Yaqing Feng

Preparation of diverse flower-like ZnO nanoaggregates for dye-sensitized solar cells

Three-dimensional (3D) ZnO nanoaggregates with different morphologies and sizes were fabricated by the hydrothermal method, including cauliflower-like microspheres with an average diameter of 1–2 μm, nano-sheet aggregated safflower-like microspheres with 3–4 μm and ixora-like nano-structures with 500–600 nm. We found that their morphology formation was dependent on the concentration of OH− and construction agent (glutamic acid) during the synthesis process, based on which we proposed the mechanism for the formation of ZnO nanoaggregates. The studies showed that, the photo to current conversion efficiencies (PCEs) of the dye-sensitized solar cells (DSSCs) in which the photoanodes were fabricated using the prepared 3D ZnO nanoaggregates were all higher than those obtained employing the ZnO nanoparticles (NPs). In particular, the PCE of the DSSC based on the cauliflower-like ZnO photoanode (4.52%) was about 21% higher than that fabricated with the ZnO NP-based photoanode. This can be attributed to the higher specific surface area of the cauliflower-like ZnO photoanode leading to a greater amount of dye adsorption, more suitable size for light scattering and better inner connection for the transportation of electrons. Moreover, when these 3D ZnO nanoaggregates were used as the scattering layers in the P25-based photoanode in DSSCs, higher PCE of up to 6.74% was achieved, compared to 5.37% obtained for the DSSC without a scattering layer.

Double-N doping: a new discovery about N-doped TiO2 applied in dye-sensitized solar cells

In this paper, we first investigated the optimal amount of ammonia to add, using ammonia as the single dopant for use in dye-sensitized solar cells (DSSCs). Using this optimal amount of ammonia, urea was introduced as the second N dopant. The DSSCs produced by double-N doped samples combine the advantages of increased visible light absorption with ammonia as the nitrogen dopant and enlarged interface area with urea as the second nitrogen dopant. Not only was Voc increased, but Jsc was also enhanced. We observed that the double-N doped sample forms a new microstructure with more mesopores, which enhance the transfer of electrolyte. Because these mesopores are the combination core of generated electrons and holes, they need to be kept in delicate balance. When urea is brought in as the double-N dopant, the doped amount of N atoms was improved. As a result, η is increased to 7.58%, a 14% improvement compared with single-N doped TiO2.

Effect of the length of the alkyl chains in porphyrin meso-substituents on the performance of dye-sensitized solar cells

A series of novel zinc porphyrin dyes which have a D–π–A structure have been designed and synthesized for DSSC applications. The donors containing a carbazole group in which the carbazole nitrogen is bonded with a butyl, hexyl or decyl chain, had a significant influence on the spectra of the TiO2 films and the electrochemical and photovoltaic properties of these sensitizers. The sensitizer with a hexyl chain (CZ-6) achieved a higher overall conversion efficiency than that with a butyl chain (CZ-4) because of its slower charge recombination rate and faster electron injection from the dye to the conduction band of the conducting glass. Furthermore, the dye with a decyl chain (CZ-10) performed the lowest conversion efficiency, resulting from the least amount of dye loading. This was due to the steric hindrance of the molecule. The highest light-to-electricity conversion efficiency (η) of 2.13% was realized for the dye CZ-6 based DSSC, which was higher than those achieved for the CZ-4- and CZ-6-sensitized DSSCs (1.69% and 1.30% respectively).

Synthesis of corrole–fullerene dyads via [4 + 2] cycloaddition reaction

Three corrole–fullerene dyads were prepared by treating anthracene-functionalized corroles with fullerene. Their structures were characterized by 1D- and 2D-NMR spectra and mass spectra. In the preliminary photo physical study of 3a by fluorescence spectroscopy, the excited corrole unit was quenched due to the introduction of fullerene. TD-DFT calculation theoretically indicated that the electron transfer occurs from the excited corrole to fullerene.

Synthesis and characterization of simple trans-AB-porphyrins for dye-sensitized solar cells

Four simple trans-AB-porphyrins 3a–3d either without any alkoxyl substituent, or with a mono-alkoxyl chain at different (ortho and para) positions of the meso-phenyl ring, or with two alkoxyl chains at two ortho positions of the meso-phenyl ring were designed and synthesized via three steps. The synthesis is simple and no expensive metal catalyst is involved. All compounds were characterized by 1H-NMR and mass spectraometry. UV-Vis absorption spectra and B band-excited fluorescence emission spectra were also obtained. The synthesized porphyrins were applied in dye-sensitized solar cells (DSSCs). Up to 3.05% conversion efficiency was realized for 3d under our experimental conditions, attributed to the two long alkoxyl chains present at the ortho positions of the meso-phenyl group. The influences of the position and the number of the alkoxyl chains at the macrocyclic meso-phenyl group on the photovoltaic performance of DSSCs are well explained via DFT calculations. It was shown that the VOC and JSC of the sensitizers are determined by μnormal, ΔGinject and LHE.

Coordinative integration of a metal-porphyrinic framework and TiO2 nanoparticles for the formation of composite photocatalysts with enhanced visible-light-driven photocatalytic activities

The development of efficient catalysts with a visible-light response is of great importance in photocatalysis. Porphyrinic metal-organic frameworks (porph-MOFs) have recently been shown as promising photocatalyst candidates due to their large surface area, high visible light harvesting efficiency, and semiconductive properties, but challenges still remain because of their rapid charge recombination. Herein, we report the design of an effectively visible-light-driven composite material, namely TP-222(Zn), containing zirconium-based porph-MOF PCN-222(Zn) linked TiO2 nanoparticles (NPs) via the compound 4-mercaptopyridine which is axially bonded to the porphyrin central Zn metal in the PCN-222(Zn) and anchored onto the surface of TiO2 NPs. The resulting composite material demonstrates the high dispersion of TiO2 NPs and their close contact with the porph-MOF matrix, and serves as an effective photocatalyst for degrading organic contaminants under visible light irradiation due to their synergistic effect. It is further confirmed by fluorescence spectroscopy and electrochemical impedance spectroscopy that the remarkably enhanced photocatalytic activity of the TP-222(Zn) composite is attributed to the efficient charge separation with electron injection from PCN-222(Zn) to TiO2 NPs. In addition, the TP-222(Zn) composite shows excellent stability and recyclability as a result of the axially coordinative interaction between TiO2 NPs/PCN-222(Zn) and the 4-mercaptopyridine. Overall, this work provides a new strategy for the fabrication of highly efficient porph-MOF-based composite materials for visible light-driven photocatalysis.

Preparation of dye-sensitized solar cells with high photocurrent and photovoltage by using mesoporous titanium dioxide particles as photoanode material

Several mesoporous TiO2 (MT) materials were synthesized under different conditions following a hydrothermal procedure using poly(ethylene-glycol)-block-poly(propylene-glycol)-block-poly(ethylene-glycol) (P123) as the template and titanium isopropoxide as the titanium source. The molar ratios of Ti/P123, and the pH values of the reaction solution in an autoclave were investigated. Various techniques such as Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), laser Raman spectrometry (LRS), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the products. Then, these materials were assembled into dye-sensitized solar cells (DSSCs). Analysis of the J–V curves and electrochemical impedance spectroscopy (EIS) were applied to characterize the cells. The results indicated that the specific surface area and crystalline structure of these materials provide the possibility of high photocurrent for the cells, and that the structural characteristics of the specimens led to increased electron transfer resistance of the cells, which was beneficial for the improvement of the photovoltage of the DSSCs. The highest photoelectric conversion efficiency of the cells involving MT materials reached 8.33%, which, compared with that of P25-based solar cell (5.88%), increased by 41.7%.

Encapsulation of modified copper phthalocyanine (CuPc) via miniemulsion polymerisation for electrophoretic display

Abstract New composite particles of copper phthalocyanine (CuPc) via double modification of crude CuPc were prepared and characterised. Crude particles were suspended into the sodium oleate solution by ball milling method to obtain CuPc-1, which was subsequently coated with styrene through a miniemulsion polymerisation procedure to acquire CuPc-2 as an electronic ink material. The CuPc-2 ink particles were characterised by ultraviolet–visible spectroscopy and chroma. Scanning electron microscopy and transmission electron microscopy were employed to analyse the morphology and structure of CuPc-2. Furthermore, the functional group of the CuPc-2 was identified by Fourier transform infrared spectroscopy. The obtained CuPc-2 ink particles were then successfully incorporated in an electrophoretic display cell, and the contrast ratio of the same device was found to be 3·80.

Improved performance of dye-sensitized solar cells based on modified kaolin/PVDF-HFP composite gel electrolytes

Dye-sensitized solar cells (DSSCs) fabricated with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) composite gel electrolytes containing variable amounts of modified kaolin were studied in this work. The kaolin was modified with silane coupling agent γ-aminopropyltriethoxysilane (KH550), and the modified kaolin (M-KL) was characterized by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The results of X-ray diffraction (XRD) and differential scanning calorimetry (DSC) indicated that the crystallinity of polymer membranes decreased with the addition of M-KL nanoparticles. The ionic conductivity and diffusion coefficient (I3−) of polymer gel electrolytes (PGEs) reached optimum values of 9.452 × 10−3 S cm−1 and 10.37 × 10−6 cm2 s−1 for 3 wt% M-KL, respectively, which contributed to higher short-circuit current density (Jsc) and photoelectric conversion efficiency (η) of the corresponding DSSCs. The optimum level of η reached 7.48% under the illumination of 100 mW cm−2, an increase of 16.3% compared with the DSSC without M-KL.

Doubly N-confused isophlorin: synthesis, structure and copper coordination

A novel doubly N-confused isophlorin (2) was prepared by the nucleophilic ring-opening reaction of N-confused, N-fused porphyrin (1) with benzenethiol. The structure, redox property and copper coordination ability of isophlorin 2 were investigated by various spectroscopic methods and theoretical calculations.