The solar response ability and low-cost fabrication of the photoanode are important factors for the effective output of the photoelectrochemical system. Modification of the photoanode by which its ability to absorb irradiation can be manipulated has gained tremendous attention. Here, we demonstrated the MoSe 2 , WSe 2 , and MoSe 2 /WSe 2 nanocrystal thin films prepared by the liquid-phase exfoliated and electrophoresis methods. Atomic force microscopy and high-resolution transmission electron microscopy show that the liquid exfoliated nanocrystals have a few layered dimensions with good crystallinity. Scanning electron microscopy demonstrated uniform distribution and randomly oriented nanocrystals, having a homogeneous shape and size. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectra confirm the equal contribution of MoSe 2 and WSe 2 nanocrystals in the formation of the MoSe 2 /WSe 2 heterojunction. Because of superior absorption of MoSe 2 /WSe 2 heterojunction in the visible region and type-II heterojunction band alignment, in situ measurement of heterojunction electrode shows almost 1.5 times incident photo-to-current conversion efficiency and photoresponsivity in comparison to individual material electrodes. Our result clearly indicates the influence of heterojunction formation between liquid exfoliated nanocrystals on effective separation of photogenerated exciton and enhances charge carrier transfer, which leads to the improvement in photoelectrochemical performance. Liquid exfoliated nanosheet-based heterojunction is attractive as efficient photoanodes for the photoelectrochemical systems.

The optical, electrical and optoelectronic properties of tin selenide crystals are of immense significance for application in photodetectors and energy conversion and storage devices. The transition metal chalcogenides possess a layered structure that interacts with each other through van der Waal forces and can also offer sites for intercalation. The low molecular weight materials like GeSe and SnSe are found in an orthorhombic structure. In this article, the optical, electrical and optoelectronic properties of as-grown tin selenide crystals are investigated. The chemical composition of the crystals grown with the aid of direct vapour transport (DVT) technique is confirmed through energy Dispersive analysis of X-rays (EDAX), at the same time the morphological analysis is accomplished using optical microscopy and Scanning Electron Microscopy (SEM). The grown crystals are characterized by powder X-ray diffraction (XRD) method to assess the structural properties of the material. The XRD evaluation found out the orthorhombic structure of the crystals with the space group 16 2h D (P cmn) having lattice parameters a = 11.490 Å, b = 4.440 Å and c = 4.135 Å. The crystallinity of grown samples was verified by transmission electron microscopy (TEM). The single crystalline nature of grown crystals was revealed by SAED pattern. The indirect optical band gap of 1.0065 eV, Urbach energy and steepness parameter are calculated utilising UV-VIS-NIR spectrophotometer. The optical absorption of as-grown SnSe crystals has been measured close to the fundamental absorption edge at room temperature. Both types of transitions, i.e. direct and indirect, are involved in the absorption process. Electrical transport properties like resistivity measurements (parallel and perpendicular path to the c-axis) had been carried out on these crystals within the temperature range 297-673 K. Anisotropy in resistivity measurements in both the directions, i.e. parallel and perpendicular direction to the c-axis was discovered. The p-type semiconducting nature was confirmed with the aid of Hall-effect measurements. For the photodetection properties of SnSe crystals, light source (670 nm) having an intensity of 3 mW/cm 2 at distinctive biasing voltages is used. The outstanding detection properties are revealed from the responsivity, specific detectivity and external quantum efficiency (EQE) of pure SnSe crystals.

2-D transition metal dichalcogenide (TMDC)-based heterostructures are promising active materials for high-performance optoelectronic devices. The low-cost, large-area, and high-quality fabrication of TMDC heterojunctions is essential for the efficient output of the device. Here, we demonstrate thin films of MoSe2–WSe2 nanocrystals deposited on a silicon substrate for enhanced photodetection. A MoSe2–WSe2 film, deposited by the electrophoretic deposition method, is initially transferred on the water surface and then prudently transferred on the p-Si (100) substrate. Scanning electron microscopy reveals the continuous and compact distribution of assembled nanocrystals with no pinhole. Energy-dispersive analysis of X-ray confirms the presence of MoSe2 and WSe2 in the transferred heterojunction film. The MoSe2–WSe2/p-Si fabricated heterojunction achieves a peak responsivity and external quantum efficiency of 336 mAW–1 and 80% (520 nm, 0.122 mW/cm2), respectively, which are ∼4 times higher in magnitude than those of pristine TMDC/Si fabricated heterojunctions. The enhanced photoresponse behavior is attributed to the superior absorbance in the visible region and type-II band alignment between MoSe2 and WSe2 nanocrystals, which facilitates improved generation and separation of charge carriers. Further, the photoresponse of MoSe2–WSe2/Si heterojunction is recorded in the temperature range of 45–300 K. The excellent heterojunction characteristic and photoresponse behavior of liquid exfoliated TMDC nanocrystals are the future gateways of highly efficient hybrid optoelectronic devices.

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The two-dimensional pristine tin selenide (SnSe), possessing desirable optical, thermal, electrical, and optoelectronic characteristics, is the future nanomaterial of technological applications. In the present study, SnSe nanosingle crystals were grown using the direct vapor transport (DVT) method. The chemical composition, morphological analysis, crystalline phase, crystallinity, optical properties, vibrational modes, and oxidation states of the elements of the grown crystals are verified by energydispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopy (XPS), optical microscopy−scanning electron microscopy (SEM), photoluminescence (PL), Raman, and X-ray diffraction.For the optoelectronic study of grown crystals, the current−voltage characteristic was measured. A photodetector based on singlecrystalline SnSe is fabricated and studied under visible light with an on/off period of 10 s. The device designates excellent photocurrent and responsivity. Moreover, the photoelectrochemical (PEC) visible-light photoresponse of the SnSe single crystals was also studied. The photovoltaic output parameters like the open-circuit voltage (V oc ), short-circuit current (I sc ), fill factor (FF), and efficiency (η%) for the cell were determined. The grown crystal shows the highest photocurrent of 1.31 μA under an illumination of 120 mW/cm 2 . Mott−Schottky plots helped in the redox analysis and energy band location. The Nyquist plot is also plotted to study electrochemical impedance. The work demonstrated the potential application of SnSe nanosingle crystals in the field of optoelectronic visible-light conditions.