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Highlights • Visible active CZTS alerted CdS/TiO 2 tandem photoanode made-up by low cost technique. • CZTS/CdS/TiO 2 /FTO shows higher current density due to strong visible light absorption. • PEC properties of photoelectrode have significantly improved by surface modification. • Efficient separation of charge carriers after deposition of CdS and CZTS on TiO 2 /FTO. Abstract A tandem photoanode consisting of Cu 2 ZnSnS 4 (CZTS) nanoparticles layer over CdS/TiO 2 heterostructure thin film on FTO substrate has been fabricated for photoelectrochemical hydrogen generation. CdS thin film has been deposited by chemical bath deposition over the spin-coated TiO 2 thin film, which is followed by the deposition of CZTS nanoparticles layer by spray coating technique resulting in a CZTS/CdS/TiO 2 /FTO photoanode. The coating of CZTS nanoparticles layer over CdS/TiO 2 films resulted in the tandem structure of different band level positions, which enhances the optical absorption in the visible region and also leads to higher separation of the photogenerated charge carriers. A substantial enhancement (39 times) in the PEC activity has been demonstrated for the CZTS/CdS/TiO 2 /FTO photoanode as compared to TiO 2 /FTO photoanode, which is due to cascade band gap from 3.2 eV to 1.7 eV and formation of heterojunction at interfaces. The enhancement in the charge transport properties of CZTS/CdS/TiO 2 /FTO photoanode has been confirmed from the electrochemical impedance spectroscopy (EIS) measurement. The EIS results confirm that the CZTS/CdS/TiO 2 /FTO photoanode exhibited lowest charge transfer resistance (R ct = 302 Ω/cm2) as compared to CdS/TiO 2 (R ct = 615 Ω/cm2) and TiO 2 (R ct = 1700 Ω/cm2) photoanode. A mechanism depicting the enhanced the performance of photoelectrochemical (PEC) CZTS/CdS/TiO 2 /FTO photoanode has been proposed. [ABSTRACT FROM AUTHOR]

In the present work, photoanodes comprising of NaNbO 3 nanorods and Ag nanoparticles decorated NaNbO 3 nanorods have been fabricated by using hydrothermal and chemical solution method respectively. Photoelectrochemical water splitting performance of the fabricated photoanodes have been measured and it is found that Ag decorated NaNbO 3 nanorods exhibit ∼4 fold enhancement in photocurrent as compared to bare NaNbO 3 nanorods. The enhancement in the photoelectrochemical water splitting activity of Ag decorated NaNbO 3 nanorods is attributed to efficient charge carrier separation and visible light sensitization due to Ag nanoparticles on NaNbO 3 nanorods. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of ZnO/MWCNT nanocomposite, and their potential application in photoelectrochemical (PEC) water splitting for hydrogen generation and photocatalytic degradation of methylene blue dye. For the synthesis of nanocomposite, ZnO nanoparticles were grown on the MWCNT surface by a simple chemical route. Microscopic studies showed that ZnO nanoparticles were well dispersed on the MWCNT surface and Raman study confirmed the intimate integration between ZnO and MWCNT. The nanocomposite exhibit higher photocatalytic degradation of methylene blue dye as compared to bare ZnO. The ZnO/MWCNT photoanode shows ∼5 times increase in photocurrent density in comparison to pure ZnO, at an applied potential of +1 V vs. Ag/AgCl. The enhanced photocurrent density of ZnO/MWCNT photoanode is attributed to the decrease in band-bending and effective interfacial electron transfer due to the conducting CNT scaffold, which facilitates the charge collection and charge transport in the ZnO/MWCNT nanocomposite. The Electrochemical impedance spectroscopy measurements confirmed the faster charge transfer at the interface in the case of nanocomposite. These results suggest substantial potential of ZnO/MWCNT nanocomposite in dye degradation and PEC water splitting applications. [ABSTRACT FROM AUTHOR]

Flexible PVDF/NaNbO 3 /RGO thin films have been synthesized and its application in nanogenerator has been explored. In order to understand the effect of the addition of nanofillers NaNbO 3 and RGO in PVDF, we have also synthesized and studied PVDF/RGO and PVDF/NaNbO 3 nanocomposite films. Even though the β-phase contents are nearly same in the three nanocomposite films, it has been found that the output voltage generated from PVDF/NaNbO 3 /RGO nanocomposite film based nanogenerator is maximum (∼2.16 V) with a short circuit current of 0.383 μA. It has been concluded that NaNbO 3 nanorods help in the alignment of the electric dipoles in PVDF and also due to the inherent piezoelectric property, it contributes in the overall piezoelectric property of the film. On the other hand presence of RGO helps to move the charges generated inside the film and further allow the dipoles of PVDF to align which leads to enhanced piezoresponse. [ABSTRACT FROM AUTHOR]

A ternary Ag/TiO 2 /CNT photoanode was prepared by grafting Ag nanoparticles on the surface of as-synthesized TiO 2 /CNT nanocomposite for the photoelectrochemical (PEC) water splitting under visible light irradiance. The ternary composite photoanode was observed to generate four times higher photocurrent density compared to binary TiO 2 /CNT nanocomposite under visible light irradiance. The Ag nanoparticles on the surface of nanocomposite act as a surface plasmon resonance (SPR) photosensitizer under visible light. The enhanced photocurrent density of Ag/TiO 2 /CNT ternary photoanode is attributed to the increased light absorption in the visible region, decrease in band-bending and effective interfacial electron transfer due to the synergetic effect of Ag nanoparticles and CNTs. The enhanced charge transfer within the Ag/TiO 2 /CNT was also confirmed by the electrochemical impedance spectroscopy. This work demonstrates a feasible route to improve the PEC performance of TiO 2 towards water splitting under sunlight irradiation. [ABSTRACT FROM AUTHOR]

Polyaniline (PANI) coupled Zinc oxide (ZnO) nanocomposite has been synthesized by the chemisorption method and demonstrated its potential applications for photocatalytic degradation of methylene blue dye and photoelectrochemical (PEC) water splitting. A ∼7 fold enhancement in the photodegradation activity and ∼3 fold enhancement in the incident photon-to-electron conversion efficiency is observed for PANI/ZnO nanocomposite as compared to bare ZnO nanorods. The observed enhancement in the photocatalytic and photoelectrochemical activity is attributed to the photosensitization effect of visible light responsive PANI and the formation of type-II heterojunction between ZnO and PANI leading to the efficient separation and faster transfer of photoinduced charge carriers at the interface. A possible mechanism for the enhanced photocatalytic activity and photoelectrochemical water splitting for PANI/ZnO nanocomposite has been proposed. [ABSTRACT FROM AUTHOR]

Very high surface area, self-assembled, highly crystalline mesoporous SrTiO3 (STO) thin films were developed for photoelectrochemical water splitting. Much improved performance of these mesoporous films compared to planar STO thin films and any other form of STO such as single crystal samples and nanostructures was demonstrated. The high performance resulted from very large surface area films and optimization of carrier concentration. [ABSTRACT FROM AUTHOR]

Cadmium sulfide nanoflowers (CdS-NF), nanorods (CdS-NR), and its nanocomposites with polyaniline (PANI) were successfully synthesized using facile chemical methods. Transmission electron microscopy (TEM) images confirmed the growth of CdS as nanoflowers and nanorods. High-resolution transmission electron microscopy (HRTEM) images showed clear lattice fringes, indicating good crystallinity of the CdS nanostructures and the formation of interface between PANI and CdS. The photocatalytic activity of CdS nanostructures and its composites was demonstrated for the degradation of methylene blue (MB) dye under visible light irradiation. The PANI/CdS nanocomposites showed enhancement in the photocatalytic activity as compared to bare CdS nanostructures, and it is attributed to efficient charge transfer between CdS and PANI. Photoluminescence study confirmed the enhancement in photogenerated electron-hole pairs separation in CdS nanostructures after the addition of PANI. The composite of PANI with CdS-NF exhibited larger improvement in the photodegradation efficiency over CdS-NF as compared to the improvement observed in PANI/CdS-NR over CdS-NR, which is attributed to the formation of more interfacial sites between PANI and CdS nanoflowers as compared to PANI and CdS nanorods. Our present work indicates that by carefully designing the semiconductor nanomaterial composites, the photocatalytic activity can be significantly enhanced. [ABSTRACT FROM AUTHOR]

Single domain CoFe 2 O 4 nanoparticles with different amount of defects/strain have been synthesized by varying the growth temperature in the hydrothermal method. Nanoparticles grown at lower temperature are of larger size and exhibit more planar defects and oxygen vacancies as compared to nanoparticles grown at higher temperatures which are of smaller sizes and exhibit less planar defects and oxygen vacancies. The nanoparticles with larger amount of defects also possess a higher value of intrinsic strain as compared to nanoparticles with fewer defects. The presence of intrinsic strain in the nanoparticles is found to shift the cationic distribution at the tetrahedral and octahedral sites. The saturation magnetization ( M s ) of the nanoparticles is found to depend upon both the intrinsic strain and size of the nanoparticles. The M s increases with the decrease in the nanoparticles size from 32 nm to 20 nm, and this is correlated to the inverse of spin canting effect due to decrease in the intrinsic strain which leads to shifting of Co 2+ ions from tetrahedral to octahedral sites. However, with further decrease in the size of the nanoparticles (16 nm), the size effect dominates over the strain effect leading to decrease in M s . The coercivity is found to be higher in the nanoparticles with larger amount of defects/strain and has been attributed to strain induced strong spin canting and pinning due to defect sites. The variation of coercivity with particle size ( D ) exhibits deviation from D 3/2 dependence for the nanoparticles with larger amount of strain/defects. [ABSTRACT FROM AUTHOR]

CdS nanorods decorated with CoFe 2 O 4 (CFO) nanoparticles have been synthesized by using a facile soft chemical method. The surface of the nanorods was carefully functionalized with citrate ions to attach the CFO nanoparticles. The CFO nanoparticles decorated CdS nanorods were found to exhibit enhanced visible light driven photocatalytic activity for the degradation of methylene blue dye as compared to CdS and CFO nanostructures. The enhancement in the photocatalytic activity is attributed to the formation of heterojunction between the CdS and CFO which significantly suppresses the recombination of the photogenerated charge carriers. Also, due to the magnetic behavior of CFO this coupled nanostructure can be easily separable from the aqueous solution by applying an external magnetic field. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (RGO) coupled CdS/ZnO core/shell nanorods have been synthesized using a soft chemical route. The photocatalytic activity of CdS/ZnO/RGO nanostructure has been examined for the degradation of methylene blue dye under solar irradiation at room temperature. The CdS/ZnO/RGO nanostructure exhibits five times enhanced photocatalytic activity as compared to CdS nanostructures which is attributed to the formation of heterojunction between the CdS and ZnO and its coupling with the reduced graphene oxide which facilitates the efficient transport of photogenerated charge carriers. Also, CdS/ZnO core/shell nanostructure exhibits very good photostability due to the presence of stable ZnO as cap layer. [ABSTRACT FROM AUTHOR]

Two sets of single domain CoFe 2 O 4 (CFO) nanoparticles have been synthesized using hydrothermal technique which are of the same sizes, but with different amount of strain/defects. The nanoparticles synthesized at a lower growth temperature (80 °C) exhibit high density of planar defects and oxygen vacancies as compared to the CFO nanoparticles grown at higher temperature (180 °C). The CFO nanoparticles with high density of defects also possess higher intrinsic strain. The nanoparticles with higher strain/defects exhibit higher coercivity and smaller value of saturation magnetization. The effect of strain on the magnetization characteristics of CFO nanoparticles is simulated using the Object Oriented MicroMagnetic Framework. The observed larger value of coercivity for the CFO nanoparticles with higher intrinsic strain is attributed to strain induced enhanced anisotropy of the nanoparticles. [ABSTRACT FROM AUTHOR]

Pure and Indium (In) doped SnO2 nanocrystalline thin films have been fabricated using sol-gel technique. The effect of In-doping on structural, optical and magnetic properties has been studied. Scanning electron microscopy (SEM) study reveals that the grains of pure and doped SnO2 possesses spherical symmetry. X-ray diffraction (XRD) study reveals that pure and In-doped SnO2 thin films possess rutile structure having tetragonal phase. UV-visible study suggests that with In-doping in SnO2, the value of the band gap first increases (upto 5% In-concentration) but further increase in concentration of In to 25% leads to decrease in band gap. It has been found from the room temperature magnetic study that pure and In-doped SnO2 thin films show ferromagnetic behaviour, however with 5% In-doping saturation magnetization value increased. The observed ferromagnetic behaviour may be due to the defects and oxygen vacancies. [ABSTRACT FROM AUTHOR]

The interest in two-dimensional and layered materials continues to expand, driven by the compelling properties of individual atomic layers that can be stacked and/or twisted into synthetic heterostructures. The plethora of electronic properties as well as the emergence of many different quasiparticles, including plasmons, polaritons, trions, and excitons with large, tunable binding energies that all can be controlled and modulated through electrical means, has given rise to many device applications. In addition, these materials exhibit both room-temperature spin and valley polarization, magnetism, superconductivity, piezoelectricity that are intricately dependent on the composition, crystal structure, stacking, twist angle, layer number, and phases of these materials. Initial results on graphene exfoliated from single bulk crystals motivated the development of wide-area, high purity synthesis and heterojunctions with atomically clean interfaces. Now by opening this design space to new synthetic two-dimensional materials "beyond graphene," it is possible to explore uncharted opportunities in designing novel heterostructures for electrically tunable devices. To fully reveal the emerging functionalities and opportunities of these atomically thin materials in practical applications, this review highlights several representative and noteworthy research directions in the use of electrical means to tune these aforementioned physical and structural properties, with an emphasis on discussing major applications of beyond graphene 2D materials in tunable devices in recent years and an outlook of what is to come in the next decade. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO), an insulating analogue to highly conducting graphene, is considered as a chemically tunable platform for optoelectronic applications. However, to be useful for such applications, detailed analysis of its optical properties with a controlled degree of de-oxidation need to be investigated. In this report, we investigated the optical behaviour of GO and chemically reduced GO (with different degrees of de-oxidation, termed as RGO-5 and RGO-10) deposited onto SiO2/Si substrates, using variable angle spectroscopic ellipsometry. GO and its chemically tuned derivatives (RGO-5 & RGO-10) have been synthesized using Hummer’s method and by its corresponding reduction using different concentrations (5 and 10 ml) of reducing agent, respectively. Optical properties such as bandgap, the refractive index, the extinction coefficient, and complex dielectric behaviour over the wavelength region 250-1650 nm have been investigated. The optical bandgap is found to reduce systematically from 3.25 eV for GO to 2.78 and 1.81 eV for RGO-5 and RGO-10 samples, respectively. Whereas, the dielectric behaviour of RGO-5 sample found to be better with a lower value of extinction coefficient as compared to GO and RGO-10 samples. [ABSTRACT FROM AUTHOR]

Highlighted with improved long-term thermal and environmental stability, all-inorganic metal halide perovskites exhibit tunable physical properties, cost-effective synthesis, and satisfactory optoelectronic performance, attracting increasing research interest worldwide. However, a less explored feature of these materials is their strong spin–orbit coupling (SOC), which is the hidden force influencing not only band structure but also properties including magnetoresistance, spin lifetime, and singlet-triplet splitting. This review provides an overview of the fundamental aspects and the latest progress of the SOC and debate regarding Rashba effects in all-inorganic metal halide perovskites, providing critical insight into the physical phenomena and potential applications. Meanwhile, crystal structures and photophysics of all-inorganic perovskite are discussed in the context of SOC, along with the related experimental and characterization techniques. Furthermore, a recent understanding of the band topology in the all-inorganic halide perovskites is introduced to push the boundary even further for the novel applications of all-inorganic halide perovskites. Finally, an outlook is given on the potential directions of breakthroughs via leveraging the SOC in halide perovskites. [ABSTRACT FROM AUTHOR]

Three sets of single domain CoFe2O4 nanoparticles of similar sizes (~ 10 nm) with different values of intrinsic strain have been synthesized at three different growth temperatures (120, 140 and 160 °C). The optical bandgap and saturation magnetization of these similar size magnetic nanoparticles are found to be strongly dependent upon the intrinsic strain present in the nanoparticles. The optical bandgap is found to decrease from 1.84 to 1.67 eV and the saturation magnetization decreases from 66.7 to 35.1 emu/g with increase in the intrinsic strain in the nanoparticles. The presence of intrinsic strain is found to affect the cationic redistribution at the tetrahedral and the octahedral sites of the nanoparticles. The decrease in the optical bandgap of CoFe2O4 nanoparticles with increase in the intrinsic strain is correlated to the presence of more Co2+ at the tetrahedral sites. The change in the saturation magnetization is also correlated to the increase in the population of Co2+ at the tetrahedral sites with increase in the intrinsic strain resulting in an enhanced spin canting at the octahedral sites. [ABSTRACT FROM AUTHOR]

In this paper, we present fabrication of 'FeS 2 ' and carbon coated FeS 2 (C–FeS 2) photo-electrodes and demonstrated that coating of carbon on FeS 2 significantly enhanced photo-electrochemical properties. The hydrothermal method has been adopted for the synthesis of FeS 2 and carbon coating on FeS 2 was achieved by CVD technique. The materials are subsequently characterized using X-ray diffraction, Raman spectroscopy and Field enhanced scanning electron microscope (FESEM) techniques for phase identification and morphological studies, respectively. The photo-electrochemical measurements revealed significant enhancement in the current density from ∼2 to 3.7 mA/cm2 (∼1.8 times higher) for C–FeS 2 in comparison to the FeS 2 photo-electrode under visible light. The enhancement in FeS 2 after carbon coating has been attributed to reduction in recombination of photo generated charge carriers, enhancement in the band bending and lowering the charge transfer resistance at the semiconductor/electrolyte interface. To date, very few studies have been reported on FeS 2 based composites for water splitting applications and use of carbon coating can be a novel approach for developing efficient solar to hydrogen conversion devices. The mechanism for the photocurrent enhancement was supported by Mott-Schottky and electrochemical impedance spectroscopy measurements. [ABSTRACT FROM AUTHOR]

The extraordinary electronic, optical, and mechanical characteristics of 2D materials make them promising candidates for optoelectronics, specifically in infrared (IR) detectors owing to their flexible composition and tunable optoelectronic properties. This review presents the recent progress in IR detectors composed of 2D materials and their hybrid structures, including graphene, black phosphorous, transition metal dichalcogenides, halide perovskite as well as other new layered materials and their heterostructures. The focus is on the short‐wave, mid‐wave, and long‐wave infrared regimes, which pose a grand challenge for rational materials and device designs. The dependence of the device performance on the optical and electronic properties of 2D materials is extensively discussed, aiming to present the general strategies for designing optoelectronic devices with optimal performance. Furthermore, the recent results on 2D material‐based heterostructures are presented with an emphasis on the relationship between band alignment, charge transfer, and IR photodetection. Finally, a summary is given as well as the discussion of existing challenges and future directions. [ABSTRACT FROM AUTHOR]

Metal halide perovskite solar cells have an appropriate bandgap (1.5–1.6 eV), and thus output voltage (>1 V), to directly drive solar water splitting. Despite significant progress, their moisture sensitivity still hampers their application for integrated monolithic devices. Furthermore, the prevalence of the use of noble metals as co‐catalysts for existing perovskite‐based devices undermines their use for low‐cost H2 production. Here, a monolithic architecture for stable perovskite‐based devices with earth‐abundant co‐catalysts is reported, demonstrating an unassisted overall solar‐to‐hydrogen efficiency of 8.54%. The device layout consists of two monolithically encapsulated perovskite (FA0.80MA0.15Cs0.05PbI2.55Br0.45) solar cells with low‐cost earth‐abundant CoP and FeNi(OH)x co‐catalysts as the photocathode and photoanode, respectively. The CoP‐based photocathode demonstrates more than 17 h of continuous operation, with a photocurrent density of 12.4 mA cm−2 at 0 V and an onset potential as positive as ≈1 V versus reversible hydrogen electrode (RHE). The FeNi(OH)x‐based photoanode achieves a photocurrent of 11 mA cm−2 at 1.23 V versus RHE for more than 13 h continuous operation. These excellent stability and performance demonstrate the potential for monolithic integration of perovskite solar cells and low‐cost earth‐abundant co‐catalysts for efficient direct solar H2 production. [ABSTRACT FROM AUTHOR]

Perovskite oxides such as PbZrxTi1−xO3 (PZT) and BaTiO3 show excellent dielectric, piezoelectric, pyroelectric, and ferroelectric properties simultaneously and have been widely used in capacitor, sensor, actuator, motor, surface acoustic wave devices, and energy storage applications. Recently, a variety of solution‐processed halide perovskite materials have been discovered to exhibit fascinating properties such as high charge mobility, strong light absorption, and even ferroelectricity. In this review, the recent progress on two classes of halide perovskite ferroelectrics is summarized. The first class is organo‐lead halide perovskite semiconductor such as MAPbI3 (MA=CH3NH3+), which is intensively pursued for solar cell and light emitting diode applications. Dynamic ferroelectric polarization is believed to be one of the essential factors to protect carriers from being scattered by charged defects in these halide perovskites. The second class is normal/multilayered halide perovskite ferroelectrics with large polarization or strong piezoelectricity. The piezoelectric coefficient of these latter perovskites can be as high as ≈1540 pC N−1, comparable to those of PZT‐based ferroelectrics. Multiaxial polarizations and morphotropic phase boundaries are also demonstrated in such halide perovskites. Overall, the fast development of halide perovskite ferroelectrics opens a new avenue for not only advancing fundamental materials science but also designing novel electronic and photoelectric devices. [ABSTRACT FROM AUTHOR]