Oxygen modulation of flexible PbS/Pb Schottky junction PEC cells with improved photoelectric performance.

Flexible photoelectric devices are emerging as a new class of photovoltaic cells. In this study, lead (Pb) foil was used as a flexible substrate to grow in situ lead sulfide (PbS) film with good uniformity and adhesion by a solvothermal elemental direct reaction, resulting in a PbS/Pb Schottky junction formed naturally between the PbS film and underlying Pb foil. We found that the photocurrent response of the photoelectrochemical (PEC) cell was greatly improved through a facile oxygen (O2)-modulation-based post-processing technique. O2 could decompose the organic residue and oxidize the Pb at the interface between the PbS film and Pb foils. Different characterization techniques, including thermogravimetric analysis, differential scanning calorimetry, x-ray diffraction, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, the change in transient photocurrent density (J p) with time (t), dark current-voltage (I-V) and absorption spectra were applied to get a full understanding of the O2 modulation effect. The oxidization treatment of the PbS film could regulate the flow of charge carriers to reduce their recombination, leading to photoresponse enhancement for the PEC cells. In particular, the process could modulate the tunneling current and interface states to optimize dark I-V characteristics. In addition, the magnitude of the barrier height can be tuned by O2 modulation, which was explained by theoretical analysis and calculation. We also demonstrated that the in situ formed PbS film has outstanding adhesion on the flexible Pb substrate. Our film synthesis method and post O2-modulation design as well as the corresponding device assembly may provide a novel perspective to the flexible PCE-cell-related research.

Improved stoichiometry and photoanode efficiency of thermally evaporated CdS film with quantum dots as precursor.

Good stoichiometry of cadmium sulfide (CdS) film facilitates its application in photovoltaic devices; however, traditional thermal evaporation usually results in a Cd-deficient CdS film at a low-substrate temperature. In this study, Cd-rich CdS quantum dots (QDs) were synthesized by a facile co-precipitation method and used as the precursor to thermally evaporate CdS film on indium tin oxide-coated glass (ITO/glass). As a consequence, the stoichiometry of CdS film was greatly improved with atomic ratio of Cd to S restored to unity. More importantly, the newly developed CdS film, with its rod-like surface microstructure, acted as an efficient photoanode in a photoelectrochemical (PEC) cell. Its properties, including surface morphology and roughness, crystal structure, chemical composition, film thickness, energy-level structure and photosensitivity, are studied in detail.

DMF-Based Large-Grain Spanning Cu2 ZnSn(Sx ,Se1- x )4 Device with a PCE of 11.76.

A main concern of the promising DMF-based Cu2 ZnSn(Sx ,Se1- x )4 (CZTSSe) solar cells lies in the absence of a large-grain spanning structure, which is a key factor for high open-circuit voltage (Voc ) and power conversion efficiency (PCE). A new strategy to achieve CZTSSe large-grain spanning monolayer is proposed, by taking advantage of the synergistic optimization with a Cu2+ plus Sn2+ redox system and pre-annealing temperatures. A series of structural, morphological, electrical, and photoelectric characterizations are employed to study the effects of the pre-annealing temperatures on absorber qualities, and an optimized temperature of 430 â„ƒ is determined. The growth mechanism of the large-grain spanning monolayer and the effect of redox reaction rate are carefully investigated. Three types of absorber growth mechanisms and a concept of critical temperature are proposed. The devices based on this large-grain spanning monolayer suppress the recombination of carriers at crystal boundaries and interfaces. The champion device exhibits a high Voc (>500 mV) and PCE of 11.76%, which are both the maximum values among DMF-based solar cells at the current stage.

A novel ethanol gas sensor-ZnS/ cyclohexylamine hybrid nanowires.

We fabricated a novel ethanol gas sensor based on organic-inorganic ZnS/cyclohexylamine (CHA) nanowires via a solvothermal route. The sensor exhibited significantly better performance with response time of approximately 0.6 s and recovery time of approximately 10 s even under a low ethanol concentration and the high surface area, small nanofiber diameter, and hybrid nature made the ZnS/CHA nanowire gas sensor have high sensitivity to ethanol gas at a lower operating current of 160 mA. Moreover, the gas sensing mechanism was proposed on the basis of the two simultaneous steps to explain the adsorbing process due to the hybrid nature. This work indicates that the ZnS/CHA hybrid can be a novel candidate for the ethanol gas sensor with high performance.

Improved upconversion luminescence properties of Gd2O3:Er3+/Gd2O3:Yb3+ core-shell nanorods.

The Gd2O3:Er3+/Gd2O3:Yb3+ core-shell nanorods (NRs) as well as Er3+ and Yb3+ homogeneously codoped Gd2O3 NRs were synthesized by the hydrothermal method. The average diameters of the NRs are approximately 20 nm and the lengths are 150-200 nm. The thickness of the Gd2O3:Yb3+ shells on the Gd2O3:Er3+ cores are approximately 5 nm. The upconversion luminescence (UCL) properties of the core-shell NRs have been studied in contrast to homogeneously codoped NRs under 978-nm laser diode excitation. Green emissions of 2H11/2, 4S3/2-4I15/2, and red emissions of 4F9/2-4I15/2 were observed. Relative intensity of the red (4F9/2-4I15/2) to the green (4S3/2/2H11/2-4I15/2) and the intensity ratio (RHS) of 2H11/2-4I15/2 to 2H11/2-4I15/2 decrease obviously in the core-shell NRs compared to the NRs. The power-dependence of UCL intensity and the thermal effect caused by 978-nm diode laser irradiation was studied. The result indicates that the cross-relaxation effect and the thermal effect in the core-shell structure is effectively depressed.

A new inorganic-organic composite of CuS/pyridine with unique sub-nanostructures.

Bur-like microspheres and microwires of CuS/pyridine composites were synthesized by a solvothermal method. The spheres or wires composed of a large number of nanoflakes with thickness of 10-20 nm and length of hundreds nanometers. Sub-nanostructures can be observed in the nanoflakes by the high-resolution transmission electron microscopy (HR-TEM) patterns. A large blue shift of band-gap absorption of CuS was observed in the composites, which was attributed to quantum confinement effect (QCE) induced by the sub-nanostructures. Pure Cu9S5 microspheres and CuS/Cu9S5 microwires were obtained by extracting the inorganic-organic composites with ethylene glycol. Possible formation mechanisms were discussed.

Unusually Dispersed AgI Quantum Dots For Efficient HTL-Free CH3NH3PbI3 Photovoltaics.

The utilization of quantum dots (QDs) to improve the performance of perovskite solar cells is attracting much attention due to their unique optical and electronic properties. Most of QDs have to be prepared in advance and then incorporated into the perovskite hosts, which could not ensure the maintenance of their QD characteristics. In this work, we intelligently developed an in situ preparation strategy to disperse AgI QDs homogeneously in the perovskite host for the MAPbI3:AgI(QDs) cross-blended layer directly on indium tin oxide (ITO) via a common and convenient spin-coating process. We combine transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman techniques to demonstrate the cross-blended MAPbI3:AgI(QDs) structure in the final perovskite devices. Furthermore, a series of simply inverted ITO/MAPbI3:AgI(QDs)/PCBM/Ag devices have been designed and fabricated. The photovoltaic performance of these solar cells shows significantly improved short-circuit current density (Jsc) and a champion power conversion efficiency of 16.41% even without a hole transport layer. The current technique induced the crystal growth toward high-quality perovskite films with a homogeneous structure, good crystallinity, less grain boundaries and defects, increased optical path length, and uniform thickness for better solar cell performance. Besides, the impact of the current strategy also lies in an accommodation effect of the hole collection at the ITO side induced by AgI QDs, which modifies the Fermi level of perovskite films, leading to significantly decreased level difference in the Fermi level/work function between the perovskite layer and ITO substrates by ultraviolet photoelectron spectra analysis. More importantly, the charge carrier dynamics of such novel MAPbI3:AgI(QDs) structures were also scrutinized by transient photovoltage analysis.

Preparation and luminescent properties of polymer fibers containing Y2O3:Eu nanoparticles by electrospinning.

In this paper, composite fibers of polyvinylpyrrolidone (PVP) and Y2O3:Eu3+ nanocrytals were prepared by electrospinning and characterized by electron microscope, Fourier transform infrared spectra (FT-IR) and X-ray diffraction (XRD). The composite fibers are in random orientation and with average diameter of approximately 300 nm and length up to several ten micrometers. The luminescent properties were investigated and compared with the pure Y2O3:Eu3+ nanocrystals. Due to certain weak interactions between nanocrystals and PVP matrix, charge transfer band in the excitation spectra show slightly red shift for the fibers relative to in the case of pure Y2O3:Eu3+ nanocrystals. The PVP polymer may modified the surface defect states of nanocrystals, yielding decreased intensity ratio of 5Do-(7)F2 to (5)D0-(7)F1 transition in the emission spectra. The fluorescence lifetimes of (5)D0 level for Eu3+ in the composite fibers and Y203:Eu3+ nanocrystals were respectively determined to be 1.40 and 1.74 ms. The decreased fluorescence lifetime in the composite fibers was attributed to increased radiative transition rate, as result of the influence of refractive index of the surrounding PVP media instead of air.

CdS/Cyclohexylamine inorganic-organic hybrid semiconductor nanofibers with strong quantum confinement effect.

Inorganic-organic hybrid semiconductor nanofibers of CdS/CHA (CHA = cyclohexylamine) were successfully synthesized by a simple solvothermal method. The fibers obtained had average diameter of 20 nm and length of several micrometers. In these fibers, periodic layer-like sub-nanometer structures with thickness of approximately 3 nm were identified by high-resolution transmission electron microscope (HR-TEM). The absorption of the hybrids exhibited a large blue-shift in contrast to the bulk, which was attributed to strong quantum confinement effect (QCE) induced by internal sub-nanometer structures. Pure hexagonal wurtzite CdS (H-CdS) nanorods were also obtained by extracting the CdS/CHA hybrids with dimethyl formamide (DMF). The rods obtained had average diameter of 20 nm and length of 200 nm. A CdS/CHA/polyvinyl alcohol (PVA) composite film emitting white light was prepared by spin coating.

Upconversion white light devices: Ln(3+)-tridoped NaYF4 nanoparticles and PVP modified films.

Upconversion (UC) white light hybrid thin films containing Ln(3+)-tridoped (Yb3+, Er3+ and Tm3+) NaYF4 nanoparticles and poly(vinyl pyrrolidone) (PVP, M(w) approximately 1300000) were prepared by a spin-coating method and characterized by X-ray diffraction (XRD), field emission scanning electron micrograph (FE-SEM) and Fourier transform infrared spectra (FT-IR). White light was generated by two different lanthanide ions, Er3+ (red and green) and Tm3+ (blue) under excitation by a 980-nm laser diode. Due to the modification of PVP to the UC populating processes, the color stability of the white light in the hybrid films was remarkably improved.

White luminescence by up-conversion from thin film made with Ln(3+)-doped NaYF4 nanoparticles.

White light-emitting thin films containing Ln(3+)-doped NaYF4 nanoparticles were prepared by a simple spin-coating method. White light was generated by two different lanthanide ions, Er3+ (red and green) and Tm3+ (blue), by upconversion process under the excitation of a 980-nm laser diode. The ratio of the intensity of the three main emissions was tuned by controlling the concentration of the nanoparticles in the thin film and the concentration of the lanthanide ions in the nanoparticles. The color coordinates corresponding to emissions of different nanoparticle concentrations and with the different pump powers were investigated. When the pump power was fixed at 900 mW, the thin film with a concentration ratio of 2.5:1 emitted pure white light with coordinates of (0.333, 0.339).

Preparation and luminescent properties of YVO4:Eu3+ nanofibers by electrospinning.

This paper describes a procedure based on electrospinning for generating europium-doped yttrium vanadate (YVO4:Eu3+) nanofibers with diameters ranging from 30 to 50 nm. The YVO4:Eu3+ nanofibers were obtained through calcining precursory nanofibers, which were prepared through the electrospinning method. Suitable electrospinning parameters, such as concentration of PVP in solution, spinneret tip-to-collector plate distance (TCD), and applied voltage between spinneret and collector plate, are used to obtain thinner and more uniform precursory nanofibers of YVO4:Eu3+, which is important for preparing smaller diameter pure YVO4:Eu3+ nanofibers. The luminescent properties of the YVO4:Eu3+ nanofibers including excitation and emission spectra and fluorescence lifetime were studied. The excitation spectrum shows a broad band extending from 200 to 350 nm, which corresponds to the strong vanadate absorption in YVO4:Eu3+. The emission spectrum is dominated by the red 5D0 --> 7F2 hypersensitive transition of Eu3+. The fluorescence lifetime of Eu3+ 5D0 --> 7F2 (619 nm) is determined to be 493 micros at room temperature, which is basically in accordance with that in the bulk (521 micros).

Association between family socioeconomic status and depressive symptoms among Chinese adolescents: Evidence from a national household survey.

Depression is a common mental disorder due to high risk of the adolescence development stage. Few studies discussed the association between family socioeconomic status (SES) and depression and its mechanism. We aimed to provide a national view of depressive symptoms among Chinese adolescents to explore the relationship between family SES and depressive symptoms. We used the data from the Chinese Family Panel Studies (CFPS). Family SES include family income and parents' educational attainment. Depressive symptoms were measured by the Center for Epidemiological Study Depression. Family SES was found to be significantly associated with adolescents' depressive symptoms. The study indicated that adolescents were more likely to have depressive symptoms when family income decreased. Poor self-confidence, mathematics performance, and physical health were associated with high risk for depressive symptoms. The presence of these factors greatly weakened the association between family SES and depressive symptoms. Therefore, adolescents' mental health is vulnerable and connected to family SES. Physical health, school performance, and self-confidence might be important mediators in the pathways of family SES affecting depressive symptoms. Prevention and intervention programs are important and necessary to improve the mental health of Chinese adolescents, and the effect of family SES should be considered in these programs.

Structure and photoluminescent properties of microstructural YBO3 : Eu3+ nanocrystals.

YBO3 : Eu3+ nanocrystals (NCs) were prepared by a hydrothermal method and characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The results demonstrate that morphology and structure of the NCs varied strongly with hydrothermal temperature. Their luminescent properties were investigated in comparison to the bulk. A large number of NO3- groups were adsorbed at the surface of hydrothermal products, which acted as luminescent killers; Two symmetry sites of Eu3+ ions in NCs, the interior and the surface sites, were identified by the site-selective excitation and time-resolved emission experiments; The intensity ratio of 5D0-7F2 to 5D0-7F, of EU3+ at the surface site increased greatly than that at the interior site; as a result, the chromaticity was improved; The total radiative transition rate of 5D0-sigmaJ7FJ for Eu3+ at the surface site was 3-5 times larger than that at the interior.

Fabrication and photoluminescent properties of Gd2O3 : EU3+ nanowires in AAO template.

Uniform Gd2O3 : Eu3+ nanowires were fabricated by using anodic aluminum oxide template (AAO). The spectral measurements indicate that with the increasing annealing temperature the excitation band of Eu3+ in Gd2O3 : Eu3+ nanowires/AAO shifted blue, the intensity ratio of 5D0-7F2 to 5D0-7F1, decreased, and the lifetime became longer. In the sample annealed at 1000 degrees C two spectral components, the sharper and broader lines were identified, corresponding to two different local environments, the Eu3+ ions in cubic phase and in amorphous phase, respectively. The 5D0-7F1 transitions of Eu3+ ions in cubic phase had longer lifetime than that in amorphous phase. In contrast to the lifetime of the 5D0-7F(j) transitions in the bulk, that in Gd2O3 : Eu3+/AAO composite films increased due to influence of the surrounding media (AAO).

Improved photoluminescence properties of ternary terbium complexes in mesoporous molecule sieves.

Ternary terbium complexes were fully encapsulated and uniformly distributed into the channels of unmodified and modified mesoporous molecule sieves of SBA-15 and characterized by transmission electron micrographs (TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis) absorption spectra, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and elemental analysis. The luminescent properties for the encapsulated complexes were systematically studied in contrast to the pure complexes, including excitation and emission spectra, fluorescence dynamics, photostability under UV exposure, and the temperature dependence of intensity and lifetime. The results indicate that the excitation bands assigned to the pi-pi* electron transition of the ligands for Tb complexes encapsulated in SBA-15 were split into different components due to decreased symmetry and disappeared at long wavelengths. Owing to suppressed vibration transitions, the outer quantum efficiency of the 5D4-7FJ (J = 0-5) emissions was enhanced largely in comparison to the pure complexes. In addition, the photostability and thermostability of the emissions were also improved considerably.

Solvothermal synthesis and photoluminescent properties of ZnS/cyclohexylamine: inorganic-organic hybrid semiconductor nanowires.

An inorganic-organic hybrid semiconductor, ZnS/CHA (CHA = cyclohexylamine) nanocomposites was successfully synthesized via a solvothermal method using CHA as solvent, which yielded uniform and ultralong nanowires with widths of 100-1000 nm and lengths of 5-20 microm. Changing the reaction conditions could alter the morphology and optical properties of the nanocomposites. The periodic layer subnanometer structures were identified by high-resolution transmission electron microscopy (HR-TEM) images, with thickness of approximately 2 nm. The composites exhibited a very large blue-shift in their optical absorption edge as well as an exciton excitation band due to a strong quantum confinement effect caused by the internal subnanometer-scale structures. The pure hexagonal wurtzite ZnS nanowires were also obtained by extracting the ZnS/CHA nanocomposites with dimethyl formamide (DMF). In addition, the luminescent properties of exciton and defect-related transitions in different samples of ZnS/CHA were discussed in detail.

Luminescent properties of pure cubic phase Y2O3/Eu3+ nanotubes/nanowires prepared by a hydrothermal method.

One-dimensional pure cubic Y(2)O(3)/Eu(3+) nanocrystals (NCs) were synthesized by a hydrothermal method at various temperatures. The NCs prepared at 130 degrees C yielded nanotubes (NTs) with wall thickness of 5-10 nm and outer diameter of 20-40 nm. The NCs prepared at 170 and 180 degrees C yielded nanowires (NWs) with diameters of approximately 100 and approximately 300 nm, respectively. Their luminescent properties, including electronic transition processes, local environments surrounding Eu(3+) ions, electron-phonon coupling, and UV light irradiation induced spectral changes have been systematically studied and compared. The results indicate that the Y(2)O(3)/Eu(3+) NTs and NWs have strong red (5)D(0)-(7)F(2) transitions. The fluorescence lifetime of (5)D(1)-(7)F(1) hardly changes in different samples, while that of (5)D(0)-(7)F(2) decreases a small amount in Y(2)O(3)/Eu(3+) NTs. The (5)D(0)-(7)F(2) lines originate from the emissions of Eu(3+) ions occupying one C(2) site, like that in the bulk powders. The phonon sideline with a frequency shift of 40-50 cm(-1) appears at the low-energy side of the (7)F(0)-(5)D(0) zero phonon line. The relative intensity of the sideline to zero phonon line increases by varying from NTs to NWs, and the spectral position of the phonon sideline shifts red. The UV light irradiation induced spectral change in the charge-transfer band was studied. The results indicate that the spectral change is dependent on sample size and is wavelength selective. A detailed model was proposed to explain the light-induced spectral change.

Synthesis and properties of a bio-based epoxy resin with high epoxy value and low viscosity.

A bio-based epoxy resin (denoted TEIA) with high epoxy value (1.16) and low viscosity (0.92 Pa s, 258C) was synthesized from itaconic acid and its chemical structure was confirmed by 1H NMR and 13C NMR spectroscopy. Its curing reaction with poly(propylene glycol) bis(2-aminopropyl ether) (D230) and methyl hexahydrophthalic anhydride (MHHPA) was investigated. For comparison, the commonly used diglycidyl ether of bisphenol A (DGEBA) was also cured with the same curing agents. The results demonstrated that TEIA showed higher curing reactivity towards D230/MHHPA and lower viscosity compared with DGEBA, resulting in the better processability. Owing to its high epoxy value and unique structure, comparable or better glass transition temperature as well as mechanical properties could be obtained for the TEIA-based network relative to the DGEBA-based network. The results indicated that itaconic acid is a promising renewable feedstock for the synthesis of bio-based epoxy resin with high performance.

Upconversion luminescence, intensity saturation effect, and thermal effect in Gd2O3:Er3,Yb3+ nanowires.

In this paper, the upconversion luminescent properties of Gd2O3:Er3+,Yb3+ nanowires as a function of Yb concentration and excitation power were studied under 978-nm excitation. The results indicated that the relative intensity of the red emission (4F(9/2)-4I(15/2)) increased with increasing the Yb3+ concentration, while that of the green emission (4S(3/2)/2H(11/2)-4I(15/2)) decreased. As a function of excitation power in ln-ln plot, the green emission of 4S(3/2)-4I(15/2) yielded a slope of approximately 2, while the red emission of 4F(9/2)-4I(15/2) yielded a slope of approximately 1. Moreover, the slope decreased with increasing the Yb3+ concentration. This was well explained by the expanded theory of competition between linear decay and upconversion processes for the depletion of the intermediate excited states. As the excitation power density was high enough, the emission intensity of upconversion decreased due to thermal quenching. The thermal effect caused by the exposure of the 978-nm laser was studied according to the intensity ratio of 2H(11/2)-4I(15/2) to 4S(3/2)-4I(15/2). The practical sample temperature at the exposed spot as a function of excitation power and Yb3+ concentration was deduced. The result indicated that at the irradiated spot (0.5 x 0.5 mm2) the practical temperature considerably increased.