Wen-Hua Zhang

Podlike N‐Doped Carbon Nanotubes Encapsulating FeNi Alloy Nanoparticles: High‐Performance Counter Electrode Materials for Dye‐Sensitized Solar Cells

Podlike nitrogen-doped carbon nanotubes encapsulating FeNi alloy nanoparticles (Pod(N)-FeNi) were prepared by the direct pyrolysis of organometallic precursors. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements revealed their excellent electrocatalytic activities in the I(-)/I3(-) redox reaction of dye-sensitized solar cells (DSSCs). This is suggested to arise from the modification of the surface electronic properties of the carbon by the encapsulated metal alloy nanoparticles (NPs). Sequential scanning with EIS and CV further showed the high electrochemical stability of the Pod(N)-FeNi composite. DSSCs with Pod(N)-FeNi as the counter electrode (CE) presented a power conversion efficiency of 8.82%, which is superior to that of the control device with sputtered Pt as the CE. The Pod(N)-FeNi composite thus shows promise as an environmentally friendly, low-cost, and highly efficient CE material for DSSCs.

Low-cost and high-performance CoMoS4 and NiMoS4 counter electrodes for dye-sensitized solar cells

Porous chalcogels CoMoS4 and NiMoS4 made by a facile solution reaction displayed good electrocatalytic activity in the redox reaction of the I(-)/I3(-) shuttle. Dye-sensitized solar cells with these ternary compounds as counter electrodes (CEs) showed photovoltaic performance similar to the devices made with noble metal platinum CE (7.46%).

Solution‐Phase Synthesis and Characterization of Single‐Crystalline SnSe Nanowires

Tin(II) selenide is an important binary IV–VI semiconductor compound with a wide range of potential applications (e.g. memory switching devices, infrared optoelectronic devices, and anode materials for rechargeable lithium batteries). Bulk SnSe has both an indirect band gap at 0.90 eV and a direct band gap at 1.30 eV. Owing to the quantum confinement effect, tunable band gaps of SnSe nanostructured materials (e.g. thin films and nanocrystals) 3] have been demonstrated, which makes them capable of absorbing a major portion of solar energy. As an earth-abundant, environmentally benign, and chemically stable material, SnSe is placed among the most promising candidates for solar cells. Most recently, the interest in the controllable synthesis of colloidal tin chalcogenide (SnX; X = S, Se, Te) nanoparticles (NPs) has grown. However, nanowires (NWs) are expected to have properties superior to those of nanoparticles owing to their anisotropic geometry and the exciton confinement in two dimensions. It has been demonstrated that, for photovoltaic applications, high-aspect-ratio nanowires have the potential for enhancement of electron transport owing to their direct electron pathway that does not rely on electron hopping, in contrast to nanoparticles. Furthermore, as remarkably powerful building blocks in nanoscale electronic and optoelectronic devices, the synthesis of versatile semiconductor nanowires with superior controllability in structure and dimension is pivotal for exploiting their device applications. In 2003, Qian and co-workers reported the tentative synthesis of SnSe nanowires with a relatively large mean diameter of 50 nm, but the yield was low and the morphology (including irregular crystals) and purity (including tin oxides) were hard to control. In 2006, Zhao et al. developed a template route to synthesize SnSe nanowires, but only polycrystalline products were obtained after a long reaction time (e.g. 36 h), and a tedious process was required to remove the hard template. To date, high-yield synthesis of monocrystalline SnSe nanowires with relatively small diameters, decent aspect ratios, and good quality has remained a challenge; optical and electrical properties and optoelectronic applications of monocrystalline SnSe nanowires have not been described. We present herein a facile, solution-phase synthetic approach to colloidal SnSe nanowires, which have a mean diameter of approximately 20.8 nm, lengths tunable from hundreds of nanometers to tens of micrometers, and more importantly, a monocrystalline structure. Their optical and electric properties are examined by UV/Vis/NIR spectroscopy, cyclic voltammetry (CV), and transient photocurrent measurements, and a quantum confinement effect is clearly revealed. Furthermore, the fabrication of hybrid solar cells based on a blend of SnSe nanowires and poly(3hexylthiophene) (P3HT) is demonstrated. Colloidal SnSe nanowires were prepared from commercially available Sn[N(SiMe3)2]2, and trioctylphosphine selenide (TOP-Se) in oleylamine (OLA) or OLA/TOPO (trioctylphosphine oxide) solvent mixture by using monodisperse bismuth nanoparticles to catalyze the nanowire growth through the solution-liquid-solid (SLS) mechanism. In a typical synthesis, an injection solution consisting of Sn[N(SiMe3)2]2 (0.2 mmol) and Bi-nanoparticle catalysts (2.4 mmol) in octadecene (ODE, 600 mL) was introduced into a three-neck flask that contained a solution of TOP-Se (0.2 mmol) in OLA (4 g) or TOPO/OLA mixture (3.5 g/2.5 g) at 290 8C. The resulting reaction solution was kept at this temperature for 1–2 min before being cooled to room temperature. The product was cleaned and precipitated using hexane and isopropyl alcohol as the solvent and antisolvent, respectively. Finally the purified nanowires were dispersed in common organic solvents such as toluene. The scanning electron microscopy (SEM) image in Figure 1a shows the ensemble of randomly aligned SnSe nanowires with lengths exceeding 10 mm. The TEM image in Figure 1b displays smooth nanowires with mean diameters of (20.8 2.2) nm ( 10.6%), which correlates to the size of monodisperse Bi-nanoparticle catalysts (Figure S1 in the Supporting Information). The frozen Bi-nanoparticle seeds were usually observed at the nanowire tips (see arrows in the [*] Dr. S. Liu, Prof. W.-H. Zhang, Prof. C. Li State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences Dalian 116023 (China) and Dalian National Laboratory for Clean Energy Dalian 116023 (China) E-mail: whzhang@dicp.ac.cn canli@dicp.ac.cn

A Graphene Composite Material with Single Cobalt Active Sites: A Highly Efficient Counter Electrode for Dye‐Sensitized Solar Cells

The design of catalysts that are both highly active and stable is always challenging. Herein, we report that the incorporation of single metal active sites attached to the nitrogen atoms in the basal plane of graphene leads to composite materials with superior activity and stability when used as counter electrodes in dye-sensitized solar cells (DSSCs). A series of composite materials based on different metals (Mn, Fe, Co, Ni, and Cu) were synthesized and characterized. Electrochemical measurements revealed that CoN4 /GN is a highly active and stable counter electrode for the interconversion of the redox couple I(-) /I3 (-) . DFT calculations revealed that the superior properties of CoN4 /GN are due to the appropriate adsorption energy of iodine on the confined Co sites, leading to a good balance between adsorption and desorption processes. Its superior electrochemical performance was further confirmed by fabricating DSSCs with CoN4  /GN electrodes, which displayed a better power conversion efficiency than the Pt counterpart.

Highly ordered periodic mesoporous ethanesilica synthesized under neutral conditions

Highly ordered mesoporous ethanesilica (MES) with 2D hexagonal structure was synthesized from 1,2-bis(trimethoxysilyl)ethane under neutral conditions for the first time. Divalent salts, such as NiCl2, MgCl2, ZnCl2, ZnSO4 and Zn(NO3)2, were used to help the formation of the ordered mesostructure. The MES samples were characterized by powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, FT-IR, 13C and 29Si solid-state NMR and thermal gravimetric analysis. A phase transition from a disordered wormhole-like structure to an ordered P6mm structure was observed upon the addition of inorganic salts. The pore size of the MES decreases from 4.7 to 3.9 nm with increasing content of the inorganic salts. Fluoride was also found to be important for the formation of ordered MES under neutral conditions.

Cu2Ge(S3–xSex) Colloidal Nanocrystals: Synthesis, Characterization, and Composition-Dependent Band Gap Engineering

A facile solution-phase route was developed to synthesize a family of monodisperse Cu2Ge(S(3-x)Se(x)) alloyed nanocrystals (NCs) with controlled composition across the entire range (0 ≤ x ≤ 3). The band gaps of the resultant NCs can be engineered by tuning the compositions with a nearly linear relationship between them. The band structures of the NCs were studied by cyclic voltammetry and UV-vis absorption spectroscopy. The conducting behavior was revealed to be p-type for these NCs by photoelectrochemical measurements. Their photovoltaic applicability was finally assessed by fabricating solar cells with the Cu2Ge(S2Se) NCs as light harvester and CdS nanorods as electron conducting materials.

An acid-free medium growth of rutile TiO2 nanorods arrays and their application in perovskite solar cells

The facile hydrothermal synthesis of rutile TiO2 nanorod arrays on FTO substrates without the use of acids has been developed. The morphology of the nanorods can be finely tuned by changing the growth parameters, and the potential of the as-made rutile TiO2 nanorods in perovskite solar cells was evaluated, showing power conversion efficiencies up to 11.1%.

The role of glutathione on shape control and photoelectrical property of cadmium sulfide nanorod arrays.

Well-aligned CdS nanorod arrays (CdS NRs) with ~100 nm in diameter and ~700 nm in length were fabricated on FTO (fluorine-doped tin oxide) substrate by using glutathione as capping agents. The growth of CdS NRs was studied in details by exploring the roles of each active binding group in glutathione. The thiol group in glutathione plays an important role in forming a compact CdS nanocrystal film, upon which the nanorods grow subsequently via the synergetic effect of thiol and dicarboxyl groups in glutathione. The influence of surface passivation with glutathione on the photoelectrical property of CdS NRs was also tested. The results revealed that glutathione ligands encapsulated in the surfaces of CdS NRs act as insulating barriers between CdS NRs and solution, hindering charge transport. Hybrid photovoltaic cells of FTO/CdS NRs/P3HT (poly(3-hexylthiophene))/Au were then assembled. The performance of the photovoltaic devices was increased with increasing the length of the as-prepared CdS nanorods and further enhanced to the highest efficiency of 0.373% after the thermal sulfuration treatment.

Solvent engineering of spin-coating solutions for planar-structured high-efficiency perovskite solar cells

Abstract Control of the morphology and coverage of high-quality perovskite films is the main issue affecting planar-structured perovskite solar cells fabricated by solution processing. In this work, the solvent engineering of mixed solutions for spin-coating uniform perovskite thin films was investigated in detail by adding different ratios of N,N -dimethylformamide (DMF) or γ-butyrolactone (GBL) to dimethyl sulfoxide (DMSO). The morphology and film thickness of the resulting perovskite films were found to be significantly altered. At 20%~40% (volume fraction) of N , N -dimethylformamide mixed with DMSO, micrometer scale grains and reduced grain boundaries were observed on the highly uniform perovskite thin films. The optimized planar-structured perovskite solar cells showed power conversion efficiency as high as 16.5% and a stabilized efficiency of 14.4% at a fixed forward bias of 0.88 V.

Synthesis and luminescence properties of highly uniform spherical SiO2@SrSi2O2N2:Eu2+ core–shell structured phosphors

The novel SiO2@SrSi2O2N2:Eu2+ core–shell structured oxynitride phosphors were synthesized by an interfacial reaction mechanism for the first time. First, SrCO3:Eu3+ layers were deposited on monodispersed and spherical SiO2 templates through the urea homogeneous precipitation methods to fabricate the SiO2@SrCO3:Eu3+ precursor particles; then the precursor particles were coated with H3BO3, which will be transformed to a protective h-BN film to prevent the agglomeration of the SiO2 templates at high temperature; at last, the SiO2@SrSi2O2N2:Eu2+ core–shell structured phosphors were synthesized through a gas reduction and nitridation method at 1350 °C under a NH3 gas flow. A uniform dense shell composed of nano-sized (∼20 nm) SrSi2O2N2:Eu2+ grains tightly adhered to the surface of the SiO2 cores. X-Ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM), high resolution transition electron microscopy (HR-TEM) as well as photoluminescence (PL) spectra were used to characterize the samples. The results indicate that the obtained submicron SiO2@SrSi2O2N2:Eu2+ phosphors consist of the outer h-BN film, the middle SrSi2O2N2:Eu2+ shell, and amorphous SiO2 cores and exhibit narrow particle size distribution, perfectly spherical morphology and non-aggregation. Under the excitation of UV and blue light, the phosphors show strong green emission due to the 4f65d–4f7 transition of Eu2+. This study opens new possibilities to facilely synthesize highly stable spherical (oxo)nitridosilicate phosphors with monodispersity and improved luminescence properties for display and lighting devices.