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In this paper, flower-like MoS 2 nanosheets microspheres were successfully synthesized by low temperature hydrothermal process using the precursors of sodium molybdate (Na 2 MoO 4 ·2H 2 O), thiourea (SC(NH 2 ) 2 ), oxalic acid (C 2 H 2 O 4 ·2H 2 O) and de-ionized water. The effects of oxalic acid concentrations and growth time on the morphology and crystallographic structure of MoS 2 nanosheets microspheres were investigated. The morphology, crystallographic structure, chemical composition of the flower-like MoS 2 nanosheets microspheres were investigated by using scanning electron microscope, X-ray diffraction, Raman spectrum, high resolution transmission electron-microscopy, and X-ray photoelectron spectroscopy, respectively. It is revealed that MoS 2 powders are composed of large, uniform flower-like microspheres, which are formed by several nanosheets gathering together perpendicular to the spherical surface. And the nanosheets are poly-crystallized hexagonal phase. The experiment results also show that the oxalic acid concentration in the precursors plays a key role on the diameter and crystalline of MoS 2 nanosheets microspheres. The formation mechanism of flower-like MoS 2 nanosheets microspheres was discussed.

Stannous sulfide (SnS) was grown on SiO2/Si substrates via chemical vapor deposition technique and characterized using optical microscopy, scanning electronic microscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, atomic force microscopy and photoluminescence (PL) spectrum, respectively. The results indicate that SnS with two distinct morphologies of “the ultra-thin SnS flakes and the micron-thick SnS crystals” can be grown on different zones of the SiO2/Si substrate. The ultra-thin SnS flakes are single crystal with thickness of 139 nm and maximum lateral sizes of 371 μm. However, the micron-thick SnS crystals are 2.2 μm-thick and a lateral size of 15 μm with square shape. The difference in morphology between the ultra-thin SnS flakes and the micron-thick SnS crystals is mainly due to the difference in the initial nucleation way. Both the ultra-thin SnS flakes and the micron-thick SnS crystals are orthorhombic structure with high-purity. PL strong peak of the ultra-thin SnS flakes is at 950 nm, and it is at 945 nm for the micron-thick SnS crystals. Their optical band gap is approximately 1.31 eV.

Well-crystallized Cu 2 ZnSnS 4 (CZTS) nanoparticles contain ultrasmall nanocrystals (~ 10 nm) have been grown directly on three-dimensional (3D) transparent porous reduced graphene oxide (rGO) thin films by a facile and scalable solution-based strategy. Few-layer rGO prepared by modified Hummers’ method was used to fabricate hierarchical ultraporous 3D rGO thin films (3DGTFs) with high transmittance (> 75% for 200-nm thick). Single-phase kesterite CZTS nanocrystalline particles were grown uniformly on the surface active sites within the 3D rGO network by hydrothermal method. The as-prepared CZTS/rGO composite thin films exhibited excellent electrocatalytic ability by taking advantages of the high conductivity and high surface area of 3DGTFs and the high catalytic activity of CZTS nanoparticles. As expected, the composite thin films demonstrate more than one order of magnitude lower in electrical resistivity and in charge transfer resistance than the individual CZTS thin films. The conversion efficiency of dye-sensitized solar cells using CZTS/rGO thin films as the counter electrode (CE) approached 6.12%, comparable to that using Pt CE (6.45%) and superior to those using individual CZTS CE (1.07%) and rGO CE (0.18%).

Vertically aligned CoS prismatic nanorods were synthesized on transparent conductive fluorine-doped tin oxide (FTO) substrates by a two-step method. First, vertically aligned Co3O4 prismatic nanorod arrays were prepared by a rapid microwave irradiation method. Second, Co3O4 were converted to CoS nanorods by solution-based ion exchange reaction (IER). The dye-sensitized solar cell (DSSC) using CoS prismatic nanorods arrays as the counter electrode (CE) achieves a power conversion efficiency of 6.06%, which is comparable with the cells based on Pt-CE (6.45%).

Two-dimensional (2D) ReS2 flakes are synthesized by the chemical vapor deposition under atmospheric pressure using Re–Te binary eutectic and sulfur as precursors. The morphologies, crystal structure, phonon vibration modes, chemical states and optical property of the 2D ReS2 flakes are characterized using optical microscopy, scanning electron microscope, transmission electron microscopy, the Raman spectroscopy, X-ray photoelectron spectroscopy and transmittance spectra. The lateral size of 2D ReS2 flakes can be tuned via changing the synthesis parameters. The monolayer 2D ReS2 flakes is single crystal structure. Its maximum lateral size is 30 μm, and optical band gap is 1.42 eV. The absorption coefficient is as large as 105 cm−1, transmittance of 92–98% and refractive index of 1.5–1.3 in the wavelength range from 400 to 800 nm. The effect of synthesis parameters on the morphologies and growth mechanism of 2D ReS2 flakes are investigated in detail. This is helpful for further application of ReS2 in electronic and optoelectronic devices.

Perovskite solar cells (PSCs) based on hole-transporting-materials (HTM)-free and carbon electrodes have attracted intensive attention due to their low material cost, simple manufacturing process, and high stability. However, their power conversion efficiencies (PCE) need further improvement. In this work, the effect of Br - component x on properties of the MAPb(I 1− x Br x ) 3 thin films as well as photovoltaic performance of PSCs were studied. The MAPb(I 1− x Br x ) 3 thin films were prepared using two-step solution deposition method in ambient air. The Br − component x was varied from 0 to 1 by changing the PbBr 2 to PbI 2 molar ratio in the precursor solution. PSCs based on the HTM-free and carbon electrodes were fabricated in ambient air in this work, aiming to realize reduction of fabrication cost and improve the stability of PSCs. The results indicated that when Br − component x increase, the XRD diffraction peaks of MAPb(I 1− x Br x ) 3 thin films continuously shift to larger diffraction angle, meanwhile, the absorption edge and PL peak continuously shift toward to the shorter wavelength. The PSCs based on MAPbI 2.7 Br 0.3 exhibits an optimal photovoltaic performance, yielding V oc of 0.95 V, J sc of 17.61 mA/cm - 2 , FF of 0.70, and PCE of 11.70%. Its PCE remains 93.3% of the initial efficiency after being exposed in the atmosphere for 700 h.

In this study, the controlled-layer and large-area two-dimensional (2D) rhenium disulfide (ReS 2 ) thin films were grown on mica substrates by chemical vapor deposition method using S powder and Re-Te powder as starting materials. The morphology, thickness and crystallographic structure of 2D ReS 2 thin films were investigated using optical microscope (OM), field emission scanning electronic microscope (SEM), atomic force microscopy (AFM) and Raman spectroscopy, respectively. In order to study the layer-dependent electrical transport property of 2D ReS 2 thin films, the back-gated field effect transistors (FETs) based on 2D ReS 2 thin films with different layer number and different channel lengths were prepared. The dependence relationship between carrier mobility and layer number of 2D ReS 2 thin films were studied and discussed. Results show that the controlled-layer and substrate-scale ReS 2 thin films can be grown on mica substrate at temperature of 650 °C. The layer number of 2D ReS 2 thin films can be adjusted from 1 to 10 layers by changing the location of the substrate. The carrier mobility of 2D ReS 2 thin films increases with an increasing number of layers (from 1 to 5 layers) and to be saturated when further increase the number of layers.

The effects of the formamidinium (FA)+ alloy fraction x and the dipping time on the properties of FAxMA1−xPbI3 thin films (where MA = methylammonium ) as well as the photovoltaic performance of perovskite solar cells (PSCs) have been studied. Mixed-organic-cation FAxMA1−xPbI3 thin films were prepared using a two-step solution deposition method in ambient air. PSCs with fluorine-doped tin oxide glass/compact TiO2/mesoporous TiO2/FAxMA1−xPbI3/carbon electrode structure were fabricated, aiming to reduce the fabrication costs and improve the stability of PSCs. The results indicated that, when the FA+ alloy fraction x was increased from 0 to 1, the x-ray diffraction (XRD) peaks shifted continuously to lower angle, while the absorption edge and photoluminescence (PL) peak shifted continuously towards longer wavelength. The Raman spectra of the FAxMA1−xPbI3 thin films, consisting of five typical peaks at 68.5 cm−1, 77.5 cm−1, 84.6 cm−1, 139.1 cm−1, and 283.2 cm−1, barely shifted with incorporation of FA+. In addition, the dipping time was shortened by using mixed solvents to prepare the PbI2 thin films. The PSCs based on FA0.4MA0.6PbI3 prepared with a dipping time of 15 min exhibited the highest average power conversion efficiency (PCE) of 8.64%, with 74.4% of the initial efficiency being retained after exposure to ambient air at room temperature with approximately 50% humidity for 700 h.

The two-dimensional (2D) SnS 2 nanoflakes and flower-shaped SnS 2 are grown on SiO 2 /Si substrate by chemical vapor deposition method using S and Sn powders as starting materials. The morphology, crystallographic structure and optical property of 2D SnS 2 nanoflakes as well as flower-shaped SnS 2 are investigated using scanning electronic microscope, X-ray diffraction, Raman spectroscopy, transmission electron microscopy and photoluminescence spectrum, respectively. When the substrate temperature is in the range from 525 to 575 °C, the flower-shaped SnS 2 with six petals grow parallel to SiO 2 /Si substrate. When the substrate temperature is in the range from 410 to 525 °C, the 2D SnS 2 nanoflakes with semi-hexagonal shape grow on substrate. However, these 2D SnS 2 nanoflakes have different orientations on the substrate, some are parallel to the substrate, some are inclined on the substrate, and others are perpendicular to the substrate. Two different forms of SnS 2 are both high-quality uniform layered structures with indirect bandgap of ~ 2.20 eV. The growth mechanism of flower-shaped SnS 2 and 2D-SnS 2 nanoflakes is discussed.

In this paper, we report the effect of the Cs+ fraction x on the structure, morphology and optical properties of mixed organic–inorganic cation CsxMA1−xPbI3 absorption layers prepared using an anti-solvent-assisted one-step solution deposition method in an ambient environment. By changing the ratios of cesium iodide (CsI) to methyl iodide (MAI) in the precursor solution, the Cs+ fraction x varies from 0 to 1. The hole-transporting-material (HTM)-free perovskite solar cells (PSCs) based on the CsxMA1−xPbI3 absorption layers were fabricated in ambient air, and their photovoltaic performance was studied. Results indicate that when the Cs+ fraction x is less than 0.3, Cs+ ions mainly replace a fraction of MA+ ions in the MAPbI3 lattice and do not lead to a change in the crystal structure of the MAPbI3. When the Cs+ fraction x is between 0.3 and 0.7, one part of Cs+ ions incorporated in the MAPbI3 lattice replaces MA+ ions (α-phase), while the other part forms a yellow photovoltaic-inactive δ-CsPbI3 phase. The CsxMA1−xPbI3 films with x ≥ 0.8 contain much of the photovoltaic-inactive δ-CsPbI3 phase. The band gap of the CsxMA1−xPbI3 films increases from 1.53 eV to 1.65 eV with the increase of the Cs+ fraction x. The PSCs based on the Cs0.1MA0.9PbI3 films exhibit remarkable improvement in device efficiency and stability.