Photoelectrochemical (PEC) water splitting powered by solar radiation offers a promising way to produce hydrogen in an environment friendly manner. However, its efficiency is still limited by slow charge separation and low light absorption in standard metal oxides like TiO2. Engineering semiconductor heterojunctions has emerged as an effective strategy to overcome these limitations by broadening spectral absorption, optimizing band alignment, and enhancing interfacial charge transfer. This work reports the fabrication of SnS2/TiO2 and ZnS/TiO2 nanotube (NT) heterojunctions, achieved via a scalable chemical vapor deposition (CVD) and magnetron sputtering approach. Structural analyses using X-ray diffraction and Raman spectroscopy confirmed the crystalline integrity of the SnS2 and ZnS overlayers. Field-emission scanning electron microscopy characterization revealed consistent decoration of sulfide nanoflakes on the TiO2 NT framework. X-ray photoelectron spectroscopy elucidated the chemical composition and electronic states of the heterojunction. High-resolution transmission electron microscopy reveals the heterojunctions' high crystallinity and well-defined interfaces. The PEC measurements in 0.5 M Na2SO4 electrolyte under simulated sunlight having intensity of 100 mW/cm2, revealed enhanced photocurrent densities for both SnS2/TiO2 (∼136 μA/cm2) and ZnS/TiO2 (∼256 μA/cm2) heterojunctions relative to bare TiO2 NT (∼70 μA/cm2), with ZnS/TiO2 exhibiting the improvement of nearly 4-fold at 1.4 V vs RHE. Along with the increased density of catalytically active surface sites provided by the sulfide layers, the enhancement is attributed to the formation of type-II band alignment at the heterojunction, which enables effective photogenerated charge separation and transportation. These findings underscore the potential of CVD-derived metal sulfide/TiO2 heterojunctions as cost-effective, large-area photoanodes for next-generation solar water oxidation technologies.

This work focuses on the impact of substrates on the structural and thermoelectric properties of tungsten diselenide (WSe2) thin films on two different substrates: silicon and quartz. In this study, a two-step method is used for the fabrication of WSe2, wherein W thin films of 100 nm were prepared on Si and quartz substrates via DC sputtering, and then, the selenization process was performed by varying 2, 3, and 4 h at 500 degrees C. The thin films on quartz show a uniform morphology compared to that on Silicon. These polycrystalline samples exhibit a hexagonal arrangement, with varying degrees of crystallinity. In the Raman spectra, two active modes are identified (E1g and A1g), which also confirm the phase of WSe2. The highest Seebeck coefficient of -326.08 mu V K-1 is obtained for the film on quartz and -113.19 mu V K-1 for that on Si at room temperature (300 K), which were selenized for 3 h. The calculated power factor for WSe2 on Si is similar to 136.32 mu W K-2. X-ray photoelectron spectra provide the electronic structures of WSe2 selenized at various temperatures and show that the valencies of Se and W ions are 2- and 4+, respectively. The thermoelectric characteristics depend upon the thermal conductivity of the substrates used, and quartz is found to be a better choice compared to Si substrates for studying the thermoelectric properties of materials.

Engineering efficient heterojunction interfaces remains a promising route to unlock enhanced photoelectrochemical (PEC) water splitting systems. In this work, we report the strategic integration of layered tantalum diselenide (TaSe2) with narrow band gap Bi2Se3 and wide band gap ZnSe to construct novel heterojunctions. A polycrystalline TaSe2 film was directly grown on flexible Ta metal foil using chemical vapor deposition, which served as a robust and conductive scaffold. X-ray diffraction and X-ray photoelectron spectroscopy analyses confirmed the successful formation of the desired heterojunctions and elucidated their crystalline, chemical, and electronic states. PEC studies demonstrated a substantial enhancement in photocurrent density upon heterojunction formation. The ZnSe/TaSe2 heterojunction exhibited a markedly enhanced photocurrent density of similar to 252.3 mu A/cm(2) at 1.4 V vs. RHE, representing nearly six-fold improvement relative to bare TaSe2 (similar to 42.7 mu A/cm(2)) and similar to 1.8-fold enhancement compared to the Bi2Se3/TaSe2 counterpart (similar to 145.3 mu A/cm(2)). This improvement is attributed to synergistic interfacial interactions at the ZnSe/TaSe2 junction, including effective charge separation and increased density of active sites. The superior conductivity of TaSe2 further facilitates rapid carrier transport and minimizes recombination losses. This study highlights the electrochemical versatility of TaSe2-based heterojunctions and establishes a rational design framework for constructing efficient photoelectrodes for solar fuel generation on scalable and flexible substrates.

The development of high-performance near-infrared (NIR) photodetectors (PDs) in self-powered operation is crucial and essential for next-generation optoelectronic applications. Herein, we report a Bi2Se3/PtSe2-based heterojunction on pyramid-Si (Pr-Si) PD that integrates topological and transition metal dichalcogenide materials with light-trapping of Pr-Si nanostructures to achieve a self-powered and highly enhanced NIR photoresponse. The Pr-Si substrate offers an enlarged surface area and efficient photon confinement, while the conformally coated semi-metallic PtSe2 nanosheets form a conductive interfacial layer that promotes charge transfer. The optimized Bi2Se3/PtSe2/Pr-Si-based PD device exhibits an similar to 9-fold enhancement in responsivity (similar to 202 A/W) compared to the PtSe2/Pr-Si-based (similar to 21.4 A/W) PD device at 5 V in the NIR region, demonstrating efficient charge transport and suppressed recombination. Additionally, the Bi2Se3/PtSe2/Pr-Si-based PD device exhibits self-powered photodetection with an similar to 10-fold increase in responsivity (similar to 853 mA/W) as compared to the PtSe2/Pr-Si-based (similar to 80.8 mA/W) PD device. The fabricated Bi2Se3/PtSe2/Pr-Si PD device exhibits stable, repeatable ON-OFF switching behavior under NIR illumination. These findings highlight the synergistic effect of the Bi2Se3 and PtSe2 heterojunction, underscoring the potential of hybrid nanostructures for high-performance, energy-efficient, and self-powered NIR photodetection.

The present study investigates the integration of charge density wave material TiSe2 pyramids grown on Ti metal foil with wide bandgap ZnSe film for sunlight-driven water-splitting. X-ray diffraction and X-ray photoelectron spectroscopy analysis verified the excellent crystallinity and successful fabrication of the ZnSe/TiSe2 pyramids heterostructure. The photoelectrochemical measurements were performed in 0.5 M Na2SO4 electrolyte under AM = 1.5 G solar condition, demonstrating ZnSe/TiSe2 exhibited photocurrent density of 175.2 µA/cm2 at 0.8 V vs Ag/AgCl. The enhanced photocurrent density is attributed to the excellent electrical conductivity between ZnSe and TiSe2, increased catalytic sites, and rapid charge carrier separation and migration due to favorable band alignment between ZnSe and TiSe2. These results underscore the potential of TiSe2-based heterostructure in optimizing solar-to-hydrogen conversion and offer insights into band engineering for improving PEC performance.

The low power consumption and potential applications of self-powered ultraviolet (UV) photodetectors (PDs) in biomedical fields have attracted significant research interest, particularly for diagnostics, environmental monitoring, and wearable devices. We report the fabrication of MoSe2/n-GaN heterojunction by utilizing the r.f. magnetron sputtering system for self-powered broadband UV photodetection. The crystalline and structural quality of MoSe2 thin film was confirmed through X-ray diffraction and Raman spectroscopy. The field emission scanning electron microscopy characterization reveals the earthworm-like morphology of MoSe2 thin film. The fabricated MoSe2/n-GaN PD device exhibits self-powered photoresponse in the UV-C region with photoresponsivity of 35.7 mA/W and detectivity of 5.3 x 1010 Jones. For UV-A region, the MoSe2/n-GaN PD device shows a responsivity of 29.5 mA/W and detectivity of 3.15 x 108 Jones in self-powered operation and exhibited a high photoresponsivity of 31.7 A/W and detectivity of 2.1 x 109 Jones at 5 V. The fabricated PD device also showed a photoresponsivity of 1.6 A/W and detectivity of 1.26 x 108 Jones in the near infra-red region at 5 V. The facile root for integrating transition-metal dichalcogenides/GaN heterojunction-based PDs showed excellent light harvesting capability under self-powered and high photoresponse in a broad wavelength range.

Gallium nitride (GaN) nanostructures are highly promising for photoelectrochemical (PEC) water splitting due to their excellent electron mobility, chemical stability, and large surface area. However, the wide bandgap ( 3.4 eV) of GaN limits its ability to absorb a broad spectrum of solar radiation, restricting its PEC performance. To address this limitation, MoS2/GaN nanorods (NRs) heterostructures for enhanced PEC applications were fabricated on thin tungsten foil using a combination of atmospheric pressure chemical vapor deposition (CVD) and laser molecular beam epitaxy (LMBE). The Raman spectroscopy and X-ray diffraction revealed the hexagonal phase of GaN and MoS2. X-ray photoelectron spectroscopy examined the electronic states of the GaN and MoS2. PEC measurements revealed that the MoS2-decorated GaN NRs exhibited a photocurrent density of approximately172 μA/cm2, nearly 2.5-fold compared to bare GaN NRs ( 70 μA/cm2). The increased photocurrent density is ascribed to the Type II band alignment between MoS2 and GaN, which promotes effective charge separation, the decrease in charge transfer resistance, and the increase in active sites. The findings of this work underscore that the CVD and LMBE technique fabricated MoS2/GaN heterostructures on W metal foil substrate can provide the vital strategy to raise the PEC efficiency toward solar water splitting.

Ultraviolet (UV) radiation has a variety of impacts, affecting human health, agricultural productivity, and the integrity of materials across diverse environments. In the modern era, self-powered UV photodetectors provide detection of UV radiation enabled by the photovoltaic effect without any power consumption. Here, topological Bi2Se3 thin film was deposited using the magnetron sputtering technique on p-GaN/sapphire (0001) substrate for multifunctional study of magneto-transport under 2 to 100 K temperature, self-powered broadband high-responsive UV photodetection, and ultrafast charge carrier dynamics properties. The magneto-transport analysis reveals weak antilocalization in Bi2Se3/p-GaN, with a coherence length of similar to 187 nm at 2 K, confirming the presence of topological surface states. Transient absorption spectra of the Bi2Se3/p-GaN heterojunction reveal oscillations attributed to the Se-Se interface, along with a notably faster carrier lifetime from the visible to near-infrared spectrum region. Under self-powered conditions, the photodetector exhibits remarkable responsivity, achieving similar to 1.9 x 10(2) mA/W at 255 nm (UV-C), similar to 2.0 x 10(2) mA/W at 295 nm (UV-B), and an impressive similar to 1.3 x 10(3) mA/W at 340 nm (UV-A) illumination, highlighting its superior sensitivity across the UV region. At 5 V bias, it achieves a high UV-A responsivity of similar to 1.1 x 10(4) A/W which is similar to 1.2 x 10(3) fold higher than pristine p-GaN/sapphire. The strong built-in electric field and high-mobility surface states in the Bi2Se3/p-GaN heterojunction facilitate efficient charge separation and rapid transport, enabling self-powered operation and superior photodetection performance, and providing valuable insights for the design of next-generation high-performance photodetectors.

The growing energy crisis and environmental degradation from fossil fuels have accelerated the pursuit of sustainable green hydrogen generation via sunlight-driven photoelectrochemical (PEC) water splitting. In this work, we present the fabrication of a ZnSe/NiSe heterojunction comprising hierarchically blade-like NiSe structures grown on a flexible Ni foil substrate with conformal ZnSe overlayers with the help of the combination of chemical vapor deposition and a magnetron sputtering system. Field emission scanning electron microscopy analysis reveals a vertically aligned blade-like NiSe morphology, while the core-level shifts characterized by X-ray photoelectron spectroscopy reflect the interfacial electronic interactions. High-resolution transmission electron microscopy illustrates the good crystallinity of ZnSe deposited on blade-like NiSe structures grown on Ni foil. This architecture enables enhanced light absorption, increased active surface area, and efficient charge separation via a favorable heterojunction. As a result, the PEC measurements of the ZnSe/NiSe photoanode demonstrate a markedly enhanced photocurrent density of similar to 0.35 mA/cm(2) when biased at 0.8 V vs RHE, outperforming bare NiSe (similar to 0.19 mA/cm(2)). The synergistic effect of interfacial engineering and morphological optimization offers a promising strategy for the development of efficient, scalable, and flexible roll-to-roll PEC devices for solar hydrogen production.

We report the enhancement in photoelectrochemical (PEC) water-splitting performance employing ZnSe sensitized with narrow-band-gap Bi2Se3 and MoS2 semiconductors. Raman, X-ray diffraction, and X-ray photoelectron spectroscopy techniques confirm the formation of Bi2Se3/ZnSe and MoS2/ZnSe heterojunctions on Ti metal foil. The PEC measurements were performed in 0.5 M Na2SO4 electrolyte and showed enhanced photocurrent density of 216.2 mu A/cm2 at 0.8 V vs Ag/AgCl for MoS2/ZnSe which is better than Bi2Se3/ZnSe (167.3 mu A/cm2) and 3-fold compared to ZnSe film (63.6 mu A/cm2). The enhanced PEC activity of the MoS2/ZnSe is attributed to the bilayer growth of MoS2, which exposed more surface area, the easy transport of charge carriers from MoS2 to ZnSe electrodes, which decreased charge recombination as well as the harvesting of a broader portion of the solar spectrum. The findings of this work provide evidence that heterojunctions grown onmetal foils may be a fruitful strategy for improving the PEC water-splitting efficiency.

The interface of two-dimensional transition metal dichalcogenides hosts collective interactions between the electronic structures that tune the charge density wave (CDW) states and the photoelectrochemical (PEC) properties of heterostructures. This work reports the influence of the interface on the CDW and PEC of a sputtered Bi2Se3/TiSe2 heterostructure on Ti metal foils. The hexagonal nanoflakes on the spiral-pyramid-like surface morphology of pristine TiSe2 confirm the Bi2Se3 decoration on the TiSe2 sample. The stoichiometric growth of TiSe2 and Bi2Se3 was revealed from X-ray photoelectron spectroscopy and Raman spectroscopy. The temperature-dependent Raman spectroscopy demonstrates the evolution of E-g(CDW) and A(1g)(CDW) optical phonon modes with increased CDW phase transition temperature for the Bi2Se3/TiSe2 heterostructure. The enhancement of photoresponsive properties of the Bi2Se3/TiSe2 heterostructure under a solar light intensity of 100 mW/cm(2) (AM = 1.5 G) in 0.5 M Na2SO4 electrolyte solution toward suitable water splitting was validated from the PEC measurements. This engineered heterostructure can pave the futuristic path to studying light-active electrodes with tunable CDW properties of pristine TiSe2 and Bi2Se3/TiSe2 heterostructures grown on flexible Ti substrates.

The green hydrogen generation by photoelectrochemical (PEC) process emerged as a viable approach to replace non-renewable energy sources, which is done by using semiconducting materials. Recently ZnSe-based heterostructure/junction promise a suitable approach to enhance the PEC performance of photoelectrode. Here we have grown Bi2Se3/ZnSe heterojunction on flexible Mo metal foil by using magnetron sputtering technique toward PEC water splitting application. The crystallinity, structural, and surface morphology of the deposited films were investigated by X-ray diffraction, Raman spectroscopy, and field emission scanning electron microscopy, respectively. The PEC measurements were performed under 100 mW/cm(2) (AM = 1.5 G) simulated solar radiation in 0.5 M Na2SO4 aqueous electrolyte solution. The PEC measurements show that Bi2Se3/ZnSe photoelectrode performs better as a photocatalyst, with a photocurrent density of similar to 96.4 mu A/cm(2) (at 0.4 V vs Ag/AgCl), which was found to be three times higher than pristine ZnSe film (similar to 32.4 mu A/cm(2)). This work suggests the importance of heterojunction towards efficient photoelectrodes for green hydrogen generation.

We report magnetron-sputtering-grown Bi2Se3/WSe2 heterojunction on thin tungsten (W) metal foil towards photoelectrochemical (PEC) water-splitting application. The crystalline and structural quality of prepared heterojunction was examined by X-ray diffraction and Raman spectroscopy. The X-ray photoelectron spectroscopy confirmed the chemical composition of Bi2Se3/WSe2. The PEC measurements were performed in 0.5 M Na2SO4 electrolyte solution under simulated sunlight (AM = 1.5 G) conditions. The PEC measurements showed the improved photocurrent density of Bi2Se3/WSe2 with an obtained photocurrent density of 205 µA/cm2, which is 2.7 times higher compared to bare WSe2. The enhanced photocurrent density of Bi2Se3/WSe2 could be attributed to the creation of additional active sites, as well as type-II band alignment between Bi2Se3 and WSe2 which helps easy separation of the photogenerated electron and hole pair by reducing charge recombination. The Bi2Se3/WSe2 heterojunction was grown on flexible W metal foil using large area chemical vapor deposition and magnetron sputtering techniques. This innovative heterojunction enhances charge separation and light absorption, leading to improved PEC efficiency. The findings of this work could inspire further research into layered heterojunction, potentially unlocking new pathways for efficient energy conversion technologies. The Bi2Se3/WSe2 heterojunction grown on thin metal foils enhanced the PEC performance for the generation of solar hydrogen fuel.

Group 10 transition metal dichalcogenide PtSe2 has drawn considerable attention toward the search for an efficient visible light photocatalyst due to its strong light–matter interaction nature. Here we report PtSe2/TiO2 heterostructure for solar energy conversion through photoelectrochemical (PEC) water splitting. The PtSe2/TiO2 heterostructure was prepared by sputtered Pt film followed by the chemical vapor deposition method. Raman spectroscopy and X-ray diffraction analysis confirmed the growth of hexagonal phase PtSe2 and anatase TiO2 corresponding to their distinguished peak characteristics. The field-emission scanning electron microscopy and transmission electron microscopy studies reveal that TiO2 nanotubes were decorated with PtSe2 nanoflakes forming PtSe2/TiO2 heterostructure. The chemical composition of the prepared samples was studied by using the X-ray photoelectron spectroscopy and indicated the sole presence of PtSe2 and TiO2 compounds. The PEC measurements were taken in 0.5 M Na2SO4 electrolyte solution under simulated sunlight (AM = 1.5 G). The maximum photocurrent density of 234.7 µA/cm2 at 1.4 V versus RHE was recorded for PtSe2/TiO2 heterostructure, which is 1.7 times higher than that of Pt/TiO2. The improved PEC performance of PtSe2/TiO2 as a result of efficient solar absorption over a wider spectrum and effective charge separation produced by type-II band alignment between PtSe2 and TiO2.

Here, we have grown crystalline MoSe2 and WSe2 nanostructures on thin flexible Mo and W metal foils at growth temperature of 450–550°C by using the single-zone atmospheric pressure chemical vapour deposition (CVD) method. Raman spectroscopy measurements confirm the structural formation with low line widths for MoSe2 on Mo foil at 450°C and WSe2 on W foil at 550°C corresponding to their optical vibrational Raman modes. X-ray diffraction (XRD) patterns show the hexagonal 2H phase of grown MoSe2 and WSe2 nanostructures attributed to their distinguished XRD peaks. The field emission scanning electron microscopy revealed the granular-layered MoSe2 surface, whereas the nano-woolforest type surface of WSe2 film. Elemental analysis using energy-dispersive X-ray spectroscopy technique confirms the formation of nearly stoichiometry MoSe2 and WSe2 compounds. Chemical composition and binding energy values of deposited films were studied by using X-ray photoelectron spectroscopy. Growth of polycrystalline and large-area MoSe2 and WSe2 film on flexible metal foils using scalable and low-cost CVD system paves the way for the fabrication of futuristic flexible energy devices on metal foils.

The fabrication of heterojunction-based photodetectors (PDs) is well known for the enhancement of PDs performances, tunable nature of photoconductivity, and broadband application. Herein, the PDs based on MoSe _2 and MoSe _2 /Bi _2 Se _3 heterojunction on sapphire (0001) substrates were deposited using a r.f. magnetron sputtering system. The high-resolution x-ray diffraction and Raman spectroscopy characterizations disclosed the growth of the 2-H phase of MoSe _2 and the rhombohedral phase of Bi _2 Se _3 thin films on sapphire (0001). The chemical and electronic states of deposited films were studied using x-ray photoelectron spectroscopy and revealed the stoichiometry growth of MoSe _2 . We have fabricated metal-semiconductor–metal type PD devices on MoSe _2 and MoSe _2 /Bi _2 Se _3 heterojunction and the photo-response measurements were performed at external voltages of 0.1–5 V under near-infrared (1064 nm) light illumination. The bare MoSe _2 PD device shows positive photoconductivity behavior whereas MoSe _2 /Bi _2 Se _3 heterojunction PD exhibits negative photoconductivity. It was found that the responsivity of MoSe _2 and MoSe _2 /Bi _2 Se _3 heterojunction PDs is ~ 1.39 A W ^−1 and ~ 5.7 A W ^−1 , respectively. The enhancement of photoresponse of MoSe _2 /Bi _2 Se _3 PD nearly four-fold compared to bare MoSe _2 PD shows the importance of heterojunction structures for futuristics optoelectronic applications.

In recent years, p-n junction devices formed by wide-bandgap semiconductors and layered transition metal dichalcogenides have been promising candidates for applications in broadband photodetection. In this work, we have deposited MoSe2 thin films on GaN by magnetron sputtering technique. Raman spectroscopy and high-resolution x-ray diffraction studies disclosed the formation of 2H-MoSe2 whereas x-ray photoelectron spectroscopy confirmed the composition of MoSe2 thin films grown on p-type GaN/sapphire (0001) substrate. The worm-type granular MoSe2 thin film was grown on the GaN surface. The metal-semiconductor-metal-based photodetectors (PDs) were fabricated on MoSe2/p-GaN heterojunction using gold electrodes with a spacing of 20 mu m. Fabricated device shows a high photoresponsivity of similar to 5.12 A/W and detectivity of similar to 3.7 x 10(8) Jones in the ultra-violet (355 nm) region, and a photoresponsivity of similar to 1.5 A/W with a detectivity of similar to 2.23 x 10(8) Jones in the near-infra-red (1064 nm) region at 5 V. Our results demonstrate that large area sputtered MoSe2/ p-GaN PDs devices are beneficial for enhancing photodetector performance.