Enhancing the performance of poly(3-hexylthiophene)/ZnO nanorod arrays based hybrid solar cells through incorporation of a third component

Sparse ZnO nanorod arrays(NRAs)are fabricated on transparent conducting oxide coated glass substrates by using a modified liquid phase epitaxial growth method.By adjusting the polymer concentrations and the spin-coating parameters,full infiltration of poly(3-hexylthiophene)(P3HT)into the as-prepared ZnO NRAs is achieved at 130°C in vacuum.A third component is incorporated into the P3HT/ZnO NRAs ordered bulk heterojunctions(BHJs)either through ZnO surface modification with N719dye or CdS shell layer or by inclusion of a fullerene derivative into the P3HT matrix.Experimental results indicate that performances of the hybrid solar cells are improved greatly with the incorporation of a third component.However,the working principles of these third components differ from one another,according to morphology,structure,optical property,charge transfer and interfacial properties of the composite structures.An ideal device architecture for hybrid solar cells based on P3HT/ZnO NRAs ordered BHJs is proposed,which can be used as a guidance to further increase the power conversion efficiency of such solar cells.     

聚苯胺/ZnO纳米线薄膜材料作为发光层的柔性光电器件 及其发光机理

综合氧化锌纳米线(ZnO NWs)的光学活性与聚苯胺(PANI)的空穴传输特性,设计并制备了一种聚合物/ZnO纳米线电致发光材料,并对其发光特性进行了研究。通过高分子络合软模板法,将有序的单晶ZnO NWs均匀生长在覆有铟锡氧化物(ITO)涂层的柔性聚乙烯对苯二甲酸乙二醇酯(PET)衬底上并嵌入PANI薄膜,获得了电致发光薄膜材料和有机/无机异质结实验器件ITO/(ZnO NWs-PANI)。有机/无机异质结器件电致发光可调,在相对低的开启电压下呈现室温蓝紫外发光,并且ZnO NWs表面覆盖PANI增加了蓝紫外发光的强度和稳定性;而无PANI的ZnO NWs阵列具有450 nm处的缺陷发射峰,这可能是电子从扩展态锌间隙Zn_i到价带的跃迁引起的。这些结果表明,基于PANI/ZnO纳米线的复合材料在柔性光电器件方面的应用极具潜力。     

Photovoltaic properties of the copper-phthalocyanine and ZnO nanorod array system affected by ethanol

Well-aligned ZnO nanorod array, fabricated on conductive indium-tin-oxide (ITO) substrate by wet chemical bath deposition (CBD) method, was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Surface photovoltage (SPV) technique was employed to study the photovoltaic properties of the copper-phthalocyanine (CuPc) and ZnO nanorod array system affected by ethanol. Prior to ethanol adsorption, two pronounced SPV response bands were exhibited for this system in the range 300-410 and 540-760 nm, respectively. Post-adsorption measurements reveal that the SPV intensity of the former band is enhanced, while that of the latter band is suppressed if ethanol was used to modify CuPc surface. Moreover, both of the SPV intensity of two response bands is enhanced if ethanol was used to modify ZnO and CuPc interface. Mechanisms of these phenomena were suggested.     

ZnO-CNT composite nanotubes as nanoresonators

This Letter reports the very first vibration analysis of the novel composite nanotubes (NTs) synthesized by coating carbon nanotubes (CNTs) with piezoelectric zinc oxide (ZnO). Timoshenko beam theory was used and modified to account for the interlayer van der Waals (vdW) interaction in the inner CNT and hybrid structures of the NTs. The distinctive vibration behaviours of the NTs were captured and the physics behind these unique features was investigated in terms of the critical role of the vdW interaction and the effect of the ZnO coating layer on the structural rigidity of the NTs. The composite NTs are found to be promising for gigahertz/terahertz electromechanical nanoresonators whose frequency can be even higher than that of the core CNTs.     

Hybrid photonics structures with grating and prism couplers based on ZnO waveguides

This paper presents the results of investigations concerning input-output systems of an electromagnetic wave in the visible and near visible spectrum for their application in structures of integrated optics. The input-output structures used in described planar optical waveguides are in a form of prism and grating couplers. The first part of the paper contains numerical analysis of grating couplers aiming at an optimization of their geometrical parameters, strictly — the depth of the grooves in the grating coupler. The second part presents the practical realization, as well as experimental tests of the planar optical waveguide with the hybrid input-output system. As the input system of the electromagnetic wave, a prism coupler was used, and in the case of the output system — a photonic structure with grating coupler was applied. The investigated planar wave guides with the input-output structures were made of a wide energy band gap semiconductor — zinc oxide (ZnO).     

Application of low-barrier metal-semiconductor-metal structures for the detection of microwave signals

New structures of sensitive elements based on asymmetric low-barrier metal-semiconductormetal structures are proposed. The structures can be used for the detection of microwave or terahertz signals. A vertical structure with different barrier heights of two metal-semiconductor junctions and a planar structure with different areas of junctions are studied. It is demonstrated that the sensitive element based on the vertical structure is superior to a detecting low-barrier Mott diode. The sensitivity of the planar element is comparable with the sensitivity of the diode but the former is easier to produce. The characteristics of a detector based on the planar low-barrier structure integrated in a broadband antenna are calculated. Possible sensitivities in a band of 1 THz are determined.     

Infrared thermography and its application in the NDT of sandwich structures

Thermographic nondestructive testing (NDT) based on the thermal resistance effect of defects is developed for the inspection of delaminated and sandwiched defects embedded in composite structures. The resolution is examined for artificial delaminated defects in carbon-fiber honeycomb structures using conventional infrared radiation heating. The experimental results have demonstrated that radiation heating is effective for revealing defects in the composite structures.An experimental and computational hybrid system is developed for detecting defects in various composite structures. The system consists of an infrared thermal video system which measures the surface temperature distribution of the structure, a computer with a PIP-1024B image board which performs image processing of thermograms, and a HP ink jet XL printer. It is found that this system is readily applicable to the detection of defects located at the interface of the core and skin in honeycomb structures and delaminations in composite materials.     

Hybrid photoanode films based on sparse ZnO rod array-TiO2 nanoparticles in dye-sensitized solar cells

ZnO-TiO2 hybrid photoanodes were fabricated via the doctor-blade method by integrating vertically-grown sparse ZnO arrays with hydrothermal TiO2 nanoparticles. A special surface-coating technique was developed to deposit a thin TiO2 layer on the surface of ZnO rods. Microstructure, optical and photoelectrochemical performance of the hybrid photoanodes were investigated. The denser ZnO array exhibited bad filling behavior of nanoparticles in the interspace of ZnO rods, strong scattering and low conversion efficiency (0.27%). The sparser array showed a much better integrated microstructure, improved transmittance and high conversion efficiency (2.68%). The surface modification of ZnO rods by the TiO2 thin layer was found useful in improving the interfacial microstructure between the ZnO rod and the TiO2 bulk film, and the total conversion efficiency of 3.01% was achieved, higher than that of the pure TiO2 nanoparticle cell (2.93%). The increased scattering effects on the incident light, the enhanced electron transportation at TiO2/dye/electrolyte interface, and the inhabited recombination were responsible for this improvement.     

Characterization of optoelectronic properties of the ZnO nanorod array using surface photovoltage technique

Well-aligned ZnO nanorod array, synthesized by wet chemical bath deposition (CBD) method on conductive indium-in-oxide (ITO) substrate, was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. Surface photovoltage (SPV) technique based on a scanning Kelvin Probe system was employed to investigate the optoelectronic behavior of ZnO nanorod array. The surface photovoltage and its time-resolved evolution process are used to determine the energy level structure of the ZnO nanorod array.     

Electrical and optical properties of light-emitting field-effect transistors based on MEH-PPV polymer composite films with ZnO nanoparticles

The optical and electrical properties of light-emitting field-effect transistor structures with an active layer based on nanocomposite films containing zinc oxide (ZnO) nanoparticles dispersed in the matrix of the soluble conjugated polymer MEH-PPV have been investigated. It has been found that the current-voltage characteristics of the field-effect transistor based on MEH-PPV: ZnO films with a composite component ratio of 2: 1 have an ambipolar character, and the mobilities of electrons and holes in these structures at a temperature of 300 K reach high values up to ～1.2 and ～1.4 cm²/V s, respectively, which are close to the mobilities in fieldeffect transistors based on ZnO films. It has been shown that the ambipolar field-effect transistor based on MEH-PPV: ZnO films emits light at both positive and negative gate bias voltages. The mechanisms of injection, charge carrier transport, and radiative recombination in the studied structures have been discussed.     

A study on the DC-electrical and thermal conductivities of epoxy/ZnO composites doped with carbon black

Thermo-electrical characterizations of hybrid polymer composites, made of epoxy matrix filled with various zinc oxide (ZnO) concentrations (0, 4.9, 9.9, 14.9, and 19.9 wt%), and reinforced with conductive carbon black (CB) nanoparticles (0.1 wt%), have been investigated as a function of ZnO concentration and temperature. Both the measured DC-electrical and thermal conductivities showed ZnO concentration and temperature dependencies. Increasing the temperature and filler concentrations were reflected in a negative temperature coefficient of resistivity and enhancement of the electrical conductivity as well. The observed increase in the DC conductivity and decrease in the determined activation energy were explained based on the concept of existing paths and connections between the ZnO particles and the conductive CB nanoparticles. Alteration of ZnO concentration with a fixed content of CB nanoparticles and/or temperature was found to be crucial in the thermal conductivity behavior. The addition of CB nanoparticles to the epoxy/ZnO matrix was found to enhance the electrical conduction resulting from the electronic and impurity contributions. Also, the thermal conductivity enhancement was mostly attributed to the heat transferred by phonons and electrons hopping to higher energy levels throughout the thermal processes. Scanning electron microscopy and energy-dispersive spectroscopy were used to observe the morphology and elements’ distribution in the composites. The observed thermal conductivity behavior was found to correlate well with that of the DC-electrical conductivity as a function of the ZnO content. The overall enhancements in both the measured DC- and thermal conductivities of the prepared hybrid composites are mainly produced through mutual interactions between the filling conductive particles and also from electrons tunneling in the composite's bulk as well.     

Room temperature Ge and ZnO embedded inside porous silicon using conventional methods for photonic application

In this paper we reported room temperature synthesis of embedded porous Si (PS) based structures using simple and low cost techniques of electrochemical etching and thermal evaporation. PS was prepared by anodization of Si wafer in ethanoic hydrofluoric acid (HF). The Ge and ZnO layers were deposited onto the PS by conventional thermal evaporation. Three samples prepared namely PS, Ge/PS and ZnO/Ge/PS. Structural analyses, SEM revealed that the structures contained 500–700 nm circular-pores and EDX suggested the presence of Ge and ZnO inside the pores. Photoluminescence (PL) spectra of the three samples revealed emissions peak at 380, 520 and 639 nm, respectively, with ZnO/Ge/PS displaying a high UV emission peak accompanied by low and broad green to red emission peaks. The Ge/PS sample shows emission peaks from green to red and the PS sample reveals a broad peak in the red region. These characteristics demonstrate the potential of the PS-based structures to emit light at a broader spectrum for prospective applications in optoelectronic devices.     

Sintering behaviour and microstructures of nanostructured ZnO–ZnS core–shell powder by spark plasma sintering

Densification of nanostructured ZnO–ZnS core–shell powder was carried out by spark plasma sintering to produce a bulk ZnO–ZnS composite. By adjusting the sintering temperature, we could fabricate a bulk ZnO–ZnS composite without destroying the original core–shell structure of the powder. X-ray diffraction and transmission electron microscopy were used to characterize the microstructural properties of the core–shell powder and its sintering behaviour. During spark plasma sintering, phase transition from a sphalerite to a wurtzite structure was observed in the ZnS shell and the crystallographic orientation of the ZnS shell was affected by the ZnO core.     

The investigation on the electronic structures of hybrid GNR-ZnO

To investigate the modification of graphene for a good semiconductor performance, the model of graphene nanoribbon (GNR) and the model of hybrid GNR-ZnO are presented, respectively. The electronic structures such as band structure, density of electronic states (DOS) are investigated by using first-principles calculations based on density functional theory. The results show that the ZnO has direct contribution to the formation of valence band with the composites, which changes the properties of graphene; the adsorption of ZnO nanostructure has an impressive impact on the graphene nanoribbon, which causes the band gap of the composite to become narrower than that of intrinsic graphene nanoribbon. In terms of the graphene nanoribbon, its differentiation of 2p state weakens gradually from the marginal zone to the central region. The mechanism of electronic structure of the graphene nanoribbon and hybrid GNR-ZnO is also discussed to give a further explanation for the change. The results provide a potential way to improve the properties of intrinsic graphene and enhance the controllability of graphene-based materials structure.     

A study on photo-generated charges property in highly ordered TiO2 nanotube arrays

In this study TiO₂ nanotube arrays were fabricated by potentiostatic anodization of titanium sheet. The X-ray diffraction (XRD) pattern and field emission scanning electron microscopy (FE-SEM) image indicated the TiO₂ nanotube arrays were of pure anatase form and highly ordered. The properties of the photo-generated charges in the nanotube arrays were investigated by transient photovoltage (TPV) technique and surface photovoltage (SPV) technique based on lock-in amplifier with dc bias, in comparison with the commercial powder derived film. The separation processes of the photo-induced charges in the system of TiO₂ nanotubes on Ti have been demonstrated to be correlated with the incident light intensity, surface trapping states, and the interfacial electric field between Ti and TiO₂. The results also show that the highly ordered nanotube film could generate much stronger SPV responses under external electric field than the commercial powder derived film.     

Vacancy filling effect of graphene on photoluminescence behavior of ZnO/graphene nanocomposite

We report on the aerosol synthesis and optical characterization of ZnO/unoxidized graphene (UG) platelets nanocomposite films with high optical transparency (>85% at visible wavelengths). The ZnO/UG composite films, in which UG nanoplatelets are embedded in nano‐grained ZnO, were fabricated from colloidal suspensions of UG platelets with an aqueous zinc precursor. From photoluminescence (PL) spectra of the UG composite films, it was found that PL intensity decreases with the addition of UG platelets. The features of PL intensity in the UG composites are in contrast to that of ZnO/graphene oxide (G‐O) platelets composites, and can be explained by the absence of an oxygen vacancy filling effect, due to the unoxidized nature of UG and an increase in defect sites in its composites. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Photoconductivity in metal-semiconductor-metal planar structures with ZnO:Ga and ZnO:Li films

Influence of UV radiation on photoelectric properties of ZnO:Ga and ZnO:Li films prepared by the electron-beam evaporation method was investigated. The photoconductivity was measured, using metal-semiconductor-metal planar structures where metallic aluminum was used as ohmic electrodes. The kinetics of rise and decay of the photoconductivity in these structures was studied. The change of photoconductivity under the action of UV radiation is considered as a result of the photoexcitation-relaxation into the conduction band and photochemical processes of absorption-desorption of oxygen at the film surface. The influence of a MgF₂ protective layer deposited on ZnO:Ga and ZnO:Li films was studied. Measurements of the spatial distribution of the potential between the anode and cathode for determination of the homogeneity of conductivity in the investigated planar structures were performed by the moving probe method.     

Electroluminescence from ZnO nanowire-based p-GaN/n-ZnO heterojunction light-emitting diodes

Vertically aligned ZnO nanowires were successfully grown on the sapphire substrate by nanoparticle-assisted pulsed laser deposition (NAPLD), which were employed in fabricating the ZnO nanowire-based heterojunction structures. p-GaN/n-ZnO heterojunction light-emitting diodes (LEDs) with embedded ZnO nanowires were obtained by fabricating p-GaN:Mg film/ZnO nanowire/n-ZnO film structures. The current–voltage measurements showed a typical diode characteristic with a threshold voltage of about 2.5 V. Electroluminescence (EL) emission having the wavelength of about 380 nm was observed under forward bias in the heterojunction diodes and was intensified by increasing the applied voltage up to 30 V.     

Fabrication of ZnO thin film-nanowires hybrid homojunction on silicon substrate

In this paper, the formation of a p–n ZnO thin film-nanowires hybrid homojunction on silicon substrate has been investigated. P-type ZnO thin film is formed by both e-beam evaporation and RF magnetron sputtering techniques. In order to fabricate 3-dimentional hybrid structures, ZnO nanowires were grown on p-type ZnO films by metal organic chemical vapor deposition techniques. The X-ray diffraction results showed that both ZnO thin films and nanowires are $c$-axis oriented. The formation of p–n ZnO homojunction is verified by current–voltage measurements. Typical diode behavior and photoconductivity were observed in both designs.     

微凝胶模板法制备P（AM-co-MAA）/ZnO有机-无机复合微球的研究

采用反相悬浮聚合法合成了甲基丙烯酸（MAA）含量不同的聚丙烯酰胺-甲基丙烯酸[P（AM-co-MAA）]微凝胶,并以其作为模板,通过外源沉积法制备了一系列微米级,表面具有纳米级颗粒堆积的P（AM-co-MAA）/ZnO有机-无机复合微球。复合微球的表面结构与微凝胶的组成和ZnO的沉积量有关。详细考察了MAA含量,Zn（Ac）2浓度,NaOH醇溶液的浓度对ZnO负载量的影响。利用扫描电子显微镜（SEM）,能谱分析仪（EDX）,X衍射分析仪（XRD）,傅里叶红外分析仪（FT-IR）等对复合微球的形貌、组成进行了表征。