Huimin Jia

Hybrid solar cells with outstanding short-circuit currents based on a room temperature soft-chemical strategy: the case of P3HT:Ag2S.

P3HT:Ag(2)S hybrid solar cells with broad absorption from the UV to NIR band were directly fabricated on ITO glass by using a room temperature, low energy consumption, and low-cost soft-chemical strategy. The resulting Ag(2)S nanosheet arrays facilitate the construction of a perfect percolation structure with organic P3HT to form ordered bulk heterojunctions (BHJ); without interface modification, the assembled P3HT:Ag(2)S device exhibits outstanding short-circuit current densities (J(sc)) around 20 mA cm(-2). At the current stage, the optimized device exhibited a power conversion efficiency of 2.04%.

First observation of visible light photocatalytic activity of carbon modified Nb2O5 nanostructures

Carbon-modified niobium oxide (Nb2O5) nanostructures, that firstly exhibited good visible light photocatalytic activity of Nb2O5 species, were synthesized by utilizing a low temperature, one-pot nonaqueous sol–gel approach. The resulting products were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption. Unlike the commercial or other reported Nb2O5 products that only respond to the UV-light irradiation, the present carbon-modified Nb2O5 nanostructures obtained at 200 °C in our experiment exhibited much better photocatalytic activity on degradation of RhB under visible light, which was about 39 times of that of commercial Nb2O5, 18 times of that of Degussa P25, and 5 times of that of carbon modified mesoporous TiO2. Moreover, these carbon-modified Nb2O5 nanostructures were also able to efficiently split water under visible light. The growth mechanism and the origin of visible light photocatalytic activity of the resulting Nb2O5 nanostructures were proposed. These carbon-modified Nb2O5 products are expected to be more suitable candidates than that of the most studied TiO2 as visible light photocatalysts.

Unraveling the Enhanced Photocatalytic Activity and Phototoxicity of ZnO/Metal Hybrid Nanostructures from Generation of Reactive Oxygen Species and Charge Carriers

An effective way for promoting photocatalytic activity of a semiconductor is deposition of noble metal nanoparticles (NPs) onto it. In this paper, we deposited Ag and Pd onto ZnO NPs to form ZnO/Ag and ZnO/Pd hybrid nanostructures. It was found that both Ag and Pd nanocomponents can greatly enhance the photocatalytic activity and phototoxicity of ZnO toward human skin cells. Using electron spin resonance spectroscopy with spin trapping and spin labeling techniques, we observed that either deposition of Ag or Pd resulted in a significant increase in photogenerated electrons and holes and production of reactive oxygen species including hydroxyl radicals, superoxide, and singlet oxygen. We compared the enhancing effects of Ag and Pd and found that Pd is more effective than Ag in promoting the generation of hydroxyl radicals and holes and the photocatalytic activity of ZnO. Conversely, Ag is more effective than Pd in enhancing electron transfer and the generation of superoxide and singlet oxygen. The mechanism underlying the differences in the effects of Ag and Pd may be related to differences in Fermi levels for Ag and Pd and band bending accompanied by effects on Schottky barriers. The results of these studies provide information valuable for designing hybrid nanomaterials having photocatalytic and photobiological activities useful for applications such as water purification and formulation of antibacterial products.

In situ fabrication of chalcogenide nanoflake arrays for hybrid solar cells: the case of In2S3/poly(3-hexylthiophene)

A novel strategy for fabricating hybrid thin film solar cell devices based on poly(3-hexylthiophene) (P3HT)/indium sulfide (In2S3) nanoflake array films is presented in this paper. We take In2S3 as an example to demonstrate that a novel chalcalgenide nanoflake array structure could be in situ fabricated on indium-tin oxide (ITO) glass substrates through a one-step solvothermal treatment of an indium nanocrystal layer and sulfur powder in the presence of absolute ethanol. The resulting products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-vis spectrophotometry. A preliminary photovoltaic performance measurement of the fabricated device (ITO/PEDOT:PSS/In2S3:P3HT/Al) shows a short circuit current density (Jsc) of 0.68 mA cm−2 and a power conversion efficiency (η) of 0.04% under an illumination of 100 mW cm−2. The in situ-fabricated special nanoflake array structure may provide a large interfacial surface area for the In2S3 nanocrystals and the poly(3-hexylthiophene) in such hybrid solar cell devices. This novel wet chemical strategy may remove the need for insulated surfactants, improve the stability of both the thin film and the fabricated device, and is expected to be expanded to fabricate other conjugated polymer/charcalgenide hybrid thin film solar cell devices.

Intrinsic charge carrier dynamics and device stability of perovskite/ZnO mesostructured solar cells in moisture

Understanding the intrinsic behaviour of perovskite solar cells is as important as breaking a new PCE record. In particular, the essential mechanisms (e.g. the effect of moisture, oxygen or temperature) behind their chemical instability remain controversial. In this work, we unconventionally and specially fabricate a robust CH3NH3PbI3 perovskite solar cell device in ∼70% relative humidity (RH) with an un-optimized PCE of 8.76%, because our main aim is to understand the essential mechanisms, not the efficiency, which drastically relies on the device assembling technique. Such a device exhibits excellent chemical and performance stability, with more than 72% of the initial PCE still maintained after 250 days storage under 40 ± 3% RH conditions without any encapsulation. In addition, the mechanism underlying the chemical and device stability is fully understood from the charge carrier dynamics and variation of the perovskite crystal. These high RH conditions may facilitate a slight and rapid decomposition/separation of CH3NH3PbI3 to form a PbI2 passivation layer as a moisture defender, which on the contrary plays a crucial role in stabilizing the PCE of CH3NH3PbI3 mesoporous solar cells. This PbI2 insulation layer made the CH3NH3PbI3/ZnO p–n junction a CH3NH3PbI3/PbI2/ZnO p–i–n junction, and maintained good junction quality. Another key factor contributing to the high stability lies in the formation of regular nano-sized ZnO arrays. Consequent transient photovoltaic (TPV) tests revealed that not only fresh CH3NH3PbI3, but also pure PbI2 thin films and CH3NH3PbI3 thin films stored for a long time, all possess a long minority carrier life time. In particular, the stored CH3NH3PbI3/ZnO thin films still maintain a relatively fast photogenerated carrier transfer stability compared with the fresh CH3NH3PbI3/ZnO thin film. We demonstrated the relatively positive role of a moderate amount of PbI2 in perovskite solar cells. This robust device fabrication and TPV measurements give a new perspective for understanding the heterojunction quality and PCE variation in perovskite solar cell fabrication.

A very facile, low temperature, one-step route to in situ fabricate copper sulfide nanosheet thin films

CuS nanosheet thin films with large areas were synthesized in situ on copper substrates through a facile, one-step treatment of copper foil and sulfur powder in the presence of N,N-dimethylformamide (DMF) at low temperature (60 °C or less). Compared with the previous reported solvothermal approach, the current low temperature route is simpler, low cost and low energy consumption. The effects of the reaction temperature on the synthesis and the optical property of CuS nanosheet films were investigated. The resulting CuS nanosheet films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV–vis spectrometer. In this study, we also demonstrated this method to prepare copper sulfide nanosheet films on ground-glass and indium tin oxide glass (ITO) substrates. We found that perfect nanosheet crystals could be obtained in all cases. The growth mechanism of CuS nanosheet-based films was proposed. The current method may open up a new way to prepare thin films of metal sulfide at low temperatures.

In situ fabrication of Cu2ZnSnS4 nanoflake thin films on both rigid and flexible substrates

Cu2ZnSnS4 (CZTS) thin film, a highly promising and low-cost absorber layer material for solar cells, has been in situ fabricated on stainless steel and FTO glass substrates for the first time, using a one-step solvothermal treatment of CuZnSn-alloyed film with sulphur or selenium powder. The resulting products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-vis-NIR spectroscopy. Raman spectroscopy was used to characterize and confirm the formation of CZTS. The effects of temperature, reaction time, the ratio of Cu/Zn/Sn, and non-elemental reactants on the formation of CZTS nanocrystal films were assessed, and we found that the reaction temperature was a key factor in determining the properties of the final products. Pure CZTS phase forms at a temperature of 250 °C or higher. Our method produces CZTS thin films at 250 °C, the lowest reaction temperature that can be used in the process and the lowest temperature of any current fabrication system. We also found that flexible substrates promote the growth of CZTS nanocrystals. Using flexible substrates in the in situ fabrication of nanocrystalline thin films may make it possible to use CZTS for industrial applications.

Composition Directed Generation of Reactive Oxygen Species in Irradiated Mixed Metal Sulfides Correlated with Their Photocatalytic Activities

The ability of nanostructures to facilitate the generation of reactive oxygen species and charge carriers underlies many of their chemical and biological activities. Elucidating which factors are essential and how these influence the production of various active intermediates is fundamental to understanding potential applications of these nanostructures, as well as potential risks. Using electron spin resonance spectroscopy coupled with spin trapping and spin labeling techniques, we assessed 3 mixed metal sulfides of varying compositions for their abilities to generate reactive oxygen species, photogenerate electrons, and consume oxygen during photoirradiation. We found these irradiated mixed metal sulfides exhibited composition dependent generation of ROS: ZnIn2S4 can generate (•)OH, O2(-•) and (1)O2; CdIn2S4 can produce O2(-•) and (1)O2, while AgInS2 only produces O2(-•). Our characterizations of the reactivity of the photogenerated electrons and consumption of dissolved oxygen, performed using spin labeling, showed the same trend in activity: ZnIn2S4 > CdIn2S4 > AgInS2. These intrinsic abilities to generate ROS and the reactivity of charge carriers correlated closely with the photocatalytic degradation and photoassisted antibacterial activities of these nanomaterials.

Fabrication and application of MFe2O4 (M = Zn, Cu) nanoparticles as anodes for Li ion batteries

In this work, MFe2O4 (M = Zn, Cu) nanoparticles were successfully prepared by a hydrothermal method. The structure, morphology, microstructure, specific surface area and electrochemical properties of the resultant particles were characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen physical adsorption, charge–discharge test and cyclic voltammetry (CV) method, respectively. The resulting ZnFe2O4 and CuFe2O4 products were sphere-like and cubic-shaped particles and their average size was about 30–40 nm and 60–70 nm, respectively. The initial discharge capacities of ZnFe2O4 and CuFe2O4 electrodes reached 1287.5 mAh g−1 and 1412.3 mAh g−1, respectively, at a current density of 0.2 mA cm−2 in a potential range of 0.0–3.0 V. This indicated that Cu is a better counter ion than Zn. The resulting MFe2O4 nanoparticles are expected to be a promising candidate of anode materials for Li ion batteries. The reaction mechanism of MFe2O4 nanoparticles in Li ion batteries was also discussed based on the CV of Li/MFe2O4 cell.

AuPt Alloy Nanostructures with Tunable Composition and Enzyme-like Activities for Colorimetric Detection of Bisulfide

Tuning the enzyme-like activity and studying the interaction between biologically relevant species and nano-enzymes may facilitate the applications of nanostructures in mimicking natural enzymes. In this work, AuPt alloy nanoparticles (NPs) with varying compositions were prepared through a facile method by co-reduction of Au3+ and Pt2+ in aqueous solutions. The composition could be tuned easily by adjusting the molar ratios of added Pt2+ to Au3+. It was found that both peroxidase-like and oxidase-like activity of AuPt alloy NPs were highly dependent on the alloy compositions, which thus suggesting an effective way to tailor their catalytic properties. By investigating the inhibitory effects of HS− on the enzyme-like activity of AuPt alloy NPs and natural enzyme, we have developed a method for colorimetric detection of HS− and evaluation of the inhibiting effects of inhibitors on natural and artificial enzymes. In addition, the responsive ability of this method was influenced largely by the composition: AuPt alloy NPs show much lower limit of detection for HS− than Pt NPs while Pt NPs show wider linear range than AuPt alloy NPs. This study suggests the facile way not only for synthesis of alloy nanostructures, but also for tuning their catalytic activities and for use in bioanalysis.