Minqiang Wang

One-pot synthesis of Ag/r-GO/TiO2 nanocomposites with high solar absorption and enhanced anti-recombination in photocatalytic applications

In this paper, we reported a simple one-pot solvothermal approach to fabricate Ag/reduced graphene oxide (r-GO)/TiO2 composite photocatalyst under atmospheric pressure. Based on the experimental data, we concluded that the introduction of Ag into classical graphene-TiO2 system (i) efficiently enlarges the absorption range, (ii) improves photogenerated electron separation and (iii) increases photocatalysis reaction sites. The optimized sample exhibits prominent photocatalysis ability as compared to pure TiO2 under simulated sunlight. We further proposed that besides the above three advantages of Ag, a different size of Ag nanoparticles is also responsible for the improved photocatalysis ability, where small size Ag nanoparticles (2-5 nm) could store a photoexcited electron that was generated from TiO2, while large-size Ag nanoparticles could utilize visible light due to their localized surface plasmon resonance (LSPR) absorption. Our present work gives new insights into the photocatalysis mechanism of noble metal/r-GO/TiO2 composites and provides a new pathway into the design of TiO2-based photocatalysts and promote their practical application in various environmental and energy issues.

CdS and CdSe quantum dots subsectionally sensitized solar cells using a novel double-layer ZnO nanorod arrays

We report a novel approach for synthesizing CdS and CdSe quantum dots subsectionally sensitized double-layer ZnO nanorods for solar cells, which are comprised of CdS QDs-sensitized bottom-layer ZnO NRs and CdSe QDs-sensitized top-layer ZnO NRs. X-ray diffraction study and scanning electron microscopy analysis indicate that the solar cells of subsectionally sensitized double-layer ZnO NRs, which are the hexagonal wurtzite crystal structure, have been successfully achieved. The novel structure enlarged the range of absorbed light and enhanced the absorption intensity of light. The I-V characteristics show that the double-layer structure improved both the current density (J(sc)) and fill factor (FF) by 50%, respectively, and power conversion efficiency (η) was increased to twice in comparison with the CdS QDs-sensitized structure.

One-Step Preparation and Assembly of Aqueous Colloidal CdSxSe1–x Nanocrystals within Mesoporous TiO2 Films for Quantum Dot-Sensitized Solar Cells

In the field of quantum dots (QDs)-sensitized solar cells, semiconductor QDs sensitizer with a moderate band gap is required in order to sufficiently match the solar spectrum and achieve efficient charge separation. At present, changing the size of QDs is the main method used for adjusting their band gap through quantum size effect, however, the pore sizes of mesoporous TiO2 film set a limit on the allowed size of QDs. Therefore, the tuning of electronic and optical properties by changing the particle size could be limited under some circumstances. In this paper, high-quality aqueous CdS(x)Se(1-x) QDs sensitizer is successfully synthesized and effectively deposited on a mesoporous TiO2 film by a one-step hydrothermal method. In addition to size, alloy QDs provide composition as an additional dimension for tailoring their electronic properties. The alloy composition and band gap can be precisely controlled by tuning the precursor (Se/Na2S·9H2O) ratio while maintaining the similar particle size. By using such CdS(x)Se(1-x) sensitized TiO2 films as photoanodes for solar cell, a maximum power conversion efficiency of 2.23% is achieved under one sun illumination (AM 1.5 G, 100 mW cm(-2)).

High-performance ZnO/Ag Nanowire/ZnO composite film UV photodetectors with large area and low operating voltage

A simple and low-cost solution-processed method is used to fabricate ZnO/Ag nanowire/ZnO composite UV photodetectors with a large area of 4 × 5 mm2, low operating voltage of 1 V and high visible transmittance of 75%. Due to the low-dimensionality confinement ability and small persistent photoconductivity effect in polycrystalline ZnO nanoparticle thin films and excellent conductivity of Ag nanowire networks, composite UV photodetectors exhibit a high on/off ratio and short response time under high light illumination, while exhibiting large detectivity and responsivity under low light illumination. Compared with traditional polycrystalline ZnO thin films, the formation of a large number of Ohmic contacts between ZnO nanoparticles and Ag nanowires in a composite structure greatly improves the extraction number and shortens the extraction time of photoelectrons. Additionally, both Schottky contact and Ohmic contact at the electrode interface can obtain a high on/off ratio and short response time. Our composite structure device is regarded as a compromise between high-performance with large-area, low-voltage and low-cost. It has many advantages compared with its counterparts include ZnO nanowires, and other ZnO composites, which is very promising in UV photodetective applications.

Arrays of ZnO/AZO (Al-doped ZnO) nanocables: a higher open circuit voltage and remarkable improvement of efficiency for CdS-sensitized solar cells.

Photoelectrode of nanocables (NCs) structure of ZnO nanowires (NWs) coated with Al-doped ZnO (AZO) shells was investigated for CdS quantum dots sensitized solar cells (QDSSCs). ZnO NWs serve as the frame for the preparation of AZO shells, in which electron transport more rapidly due to the more higher electron mobility of AZO (n-ZnO) than that of i-ZnO. AZO shells were assembled onto the surface of ZnO NWs via a spin-coating method. Optical band-gap of the ZnO/AZO films varies from 3.19 eV for pure ZnO to 3.25 eV for AZO (15%) depending on the Al-doping concentration. The PL intensity of AZO/ZnO, V(oc), J(sc) and η of the cells first increased and then decreased with the increase in the Al-doping (from 0% to 20%) and post-annealed temperature. Remarkably, the value of V(oc) can achieve above 0.8 V after Al-doping. The dark current and absorption spectrum provided direct evidence of the increase in J(sc) and V(oc), respectively. Moreover, we discussed the effect of Al-doping on optical band-gap of the samples and the transfer of electron.

Developing seedless growth of ZnO micro/nanowire arrays towards ZnO/FeS2/CuI P-I-N photodiode application

A seedless hydrothermal method is developed to grow high density and vertically aligned ZnO micro/nanowire arrays with low defect density on metal films under the saturated nutrition solution. In particular, the mechanism of seedless method is discussed here. A buffer layer can be confirmed by transmission electron microscopy (TEM), which may release the elastic strain between ZnO and substrate to achieve this highly mismatched heteroepitaxial structures. Based on ZnO micro/nanowire arrays with excellent wettability surface, we prepared ZnO-FeS2-CuI p-i-n photodiode by all-solution processed method with the high rectifying ratio of 197 at ±1 V. Under AM 1.5 condition, the Jsc of 0.5 mA/cm2, on-off current ratio of 371 and fast photoresponse at zero bias voltage were obtained. This good performance comes from excellent collection ability of photogenerated electrons and holes due to the increased depletion layer width for p-i-n structure. Finally, the high responsivity around 900 nm shows the potential as near infrared photodetectors applications.

Equilibrium self-assembly of close-packed ordered PbTe nanocrystal thin film and near-infrared photoconductive detector

A PbTe thin film with near-infrared photoconductive characteristics is assembled from monodisperse PbTe nanocrystals (NCs). Monodisperse PbTe NCs show large absorption tunability (>400 nm) by a rapid injection solution-phase synthesis route. In order to obtain smooth close-packed NC thin films on a Si/SiO2 substrate with Ti/Au contacts the equilibrium self-assembly method is employed, which is conveniently controlled by adjusting the velocity of the argon flow and the evaporation temperature. According to atomic force microscope (AFM) and scanning electron microscope (SEM) analysis, we propose a schematic diagram of the PbTe NC assembly process to form the PbTe NC film. The PbTe NC thin film exhibits a good photoconductive gain after ethylenediamine treatment. This phenomenon thus illustrates that the PbTe NC thin film has near-infrared photoconductive characteristics.

One-dimensional (1D) [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanorods as an efficient additive for improving the efficiency and stability of perovskite solar cells

We report a novel one dimensional (1D) [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanorod material as an efficient additive to form a wrinkle-like bicontinuous perovskite layer, where 1D PCBM nanorods can distribute homogenously throughout the film with an enlarged grain size. The resultant interconnected 1D PCBM nanorod within the perovskite material can also efficiently facilitate the photo-generated charge separation and carrier transportation process. An improved solar cell performance, from 9.5% up to 15.3%, was achieved using the optimized 1D PCBM nanorod content, along with enhanced device working stability. This work gives a new insight towards designing high performance organic–inorganic perovskite solar cells.

Semi-Transparent ZnO-CuI/CuSCN Photodiode Detector with Narrow-Band UV Photoresponse.

UNLABELLED The ZnO homogeneous pn junction photodiode is quite difficult to fabricate due to the absence of stable p-type ZnO. So exploring reliable p-type materials is necessary to build a heterogeneous pn junction with n-type ZnO. Herein, we develop a simple and low-cost solution-processed method to obtain inorganic p-type CuI/CuSCN composite film with compact morphology, high conductivity, and low surface state. The improved performance of CuI/CuSCN composite film can be confirmed based on high-rectification ratio, responsivity, and open voltage of ZnO-CuI/CuSCN photodiode UV detectors. Moreover, photodiodes with novel top electrodes are investigated. Compared with commonly used Au and graphene/Ag nanowire (NWs) electrode, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) ( PEDOT PSS) electrode prepared by Meyer rod-coating technique opens one route to obtain a semitransparent photodiode. The photodiode with PEDOT PSS as the top electrode under reverse illumination has the highest photocurrent density due to higher UV transmittance of PEDOT PSS transparent electrode compared with ITO glass. The low-energy consumption, and high responsivity, UV to visible rejection ratio and air stability make this ZnO-CuI/CuSCN photodiode quite promising in the UV-A detection field.

Microstructures, surface states and field emission mechanism of graphene–tin/tin oxide hybrids

The effects of microstructures and surface states on the field emission, which are important to a good understanding of the field emission mechanism, are unclear. In this paper, the microstructures and surface states of graphene-Sn/SnO2 hybrids were analyzed, and the field emission mechanism was explored. Raman spectra and images revealed that SnO2/Sn droplets are strongly bound on graphene surface, and there exist oxygen vacancies at the surface of graphene-Sn/SnO2 hybrids. Among X-ray photoelectron spectroscopy spectra, the peak of O 1s shifts 1.6 eV toward higher binding energies in the 5 min sample with the best field emission properties, which indicates that the field emission improvement in graphene-Sn/SnO2 hybrids arises from the band-bending effect and a lower work function.