Chemical conversion synthesis of ZnS shell on ZnO nanowire arrays: morphology evolution and its effect on dye-sensitized solar cell

Heterostructured ZnO/ZnS core/shell nanowire arrays have been successfully fabricated to serve as photoanode for the dye-sensitized solar cells (DSSCs) by a facile two-step approach, combining hydrothermal deposition and liquid-phase chemical conversion process. The morphology evolution of the ZnS coated on the ZnO nanowires and its effect on the performance of the DSSCs were systematically investigated by varying the reaction time during the chemical conversion process. The results show that the compact ZnS shell can effectively promote the photogenerated electrons transfer from the excited dye molecules to the conduction band of the ZnO, simultaneously suppress the recombination for the injected elelctrons from the dye and the redox electrolyte. As reaction time goes by, the surface of the nanowires becomes coarse because of the newly formed ZnS nanoparticles, which will enhance the dye loading, resulting in increment of the short-circuit current density (J(SC)) . Open-circuit photovoltage decay measurements also show that the electron lifetime (τ(n)) in the ZnO/ZnS core/shell nanostructures can be significantly prolonged because of the lower surface trap density in the ZnO after ZnS coating. For the ZnO/ZnS core/shell nanostructures, the J(SC) and η can reach a maximum of 8.38 mA/cm(2) and 1.92% after 6 h conversion time, corresponding to 12- and 16-fold increments of as-synthesized ZnO, respectively.     

Enhanced photoelectrochemical performance of bridged ZnO nanorod arrays grown on V-grooved structure

Bridged ZnO nanorod arrays on a V-grooved Si(100) substrate were used as the photoanode of a photoelectrochemical (PEC) cell for water splitting. Photolithography followed by reactive ion etching was employed to create a V-grooved structure on a Si substrate. ZnO nanorod arrays were grown via a hydrothermal method. The light trapping and PEC properties are greatly enhanced using the bridged ZnO nanorod arrays on a V-grooved Si substrate compared with those on a flat one. Increased short circuit photocurrent density (J(SC), 0.73?mA?cm(-2)) and half-life time (1500?s) are achieved. This improved J(SC) and half-life time are 4 times and 10 times, respectively, higher than those of the ZnO nanorod arrays grown on a flat substrate. The overall PEC cell performance improvement for the V-groove grown ZnO array is attributed to the reduced light reflection and enhanced light trapping effect. Moreover, V-groove ZnO showed stronger adhesion between ZnO nanorod arrays and the substrate.     

Synthesis and photovoltaic properties of a new thiophene-cyclopentadiene-based conjugated polymer

A new low-band gap polymer containing thiophene and cyclopentadiene, poly(5,2,2'-dioctyldithio-phenylcyclopentadiene) (PDTCP), has been synthesized via the FeCl3 oxidative polymerization. PDTCP showed a broad absorption band and a low energy band gap of 1.82 eV. The photoluminescence (PL) of PDTCP is completely quenched upon addition of PCBM indicative of efficient charge transfer. Bulk heterojunction organic photovoltaic cells (OPVs) fabricated from PDTCP as an electron donor showed an open-circuit voltage (V(OC)) of 0.50 V, a short-circuit current (J(SC)) of 1.24 mA/cm2, and the power conversion efficiency of up to 0.20% under AM 1.5 (100 mW/cm2).     

Photovoltaic performance of dye-sensitized solar cell low temperature growth of ZnO nanorods using chemical bath deposition

Nanostructured ZnO photoelectrodes were synthesized on fluorine-doped tin oxide (FTO) glass substrates that were spin-coated with a sol-gel based ZnO seed layer via a chemical bath deposition (CBD) method at varying times of 1, 2, 4, and 8 h. Then, TiO2 nanoparticulate electrodes were prepared on ZnO nanorods using the doctor blade technique. The uniformly grown ZnO nanorod layer had a length of approximately 710 nm on the FTO glass substrate with wurtzite structures which was confirmed through X-ray diffraction patterns. The length and diameter of the ZnO nanorods increased with an increase in the deposition time. The DSSCs fabricated with TiO2 nanoparticulate/grown ZnO nanorods and grown for 8 h showed the maximum efficiency (5.51%) with a short circuit current density (J(sc)) of 12.21 mA/cm2 and an open circuit voltage (V(oc)) of 0.70 at 100 mW/cm2 light intensity.     

Soluble copper phthalocyanine applied for organic solar cells

A soluble derivative of copper phthalocyanine, that is 2,9,16,23-tetra carboxyl copper phthalocyanine (CuTCPc), is synthesized in this paper. The applications of CuTCPc as donor and interlayer materials in solar cell devices are investigated. The results demonstrate that when CuTCPc is used as a donor material, the performance of the device ITO/CuTCPc/PCBM/Al shows an open circuit voltage (V(OC)) of 0.54 V, a short circuit current (J(SC)) of 0.825 mA/cm2, a fill factor (FF) of 32.3% and the power conversion efficiency (nu) of 0.14%. When CuTCPc acts as an interlayer, the performance of the device ITO/CuTCPc/P3HT:PCBM/Al is improved: J(SC) increases to 3.12 mA/cm2, V(OC) increases to 0.59 V, FF increases to 33.8%, and the corresponding nu is 0.62%.     

Novel photoactive fluorene-based terpolymers incorporating carbazole for photovoltaic application

A series of novel photoactive conjugated terpolymers based on N-alkyl carbazole, 9,9-didecylfluorene, and bis(thienyl)benzothiadiazole were synthesized by the Pd-catalyzed Suzuki polymerization method with various molar ratios of the carbazole derivatives. Electron-deficient benzothiadiazole and electron-rich carbazole moieties were incorporated into the polymer backbone to obtain the broad absorption spectrum and to improve the hole-transporting characteristics, respectively. The polymer solar cell (PSC) was fabricated with a layered structure of ITO/PEDOT: PSS/polymer:C71-PCBM (1:3)/LiF/Al. The best performance of PSC was obtained at P1:C71-PCBM whose reaches a power conversion efficiency (PCE) of 2.62%, with a short circuit current density (J(SC)) of 8.61 mA/cm2, an open circuit voltage (V(OC)) of 0.82 V, and a fill factor (FF) of 0.37 under AM 1.5 G irradiation (100 mW/cm2).     

ZnO and conjugated polymer bulk heterojunction solar cells containing ZnO nanorod photoanode

Hybrid solar cells based on poly(3-hexylthiophene) (P3HT) and ZnO nanoparticle bulk heterojunctions (BHJ) combined with ZnO nanorod arrays were fabricated and analyzed. The dispersion of ZnO nanoparticles in P3HT is assisted by dye molecules, which function as a surface modifier for ZnO nanoparticles to improve compatibility between ZnO nanoparticles and P3HT. Compared to the ZnO nanorod/P3HT devices, the optimized cells with the ZnO nanoparticles dispersed in P3HT can significantly increase the short-circuit current and the overall power conversion efficiency from 1.36 mA cm(-2) to 2.51 mA cm(-2) and from 0.18% to 0.45% with 625 nm long ZnO nanorod arrays, respectively. The novel scheme of using the light-absorbing dye molecules both as light absorber and as surfactant for ZnO nanoparticles presents a facile route towards forming bulk heterojunction hybrid solar cells based on semiconducting nanomaterials and conjugated polymers.     

Efficient field emission from vertically grown planar ZnO nanowalls on an ITO-glass substrate

Vertically grown planar ZnO nanowalls, with typical dimensions of 40-80?nm thickness and several micrometers wide, were electrodeposited on an indium-tin-oxide (ITO)-glass substrate at 70?°C. X-ray photoelectron spectroscopy (XPS) studies reveal that the nanowalls consist of ZnO covered with a Zn(OH)(2) overlayer. An x-ray diffraction (XRD) study shows that these nanowalls have the wurtzite structure and are highly crystalline. The corresponding Raman and photoluminescence spectra further indicate the presence of oxygen deficiency. These ZnO nanowalls exhibit excellent field emission performance, with not only a considerably lower turn-on field of 3.6?V?μm(-1) (at 0.1?μA?cm(-2)) but also a higher current density of 0.34?mA?cm(-2) at 6.6?V?μm(-1) than most ZnO nanowires and other one-dimensional nanostructures reported to date.     

Improvement in performances of dye-sensitized solar cell with SiO2-coated TiO2 photoelectrode

The pure TiO2 and the nano-porous SiO2-coated TiO2 (STO) films were deposited on the FTO substrates by spray technique for the application of dye-sensitized solar cells (DSSCs). XRD pattern shows the pure TiO2 and STO films exhibits the same structure. We found that there is no much difference in dye absorption between the STO and the pure TiO2 films. The electrochemical impedance spectra reveal that insulating nature of the porous SiO2 increases surface resistance of the TiO2 film and supresses back transfer of the photogenerated electrons to the electrolyte. The field-emission scanning electron microscopy (FE-SEM) and energy dispersion X-ray spectroscopy (EDS) reveal that the surface morphology and the existence of SiO2 layer on the surface of the TiO2 films, respectively. The photoelectrochemical results show that the short-circuit photocurrent (J(SC)) increased from 16.73 mA cm(-2) to 18.31 mA cm(-2) and the open-circuit voltage (V(OC)) value changed from 0.71 V to 0.74 V for the STO films. The efficiency of cell has been greatly improved from 8.25 to 9.3%.     

Different hierarchical nanostructured carbons as counter electrodes for CdS quantum dot solar cells

CdS quantum dot sensitized solar cells based on TiO(2) photoanode and nanostructured carbon as well as Pt as counter electrodes using iodide/triiodide and polysulfide electrolytes were fabricated to improve the efficiency and reduce the cost of solar cells. Compared with conventional Pt (η = 1.05%) and CMK-3 (η = 0.67%) counter electrodes, hollow core-mesoporous shell carbon (HCMSC) counter electrode using polysulfide electrolyte exhibits much larger incident photon to current conversion efficiency (IPCE = 27%), photocurrent density (J(sc) = 4.31 mA.cm(-2)) and power conversion efficiency (η = 1.08%), which is basically due to superb structural characters of HCMSC such as large specific surface area, high mesoporous volume, and 3D interconnected well-developed hierarchical porosity network, which facilitate fast mass transfer with less resistance and enable HCMSC to have highly enhanced catalytic activity toward the reduction of electrolyte shuttle.     

Highly efficient blue light-emitting diodes based on diarylanthracene/triphenylsilane compounds

New host materials have been designed and synthesized, (4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)triphenylsilane (ANPTPS) and (9,9-dimethyl-7-(10-(naphthalen-2-yl)anthracen-9-yl)-9H-fluoren-2-yl)triphenylsilane (ANFTPS), and photophysical characteristics investigated to determine suitability as candidates for blue light-emitting materials. To explore the electroluminescent properties, multilayered OLEDs were fabricated with the device structure of ITO/NPB/Host (ANPTPS and ANFTPS): 8% Dopant (PFVtPh and PCVtPh)/Bphen/Liq/Al. By using a host (ANPTPS) and a dopant (PFVtPh) as the emitting layer, high-efficiency blue OLEDs were fabricated with a maximum luminance of 3991 cd/cm2 at 8.0 V, a luminous efficiency of 5.99 cd/A at 20 mA/cm2, a power efficiency of 3.11 lm/W at 20 mA/cm2, an external quantum efficiency of 4.13% at 20 mA/cm2, and CIEx, y coordinates of (x = 0.15, y = 0.18) at 8.0 V.     

Graphene supported platinum nanoparticle counter-electrode for enhanced performance of dye-sensitized solar cells

Composites of few layered graphene (G) and platinum (Pt) nanoparticles (NP) with different loadings of Pt were used as counter electrode (CE) in dye-sensitized solar cell (DSSC). NPs were deposited directly on to G using pulsed laser ablation method (PLD). DSSCs formed using the composite CEs show improved performance compared to conventional Pt thin film electrode (Std Pt) and unsupported Pt NPs. Composite with 27% loading of Pt shows 45% higher efficiency (η = 2.9%), greater short circuit current (J(sc) = 6.67 mA cm(-2)), and open circuit voltage (V(oc) = 0.74 V) without any loss of the fill factor (FF = 58%) as compared to the cells fabricated using Std Pt electrodes. Values of η, J(sc) and V(oc) for DSSC using Std Pt CE were 2%, 5.05 mA cm(-2) and 0.68 V, respectively. Electrochemical impedance spectroscopy using I(-)(3)/I(-) redox couple confirm lower values of charge transfer resistance for the composite electrodes, e.g., 2.36 Ω cm(2) as opposed to 7.73 Ω cm(2) of Std Pt. The better catalytic activity of these composite materials is also reflected in the stronger I(-)(3) reduction peaks in cyclic voltammetry scans.     

Efficient inverted bulk heterojunction photovoltaic devices using a transparent polymeric interfacial buffer layer with C60 pendant and UV curable groups

We demonstrate the synthesis of a transparent, polymeric n-type material (M1) consisting of C60 pendant and UV curable groups in side chains. This material (M1) is employed as a polymeric n-type interfacial buffer layer for an efficient inverted bulk heterojunction (BHJ) photovoltaic device based on regioregular poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PC61BM) active layer. Under simulated solar illumination of AM 1.5G (100 mW/cm2), the highest efficient devices fabricated with a configuration of ITO/interfacial buffer layer (M1,10 nm)/P3HT:PC61BM (1:0.9 w:w) (120 nm)/PEDOT:PSS (30 nm)/Ag (100 nm) achieve an average power conversion efficiency PCE of 2.16%, with short-circuit current J(SC) = 6.70 mA/cm2, fill factor FF = 54.2%, and open-circuit voltage V(OC) = 0.60 V. This result is comparable to the inverted BHJ photovoltaic devices fabricated with Cs2CO3, one of widely used as a buffer layer. The synthesized M1 have thus proven to be promising polymeric interfacial buffer layer for high efficient BHJ photovoltaic devices.     

Direct growth of ZnO nanosheets on FTO substrate for dye-sensitized solar cells applications

ZnO nanosheets were directly grown on fluorine-doped tin oxide (FTO) substrate via simple solution process at low temperature by using zinc chloride and hexamethylenetetramine (HMTA). The morphological characterizations by SEM and TEM confirmed that the deposited structures are nanosheets in which some are assembled in flower-shaped morphologies. The detailed structural investigations revealed that the deposited nanosheets are pure and crystalline ZnO and composed of Zn and O only. The obtained ZnO nanosheets on FTO substrate were used as a photoanode to fabricate the dye sensitized solar cells (DSSCs). The fabricated DSSCs exhibited an overall light-to-electricity conversion efficiency of 1.45%. A short-circuit current of 4.51 mA/cm2, open-circuit voltage of 0.610 V, and a fill factor of 0.53 were achieved from the fabricated ZnO nanosheets-based DSSCs.     

Fibers of reduced graphene oxide nanoribbons

Reduced graphene oxide nanoribbon fibers were fabricated by using an electrophoretic self-assembly method without the use of any polymer or surfactant. We report electrical and field emission properties of the fibers as a function of reduction degree. In particular, the thermally annealed fiber showed superior field emission performance with a low potential for field emission (0.7?V?μm(-1)) and a giant field emission current density (400?A?cm(-2)). Moreover, the fiber maintains a high current level of 300?A?cm(-2) corresponding to 1?mA during long-term operation.     

Highly efficient red phosphorescent organic light-emitting devices using iridium(III) complexes based on 2-(biphenyl-3-yl)quinoline derived ligands

Red phosphorescent emitters were synthesized based on Ir(III) phenylquinoline complexes for applications to OLEDs. Ir(III) complexes 1-3 were based on 2-(biphenyl-3-yl)-quinoline units connected to various phenyl groups such as 5-phenyl, 5-(4-fluorophenyl), and 6-phenyl groups. The EL efficiencies were quite sensitive to the structural features of the dopants in the emitting layers. In particular, a high-efficiency red OLED was fabricated using complex 1 as the dopant in the emitting layer. This OLED showed a maximum luminance, luminous efficiency, power efficiency, external quantum efficiency and CIE(x,y) coordinates of 21,600 cd/m2 at 16 V, 11.80 cd/A at 20 mA/cm2, 3.57 Im/W at 20 mA/cm2, 10.90% at 20 mA/cm2, and (x = 0.63, y = 0.32) at 12 V, respectively.     

Poly(glycidyl methacrylate-acrylonitrile)-based polymeric electrolytes for dye-sensitized solar cell applications

Poly(glycidyl methacrylate-acrylonitrile) P(GMA-AN) copolymer was synthesized and used as a polymer electrolyte in dye-sensitized solar cells (DSSCs). P(GMA-AN)-based polymer electrolyte is obtained by adding 1-methyl-3-propylimidazolium iodide (PMII) as a room temperature ionic liquid (RTIL), tetrabutylammonium iodide (TBAI), iodide (I2) as the source of redox couple (I3(-)/I(-)) in order to improve the power conversion efficiency (PCE) by addition of optimized plasticizer contents such as ethylene carbonate (EC) and propylene carbonate (PC) in an acetonitrile solvent. These polymer electrolyte results revealed that more stable photovoltaic performance such as PCE of 4.97% with enhanced short-circuit current density (J(SC), 10.42 mA/cm2) and open circuit voltage (V(OC), 0.75 V) and fill factor (FF) of 0.63 under standard light intensity of 100 mW/cm2, irradiation of AM 1.5 sunlight. It is expected that these polymer electrolyte is an attractive alternative to liquid electrolytes for the fabrication of the long term stable DSSCs.     

Electrocoagulation of simulated reactive dyebath effluent with aluminum and stainless steel electrodes

Reactive dyebath effluents are ideal candidates for electrocoagulation due to their intensive color, medium strength, recalcitrant COD and high electrolyte (NaCl) content. The present study focused on the treatability of simulated reactive dyebath effluent (COD(o)=300 mg/L; color in terms of absorbance values A(o,436)=0.532 cm(-1), A(o,525)=0.693 cm(-1) and A(o,620)=0.808 cm(-1)) employing electrocoagulation with aluminum and stainless steel electrodes. Optimization of critical operating parameters such as initial pH (pH(o) 3-11), applied current density (J(c)=22-87 mA/cm(2)) and electrolyte type (NaCl or Na(2)SO(4)) improved the overall treatment efficiencies resulting in effective decolorization (99% using stainless steel electrodes after 60 min, 95% using aluminum electrodes after 90 min electrocoagulation) and COD abatement (93% with stainless steel electrodes after 60 min, 86% with aluminum electrodes after 90 min of reaction time). Optimum electrocoagulation conditions were established as pH(o) 5 and J(c)=22 mA/cm(2) for both electrode materials. The COD and color removal efficiencies also depended on the electrolyte type. No in situ, surplus adsorbable organically bound halogens (AOX) formation associated with the use of NaCl as the electrolyte during electrocoagulation was detected. An economical evaluation was also carried out within the frame of the study. It was demonstrated that electrocoagulation of reactive dyebath effluent with aluminum and stainless steel electrodes was a considerably less electrical energy-intensive, alternative treatment method as compared with advanced chemical oxidation techniques.     

Highly efficient blue light-emitting materials based on arylamine substituted DPVBi derivatives

A series of arylamine substituted DPVBi derivatives (1-4) were synthesized via the Horner-Wadsworth-Emmons reaction. Their electroluminescent properties were examined by fabricating a multilayer OLED device with the following structure: ITO/DNTPD (40 nm)/NPB (20 nm)/2% DPVBi derivatives (1-4) doped in MADN (20 nm)/Alq3 (40 nm)/Liq (1.0 nm)/Al. All devices showed efficient blue emission. In particular, a high efficiency blue OLED was fabricated using compound 1 as a dopant in the emitting layer. The maximum luminance, luminous efficiency, power efficiency and CIE coordinates of the blue OLED using compound 1 as a dopant were 16110 cd/m2 at 10 V, 10.1 cd/A at 20 mA/cm2, 4.37 Im/W at 20 mA/cm2, and (x = 0.197, y = 0.358) at 8 V, respectively. Moreover, a device using compound 4 as the dopant exhibited efficient deep blue emission with a luminance, luminous efficiency, power efficiency and CIE coordinates of 7005 cd/m2 at 10 V, 6.25 cd/A at 20 mA/cm2, 2.50 Im/W at 20 mA/cm2 and (x = 0.151, y = 0.143) at 8 V, respectively.     

Single-crystal SnO(2) nanoshuttles: shape-controlled synthesis, perfect flexibility and high-performance field emission

Vertically aligned single-crystal SnO(2) nanoshuttle arrays with uniform morphology and a relatively high aspect ratio were synthesized by a simple hot-wall chemical vapor deposition (CVD) method. It was found that regulating the growth temperature gradient could change the shape of the SnO(2) nanostructure from nanoshuttles to nanochisels and nanoneedles, and a self-catalyzing growth process was responsible for tunable morphologies of SnO(2) nanostructures. The as-synthesized SnO(2) nanoshuttles showed ultrahigh flexibility and strong toughness with a large elastic strain of ～ 6.2, which is much higher than reported for Si and ZnO nanowire as well as most crystalline metallic materials. The field emitter fabricated using SnO(2) nanoshuttle arrays has a low turn-on electric field of around 0.6 V μm(-1), and a high field emission current density of above 10 mA cm(-2), which is comparable with the highest emission current density of carbon nanotube and nanowire field emitters.