoan...

Triple Planar Heterojunction of SnO2/WO3/BiVO4 with Enhanced Photoelectrochemical Performance under Front Illumination

The performance of a BiVO4 photoanode is limited by poor charge transport, especially under front side illumination. Heterojunction of different metal oxides with staggered band configuration is a promising route, as it facilitates charge separation/transport and thereby improves photoactivity. We report a ternary planar heterojunction photoanode with enhanced photoactivity under front side illumination. SnO2/WO3/BiVO4 films were fabricated through electron beam deposition and subsequent wet chemical method. Remarkably high external quantum efficiency of ~80% during back side and ~90% upon front side illumination at a wavelength of 400 nm has been witnessed for SnO2/WO3/BiVO4 at 1.23 V vs. reversible hydrogen electrode (RHE). The intimate contact between the heterojunction films enabled efficient charge separation at the interface and promoted electron transport. This work provides a new paradigm for designing triple heterojunction to improve photoactivity, particularly under front illumination, which would be beneficial for the development of tandem devices.

Charge-separation enhancement in inverted polymer solar cells by molecular-level triple heterojunction: NiO-np:P3HT:PCBM

Hole collection and transport are crucial physical processes in bulk-heterojunction (BHJ) solar cells, which represent major bottlenecks due to their limitations in power conversion efficiency (PCE). Hence, a more efficient alternative is needed to accept and transport holes to the collection electrode in BHJ solar cells. Here, we bring both electron and hole collection centres close to the point of exciton generation by infiltrating P3HT poly(3-hexylthiophene):PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) blend into a highly porous interconnected p-type NiO-nanoparticle (NiO-np) network, through solvent-assisted grafting. In this study, a hybrid polymer solar cell is demonstrated with a P3HT:PCBM:NiO-np triple-heterojunction active layer which showed greatly improved rectification behaviour, long electron lifetime and generated higher PCE of 4% under AM 1.5 solar illumination with a 75% increase in PCE with respect to the P3HT:PCBM device. The optimum NiO-np amount and active-layer thickness were found to be 2% and 250 nm, respectively.

Nano-engineering of hybrid organic heterojunctions with carbon nanotubes to improve photovoltaic performance

Organic–inorganic hybrid photovoltaics are beginning to show significant promise as a low cost highly efficient route towards renewable energy generation. Of the hybrid architectures available, carbon nanotube incorporated organic photovoltaics is considered to be among the most promising. Herein, the optical and electronic effects of localizing multiwalled carbon nanotubes in the donor polymer is investigated in comparison to its incorporation into the bulk heterojunction architecture (triple heterojunction scheme) through photoluminescence quenching and dark diode characteristics analysis. A significant improvement in photoluminescence quenching is observed when the nanotubes are localized in the donor polymer where the active layer is formed through a sequential deposition route in comparison to the triple heterojunction scheme. However, the former architecture also leads to a higher recombination of carriers due to the introduction of trap states as observed through space charge limited conduction analysis. In comparison, the triple heterojunction scheme shows a lower dark current and hence a significantly improved photovoltaic device performance (3.8% in comparison to 2.6% for the sequentially deposited architecture). This indicates that the formation of the triple heterojunction is the more ideal scheme for improving device performances in organic–inorganic hybrid architectures.

Influence of functional derivatives of an amino-coumarin/MWCNT composite organic hetero-junction on the photovoltaic characteristics

A layer of a coumarin derivative\\multiwall carbon nanotube (MWCNT) composite was sandwiched between an indium tin oxide (ITO) layer and a top metal electrode. This layer acted as the active hetero-junction (middle hetero-junction) in a triple hetero-junction organic solar cell. The composition of the organic material in the middle hetero-junction component, second from the ITO layer, was varied, keeping the weight percentage of the MWCNTs constant, to investigate the photovoltaic properties of the cell. The choice of amino-coumarin and its derivatives were dictated by the need for a high efficiency organic up-converter. Amino-coumarin is a two photon absorbing organic donor whereas CNTs are acceptors and ballistic charge transport media. For those reasons, amino-coumarin-CNT composite materials were selected as a photo active layer to will absorb the sub-band photons effectively. Additionally, the radial self-assembling of the CNTs inside the organic matrix (during synthesis) enhances the photovoltaic characteristics of the material. The photo induced charge transport mechanism between the MWCNTs and organics was analyzed using photo luminescence (PL) measurements. By the use of 15wt% of CNTs with the organics, more than 90% of the PL signal was quenched, indicating an ultrafast transport mechanism between the donor and acceptor materials.

Enhanced Photocurrent Responses and Antiphotocorrosion Performance of CdS Hybrid Derived from Triple Heterojunction

The enhanced photocurrent responses and dramatic antiphotocorrosion performance of CdS hybrid were obtained by formation of triple heterojunction (TH), i.e., n-CdS/n-TiO2/p-BDD:n-TiO2 cube tubes were vertically grown on p-type boron-doped diamond (BDD) film. Then n-CdS nanoparticles (NPs) were randomly assembled onto the surface of TiO2 and BDD, forming a film of CdS NPs. This triple heterojunction CdS hybrid reveals 36.5% improvement of initial photocurrent and 78% reduction of photocorrosion rate in contrast with that of the coupled CdS/TiO2 hybrid, which has only single heterojunctions (SH). The mechanisms of TH on charge separation and transport during the photocatalytic reaction have been emphasized. Except for the CdS/TiO2 (n–n) heterojunction, another two p–n heterojunctions, i.e., p-BDD/n-CdS and p-BDD/n-TiO2 exist in the TH. The conduction band (CB) position of TiO2 is lower than the corresponding band positions of CdS and BDD, so TiO2 can act as an acceptor for the photogenerated electrons. Also...

Photoluminescence Quenching in Carbon Nanotube‐Polymer/Fullerene Films: Carbon Nanotubes as Exciton Dissociation Centres in Organic Photovoltaics

Photoluminescence quenching is observed in acid functionalized multiwall carbon nanotubes incorporated polymer: fullerene films, suggesting efficient charge transfer, believed to be due to nanotubes acting as exciton dissociation centres. The fabricated photovoltaic devices with triple heterojunction interfaces show increased short circuit current density compared to the device without nanotubes.

Computational modelling of the refractive index and reflectivity of a quantum well solar cell

In this paper the modelling of the refractive index and reflectivity of a quantum well solar cell (QWSC) is theoretically developed and computationally analysed. The model is based on the Modified Single Effective Oscillator model combined with the Fresnel equation. The model takes into consideration the effects of the design parameters including concentration levels, structural properties of the device (well length, etc.), operating temperature and electric field effects (due to doping concentration). Prior to analysis the authors show the model to have a solid foundation given it generates accurate results which match with experimental data for an AlGaAs/GaAs triple heterojunction cell. This justifies and promotes further work where the theoretical and computational analysis is repeated for a QWSC structure. In the case of the QWSC the results generated are for a bare AlGaAs/GaAs cell and the same cell with a ZnS anti-reflection coating. The results generated show promise for the new model however experimental verification is required. The analysis is performed for AM 1.5G spectrum. The model is intended to be an aid to QWSC designers.

Triple heterojunction ALGaAs-GaAs solar cells with front V-groove surface

The Light trapping (V-groove surface) technique is applied to increase the efficiency of a recently proposed Triple Heterojunction (THJ) AlGaAs-GaAs solar cell. An analytical model is presented as a function of the cell's design parameters. Optimum doping, thickness values of each layer, AR coating materials combination and thickness are also presented.

A new double heterojunction AlGaAs-GaAs structure for space solar cells

One means of future development in GaAs space solar cells is to increase power to area ratio. A new structure of double heterojunction with GaAs/AlGaAs heterojunction back surface field(triple heterojunction) is theoretically proposed in this work. This study uses a computer program(THJ) for modelling and optimizing the electrical characteristics of the new structure. An increase in the current density of about 9% (at AMO) can be gained by using the proposed structure rather than previous design.