Highly ordered TiO 2 nanowire (NW) arrays were constructed by hydrothermal process as support materials for quantum dot sensitized solar cells (QDSSCs). The CdS x Se 1−x alloyed quantum dots (QDs) with tunable composition have been assembled onto the TiO 2 NW arrays via a facile hydrothermal method to form CdS x Se 1−x /TiO 2 NW photoanodes. The light absorption range of the CdS x Se 1−x /TiO 2 NW photoanodes can be controlled by changing the atomic ratio of S to Se. Based on CdS x Se 1−x /TiO 2 NW photoanodes, the photovoltaic performance of these CdS x Se 1−x /TiO 2 NW solar cells gradually improved as the increase of Se content in CdS x Se 1−x alloyed QDs. Among all sample CdS x Se 1−x /TiO 2 NW solar cells which were prepared with different feed molar ratio of S:Se, the CdS 0.27 Se 0.73 /TiO 2 NW solar cell (prepared with S:Se = 0:4) produced the highest power conversion efficiency up to 2.46 %. The results of investigation into optical properties and incident photon-to-current conversion efficiency indicates that the enlarged light absorption range and effective photo-to-electrical efficiency can be obtained with Se-rich CdS x Se 1−x /TiO 2 NW photoanodes, which contribute to the enhanced photovoltaic performance of the CdS 0.27 Se 0.73 /TiO 2 NW solar cell.
Zhen Li,Guizhang Guo,Zhou Yu,Zengyue Ma,Yonggang Lei,Libo Yu,Junke Wang
The use of quantum dots (QDs) to sensitize titanium TiO 2 in photoelectrochemical cells (PECs) for solar-driven water splitting represents a highly promising method for converting solar energy into storable chemical energy in the form of hydrogen. The characteristics and interfaces of the QDs play a crucial role in determining the range of light absorption and the efficiency of charge transport and separation upon photoexcitation. Herein, we build CdS x Se 1-x QDs sensitized TiO 2 photoanodes with different amount of Se source by one-step hydrothermal process using thioglycolic acid (TGA) as bifunctional linker. Our results demonstrate that TGA can both anchor QDs to TiO 2 and decompose S for CdS x Se 1-x QDs preparation. The influence of Se source dosage on PEC performance of CdS x Se 1-x /TiO 2 photoanode has been investigated. UV–vis absorption data shows the increase of Se source can enlarge light response range. X-ray photoelectron spectroscopy, transient open-circuit voltage decay and electron lifetime tests indicate proper thickness of SeO 2 which formed on CdS x Se 1-x QDs has the effect to block charges recombination between CdS x Se 1-x /TiO 2 photoanode and electrolyte, improving the electron lifetime of photogenerated electrons. Consequently, the photoelectrochemical cell (PEC) constructed with a CdS x Se 1-x /TiO 2 photoanode, prepared using 0.8 mmol of selenium source, has achieved a photocurrent density of 14.31 mA cm −2 and a photoconversion efficiency of 15.74 %. These results indicate significant potential for the production of green hydrogen.
The combination of two-dimensional (2D) materials with non-2D materials (quantum dots, nanowires and bulk materials), i.e. mixed-dimensional van der Waals (md-vdW) heterostructures endow 2D materials with remarkable electronics properties. However, it remains a big challenge to synthesize md-vdW heterostructures because of the difference of crystal symmetry between 2D and non-2D materials. Meanwhile, it is difficult to initiate the nucleation due to the lack of chemical active sites on chemical inert surfaces of 2D materials. Herein, we design a general chemical vapor deposition method for synthesizing a broad class of md-vdW heterostructures with well-aligned hexagonal symmetry including MoS2/FeS, MoS2/CoS, MoS2/MnS, MoS2/ZnS, Mo(SxSe1–x)2/ZnSxSe1–x, Mo(SxSe1–x)2/CdSxSe1–x. Combining with DFT calculation, we find that the hexagonal symmetry and the centered clusters of MoS2 and Mo(SxSe1–x)2 nanoflakes are two crucial factors to launch the hexagonally oriented growth and nucleation of non-2D materials on 2D materials. Our discovery opens an opportunity for the versatile hetero-integration of 2D materials and allows systematic investigation of physical properties in a wide variety of md-vdW heterostructures.
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