MoSe2 from monolayer to bulk phase can realize the transition from a direct bandgap semiconductor to an indirect bandgap semiconductor. Its bandgap varies between 1.1 and 1.55 eV, which matches the solar spectral range, so Si-based heterojunction solar cells with MoSe2 as an active layer have great significance in the development of low-cost, high-efficiency and high-flexibility photovoltaic devices. In this work, MoSe2 thin films were synthesized by chemical vapor deposition using MoO3 and Se powders as precursor sources. The effects of different process parameters (Se source temperature, Mo source temperature, growth time, carrier gas flow rate and hydrogen ratio) on the synthesis of MoSe2 thin films were systematically investigated. The optimized experimental parameters were determined as follows: the molybdenum source temperature of 800[Formula: see text], the selenium source 20 cm away from molybdenum source, the growth time of 10 min, the carrier gas flow rate of 60 sccm, the hydrogen ratio of 10%. Then MoSe2/Si heterojunction solar cells were constructed via wet chemical transfer. The open-circuit voltage, short-circuit current density, filling factor and photovoltaic conversion efficiency of the fabricated solar cells were 0.19 V, 5.71 mA/cm2, 30.47% and 0.33%, respectively. Main factors affecting the photovoltaic performance of the MoSe2/Si solar cells have also been discussed. This work is very helpful for the development of MoSe2 material and relevant application in the field of solar cells.
Two-dimensional transition metal dichalcogenides (TMDCs) are widely used in electronic and optoelectronic devices. However, the conventional chemical vapor deposition (CVD) method is difficult to synthesize large-area monolayer WS2 nanosheets stably, which limits the application of WS2 in the field of photoelectric detection. In this work, we propose an innovative NaCl-assisted CVD method that allows freely adjustable substrate positions for synthesizing monolayer WS2 nanosheets. The obtained maximum grain size of the monolayer WS2 nanosheets is up to 30 μm. Subsequently, we investigated the effect of the HfO2 passivation layer on the performance of the metal–semiconductor–metal (MSM) WS2-based photodetectors. The HfO2 passivation layer brought an overall improvement to the performance of the fabricated photodetectors, exhibiting a high responsivity of 1093.1 AW–1, a high specific detectivity of 2.6 × 1012 Jones, and a high external quantum efficiency of 2.1 × 105%. Furthermore, the physical mechanism of the fabricated photodetectors has been discussed to explain how the HfO2 passivation layer takes effect in the improvement of the WS2-based photodetectors. This result can accelerate the development of optoelectronic devices based on TMDCs.
The α-Fe2O3 nanoparticles were prepared via the co-precipitation process, and they were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The effect of the water bath temperature on the average grain size of the α-Fe2O3 nanoparticles was investigated. The minimum grain size of the α-Fe2O3 nanoparticles was 19.6 nm when the water bath temperature was 40 °C. Furthermore, the α-Fe2O3 nanoparticles were successfully modified with silica (SiO2) and chitosan (CTS) using the idea of nanoarchitectonics. the experimental results showed that, the average diameter of the as-prepared α-Fe2O3/SiO2 nanocomposites was around 65 nm; while, the average hydrodynamic diameter of the α-Fe2O3/CTS nanocomposites increased gradually with the increase of chitosan in solution. When the mass ratio of chitosan and the α-Fe2O3 nanoparticles reached 40:1, the diameter distribution range of the α-Fe2O3/CTS nanocomposites was very wide of 100– 900 nm, so the mass ratio of chitosan and the α-Fe2O3 nanoparticles was selected from 10:1 to 20:1 to be applied.
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