Photo Carrier Research Articles

Hybrid magnetic core-shell TiO2@CoFe3O4 composite towards visible light-driven photodegradation of Methylene blue dye and the heavy metal adsorption: isotherm and kinetic study.

Magnetic core-shell TiO2@CoFe3O4 (TCM) composite photocatalytic particles with a core-shell structure were synthesized by the co-precipitation method as a novel catalyst for methylene blue (MB) dye degradation and adsorption efficiency of heavy-metal ion Pb(II) from aqueous solution. Various analytical techniques have verified the formation of the TCM core-shell through TEM, XRD, FT-IR, Raman, PL, and UV analysis. The presence of TiO2 and cobalt magnetite in the TCM core shell is confirmed by XRD analysis. The formation of a homogenous CoFe3O4shell on TiO2 spheres is confirmed by HR-TEM investigation. TiO2 nanoparticle has a rutile structure with an average crystallite size of about 57.44 and a TCM core-shell of about 64.62nm. From UV and PL studies, it was found that the core shell absorbs the visible range of the electromagnetic spectrum, which improves the effective separation between photo carriers. This study focused on several factors that influence metal ion adsorption, including initial concentrations, adsorbent dose, pH, and contact time. The TCM nanocomposite successfully separated the heavy metal ion Pb(II) from aqueous solutions, and the model predictions exactly matched the experimental results. For TCM material, the maximum adsorption efficiency for Pb(II) was 33.09mg/g. The photocatalytic performance of TiO2 and TCM is about 12% and 91% after 60min for MB dye degradation. It was found that TiO2@CoFe3O4 core-shell nanoparticles perform better as photo catalysts than pure TiO2 and CoFe3O4due to their high efficiency and reusability. Furthermore, the analysis revealed that heavy metal adsorption from aqueous solutions could be reused over seven cycles with no adsorption capacity modification.

Surmounting the interband threshold limit by the hot electron excitation of multi-metallic plasmonic AgAuCu NPs for UV photodetector application

Sharply improved photoresponse characteristics are demonstrated by the multi-metallic AgCu, AuCu and AgAuCu NP based UV-PDs through the superior photo carrier injection by the strong elemental composition-dependent hot electrons and localized surface plasmon resonance (LSPR).

Significantly improved photo carrier injection by the MoS2/ZnO/HNP hybrid UV photodetector architecture

A unique ultraviolet (UV) photodetector architecture of MoS2/ZnO/HNP is explored and significantly increased photocurrent (Iph) of 4 × 10−3 A is demonstrated under the 385 nm illumination of 54.9 mW/mm2 at 10 V. This leads to the superior device performance factors: i.e., photoresponsivity of 21,111 mA/W, detectivity of 7.9 × 1011 jones and EQE of 6,800 %. These device performance factors confirm that the proposed photodetector configuration is superior as compared to the similar versions of ZnO-based UV photodetectors. The hybrid MoS2/ZnO/HNP architecture is constructed by the 2-D transition metal dichalcogenide MoS2 nanoflakes, wide-bandgapZnO quantum dots (QDs) and plasomonic PdAg hybrid nanoparticles (HNPs). The increased Iph is related to the hot carrier injection through the strongly improved localized surface plasmon resonance (LSPR) by the PdAg HNPs and additional photo carriers from the 2-D MoS2 nanoflakes on top of the original photo-induced carriers in the ZnO QD layer. The PdAg HNPs are fabricated by a unique two-step solid-state dewetting (SSD) technique, having the core-shelled PdAg NPs with the high-density small background Ag NPs. This HNP configuration offers very high-density hot spots and significantly improved LSPR. The photocurrent enhancement of MoS2/ZnO/HNP architecture is systematically studied by the finite-difference time-domain (FDTD) simulations.

Воздействия гамма-излучения на слоистую структуру кремний – ниобат лития.

In this work, it is shown that when an ionizing radiation pulse acts on surfactant-type devices in which a silicon single crystal is deposited with a gap on a piezoelectric substrate made of lithium niobate, the output signal is distorted. It was found that, depending on the type of conductivity of the material deposited on the lithium niobate, a different character of recovery of the device parameters was observed. The effect of ionizing radiation on air-gap devices operating as a memory correlator showed that the previously recorded signals were erased at a dose rate of ≥ 106 rad. To explain these dependencies, a model is used based on the fact that photo carriers excited by ionizing radiation in the depleted layer are captured by traps at the silicon-air interface for devices with an air gap and at the silicon-silicon oxide interface for monolithic structures The presented model, which takes into account traps not at the interface, explains most of the effects that cause a change in the output high frequency (RF) signal.

Engineering of bionic Fe/Mo bimetallene for boosting the photocatalytic nitrogen reduction performance

The “FeMo cofactors” in biological nitrogenase play a decisive role in nitrogen reduction. Herein, a novel bionic Fe/Mo bimetallene was applied in photocatalytic nitrogen reduction. The surface coating Fe/Mo bimetallene of Bi2Mo0.3W0.7O6 (BMWO) nanocrystals could effectively promote the separation and transportation of photogenerated carriers by multi–electron redox reactions and deliver 2.8 times longer photo–carrier lifetime. Consequently, the nitrogen fixation activity of Fe/Mo bimetallene–coated BMWO nanocrystal photocatalyst was obviously enhanced (218.93 μmol g–1h−1), which was about 4.8 times that of unmodified BMWO nanocrystals. This work provides a novel approach to design bionic Fe/Mo bimetallene–modified inorganic semiconductor photocatalysts for nitrogen reduction.

Signature of linear-in- k Dresselhaus splitting in the spin relaxation of X -valley electrons in indirect band gap AlGaAs

GaAs/AlGaAs quantum well (QW) system is utilized to investigate the electron spin relaxation in the satellite X-valley of indirect band gap Al0.63Ga0.37As epitaxial layers through polarization resolved photo-luminescence excitation spectroscopy. Solving the rate equations, steady state electronic distribution in various valleys of AlxGa1-xAs is estimated against continues photo carrier generation and an expression for the degree of circular polarization (DCP) of photoluminescence coming from the adjacent quantum well (QW) is derived. Amalgamating the experimental results with analytical expressions, the X-valley electron spin relaxation time ({\tau}_S^X) is determined to be 2.7 +/- 0.1 ps at 10 K. To crosscheck its validity, theoretical calculations are performed based on Density Functional Theory within the framework of the projector augmented wave method, which support the experimental result quite well. Further, temperature dependence of {\tau}_S^X is studied over 10-80 K range, which is explained by considering the intra-valley scattering of carriers in the X-valley of indirect band gap AlGaAs barrier layer. It is learnt that the strain induced modification of band structure lifts the degeneracy in X-valley, which dominates the electron spin relaxation beyond 50 K. Furthermore, the DCP spectra of hot electrons in indirect band gap AlGaAs layers is found to be significantly different compared to that of direct bandgap AlGaAs. It is understood as a consequence of linear k dependent Dresselhaus spin splitting and faster energy relaxation procedure in the X-valley. Findings of this work could provide a new horizon for the realization of next generation spin-photonic devices which are less sensitive to Joule heating.

Direct Bandgap-like Strong Photoluminescence from Twisted Multilayer MoS2 Grown on SrTiO3.

While direct bandgap monolayer 2D transition metal dichalcogenides (TMDs) have emerged as an important optoelectronic material due to strong light-matter interactions, their multilayer counterparts exhibit an indirect bandgap resulting in poor photon emission quantum yield. We report strong direct bandgap-like photoluminescence at ∼1.9 eV from multilayer MoS2 grown on SrTiO3, whose intensity is significantly higher than that observed in multilayer MoS2/SiO2. Using high-resolution electron microscopy we observe interlayer twist and >8% increase in the van der Waals gap, which leads to weaker interlayer coupling. This affects the evolution of the band structure in multilayer MoS2 as probed by transient absorption spectroscopy, causing higher photo carrier recombination at the direct gap. Our results provide a platform that could enable multilayer TMDs for robust optical device applications.

Efficient and Stable Perovskite Solar Cells by Fluorinated Ionic Liquid–Induced Component Interaction

The instability of organic cations in lead halide perovskite materials is a major obstacle for the commercial breakthrough of perovskite photovoltaics due to desorption of organic cations during the thermal annealing and device operation. Herein, a novel strategy is reported to improve the performance and stability of organic halide perovskite solar cells containing organic cations by adding a small amount of the ionic liquid methylammonium difluoroacetate (MA+DFA−). Nuclear magnetic resonance and Fourier‐transform infrared spectroscopy measurements show that MA+DFA− can anchor the organic cations via hydrogen bonding and enhance the Pb–O interaction in perovskite precursors, leading to the retardation of the perovskite crystallization and improved stability of the perovskite precursor solution. Dynamic light scattering and scanning electron microscopy verify the defect‐passivation effect of MA+DFA− on the perovskite precursors and films. The passivated perovskite film shows superior photo carrier dynamics as investigated by time‐resolved photoluminescence and transient absorption spectra. Moreover, the hydrogen bonding of the perovskite with MA+DFA− imparts excellent ambient and thermal stability to the film as revealed by X‐ray diffraction measurements. As a result, devices with a high efficiency of 21.46% and excellent stability over 180 days in nitrogen atmosphere at room temperature are achieved with the ionic liquid.

Preservation of open circuit voltage in a quantum dot solar cell using GaSb quantum confined superlattice

Quantum dot solar cell (QDSC) is still far below the celebrated Shockley- Queisser limit due to an enhancement in photocurrent only. However, there is very less number of literatures that reports regarding voltage preservation in QDSC, which is one of the most important paradigms in achieving high efficiency. Here a single junction QD embedded intermediate band solar cell (SJ QDIBSC) is designed, which not only preserves the open circuit voltage, but also shows an improvement in short circuit current at the same time. In this work a number of 1-D quantum confined highly mismatched GaSb superlattice is used in the bulk GaAs solar cell, which results an increment in carrier lifetime of minority photo carriers as well as two-photon sub-bandgap photocurrent generation. This model is simulated and validated using Silvaco ATLAS TCAD tool.

Effect of photodeposition conditions on Ni–CdS photocatalysts and its role in the photoactivity for H2 production from ethanolic solutions

The incorporation of Ni-based cocatalysts on CdS by photodeposition has been investigated as a way of improving the photocatalytic efficiency of CdS for the production of hydrogen from ethanolic solutions under solar light. Specifically, this work investigates the effect of the concentration of CdS in the suspensions used in the photodeposition of Ni over the structure, chemical state, and dispersion of the Ni species deposited on CdS. The change in the concentration of CdS during photodeposition leads to changes in the light absorption capacity of CdS by insertion of Ni2+ ions in its structure, and also in the concentration of heterojunctions formed by the close interaction between the Ni species (Ni(OH)2) and CdS. The Ni–CdS photocatalyst prepared with the lower CdS concentration in the suspension during the photodeposition of Ni showed the highest photoactivity for the production of hydrogen from ethanolic solutions. This outcome is related to the combination of an improvement in the light absorption ability, i.e. narrow band gap associated with a higher insertion of Ni2+ ions in the structure, and an increase in the heterojunctions of Ni(OH)2 on CdS which improves the photo carrier generation, separation and availability on the photocatalyst surface, thus resulting in a more efficient photoproduction of hydrogen.

Analytical solution of magneto-photothermal theory during variable thermal conductivity of a semiconductor material due to pulse heat flux and volumetric heat source

In this investigation, the variable thermal conductivity, which depends on a linear function of temperature, is studied during photothermal excitation processes. The influence of the external magnetic field in the context of volumetrically heat source (optically external source) of an elastic semiconductor medium is investigated. The influence of pulse heat flux and thermal memory of the generalized thermoelasticity theory is taken into consideration. The governing equations are obtained in one dimension (1D) by cylindrical coordinates. The interactions between Photo (carrier density)-elastic and magneto-thermal waves are described analytically. The Laplace transform method in 1D is used to obtain the solutions of principal physical field quantities under investigation. The mechanical deformation during the mechanical loads and thermal gradient temperature are applied on the outer surface of the medium. Fourier series expansion and some numerical techniques are used to get the complete solution of physical fields in the physical time-domain. The resulting physical quantities are obtained numerically, discussed, and graphically presented for an example of a semiconductor material.

Application of MEG in Increasing External Quantum Efficiency Over 100%

This review paper focuses on increasing the efficiency of Solar cell using Quantum Dot. The principle idea is using MEG (Multiple exciton Generation). MEG is more efficient in quantum confined nanostructures than in bulk semiconductors because the momentum preservation prerequisite is relaxed. Even the carrier-carrier interactions are huge due to strong confinement. The carrier multiplication decoupling from the effective band gap allows amplified photo-voltage for corresponding carrier multiplication. Along with this, it was also found that external quantum efficiency (EQE) would reach almost 100%, sometimes even exceeding it, for energy which is greater than twice the band gap energy. This is due to the fact that high energy photons have the ability to produce more than one photo carrier pair. MEG is definitely a promising route to increasing solar cell efficiency. If a threshold of twice the band gap energy could be realized for impact ionization in a colloid Quantum Dot cell, the theoretical maximum possible conversion efficiency would shift to above 60%. The goal is to capture maximum energy incident on a given plane and targeting highyield transportation of the resultant photo generated charge.

Light trapping effect of textured FTO in perovskite solar cells

Hybrid organic–inorganic halide perovskites solar cells (PVSCs) have made great progress in just a few years. With maximum efficiencies evolving from 3.8% to 22.1%. The ongoing efficiency improvements are obtained mainly through the optimization of material process and the enhancement of interface. Whereas the conflict between generating photo carriers and collecting carriers is still a challenge for PVSCs. Light trapping design provides a promising way to solve the problem. However, there are few reports about light trapping effect in PVSCs. In this contribution, FTO substrates with different texture etched by laser were used to fabricate PVSCs. The influence of roughness on absorption of the perovskites layer and extraction properties of the carriers across the interface were discussed. The results showed that the device on the FTO substrate etched by laser with 4A current intensity showed a highest power conversion efficiency, with an enhancement of 13.2% compared with that on the unetched substrate due to the improved scattering of light in the photoactive layer. Our result is expected to open up a new way to enhance the PCE of PVSCs.

Emerging solar cells energy trade-off: Interface engineering materials impact on stability and efficiency progress

Emerging solar cell (ESC) carrier's dynamic transfer difficulties and instability at dissimilar material's interface seems to be potential distress. Electrical permittivity influences on photo carrier dynamics of nonpolarized organic and polarized organic-inorganic perovskite solar cell. ESC electrical efficiency and stability are consider to be managed broadly by carrier accumulation, extraction, and conduction techniques. Active materials optoelectric interaction and carrier accumulation are petite known. Its energetic dealings with dissimilar interface materials how support to faster carrier extraction and conduction are still in haze. In this drill, focus on active to interface materials key properties are imperative to find a way to promote electrical energy conversion and its steadiness. Selected advanced interface engineering materials (IEMs) architectures, conduction, and multifarious relations to active materials for efficient energy transfer ability and stability are reported precisely by the model. The interface structure consistency supports to systematize energy transfer, otherwise, disorder or energy loss is anticipated. Therefore, active material linkage to IEM photophysical, quantum, and choice of materials technologies are focused comprehensively to explore the pathway of ESC stability and efficiency progression.

Influence of substrate effects in magnetic and transport properties of magnesium ferrite thin films

In order to study the substrate influence in Mg ferrite properties, thin films were simultaneously grown by DC magnetron sputtering on different substrates (MgO (100) and SrTiO3 (100)). In both cases samples show high values of saturation magnetization and Curie temperatures above room temperature. While in the case of the sample grown on MgO the hysteresis loops indicate the existence of more than one ferrimagnetic component and lower value of remanence to saturation ratio, the deposited one on SrTiO3 is mono-component and has a rectangular-shape magnetic loop at all temperatures below 300 K. The difference is attributed to different microstructures due to the misfit strain caused by the different lattice constants between substrates and ferrite. The electric transport and photoconductivity properties have been investigated on both samples. Thin film growth on STO presents an increase around 40% of the photoconductance in the near UV range. The photocurrent shows two clear onsets that coincide with the indirect and direct band gaps of STO indicating the important role of this substrate in the generation of photo carriers.

Ultraviolet light-induced terahertz modulation of an indium oxide film.

Active ultraviolet light-induced terahertz modulation of an indium oxide film is investigated. A large absorption modulation of ~66% is achieved upon illumination with a low intensity UV laser (11 mW/cm2). The interaction between indium oxide and a flexible metamaterial structure is investigated owing to the large UV-induced enhancement of photo carriers observed in an indium oxide film. We are able to realize absorption peak shifts of 37 GHz by changing the UV excitation light intensity. We also propose a multi-frequency switch by building a circular metallic split ring resonator whose gaps are filled with silicon, germanium, and indium oxide. In future, a photo-excited tunable multi-frequency metamaterial switch can be realized by irradiating the structure with multi-wavelength laser beam.

Heterojunction solar cells based on graphene woven fabrics and silicon

Graphene-on-semiconductor has been proved to be a quality heterojunction with efficient photoelectric conversion. In this work, we constructed Schottky junction solar cells by combing graphene woven fabrics (GWFs) and n-doped single crystal silicon, and examined the performance of solar cells when GWFs of different meshes were used. Sparse GWFs possessed high optical transparency but led to poor carrier collection, whereas dense GWFs could collect carriers efficiently but generated too few photo carriers due to low transparency. The GWFs with an optimal mesh could provide a good balance between the generation and collection of photo-induced carriers to deliver high power conversion efficiency.

Modeling tools for design of type-II superlattice photodetectors

In this paper, we present a range of modeling tools that are used in the design and performance evaluation of type-II superlattice detectors. Among these is an optical and photo carrier transport model for the spectral total external QE, which takes into account carrier diffusion length. Using this model, the diffusion length is extracted from external quantum efficiency measurements. It can also be used to fine-tune an optical cavity in relation to the wavelength range of interest for optimal quantum efficiency. Furthermore, an electrical device model for band bending, dark current and doping optimization is described. The modeling tools are discussed and examples of their use are given for MWIR type-II detectors based on InAs/AlSb/GaSb superlattices.

The enhanced photo absorption and carrier transportation of InGaN/GaN Quantum Wells for photodiode detector applications

We have conducted a series of measurements of resonantly excited photoluminescence, photocurrent and photovoltage on InGaN/GaN quantum wells with and without a p-n junction under reverse bias condition. The results indicate that most of the resonantly excited photo-generated carriers are extracted from the quantum wells when a p-n junction exists, and the photon absorption of quantum wells is enhanced by the p-n junction. Additionally, the carrier extraction becomes more distinct under a reverse bias. Our finding brings better understanding of the physical characteristics of quantum wells with p-n junction, which also suggests that the quantum well is suitable for photodiode detectors applications when a p-n junction is used.

Metal oxide composite thin films made by magnetron sputtering for bactericidal application

Abstract To broaden the application of antibacterial catalysts, ZnO/Ag2O composite thin films with different Ag2O contents have been successfully synthesized on non-woven fabric at room temperature by radio frequency (RF) sputtering with a single ceramic target formed by hot pressing ZnO/Ag2O nanocomposite powder in Ar atmosphere at 180 °C for 30 min. The composite thin films were also sputtered on glass substrates for characterizations. The best sputtering condition was found with the Ar/O2 gas flow ratio at 7:1 to obtain pure Ag2O thin film. The deposition of Ag2O nanoparticles on commercially available ZnO particles was also confirmed by HR-TEM prior to hot pressing for synthesizing ceramic targets. In this work, an appropriate amount of Ag2O incorporated in the composite film was endeavored by forming p–n junction to lower the cost without decreasing bactericidal ability of composite film. The amount of 45 wt% Ag2O in composite thin film to provide bactericidal effect was found to be as good as pure Ag2O. The feasibility in bactericide is due to the light sensitization of low bandgap Ag2O and the formation of nano p–n heterojunction between p-type Ag2O and n-type ZnO for efficient photo carrier separation. The dependence of antibacterial effect of ZnO/Ag2O thin films on the Ag2O content is demonstrated and elucidated in this work.