Wenxiu Que

Highly Efficient Flexible Perovskite Solar Cells Using Solution-Derived NiOx Hole Contacts

A solution-derived NiOx film was employed as the hole contact of a flexible organic-inorganic hybrid perovskite solar cell. The NiOx film, which was spin coated from presynthesized NiOx nanoparticles solution, can extract holes and block electrons efficiently, without any other post-treatments. An optimal power conversion efficiency (PCE) of 16.47% was demonstrated in the NiOx-based perovskite solar cell on an ITO-glass substrate, which is much higher than that of the perovskite solar cells using high temperature-derived NiOx film contacts. The low-temperature deposition process made the NiOx films suitable for flexible devices. NiOx-based flexible perovskite solar cells were fabricated on ITO-PEN substrates, and a preliminary PCE of 13.43% was achieved.

Controllable synthesis of brookite/anatase/rutile TiO2 nanocomposites and single-crystalline rutile nanorods array

The synthesis of nano-TiO2 materials have attracted intense interest due to their importance in a wide area of applications. In this study, we report a facile method to synthesize mixed-phase TiO2 nanocomposites by using a one-step approach under mild solvothermal conditions. Differently from previous reports, this method not only yields rutile/brookite/anatase TiO2 nanocomposites with high photocatalytic activities, but also can obtain highly oriented single-crystal rutile nanorod arrays selectively deposited on FTO. These products were characterized by XRD, FTIR, FESEM, TEM, HRTEM, and BET. Results indicate that in the brookite/anatase/rutile coexisting nanopowders, the brookite and anatase phases were crystallized into irregular nanoparticles <20 nm in diameter, whereas the rutile phase was crystallized into single-crystalline nanorods ∼20 nm in diameter and 100 to 500 nm in length. The single-crystalline rutile nanorods could form a film with controllable thickness up to ∼7 μm. The sample with 29.9% anatase, 27.9% brookite, 42.2% rutile was shown to have the highest photocatalytic activity, yielding over 90% bleaching of methyl orange solution in 20 min. The degradation rate constant k of this sample was 0.10180 min−1, almost twice as high as that of P25 (k = 0.05397 min−1). DFT calculations were used to confirm the band structures and density of states in brookite, anatase, and rutile phases.

Photocatalytic Degradation of Methyl Orange over Nitrogen–Fluorine Codoped TiO2 Nanobelts Prepared by Solvothermal Synthesis

Anatase type nitrogen-fluorine (N-F) codoped TiO(2) nanobelts were prepared by a solvothermal method in which amorphous titania microspheres were used as the precursors. The as-prepared TiO(2) nanobelts are composed of thin narrow nanobelts and it is noted that there are large amount of wormhole-like mesopores on these narrow nanobelts. Photocatalytic activity of the N-F codoped TiO(2) nanobelts was measured by the reaction of photocatalytic degradation of methyl orange. Results indicate that the photocatalytic activity of the N-F codoped TiO(2) nanobelts is higher than that of P25, which is mainly ascribed to wormhole-like mesopores like prison, larger surface area, and enhanced absorption of light due to N-F codoping. Interestingly, it is also found that the photocatalytic activity can be further enhanced when tested in a new testing method because more photons can be captured by the nanobelts to stimulate the formation of the hole-electron pair.

Recent progress in layered transition metal carbides and/or nitrides (MXenes) and their composites: synthesis and applications

Since their inception in 2011, from the inaugural synthesis of multi-layered Ti3C2Tx by etching Ti3AlC2 with hydrofluoric acid (HF), novel routes with a myriad of reducing agents, etchants and intercalants have been explored and many new members have been added to the two-dimensional (2D) material constellation. Despite being endowed with the rare combination of good electronic conductivity and hydrophilicity, their inherent low capacities, for instance, temper their prospect for application for electrodes in energy storage systems. MXene-based composites, however, with a probable synergistic effect in agglomeration prevention, facilitating electronic conductivity, improving electrochemical stability, enhancing pseudocapacitance and minimizing the shortcomings of individual components, exceed the previously mentioned capacitance ceiling. In this review, we summarise the development and progress in the synthesis of various multi-layered carbides, carbonitrides and nitrides, and intercalants, as well as the subsequent processing in order to delaminate them into single- and/or few-layered and incorporate into MXene-based composites, focusing on their performance and application as transparent conductive films, environmental remediation, electromagnetic interference (EMI) absorption and shielding, electrocatalysts, Li-ion batteries (LIBs), supercapacitors and other electrochemical storage systems.

A facile method to crystallize amorphous anodized TiO2 nanotubes at low temperature

Anodic growth of TiO(2) nanotubes has attracted intensive interests recently. However, the as-prepared TiO(2) nanotubes are usually amorphous and they generally need to be crystallized by sintering above 450 °C. Here, we report on a facile method to crystallize amorphous anodized TiO(2) nanotubes at a low temperature. We find that, simply by immersing them into hot water, the anodized TiO(2) nanotubes can be transformed from amorphous to crystalline state at a temperature as low as 92 °C. Results indicate that the hot water treatment might be a versatile strategy to crystallize amorphous anodized TiO(2) nanotubes at low temperature. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, UV-vis spectroscopy, and Brunauer-Emmett-Teller (BET) analysis via N(2) adsorption are used to characterize the resulting samples. In addition, the TiO(2) nanotubes in powder form are taken as photocatalysts to explore their potential applications. Results indicate that the sample after 35 h of hot water treatment shows the highest photoactivity, which is as efficient as the commercial photocatalyst Degussa P25. The photocatalytic testing results demonstrate that the hot water treatment reported in this study can be an alternative approach to the conventional methods.

High efficiency hysteresis-less inverted planar heterojunction perovskite solar cells with a solution-derived NiOx hole contact layer

A hysteresis-less inverted planar heterojunction perovskite solar cell with 14.42% power conversion efficiency (PCE) was successfully fabricated by employing a solution-derived NiOx film as the hole selective contact. Here, the non-stoichiometric transparent NiOx film is composed of a lot of small NiOx nanocrystals with a cubic crystal structure. Inverted planar heterojunction perovskite solar cells based on the as-prepared NiOx hole selective contacts show a much higher PCE and air storage stability than the control device fabricated from the PEDOT:PSS film as the hole selective contact, since NiOx has a better electron blocking property due to its high conduction band edge position. The thickness of the NiOx contact strongly influences the performance of the NiOx-based perovskite solar cells, which include the PCE, hysteresis behaviors and air storage stability due to the thickness-dependent morphology of the NiOx contact.

Enhanced Photocatalytic Activity of ZnO Microspheres via Hybridization with CuInSe2 and CuInS2 Nanocrystals

ZnO microspheres sensitized by CuInSe(2) and CuInS(2) nanoparticles, which were synthesized by a solvothermal method and have a size about 20 and 3.5 nm, respectively, were used to a photodegradation of rhodamine B under an irradiation of mercury lamp. Results show that the photocatalytic activities of the ZnO/CuInSe(2) and the ZnO/CuInS(2) are much higher than that of the ZnO microspheres because of a formation of the heterojunction in two systems. It is also noted that the ZnO/CuInS(2) exhibits a higher photocatalytic activity than the ZnO/CuInSe(2), which is probably related to more suitable band gap to sunlight for CuInS(2) nanocrystals and the larger specific surface due to a small size. Particularly, the ZnO/CuInSe(2)/CuInS(2) shows the highest photocatalytic activities in all measured photocatalysts, which should be attributed to the formation of double heterojunctions among ZnO, CuInSe(2), and CuInS(2).

Double-Layer Electrode Based on TiO2 Nanotubes Arrays for Enhancing Photovoltaic Properties in Dye-Sensitized Solar Cells

The present work reports a rapid and facile method to fabricate a novel double-layer TiO2 photoanode, which is based on highly ordered TiO2 nanotube arrays and monodispersive scattering microspheres. This double-layer TiO2 sphere/TNTA photoanode have got many unique structural and optical properties from TiO2 scattering microspheres, such as high specific surface area, multiple interparticle scattering, and efficient light-harvesting. Results indicate that this as-fabricated double-layer TiO2 sphere/TNTA front-illumination dye-sensitized solar cell, which is fabricated from the TiO2 nanotube arrays with a 17.4 μm length after TiCl4 treatment, exhibits a pronounced power conversion efficiency of 7.24% under an AM1.5 G irradiation, which can be attributed to the increased incident photon-to-current conversion and light-harvesting efficiency.

Facile synthesis of ZnO/CuInS2 nanorod arrays for photocatalytic pollutants degradation.

Vertically-aligned ZnO nanorod arrays on a fluorine-doped tin oxide glass substrate were homogeneously coated with visible light active CuInS2 quantum dots by using a controllable electrophoretic deposition strategy. Compared with the pure ZnO nanorod arrays, the formation of high-quality ZnO/CuInS2 heterojunction with well-matched band energy alignment expanded the light absorption from ultraviolet to visible region and facilitated efficient charge separation and transportation, thus yielding remarkable enhanced photoelectrochemical performance and photocatalytic activities for methyl orange and 4-chlorophenol degradation. The ZnO/CuInS2 film with the deposition duration of 80min showed the highest degradation rate and photocurrent density (0.95mA/cm(2)), which was almost 6.33 times higher than that of the pure ZnO nanorod arrays film. The CuInS2 QDs sensitized ZnO nanorod arrays film was proved to be a superior structure for photoelectrochemical and photocatalytic applications due to the optimized CuInS2 loading and well-maintained one-dimensional nanostructure.

ZnO/CdS/CdSe core/double shell nanorod arrays derived by a successive ionic layer adsorption and reaction process for quantum dot-sensitized solar cells

Well-aligned one-dimensional ZnO nanorod arrays were grown on transparent conducting glass, and CdS and CdSe quantum dot thin films were then deposited on the nanorod arrays in turn by an effective successive ionic layer adsorption and reaction process to form a ZnO/CdS/CdSe core/double-shell structure electrode. As revealed by the images of filed-emission scanning electron microscopy and transmission electron microscopy, the CdS and CdSe quantum dot thin films were uniformly deposited on the ZnO nanorods and the thickness of the CdS and CdSe shell can be controlled by varying the number of the adsorption and reaction cycles. For a typical sample that was prepared by a 10 times adsorption and reaction cycle, the thickness of the CdS and CdSe shell was about 4.0 and 5.5 nm, respectively. A short circuit density of 12.1 mA cm−2 and a power conversion efficiency of 1.72% were obtained for the solar cell based on the optimal ZnO/CdS/CdSe core–shell nanorod array electrode under the illumination of one sun (AM1.5, 100 mW cm−2).