Increased Light Absorption Research Articles

Near Unity Absorbance and Photovoltaic Properties of TMDC/Gold Heterojunction for Solar Cell Application

In this paper, near unity broadband absorption of Van der Waals semiconductors on a metallic substrate, and their photovoltaic performances in the visible spectrum are simulated. Ultrathin layered semiconductors such as Molybdenum disulfide (MoS2), Tungsten disulfide (WS2), Molybdenum di-selenide (MoSe2), Tungsten di-selenide (WSe2), Molybdenum ditelluride (MoTe2), and Tungsten ditelluride (WTe2) can create strong interference by damping optical mode in their multilayer form and increase light absorption at their heterojunctions with noble metals. From our simulation, it is observed that this absorbance can reach up to 94% when the semiconductors are placed on a gold substrate. The optimum thickness of these semiconductors in their heterostructures with gold is analyzed to create resonant absorption to generate the maximum amount of current density. The power conversion efficiency of the designed Schottky junction solar cells is calculated from their current density vs bias voltage characteristics that ranges from 1.57% to 6.80%. Moreover, the absorption coefficient, dark current characteristic, electric field intensity distribution in the device, and carrier generation rate during light illumination are presented with a view to characterizing and comparing among the parameters of TMDC based nanoscale solar cell.

RETRACTED ARTICLE: Artificial photoactive chlorophyll conjugated vanadium carbide nanostructure for synergistic photothermal/photodynamic therapy of cancer

Optically active nanostructures consisting of organic compounds and metallic support have shown great promise in phototherapy due to their increased light absorption capacity and high energy conversion. Herein, we conjugated chlorophyll (Chl) to vanadium carbide (V2C) nanosheets for combined photodynamic/photothermal therapy (PDT/PTT), which reserves the advantages of each modality while minimizing the side effects to achieve an improved therapeutic effect. In this system, the Chl from Leptolyngbya JSC-1 extracts acted as an efficient light-harvest antenna in a wide NIR range and photosensitizers (PSs) for oxygen self-generation hypoxia-relief PDT. The available large surface of two-dimensional (2D) V2C showed high Chl loading efficiency, and the interaction between organic Chl and metallic V2C led to energy conversion efficiency high to 78%. Thus, the Chl/ V2C nanostructure showed advanced performance in vitro cell line killing and completely ablated tumors in vivo with 100% survival rate under a single NIR irradiation. Our results suggest that the artificial optical Chl/V2C nanostructure will benefit photocatalytic tumor eradication clinic application.Graphical

Excited-State Properties of CuInP2S6 Monolayer as Photocatalyst for Water Splitting.

In recent years, two-dimensional (2D) materials of ferroelectricity have been illustrated to have great potential in solar energy conversion processes such as photocatalytic water splitting, although the optical properties of such materials are rarely discussed. In combination with the first-principles calculations, many-body Green's function method was used to obtain the excited-state properties of the representative CuInP2S6 to unravel the ingredients affecting the photocatalytic behavior. In particular, quasiparticle (QP) band gap correction and bound exciton binding energy are 1.25/1.38 and 0.93/0.87 eV for paraelectric/ferroelectric CuInP2S6, respectively. In addition to facilitating the charge carrier recombination, here we emphasize that the large exciton binding energy reduces the reduction potential of the photoexcited electrons. In bilayer structures, the improved photocatalytic performance should be ascribed to the type-II band alignment and large band edge offsets (0.44 and 0.33 eV for CuInP2S6), rather than the increased light absorption due to the reduced band gap.

WS2 coating and Au nanoparticle decoration of ZnO nanorods for improving light-activated NO2 sensing

ZnO-based heterogenous nanostructures are considered as excellent active materials for fabricating highly sensitive and selective gas sensors. In this work, nanocomposite WS2/Au/ZnO nanorods were synthesized by covering WS2 thin coatings on the surface of ZnO nanorods and embedding Au nanoparticles between the WS2 coatings and the ZnO nanorods, and the light activated sensing performance of the sensor using the WS2/Au/ZnO nanorods as the sensing material was evaluated. With an average ZnO nanorod diameter of 60 nm, WS2 coating thickness of 10 nm, and Au nanoparticle diameter of 5 nm, the WS2/Au/ZnO nanorods present high photoactivity because of widened photoresponse region, increased light absorption, and quenched photoluminescence. The performance for sensing NO2 gas of the WS2/Au/ZnO nanorod-based sensor under 365, 455 or 655 nm light activation was compared with that of a bare ZnO nanorod-based sensor. The WS2/Au/ZnO nanorod-based sensor exhibits better sensing performance than the bare ZnO nanorod-based sensor under 365 or 455 light activation, with the response to 20 ppm NO2 of the former 40% higher than that of the latter. The improved sensing performance is attributed to the co-sensitization of semiconductors and metals.

A novel g-C3N4 nanosheet/Ag3PO4/α-Bi2O3 ternary dual Z-scheme heterojunction with increased light absorption and expanded specific surface area for efficient photocatalytic removal of TC.

A novel ternary dual Z-scheme 2D g-C3N4 nanosheet/Ag3PO4/α-Bi2O3 (CNN/AP/BO) photocatalyst was successfully synthesized by an in situ deposition and hydrothermal-calcination method. The coupling of AP and BO remarkably enhanced the photocatalytic tetracycline (TC) degradation under visible light illumination, with an optimal removal efficiency of 91.6% (60 min), which can be attributed to the extended visible-light absorption and increased specific surface area owing to the interfacial intimate coupling with well-matched energy band positions between semiconductors. The improved photocatalytic activity resulted from the abundant free radicals by the order of ˙O2- > h+ > ˙OH based on the electron spin resonance (ESR) and quenching experiment results. In addition, the possible mechanism of TC degradation over the ternary dual Z-scheme heterojunction CNN/AP/BO was proposed.

Coordinating light management and advance metal nitride interlayer enables MAPbI3 solar cells with >21.8% efficiency

Due to the continuous increase in power conversion efficiencies (PCEs), perovskite solar cells (PSCs) are widely considered as the most promising technology for third generation photovoltaics. Improving optical absorption while reducing electrical losses is still a challenge towards attaining PCE values closer to the Shockley-Queisser limit. However, frequently used strategies to improve light absorption (e.g. via texturing the front surface) often cause electrical recombination losses. Here, we successfully relaxed the competing mechanisms between electrical and optical properties by integrating a modulated textured substrate and an amorphous metal nitride interface modification layer to combine enhanced light scattering and reducing interfacial recombination losses in PSCs. This comprehensive electro-optical management presents several advantages, including increased light absorption, promoting bandgap alignment and passivating the underlying perovskite defects. Consequently, the resulting MAPbI3 solar cells exhibit a high open-circuit voltage of 1.17 V and the concomitant high PCE of 21.84%. In addition, we also use numerical simulations to propose approaches towards achieving high efficiency (PCE>30%) PSCs. Besides expanding the pool of available strategies for improving the efficiency of PSCs, from photon management to interface engineering, our work also offers a systematic guidance for the design and fabrication of high performance photovoltaic devices.

Varying heterojunction thickness within space charge region for photocatalytic water splitting

Photocatalytic overall water splitting for converting solar energy into hydrogen is a potential means of pursuing a renewable, scalable, and eco-friendly energy source. It is challenging to achieve the 5%–10% solar-to-hydrogen (STH) efficiency needed to be economically viable for renewable solar hydrogen production. Here, we report a heterojunction in which the thickness within the space charge region can be precisely adjusted to enhance the redox capacity, increase light absorption, and reduce carrier transport distance. The fully stacked two catalysts and aqueous-solution-exposed surfaces exhibit advantages of an enhanced built-in-electric field and a highly effective surface area. Based on that, an Ag 3 PO 4 /CdS/Pt photocatalyst exhibits overall water splitting with an STH efficiency, dramatically improving from zero to 0.75% under visible light at ambient pressure by tuning CdS/Ag 3 PO 4 thickness from 200 nm/120 nm to 60 nm/30 nm. The STH efficiency can be further enhanced to 2% under visible light in 0.01 mol L −1 Na 2 S solution. • Heterojunction with varying thickness within space charge region to improve redox ability • Ag 3 PO 4 -CdS-Pt heterojunction photocatalyst prepared using electron beam evaporation • High photocatalytic water-splitting efficiency achieved by the Ag 3 PO 4 -CdS-Pt samples • The photocatalytic efficiency is enhanced by tuning the Ag 3 PO 4 /CdS film thickness Lv and Huang report a strategy for highly efficient water splitting by controlling the thickness of films within the space charge region. An Ag 3 PO 4 -CdS-Pt photocatalyst exhibits overall water splitting with solar-to-hydrogen efficiency changing from 0% to 0.75% under visible light by adjusting its thickness.

Extracting epsilon-near-zero wavelength of ultrathin plasmonic film.

Strong optical nonlinearities of plasmonic thin films exist at their epsilon-near-zero (ENZ) wavelengths, which are essential to be acquired first for the design and fabrication of ENZ photonic devices. However, it has been challenging to obtain the ENZ wavelength precisely when the film thickness is reduced to tens of nanometers or less. By enhancing both electric field intensity and light-matter interaction distance in the film, we propose that the ENZ wavelength and the medium model of ultrathin films can be extracted accurately from the transmittance and reflectance spectra under oblique light excitation. A characteristic valley in the transmittance spectrum, which originates from the increased light absorption caused by the ENZ electric field enhancement, can be used to determine the ENZ wavelength with significantly improved fitting accuracy of the Drude parameters. The work in this paper provides an accurate and effective method for the acquisition of ENZ wavelength and will contribute to the research of nonlinear plasmonic devices.

Photocatalytic water splitting ability of Fe/MgO-rGO nanocomposites towards hydrogen evolution

Photocatalytic water splitting has greatly stimulated as an ideal technique for producing hydrogen (H2) fuel by employing two renewable sources, i.e., water and solar energy. Here, we have adopted a facile hydrothermal approach for the successful synthesis of reduced graphene oxide (rGO) incorporated Fe/MgO nanocomposites followed by thermal treatment at inert atmosphere to investigate their ability for photodegradation and photocatalytic hydrogen evolution via water splitting. Transmission Electron Microscopy images of Fe/MgO-rGO nanocomposite ensured the distribution of Fe/MgO nanoparticles throughout rGO sheets. Notably, all rGO supported nanocomposites, especially the one, thermally treated at 500 °C at Argon (Ar) atmosphere has demonstrated significantly higher photocatalytic efficiency towards the photodegradation of a toxic textile dye, rhodamine B, than pristine MgO and commercially available Degussa P25 titania nanoparticles as well as other composites. Under solar irradiation, Fe/MgO-rGO (500) nanocomposite exhibited 86% degradation of rhodamine B dye and generated almost four times higher H2 via photocatalytic water splitting compared to commercially available P25 titania nanoparticles. This promising photocatalytic ability of the Fe/MgO-rGO(500) nanocomposite can be attributed to the improved morphological and surface features due to heat treatment at inert atmosphere as well as escalated charge carrier separation with increased light absorption capacity imputed to rGO incorporation.

Design and fabrication of hollow structured Cu2MoS4/ZnIn2S4 nanocubes with significant enhanced photocatalytic hydrogen evolution performance

The unique architecture is very significant for photocatalysts to achieve high photocatalytic efficiency. Herein, hollow Cu2MoS4/ZnIn2S4 heterostructural nanocubes with intimate-contact interface have been prepared for the first time via a self-template way, which can promote the photocatalysis hydrogen evolution. First, novel hollow structured Cu2MoS4 nanocubes were successfully synthesized using Cu2O as a precursor, then the ZnIn2S4 nanosheets were in-situ grew on the surface of hollow Cu2MoS4 nanocubes. The unique hollow heterostructures have markedly enhanced photocatalytic efficiency, and 15 wt% Cu2MoS4/ZnIn2S4 sample exhibits the highest hydrogen production rate of 8103 μmol·h−1·g−1, which is approximately four times higher than pure ZnIn2S4. The improved photocatalytic performance is mainly attributed to the following two points: (1) the hollow nanocube structure can provide rich active sites and increase light absorption; (2) forming a built-in electric field is conducive to transfer the holes generated by ZnIn2S4 to Cu2MoS4, which can effectively promote charge separation. This work may provide insights for the design of hollow architecture cage materials for high photocatalytic performance.

ZnO hierarchical structures as sacrificial inclusions for enhanced performance under full sun and indoor light in bifacial dye sensitized solar cells

We have already demonstrated a facile strategy for improving light scattering in bifacial dye sensitized solar cells (DSSCs) through fugitive inclusions of ZnO micro-flowers leading to enhanced photovoltaic performance without adversely affecting the transparency (Sasidharan et al., 2020). In the present work, we were able to further ameliorate the light scattering properties by employing micron sized ZnO hierarchical structures (fibril and sheet like aggregates) as sacrificial inclusions. ZnO hierarchical structures being deposited over TiO2 active layer were selectively etched off, leaving behind imprints over the TiO2 layer, which act as scattering centers to enhance the photocurrent of DSSCs owing to the increased light absorption. The present strategy extends the possibility to improve the performance of DSSCs under both one sun (100 mW/cm2) as well as indoor/ambient light conditions without compromising transparency to larger extend. By employing this strategy on a 6 µm thick TiO2 photoanode and implementing it in a DSSC using N719 sensitizer and iodide/triiodie electrolyte, power conversion efficiency of 15.5% could be achieved under indoor illumination (1000 lx) from a compact fluorescent lamp. A detailed study of the charge transfer dynamics at various interfaces were carried out using a range of electrical and optical perturbation techniques.

TiO2 nanotube arrays sensitized by copper (II) porphyrins with efficient interfacial charge transfer for the photocatalytic degradation of 4-nitrophenol

In this paper, photocatalysts based on TiO2 nanotubes (TNTs) and TiO2 nanotube arrays (TNTAs) sensitized by Cu(II) meso-tetrakis(N-ethylpyridinium-4-yl) porphyrin (CuTEPyP) were synthesized and their structures were characterized by various analytical methods. The photocatalytic activities of both composites were then investigated through degradation of 4-nitrophenol (4-NP) in aqueous solutions under visible light irradiation. It was found that CuTEPyP/TNTAs could eliminate 95% 4-NP within 4 h, which was considerably higher than the yield obtained with CuTEPyP/TNTs (56%) under the same conditions. Compared to CuTEPyP/TNTs, the improved photocatalytic activity of CuTEPyP/TNTAs can be ascribed to increased light absorption, high separation rate of photo-generated charge pairs, and efficient charge transfer. A plausible photocatalytic degradation mechanism involving hydroxyl radicals, superoxide radical anions and singlet oxygen species was also proposed. This work presents an efficient paradigm for eliminating 4-NP under visible light irradiation.

Broadband responsivity enhancement of Si photodiodes by a plasmonic antireflection bilayer.

Randomly distributed plasmonic Ag nanoparticles (NPs) with various sizes were fabricated by a reflow process to an island-shaped Ag thin-film deposited on a Si photodiode. These NPs conformally enclosed by an antireflective (AR)-type SiNx/SiO2 bilayer reveal significantly diminished reflectance in a broad wavelength (500 nm - 1100 nm) as compared to the cases of Ag NPs or SiO2 layer enclosing Ag NPs on the Si substrate. Accordingly, the forward scattering and the total reflection along with wide-angle interference in between the dielectric bilayer incorporating the Ag NPs induce highly increased light absorption in the Si substrate. The fabricated Si photodiode adopting the plasmonic AR bilayer shows the responsivity peak value of 0.72 A/W at 835 nm wavelength and significant responsivity enhancement up to 40% relative to a bare Si photodiode in a wavelength range of 500 nm to 1000 nm.

P‐4.2: Study on Optical Performances of Transparent LCD with Dichroic Dye‐doped Liquid Crystal

With the development of the Internet of Things, transparent display is playing an increasingly important role in people's lives. The most important optical index of transparent display is transmittance. Due to no need for polarizer, transparent liquid crystal display (TLCD) with dichroic dye‐doped can achieve very high transmittance. In this paper, optical performance and image quality improvement of TLCD with dye‐doped liquid crystal were studied. A new TN pixel design with common electrode of ITO instead of metal to form stored capacitance was used to achieve high aperture ratio (AR). And it was found that bright transmittance of NWSC is higher than that of NBSC due to high anchoring effect of PI to positive liquid crystal. In addition, the transmittance decreases gradually with increasing cell gap due to the increased light absorption by the long axis of dye molecules. The results showed that the TLCD with Dichroic Dye‐doped Liquid Crystal (DDLC) has a good display effect.

Highly active Z-scheme heterojunction photocatalyst of anatase TiO2 octahedra covered with C-MoS2 nanosheets for efficient degradation of organic pollutants under solar light

The construction of a Z-scheme photocatalyst by coupling semiconductors with conductors is an efficient way to achieve high pollutant degradation efficiency. In this study, a hydrothermal approach was used to fabricate a Z-scheme photocatalyst consisting of C-MoS2 sheets wrapped around octahedral anatase TiO2 nanocrystals. The catalyst showed excellent photocatalytic efficiency (99%) for methylene blue degradation with low catalyst loading (0.2 g L-1) under the simulated solar light within 60 min. High photocatalytic degradation efficiencies were also observed for Rhodamine B, methyl orange, and tetracycline under solar irradiation. The C-MoS2 acts as an electron mediator and serves as a carrier transmission bridge for the efficient electron-hole separation. The electron-rich (101)-faceted TiO2 benefits the Z-scheme recombination of electrons from the conduction band of TiO2 and holes at the valence band of MoS2. The semiconductor coupling of (101)-exposed octahedral TiO2 and 2H-MoS2 as well as the introduction of solid-state electron mediators, 1T-MoS2 and carbon, resulted in increased light absorption and accelerated charge transfer at the contact interface, which enhanced the photocatalytic activity of the photocatalyst significantly compared to those of P25, MoS2/TiO2, and C-MoS2. The efficient separation of electron-hole pairs prolongs their lifetime for oxidation and reduction reactions in the degradation process.

CdSe 1D/2D Mixed-Dimensional Heterostructures: Curvature-Complementary Self-Assembly for Enhanced Visible-Light Photocatalysis.

Mixed-dimensional heterostructures (MDHs), which combine nanomaterials of different dimensionalities deliver on the promise to bypass intrinsic limitations of a given low-dimensional material. Here, a strategy to engineer MDHs between two low-dimensional materials by curvature-complementary self-assembly is described. CdSe nanotubes rolled from 2D nanosheets and 1D CdSe nanorods, with negative and positive curvatures, respectively, are selected to illustrate complementary curvature self-assembly. The assembly process, optical, and photoelectrical properties of the CdSe MDHs are thoroughly investigated. Several remarkable features of CdSe MDHs, including increased light absorption, efficient charge separation, and appropriate bandgap structure are confirmed. The MDHs significantly alleviate the sluggish kinetics of electron transfer in the quantum sized CdSe subunits (onset potential of 0.21V vs RHE for MDHs; 0.4V lower than their low-dimensional building blocks), while the spatial nano-confinement effect in the CdSe MDHs also assists the interfacial reaction kinetics to render them ideal photocatalysts for benzylamine oxidation (conversion >99% in 4h with a two times higher rate than simple mixtures). The results highlight opportunities for building MDHs from low-dimensional building blocks with curvature-complementary features and expand the application spectrum of low dimensional materials in artificial photosynthesis.

The importance of the shape of Cu2O nanocrystals on plasmon-enhanced oxygen evolution reaction in alkaline media

Cu2O nanostructures of cubic or octahedral shape as well as decorated with gold nanoparticles were synthesized by a chemical process. The electrochemical activity of these nanostructures for the oxygen evolution reaction (OER) in alkaline media was assessed in the dark and under solar light irradiation. Electrodes modified with cubic-shaped Cu2O and Cu2O-Au nanostructures revealed both enhanced electrocatalytic OER activity over the octahedral-shaped ones, for which hydroxylation of the (111) surfaces might hinder the OER as supported by numerical computations. Illumination of Cu2O nanostructures with solar light did not enhance the electrocatalytic OER. Cu2O-Au nanostructures, however, showed improved OER activity with an overpotential of 200 mV (10 mA cm−2) and a Tafel slope of 97 mV dec−1. The enhanced OER activity was ascribed to increased light absorption due to the plasmonic properties of Cu2O-Au cubes.

Enhanced photoelectrochemical performance of Si/TiO2 with a high atomic density SiO2 buffer layer

Nanostructured Si is a promising material for photoelectrochemical water splitting, but it has the problem of being well oxidized in water. Depositing a TiO2 layer on the Si surface is an effective way to protect it from oxidation and increase light absorption. However, the lattice mismatch between Si and TiO2 acts as a defect that causes an efficiency reduction. To improve the interface and electrical properties of TiO2/Si, nitric acid oxidation of Si (NAOS) is used to form a high-density SiO2 layer and analyze the effect of photoelectrochemical properties. Due to the lattice mismatch, the TiO2/Si sample (−3.12 mA/cm2) decreases about 1.8 times when using SiO2. In TiO2/SiO2/Si samples (-5.70 mA/cm2) further decrease after post-oxidation annealing (POA) (−7.70 mA/cm2). As a result, it can be seen that by fabricating an ultra-thin high-density SiO2 layer, the lattice mismatch at the TiO2/Si interface is reduced and the photocurrent density is improved.

Whey protein addition and its increased light absorption and tinctorial strength of model solutions colored with anthocyanins

Anthocyanins (ACN) are pigments with vivid colors, but their application as food colorants is restricted by their limited stability and color expression. Anthocyanins exhibit higher stability in dairy systems than in buffers at similar pH, suggesting that pigments may be able to interact with dairy components such as proteins, resulting in improved performance as colorants. Our objective was to determine the type of interaction between whey proteins (WP) and ACN leading to color enhancements and to determine the role of the ACN chemical structure in this interaction. Model solutions colored with semipurified pigments from sources with different ACN profiles (Berberis boliviana, grape skin, purple corn, black carrot, and red cabbage) were mixed with different concentrations of whey protein isolate (WPI) in pH 3 buffer. Absorption spectra of these solutions were acquired using an absorbance microplate reader, and color parameters were calculated from spectral data. Isolated ACN 3-glucosides were used to determine the role of the aglycone structure in the WP-ACN interaction using visible and fluorescence spectroscopy. In silico modeling was used to visualize potential differences in the interaction between β-lactoglobulin and ACN. Addition of WPI resulted in hyperchromic shifts at the wavelength of maximum absorption in the visible range (λvis-max) of up to 19%, and a significant increase in tinctorial strength for all ACN sources (ΔE > 5). Moreover, ACN acylation did not seem to play a significant role in the WP-ACN interaction. When using isolated ACN, WPI addition resulted in hyperchromic shifts at the λvis-max only for methoxylated ACN such as petunidin-3-glucoside (up to 24%), and malvidin-3-glucoside (up to 97%). The bimolecular quenching constant values (Kq > 1010M-1s-1) strongly suggested that the predominant type of quenching interaction was static. Analysis of enthalpy, entropy, and Gibbs free energy showed that this binding was spontaneous; depending on the chemical structure of the ACN, the predominant binding forces could be hydrophobic interactions or hydrogen bonding. Modeling suggested that methoxylations in the B ring of the aglycon structure promoted interactions with electron acceptor amino acids. Overall, WP could be used to enhance the tinctorial strength of select ACN depending on their structural characteristics. Therefore, ACN source selection may play a key role for specific applications in dairy products.

Plasmonic Enhanced InP Nanowire Array Solar Cell through Optoelectronic Modeling

Vertical nanowire (NW) arrays are a promising candidate for the next generation of the optoelectronics industry because of their significant features. Here, we investigated the InP NW array solar cells and obtained the optoelectronic properties of the structure. To improve the performance of the NW array solar cells, we placed a metal layer of Au at the bottom of the NWs and considered their top part to be a conical-shaped parabola. Using optical and electrical simulations, it has been shown that the proposed structure improves the absorption of light in normal incidence, especially at wavelengths near the bandgap of InP, where photons are usually not absorbed. Under inclined radiation, light absorption is also improved in the middle part of the solar spectrum. Increased light absorption in the cell led to the generation of more electron–hole pairs, resulting in an increase in short circuit current density from 24.1 mA/cm2 to 27.64 mA/cm2, which is equivalent to 14.69% improvement.