Chemical bath deposition of ZnO nanorods for dye sensitized solar cell applications

ZnO nanorods using various molar concentrations have been synthesized through the chemical bath deposition method. X-ray diffraction result shows that the ZnO nanorods are of hexagonal structure. The morphology of the ZnO nanorods has been examined by scanning electron microscopy. The ZnO nanorods have diameters ranging from 100 to 200 nm and length of 1–3 μm. Dye-sensitized solar cells have been assembled by using ZnO nanorod film photoelectrode sensitized using natural dye extracted from lantana camara as sensitizer. The ZnO nanorods have been used as electrode material to fabricate dye sensitized solar cells which exhibited an efficiency of 0.71 %, the maximum efficiency was obtained for films deposited for 0.07 M concentration.     

Synthesis and characterization of flower like ZnO nanorods for dye-sensitized solar cells

Flower like ZnO nanorods have been prepared by chemical bath deposition method. X-ray diffraction result shows that flower like ZnO nanorods exhibit hexagonal structure. Dye sensitized solar cells have been assembled by using ZnO nanorod film photoelectrode sensitized using natural dye extracted from daucus carota as sensitizer. The flower like ZnO nanorods have been used as photo-anode material to fabricate the dye sensitized solar cell which exhibited an overall light to electricity conversion efficiency of 0.78 % with a fill factor of 0.39, short-circuit current density of 3.70 mA/cm² and open-circuit voltage of 0.26 V.     

Study of Influence of Annealing Time on Some Physical Properties of ZnO:Cu Nanorods Grown by a Simple Chemical Bath Deposition Method

A simple chemical bath deposition method was used to prepare high density ZnO nanorods on ZnO seeded Si substrates. Upon the nanorods growth, Cu-doping was achieved by diffusion process at 500 ^°C for different times in vacuum ambient. The structural, optical, and magnetic properties of the obtained ZnO:Cu nanorods were then examined. XRD analysis showed that undoped and ZnO:Cu samples were highly c-axis oriented with a hexagonal wurtzite structure. SEM analysis indicated that ZnO:Cu nanorods had diameters of ～200 nm and lengths of ～1.5 μm. X-ray photoemission spectroscopy demonstrated that Cu was successfully doped into ZnO in a divalent state. Photoluminescence results showed that Cu-doping caused a decrease in the green band intensity of nanorods compared to undoped ZnO. Room temperature magnetic measurements showed that pure ZnO nanorods exhibited ferromagnetism that might be ascribed to defect-induced d⁰ ferromagnetism. All the ZnO:Cu nanorods also showed the room temperature ferromagnetism that was attributed to the bound magnetic polarons (BMPs).     

Effect of Sn doping on structural, optical, electrical and wettability properties of oriented ZnO nanorod arrays

Herein we present a modified sol gel route for the one step fabrication of oriented ZnO nanorod arrays. The method is seed layer free, and nanorods directly attach to a substrate. We also present the effect of tin (Sn) content on the crystallinity, microstructural, optical and electrical properties of the ZnO nanorod arrays. Thermo gravimetric (TG) curves of gel precursors showed that most of the organic groups and other volatiles were removed at about 450 °C. X-ray diffraction patterns confirmed that the films were polycrystalline in nature with (002) preferred orientation. The texture coefficient, grain size, dislocation density and lattice parameters of the ZnO arrays were determined. The SEM micrographs revealed that the undoped and 1 at.%Sn doped films were composed of nanorods and the concentration of 2 at.%Sn doping hindered the rod like structure growth and modulated into granular nature. UV-visible transmission spectroscopy indicated that the transparency of the films increased with Sn content. On Sn doping, the films also exhibited a red shift and slight shrinkage of band gap. The electrical studies revealed that 1 at.% of Sn doping enhanced electrical conduction in ZnO films and beyond that the distortion caused in the lattice reduced the conductivity. The contact angle of the ZnO nanostructures varied between 91° and 115° depending upon the Sn content. Therefore, 1 at.%Sn doping into ZnO nanorods improves the crystallinity, electrical conductivity and water contact angle.     

Synthesis and fabrication of Mg-doped ZnO-based dye-synthesized solar cells

Undoped and 2, 4 and 6 at.% Mg-doped ZnO nanorods were successfully deposited on ZnO seeded fluorine tin oxide substrates by a simple chemical bath deposition technique to form a photoanode. It was seen that all the samples had a hexagonal wurtzite structure with compact rod morphology. From Tauc’s plot results, as compared to the undoped one (3.26 eV), the optical band gap of the ZnO:Mg samples increased to 3.32 eV for 4 at.% Mg-doping concentration and then decreased to 3.27 eV for 6 at.% Mg-doping. Photoluminescence results measured at 300 K indicated that ZnO nanorods had a ultra-violet peak with a wavelength of 382 nm, a blue peak at 420 nm and a deep level band in the range of 450–800 nm. Undoped and Mg-doped ZnO nanorods were subsequently used to realize ZnO-based dye-synthesized solar cells which exhibited the best power conversion efficiency of 0.144 % for 4 at.% ZnO:Mg sample.     

Optical and structural properties of Mg doped ZnO thin films by chemical bath deposition method

The chemical bath deposition method has often been employed to successfully deposit pure and Mg doped ZnO thin films on a glass substrate. The impact of Mg creates a strained stress in ZnO films affecting its structural and optical properties. XRD patterns revealed that all thin films possess a polycrystalline hexagonal wurtzite structure and Mg doped ZnO thin films (002) plane peak position is shifted towards a lower angle due to Mg doping. From the SEM image, it is understood that the Mg doped ZnO thin films are uniformly coated and are seen as dense rods like pillers deposited over the film. The energy dispersive X-ray analysis confirmed the presence of Mg in doped ZnO thin films. The transmittance spectra exhibit that it is possible for Mg doping to enhance ZnO thin films. The optical energy gap of the films was assessed by applying Tauc’s law and it is observed to show an increasing tendency with an improvement in Mg doping concentrations. The optical constants such as reflectance, index of refraction, extinction coefficient and optical conductivity are determined by using transmission at normal incidence of light by using wavelength range of 200–800 nm. In PL spectra, the band edge emission shifted to the blue with increasing amount of Mg doping.     

Enhanced H2 sensing properties of a-plane ZnO prepared on c-cut sapphire substrate by sputtering

Zinc oxide (ZnO) thin films have been prepared on c-plane sapphire substrate by magnetron sputtering technique. The influence of deposition time on the structural, optical and photoluminescence properties of the films have been investigated. XRD patterns reveal the growth of preferentially oriented (101) non-polar a-plane ZnO film with hexagonal wurtzite structure. The PL peak shifts towards lower wavelength for deposition time up to 20 min, which is in consistent with the results obtained from UV absorption studies. The blue shift in the PL peak confirms the possibility for quantum confinement effect. The band gap energy of the film increases from 3.33 to 3.38 eV, indicating enhanced quantum confinement effects. FESEM micrographs showed that the films have a smooth and dense morphology with uniform grain growth. Hydrogen sensing measurements indicated that a-plane ZnO film on c-sapphire showed higher response than c-plane ZnO film reported earlier. The sensor response of 44 nm thick ZnO film exhibit highest response of 145 towards 500 ppm H₂ gas at the operating temperature of 200 °C.     

ZnO@CdS core–shell thin film: fabrication and enhancement of exciton life time by CdS nanoparticle

In the present study photoluminescence behavior of ZnO and ZnO@CdS core–shell nanorods film has been reported. ZnO nanorods were grown on the glass coated indium tin oxide (ITO) surface by seeding ZnO particle followed with nanorods growth. These nanorods were coated with CdS by chemical bath deposition techniques to have ZnO@CdS thin film and further annealed at 200 °C for their adherence to the ITO surface. The coating was characterized for surface morphology using SEM and optical behavior using UV–visible spectrophotometer. Energy dispersive X-ray (EDX) was used for compositional analysis and time resolve photoluminescence decay for excitons life time measurement. The absorption spectrum reveals that the absorption edge of ZnO@CdS core–shell heterostructure shifted to 480 nm in the visible region whereas ZnO nanorods have absorption maxima at 360 nm. The excitons lifetime of ZnO@CdS was found to be increased with the thickness of the CdS layer on ZnO nanorod. These ZnO@CdS core–shell nanostructures will be of great use in the field of photovoltaic cell and photocatalysis in a UV–visible region.     

A novel, substrate independent three-step process for the growth of uniform ZnO nanorod arrays

We report a three-step deposition process for uniform arrays of ZnO nanorods, involving chemical bath deposition of aligned seed layers followed by nanorod nucleation sites and subsequent vapour phase transport growth of nanorods. This combines chemical bath deposition techniques, which enable substrate independent seeding and nucleation site generation with vapour phase transport growth of high crystalline and optical quality ZnO nanorod arrays. Our data indicate that the three-step process produces uniform nanorod arrays with narrow and rather monodisperse rod diameters (∼ 70 nm) across substrates of centimetre dimensions. X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction were used to study the growth mechanism and characterise the nanostructures.     

Effects of Na-doping on the efficiency of ZnO nanorods-based dye sensitized solar cells

Na-doped ZnO nanorods (Zn_1?xNa_xO: x = 0.0, 0.02, 0.04) were grown by a chemical bath deposition method on ZnO seeded FTO substrates. The influence of Na-doping on the efficiency of ZnO nanorods-based dye-sensitized solar cells (DSSCs) was investigated. Undoped and Na-doped ZnO nanorods were used as photo-anodes for the fabricated DSSCs. X-ray diffraction measurements exhibited that all the samples had a wurtzite structure of ZnO with a preferred orientation of (002) plane. Scanning electron microscopy images of the samples revealed that all the samples displayed hexagonal shaped nanorods. It was observed from optical measurements that the band gap energy gradually decreased from 3.29 to 3.21 eV for undoped and 4 at.% Na-doped ZnO nanorods, respectively. Photoluminescence spectrum for undoped ZnO showed three peaks located at 379, 422, and 585 nm corresponding to UV emission, zinc vacancy, and deep level emission (DLE) peaks, respectively. When ZnO nanorods were doped with 2 at.% Na, the intensity of UV peak increased whereas the intensity of DLE peak decreased. The maximum conversion efficiency of DSSCs was found to be 0.22 % with a J_sc of 0.80 mA/cm², V_oc of 0.49 V, and fill factor of 0.523 as ZnO nanorods were doped with 2 at.% Na atoms.     

可见光诱导TiO2光催化及其机理研究进展

简述了二氧化钛的光催化机理。针对其禁带宽度较大,只能被小于387nm的紫外光所激发的缺点,综述了近年来国内外针对纳米TiO2可见光催化的改性方法和改性机理研究进展,包括离子掺杂、半导体复合、表面光敏化等方法。最后展望了提高纳米TiO2可见光光催化活性研究的前景。     

Annealing effects on the structural and optical properties of growth ZnO thin films fabricated by pulsed laser deposition (PLD)

Annealed ZnO thin film at 300, 350, 400, 450 and 500 °C in air were deposited on glass substrate by using pulsed laser deposition. The effects of annealing temperature on the structural and optical properties of annealed ZnO thin films by grazing incident X-ray diffraction (GIXRD), transmittance spectra, and photoluminescence (PL) were investigated. The GIXRD reveal the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The particle size is calculated using Debye–Scherrer equation and the average grain size were found to be in the range 5.22–10.61 ± 0.01 nm. The transmittance spectra demonstrate highly transparent nature of the films in visible region (>70 %). The calculation of optical band gap energy is found to be in the range 2.95–3.32 ± 0.01 eV. The PL spectra shows that the amorphous film gives a UV emission only and the annealed films produce UV, violet, blue and green emissions this indicates that the point defects increased as the amorphous film was annealed.     

Substrate temperature dependent physical properties of sprayed Zn0.76Mg0.24O films

The composition, microstructural and opto-electronic properties of Zn_1?x Mg _x O thin films grown by spray pyrolysis have been studied. The films were prepared on glass substrates at different substrate temperatures in the range, 200–350 °C for a fixed magnesium composition of x = 0.24. The films showed the predominant (002) reflection corresponding to the hexagonal wurtzite structure of ZnO. The preferred orientation doesn’t change with the deposition temperature. The films prepared at 300 °C showed good crystallinity with an average surface roughness of 6.2 nm. The optical studies revealed that the optical transmittance increased slightly with the increase of substrate temperature of the films. The variation of energy band gap, photoluminescence and electrical resistivity of the grown layers was also studied.     

Structural and optical characterization of CdS and CdHgTe thin films for the fabrication of CdHgTe/CdS structure

This article presents the deposition and characterization of CdS and CdHgTe thin films for the fabrication of CdHgTe/CdS structure. The growth of CdS and CdHgTe thin films on FTO-coated conducting glass substrates have been performed by chemical bath deposition (CBD) and electrodeposition methods, respectively. The deposition conditions have been optimized for getting better quality layers of CdS and CdHgTe. The grown layers of both CdS and CdHgTe have been characterized by photoelectrochemical cell (PEC) measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis spectrophotometer. Annealing effect of the deposited films has also been investigated. Finally the fabrication of CdHgTe/CdS structure has been performed and investigated by I–V characteristics. PEC, XRD, SEM and UV–vis spectrophotometer studies reveal that chemically deposited CdS layers are n-type with band gap values vary from 2.29 to 2.41 eV and cubic with (111) preferential orientation, and have spherical grain distributed over the surface. However, electrodeposited CdHgTe layers are p-type with band gap values varying from 1.50 to 1.53 eV and cubic with highly oriented CdHgTe crystallites with the (111) planes parallel to the substrate, and have uniform distribution of granular grains over the surface. The fabricated CdHgTe/CdS structure gave an open-circuit photovoltage and a short-circuit photocurrent of 510 mV and 13 mA/cm² respectively, under AM 1.5 illumination.     

Influence of Fe dopant concentration and annealing temperature on the structural and optical properties of ZnO thin films deposited by sol–gel method

Nanostructured Fe doped ZnO thin films were deposited onto glass substrates by sol–gel spin coating method. Influence of Fe doping concentration and annealing temperature on the structural, compositional, morphological and optical properties were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–Vis spectroscopy and photoluminescence (PL) measurements. XRD analysis showed that all the films prepared in this work possessed a hexagonal wurtzite structure and were preferentially oriented along the c-axis. Pure ZnO thin films possessed extensive strain, whereas Fe doped films possessed compressive strain. In the doped films, least value of stress and strain was observed in the 0.5 at.% Fe doped thin film, annealed at 873 K. Average crystallite size was not significantly affected by Fe doping, but it increased from 15.57 to 17.79 nm with increase in annealing temperature from 673 to 873 K. Fe ions are present in +3 oxidation state as revealed by XPS analysis of the 0.5 at.% Fe doped film. Surface morphology is greatly affected by changes in Fe doping concentration and annealing temperature which is evident in the SEM images. The increase in optical band gap from 3.21 to 3.25 eV, with increase in dopant concentration was attributed to Moss–Burstein shift. But increase in annealing temperature from 673 to 873 K caused a decrease in band gap from 3.22 to 3.20 eV. PL spectra showed emissions due to excitonic combinations in the UV region and defect related emissions in the visible region in all the investigated films.     

Influence of Al concentration on structural and optical properties of Al-doped ZnO thin films

Undoped ZnO and Al-doped zinc oxide (ZnO:Al) thin films with different Al concentrations were prepared onto Si (100) substrate by pulsed filtered cathodic vacuum arc deposition system at room temperature. The influence of doping on the structural and optical properties of thin films was investigated. The preferential (002) orientation was weakened by high aluminum doping in films. Raman measurement was performed for the doping effects in the ZnO. Atomic force microscopy images revealed that the surface of undoped ZnO film grown at RT was smoother than that of the Al-doped ZnO (ZnO:Al) films. The reflectance of all films was studied as a function of wavelength using UV–Vis–NIR spectrophotometer. Average total reflectance values of about 35 % in the wavelength range of 400–800 nm were obtained. Optical band gap of the films was determined using the reflectance spectra by means of Kubelka–Munk formula. From optical properties, the band gap energy was estimated for all films.     

Dopant induced polarity inversion in polar ZnO nanorods

Highly oriented and polarity controlled ZnO nanorod thin films are deposited by chemical bath deposition where the preferred polarity depends on the anionic nature of the Zn salt. Significant differences are noticed in magnesium (Mg) doping concentration on Zn- and O-polar ZnO nanorods. Higher doping concentration is achieved in Zn polar nanorods, which is characterized with different spectroscopic techniques. A noteworthy contribution in morphological changes is noted upon by Mg doping on both Zn- and O-polar ZnO nanorods. Polarity inversion of the individual nanorods are found at certain doping condition, characterized by chemical etching rate measurements and Schottky Barrier Height determination of the individual nanorod.     

ZnO纳米棒阵列和薄膜的同步外延生长及其光电化学性能

使用化学气相沉积法在a面蓝宝石衬底上同步外延生长氧化锌(ZnO)竖直纳米棒阵列和薄膜,研究了阵列和薄膜的光电化学性能。结果表明,纳米结构中的竖直单晶纳米棒有六棱柱形和圆柱形,其底部ZnO薄膜使竖直纳米棒互相联通。与ZnO纳米薄膜的比较表明,这种纳米结构具有优异的光电化学性能,其入射光电流效率是ZnO纳米薄膜的2.4倍;光能转化效率是ZnO纳米薄膜的5倍。这种纳米结构优异的光电化学性能,可归因于其高表面积-体积比以及其底部薄膜提供的载流子传输通道。本文分析了这种纳米结构的生长过程,提出了协同生长机理：Au液化吸收气氛中的Zn原子生成合金,合金液滴过饱和后ZnO开始成核,随后在衬底表面生成了ZnO薄膜。同时,还发生了Zn自催化的气-固(VS)生长和Au催化的气-液-固(VLS)生长,分别生成六棱柱纳米棒和圆柱形纳米棒,制备出底部由薄膜连接的竖直纳米棒阵列。     

Influence of incorporation of Al3+ ions on the structural, optical and AC impedance characteristics of spin coated ZnO thin films

Aluminium doped zinc oxide thin films were deposited onto glass substrate using spin coating technique. The effects of Al doping on structural, optical and electrical properties of these films were investigated. X-ray diffraction analysis showed that all the thin films were of polycrystalline hexagonal wurtzite structure with (002) as preferential orientation except 2 at.% of Al doped ZnO films. The optical band gap was found to be 3.25 eV for pure ZnO film. It increases up to 1.5 at.% of Al doping (3.47 eV) and then decreased slightly for the doping level of 2 at.% (3.42 eV). The reason for this widening of the optical band gap up to 1.5 at.% is well described by Burstein–Moss effect. The photoluminescence spectra of the films showed that the blue shift and red shift of violet emission were due to the change in the radiative centre between zinc vacancy and zinc interstitial. Variation in ZnO grain boundary resistance against the doping concentration was observed through AC impedance study.     

Fabrication and application in hybrid solar cell of ZnO nanorod arrays

Well-aligned ZnO nanorod arrays (ZNRAs) were grown on coated indium tin oxide coated glass substrates from aqueous solutions at low temperature. Morphologies, crystalline structure and optical transmission were investigated by a scanning electron microscope, X-ray diffraction and UV–Visible transmission spectra, respectively. The results showed that ZNRAs grew vertically from the substrates, having uniform thickness and length distribution, ZnO nanorods were wurtzite-structured (hexagonal) ZnO. The high optical transmission in the visible region was also achieved. Furthermore, a hybrid solar cell was be constructured using ZNRAs as inorganic layer, and a power conversion efficiency of 0.47 % was achieved.