Performance of polymer/ZnO hybrid photovoltaic devices determined by reaction time for oriented ZnO nanorod growth

The performance of hybrid polymer/metal oxide photovoltaic devices based on poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) and oriented ZnO nanorods is studied. The ZnO nanorods on indium tin oxide-coated glass were prepared by hydrothermal method, where the length and the defect concentration of ZnO nanorods were controlled by the reaction time (T_r) for nanorod growth. Increasing T_r results in longer ZnO nanorods and higher defect concentration. Results show that both photocurrent and electron lifetime have strong dependence on the nanorod length (i.e., growth time) due to the exponential attenuation of incident light intensity in the device, offering a peak conversion efficiency of 0.337% under 1.5 AM illumination for T_r = 120 min. Combinational analyses of the data in this experiment and the previous data for the electrodeposited ZnO nanorods provide the insights into the dependence of the device performance on the intrinsic property of the ZnO nanorods.     

Mechanical properties of electrospun PVA/MWNTs composite nanofibers

Composites of polyvinyl alcohol (PVA) and multi-walled carbon nanotubes (MWNTs) were prepared by electrospinning. A PVA/MWNTs solution was electrostatically spun to form filler wrapped nanofibers, with a diameter of ∼ 100-200 nm. As the concentration of filler in the composite was varied, the coloration of the fiber sheets changed. The SEM and TEM analyses of the fiber sheets revealed that the deformation of the fiber increases with increasing nanotube concentration. The mechanical properties were studied using a universal testing machine (UTM). The analysis is presented in detail. It is argued that the degree of dispersivity orientation and anisotropy of the nanotubes and the amount of interfacial stress in the filler/polymer are the predominant factors determining the variation in the tensile properties of the composites with the filler concentration.     

Hybrid p-type ZnO film and n-type ZnO nanorod p-n homo-junction for efficient photovoltaic applications

Simple hybrid p-n homo-junctions using p-type ZnO thin films and n-type nanorods grown on fluorine tin oxide (FTO) substrates for photovoltaic applications are described. The ZnO nanorods (1.5 μm) were synthesized via an aqueous solution method with zinc nitrate hexahydrate and hexamethylenetetramine on ZnO seed layers. The 10-nm-thick ZnO seed layers showed n-type conductivity on FTO substrates and were deposited with a sputtering-based method. After synthesizing ZnO nanorods, aluminum-nitride co-doped p-type ZnO films (200 nm) were efficiently grown using pre-activated nitrogen (N) plasma sources with an inductively-coupled dual-target co-sputtering system. The structural and electrical properties of hybrid p-n homo-junctions were investigated by scanning electron microscopy, transmittance spectrophotometry, and I-V measurements.     

Influence of silver doping on the phase transformation and crystallite growth of electrospun TiO2 nanofibers

Ag doped TiO₂ nanofibers were fabricated by electrospinning technique using polyvinyl pyrrolidone (PVP) and titanium isopropoxide (TiP) as precursor. The effects of silver and calcination temperature on the preparation of electrospun TiO₂ nanofibers were investigated. The calcination temperature determines the TiO₂ phases as ether anatase or rutile. When the calcination temperature increased, crystallite size of TiO₂ nanofiber increased. The crystallite size of Ag doped TiO₂ nanofiber is smaller than that of the pure TiO₂ nanofiber because silver is retrained in this phase transformation. Silver controlled the phase transformation as well as had an inhibition effect on the growth of anatase crystallite.     

Spin coated graphene films as the transparent electrode in organic photovoltaic devices

Many research efforts have been devoted to the replacement of the traditional indium-tin-oxide (ITO) electrode in organic photovoltaics. Solution-based graphene has been identified as a potential replacement, since it has less than two percent absorption per layer, relative high carrier mobility, and it offers the possibility of deposition on large area and flexible substrates, compatible with roll to roll manufacturing methods. In this work, soluble reduced graphene films with high electrical conductivity and transparency were fabricated and incorporated in poly(3-hexylthiophene) [6,6]-phenyl-C₆₁-butyric acid methyl ester photovoltaic devices, as the transparent electrode. The graphene films were spin coated on glass from an aqueous dispersion of functionalized graphene, followed by a reduction process combining hydrazine vapor and annealing under argon, in order to reduce the sheet resistance. The photovoltaic devices obtained from the graphene films showed lower performance than the reference devices with ITO, due to the higher sheet resistance (2 kΩ/sq) and the poor hydrophilicity of the spin coated graphene films.     

Synthesis and morphology of electrospun PVA/PLZT composite and single phase PLZT nanofibers

Polyvinyl alcohol/lead lanthanum zirconate titanate (PVA/PLZT) composite nanofibers were prepared by the electrospinning method. The PLZT sol was prepared by using lead acetate trihydrate, titanium isopropoxide and zirconium propoxide molecular precursors based on sol-gel procedure. The influence of applied voltage, flow rate and needle-to-collector distance on the composite fiber morphology and diameters has been studied. The nanofibers were characterized by X-ray diffraction, TGA-DSC, FTIR spectroscopy and scanning electron microscopy (SEM). Single phase with perovskite structures PLZT nanofibers were also obtained by calcining the PVA/PLZT nanofibrous mat at 650 °C for 2 h. A linear correlation was observed between the single perovskite phase evolution and the calcination temperature.     

Structural and optical properties of electrospun ZnO nanofibres applied to P3HT:PCBM organic photovoltaic devices

Electrospun ZnO nanofibres with a diameter in the range of 74–125 nm were synthesised by optimising various parameters. Zinc acetate was used as a precursor and optimised to obtain a homogeneous and interconnected porous ZnO nanofibres network. The ZnO/poly(vinylpyrrolidone) composite nanofibres were calcined at 450 °C for 2.5 h to obtain continuous nanofibres network. The morphology of the nanofibres was studied by scanning electron microscopy and imageJ software. The structural and optical properties of the synthesised nanofibres were studied by surface profiler, X-ray diffraction and ultraviolet–visible spectroscopy. The grain size increased while the bandgap was observed to decrease with increased precursor concentration. The effect of precursor concentration was also studied to improve the power conversion efficiency of ZnO nanofibres/poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61-butyric acid methyl ester (PCBM) photovoltaic device. The efficiency was improved from 0.896 ± 0.007% to 2.29 ± 0.03% by introducing the electrospun ZnO nanofibres.     

Fabrication of TiO2/ZnO composite nanofibers by electrospinning and their photocatalytic property

TiO₂/ZnO composite nanofibers with diameters in the range of 85–200 nm were fabricated via the electrospinning technique using zinc acetate and titanium tetra-isopropoxide as precursors, cellulose acetate as the fiber template, and N,N-dimethylformamide/acetone 1:2 (v/v) mixtures as the co-solvent. After treated with 0.1 mol/L NaOH aqueous solution, TiO₂/zinc acetate/cellulose acetate composite nanofibers were transformed into TiO₂/Zn(OH)₂/cellulose composite nanofibers. TiO₂/ZnO composite nanofibers were obtained by calcinating the hydrolyzed composite fibers at 500 and 700 °C for 5 h. The structure and morphology of composite nanofibers were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. With the blending of ZnO into TiO₂, a new crystallite ZnTiO₃ was formed in addition to the ZnO and TiO₂ crystallites, and the ultraviolet light absorption efficiency was enhanced according to the UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of TiO₂/ZnO composite nanofibers toward the decomposition of Rhodamine B and phenol was investigated. Almost 100% Rhodamine B and 85% phenol were decomposed in the presence of TiO₂/ZnO composite nanofibers under mild conditions. The results demonstrated that the blending of ZnO in the TiO₂/ZnO composite nanofibers increased the photocatalytic efficiency. The optimum ZnO content in the TiO₂/ZnO composite nanofibers was 15.76 wt% to reach the most efficient photocatalytic activity. A schematic diagram of photocatalytic mechanism of TiO₂/ZnO composite nanofibers was also presented.     

Epitaxial growth of ZnO nanorods on electrospun ZnO nanofibers by hydrothermal method

In this paper, we report a new ZnO nanofibers-nanorods structure which was successfully prepared by the electrospun ZnO nanofibers as seed to guide hydrothermal epitaxial growth of the ZnO nanorods. The structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL). The XRD results indicate that ZnO nanofibers obtained at 600° have high crystallinity with a typical hexagonal wurtzite structure. Furthermore compared with the strongest diffraction of ZnO nanofibers in (101) plane, the diffraction from (002) plane of ZnO nanofibers-nanorods becomes the strongest. The SEM shows that the diameters of epitaxial-grown ZnO nanorods on ZnO nanofibers were approximately 100–200?nm. The PL spectrum shows that the ZnO nanofibers-nanorods have a broad green-yellow emission around 537?nm, in contrast to that of ZnO nanofibers, the peak had obvious redshift about 24?nm and the luminous intensity weakened.     

Optimization of ZnO/Ag/ZnO multilayer electrodes obtained by Ion Beam Sputtering for optoelectronic devices

We investigated the electrical and optical properties of ZnO/Ag/ZnO multi-layer electrodes obtained by ion beam sputtering for flexible optoelectronic devices. This multi-layer structure has the advantage of adjusting the layer thickness to favor antireflection and the surface plasmon resonance of the metallic layer. Inserting a thin (Ag) metallic layer between two (ZnO) oxide layers decreases the sheet resistance while widening the optical transmittance window in the visible. We found that the optimal electrode is made up of a 10 nm thin Ag layer between two 35 nm and 20 nm thick ZnO layers, which resulted in a low sheet resistance (R_sq = 6 Ω/square), a high transmittance (T ≥ 80% in the visible) and the highest figure of merit of 1.65 × 10^-2 square/Ω.     

Technology of ZnO nanofibers based devices

In the presented work, the possibility of fabrication of ZnO single- and multi-nanofiber structures using a standard microelectronic device technology were studied. An innovative fabrication step, namely, selective wet chemical nanofibers etching through a photoresist mask, was used to define the active area, along with mesa etch in the Si/SiO₂ substrate. Test structures in the configuration of a resistor and Schottky diode with chemically active electrospun ZnO nanofibers were prepared. The Ti/Au ohmic and Pt Schottky contacts were fabricated using a lift-off photolithography process. Optical and scanning electron microscopy studies were done to characterize ZnO nanofibers and topography of contacts. The measurements made for electrical characterization showed linear I–V dependence and saturation of the current for single ZnO nanofiber structures.     

Study of solvent dependence of Methyl Red and C60 based organic photovoltaic devices

In this work, the effect of solvent on the photovoltaic properties of Methyl Red (MR) dye and C₆₀ based device has been reported. It can be assumed for a dye based photovoltaic device that there is an effect of solvent on the film morphology which controls the charge transport mechanism. To observe this effect of solvent on the film morphology two different solvents namely chlorobenzene and toluene are used to prepare the solutions of MR and C₆₀. The devices made with chlorobenzene and toluene solvents are termed as chlorobenzene cell and toluene cell respectively. For each solvent different devices are prepared by varying the weight ratio of MR and C_60. These cells are characterized through different photovoltaic measurements. Experimental data reveal that the photovoltaic response is higher in case of chlorobenzene cell than that of the toluene cell. The power conversion efficiency for toluene cell for a particular concentration of MR:C₆₀ is 0.781 × 10^− 7 whereas for chlorobenzene cell it is 1.026 × 10^− 5. Maximum V_oc and J_sc obtained for toluene cell are 19.5 mV and 33.73 ?nA/cm² whereas for chlorobenzene cell these are 720 mV and 158.0 nA/cm² respectively. Scanning electron microscope images indicate the difference in nano-morphology and cluster sizes between the cells. The cluster size is quite large in case of toluene cell with comparison to chlorobenzene cell. From the transient photocurrent measurement it is observed that the charge transport process is quite faster in chlorobenzene cell which prevents excess recombination resulting in a higher efficiency in chlorobenzene cell.     

Electrical and non-linear optical studies on electrospun ZnO/BaO composite nanofibers

Nanocapacitors and nonvolatile ferroelectric random access memories require nanoscale thin film coatings with ferroelectric properties.One dimensional ferroelectric nanofibers are used in ferroelectric...     

Preparation and photoluminescence properties of electrospun nanofibers containing PMO-PPV and Eu(ODBM)3phen

This communication explores a facile approach for fabricating nanofibers containing luminescent conjugated polymer, poly(2-methoxy-5-octoxy)-1,4-phenylene vinylene)-alt-1,4-(phenylene vinylene) (PMO-PPV), and rare earth complex, Eu(ODBM)₃phen (ODBM: 4-n-Octyloxydibenzoylmethanato; phen: 1,10-phenanthroline) via an electrospinning technique. The morphology and photoluminescent properties of the electrospun fibers were characterized by scanning electron microscopy, fluorescence spectrophotometer and UV optical microscopy. The electrospun fibers with diameters ranging from 70 nm to 200 nm as well as parallel orientation show strong green and red photoluminescence. This is the first but important approach towards novel applications of luminescent conjugated polymers and rare earth complex nanofibers. This kind of eletrospun nanofiber is a promising candidate for optical and electrical nanomaterials.     

感应耦合辅助磁控溅射氧化锌薄膜在铜铟硒薄膜太阳能电池中的界面

薄膜铜铟硒太阳能电池由于前后电极间欧姆接触导致电流损耗,高阻氧化锌层可以消除因表面空洞或表面损坏造成的前后电极短路,这种作用大小取决于氧化锌薄膜表面形貌和电阻率.本论文研究了用感应耦合等离子辅助磁控溅射氧化锌薄膜在铜铟硒薄膜太阳能电池中的应用,并分析氧化锌薄膜层和铜铟硒层的界面结构特点.实验用氧化锌陶瓷靶在氧气和氩气环境下进行溅射,当溅射气压为4mTorr,射频功率300W,直流偏压30V时,制备的氧化锌具有表面形貌均匀致密,电阻率为7×108Ω·cm、透光率80%以上等特性,与吸收层铜铟硒构成良好的异质结界面.     

CO gas sensing of Pd-doped ZnO nanofibers synthesized by electrospinning method

Pure and Pd-doped ZnO nanofibers were synthesized by electrospinning method, and characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The diameters of the fibers annealed at 600 °C range from 70 to 160 nm. Compared with pure ZnO nanofiber sensor, the Pd-doped ZnO nanofiber sensor exhibits improved sensing properties to CO at 220 °C. Moreover, this sensor processes considerable sensitivity to low concentration CO in the range of 1-20 ppm with good selectivity. The response and recovery times are in the range of 25-29 s and 12-17 s, respectively. The sensing mechanism is also discussed.     

Enhancement of operation efficiency of grid interconnected photovoltaic systems

Photovoltaic (PV) generation is emerging as an important part of the electric energy system. Various interconnection and operation technologies are needed to accommodate the PV systems into power grid operation and control. Due to the volatility of PV power outputs, it is a challenging task to enhance the overall operational efficiency of grid interconnected PV systems. This paper presents a cross-entropy (CE) based technique to optimize the generation schedule of the grid interconnected PV systems incorporating the volatility of the PV power outputs. Numerical simulation results are presented to demonstrate the effectiveness of the proposed technique.     

Interface modification of ITO thin films: organic photovoltaic cells

In this paper we review our recent studies of the surface characterization of commercially available indium-tin-oxide (ITO) thin films, using photoelectron spectroscopies (XPS and UPS) and electrochemistry of chemisorbed probe molecules such as ferrocene dicarboxylic acid (Fc(COOH)₂). The modification of these ITO films through chemisorption of carboxylic acid-substituted small molecules, such as Fc(COOH)₂, 3-thiophene acetic acid (3-TAA), and the subsequent modification of these interfaces with electrochemically grown conducting polymer (CP) films is also introduced. We report preliminary results of our studies changes in performance of vacuum deposited organic photovoltaic (PV) cells as a result of these ITO substrate modification steps. The surfaces of as-received ITO films, and those cleaned by various solution and plasma-etching processes, are unavoidably hydrolyzed to In(OH)₃-like and InOOH-like surface species, which leaves the ITO surface with at most 40-50% of the electronically active sites available for electron transfer reactions. Modification of the ITO surface with electroactive small molecules such as Fc(COOH)₂ and 3-TAA provides for better wettability of organic layers to the polar ITO surface and enhanced electrical contact (lower series resistance, R_S) between the ITO anode, spin-cast or electrodeposited PEDOT:PSS layers and copper phthalocyanine (CuPc) layers in multilayer (CuPc/C₆₀/BCP) excitonic PV cells. Improvements in PV J/V (current/voltage) responses are noted mainly through increases in short-circuit photocurrent and lowered series resistances (R_S) when electroactive small molecules are chemisorbed to the ITO surface, prior to spin-casting of conducting polymer, PEDOT:PSS, layers.     

Thickness dependence of the MoO(3) blocking layers on ZnO nanorod-inverted organic photovoltaic devices

Organic solar cells based on vertically aligned zinc oxide nanorod arrays (ZNR) in an inverted structure of indium tin oxide (ITO)∕ZNR∕poly(3-hexylthiophene): (6,6)-phenyl C61 butyric acid methyl ester(P3HT:PCBM)∕MoO(3)∕aluminum(Al) were studied. We found that the optimum MoO(3) layer thickness condition of 20 nm, the MoO(3) can effectively decrease the probability of bimolecular recombination either at the Al interface or within the active layer itself. For this optimum condition we get a power conversion efficiency of 2.15%, a short-circuit current density of 9.02 mA∕cm(2), an open-circuit voltage of 0.55V, and a fill factor of 0.44 under 100 mW∕cm(2) irradiation. Our investigations also show that the highly crystallized ZNR can create short and continuous pathways for electron transport and increase the contact area between the ZNR and the organic materials.