Mesoporous inverse opal TiO2 film as light scattering layer for dye-sensitized solar cell

The light harvesting efficiency of dye-sensitized solar cells was enhanced by using a scattering layer. Such as sphere type TiO2, inverse photonic crystal TiO2, hollow spherical TiO2. Among these materials, the TiO2 with inverse photonic crystal (IPC) structure, synthesized by self-assembly using spherical templates, has attracted much attention due to their photonic crystal characteristics and light scattering effects. However, when applied in the DSSCs, the surface area of IPC is very low that caused insufficient adsorption amount of dye molecules. In the present work, a scattering layer with mesoporous inverse photonic crystal (MIPC) TiO2 film was fabricated by the sol-gel reactions with surfactant-assisted sol-gel method using poly(methyl methacrylate) as the template and titanium (IV) isopropoxide as the TiO2 precursor. After removing the PMMA and surfactant, a highly ordered macroporous structure with mesopores were successfully obtained. The surface area and total pore volume of the MIPC were 82 m2/g and 0.31 cm3/g, respectively, which is much larger than those of the IPC. The DSSCs with the scattering layer of MIPC film exhibited 18 and 10% higher photo-conversion efficiency than those of cells only with a nano-crystalline TiO2 film and with scattering layer of IPC film. From UV-visible spectra of dye solutions, the MIPC film showed a higher amount of absorbed dye molecules than those of the reference and IPC films. Accordingly, an increase in the photo-current density through abundant adsorption of the dye, coupled with inherent light scattering ability can improve overall photo-conversion efficiency.     

Three-dimensional photonic crystal fluorinated tin oxide (FTO) electrodes: synthesis and optical and electrical properties

Photovoltaic (PV) schemes often encounter a pair of fundamentally opposing requirements on the thickness of semiconductor layer: a thicker PV semiconductor layer provides enhanced optical density, but inevitably increases the charge transport path length. An effective approach to solve this dilemma is to enhance the interface area between the terminal electrode, i.e., transparent conducting oxide (TCO) and the semiconductor layer. As such, we report a facile, template-assisted, and solution chemistry-based synthesis of 3-dimensional inverse opal fluorinated tin oxide (IO-FTO) electrodes. Synergistically, the photonic crystal structure possessed in the IO-FTO exhibits strong light trapping capability. Furthermore, the electrical properties of the IO-FTO electrodes are studied by Hall effect and sheet resistance measurement. Using atomic layer deposition method, an ultrathin TiO(2) layer is coated on all surfaces of the IO-FTO electrodes. Cyclic voltammetry study indicates that the resulting TiO(2)-coated IO-FTO shows excellent potentials as electrodes for electrolyte-based photoelectrochemical solar cells.     

Layer‐by‐Layer Approach to (2+1)D Photonic Crystal Superlattice with Enhanced Crystalline Integrity

Large‐area polystyrene (PS) colloidal monolayers with high mechanical strength are created by a combination of the air/water interface self‐assembly and the solvent vapor annealing technique. Layer‐by‐layer (LBL) stacking of these colloidal monolayers leads to the formation of (2+1)D photonic crystal superlattice with enhanced crystalline integrity. By manipulating the diameter of PS spheres and the repetition period of the colloidal monolayers, flexible control in structure and stop band position of the (2+1)D photonic crystal superlattice has been realized, which may afford new opportunities for engineering photonic bandgap materials. Furthermore, an enhancement of 97.3% on light output power of a GaN‐based light emitting diode is demonstrated when such a (2+1)D photonic crystal superlattice employed as a back reflector. The performance enhancement is attributed to the photonic bandgap enhancement and good angle‐independence of the (2+1)D photonic crystal superlattice.     

NPC太阳电池的TiO2薄膜结构的研究

采用溶胶凝胶法、粉末涂敷法和磁控溅射法在导电玻璃上制得纳米TiO2薄膜。电子衍射和X射线衍射实验表明该薄膜主要是锐钛矿相结构，透射电子显微镜实验证明了薄膜晶粒为纳米尺度，扫描电子显微镜实验观察了薄膜的表面形貌。分析并讨论了利用以上各种方法制得的纳米TiO2薄膜的结构及其所组成的染料敏化太阳电池的性能。发现由致密TiO2层和多孔TiO2层组成的多层TiO2薄膜组装的太阳电池的性能优于任一种单层TiO2薄膜。     

Inverse Mopho butterfly: a new approach to photonic crystal

In this paper we showed a new approach for the fabrication of a photonic crystal with a three-dimensional structure. By replicating biomaterials such as the wing of Mopho butterfly with TiO2 nanoparticles using the nanoparticles infiltration method, we can derive photonic crystals with unique structures, which is difficult to fabricate by other approaches. New optical properties are anticipated.     

The optical responses of one-dimensional photonic crystals based on the transparent Ag‐anodic aluminum oxide composites with super low-refractive index

The super low refractive index of less than 1 is obtained through adjusting the deposition time of nano-metal Ag in Ag-anodic aluminum oxide (Ag-AAO) composite films. It is very interesting that the Ag-AAO composite films with super low refractive index are still transparent. Based on the results, the Ag-AAO composite films and titanium dioxide (TiO₂) films were used to assemble 1D TiO₂/Ag-AAO photonic crystal (PC) structure and its optical responses were simulated in the 500-2500 nm range by using the finite difference time domain method. It is found that the increase of Ag-AAO layer thickness makes the photonic band gap (PBG) become broad greatly, but has few effects on the blue edge of the PBG, which is different from the effect of TiO₂ layers. It is more important that a broad omnidirectional PBG can be easily obtained from the simple 1D TiO₂/Ag-AAO photonic crystal structure through the modulation of both the TiO₂ and Ag-AAO layer thicknesses. Furthermore, the absorption of 1D TiO₂/Ag-AAO PC structure at the PBG edges is very strong due to the photon localization in Ag-AAO layer. The different roles of Ag-AAO layer in the above mentioned 1D PC structure are mainly attributed to the different transmission process of optical pulse in Ag-AAO layer.     

棱镜耦合光子晶体表面波及其传感特性研究

构造一种棱镜耦合一维光子晶体结构,利用传输矩阵方法对该结构中光的传输特性进行研究.结果表明:光在这种棱镜耦合一维光子晶体结构中传播时,会在光子晶体表面产生非辐射传播模,即表面波,而且在反射谱中表面波所在的角度位置、反射率的大小以及反射峰的半峰全宽受到一维光子晶体的介质折射率和介质厚度的调制.此外,表面波对应的角度位置对...     

Enhancement of crystallinity and optical properties of bilayer TiO2/ZnO thin films prepared by atomic layer deposition

Bilayer and multilayer thin films are becoming increasingly important in the development of faster, smaller and more efficient electronic and optoelectronic devices. One of the motivations of applying bilayer or multilayer structures is to modify the optical properties of materials. Atomic layer deposition (ALD) is a variant of Chemical Vapour Deposition that can produce uniform and conformal thin films with well controlled nanostructures. In this study, we have demonstrated new findings of the use of ALD fabricated bilayer TiO2/ZnO thin films with enhanced crystallinity and optical properties. TiO2 films have been deposited at 300 degrees C for 1000 (51 nm in thickness) or 3000 (161 nm in thickness) deposition cycles onto glass and Si substrates. ZnO films are subsequently deposited on the TiO2 layers at 280 degrees C for 500 deposition cycles (55 nm). The crystallinity and optical properties of the TiO2/ZnO thin films have been analysed by X-ray diffraction, photoluminescence, UV-Vis spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy. XRD diffraction pattern confirmed the presence of ZnO with wutrtize crystal structure and TiO2 with anatase structure. It shows that the crystallinity of the TiO2 films has been improved with the deposition of ZnO. The intensity of UV luminescence has increased by almost 30% for TiO2/ZnO bilayer as compared to the single layer TiO2. The possible mechanism for the enhancement of the optical properties of bilayer TiO2/ZnO thin films will be discussed.     

有序多孔结构二氧化钛薄膜的制备和应用

本文探讨了一种制备二氧化钛高度有序多孔结构的方法及其在染料敏化太阳电池中的应用。采用聚苯乙烯悬浮液,采取垂直沉积法得到了聚苯乙烯胶体晶体;以该模板制备了高度有序的纳米二氧化钛反蛋白石多孔薄膜。对胶体晶体模板和二氧化钛反蛋白石有序膜的微观结构进行表征和讨论。用所制得的二氧化钛反蛋白石有序膜组装成染料敏化太阳电池。通过电流...     

The immune toxicity of titanium dioxide on primary pulmonary alveolar macrophages relies on their surface area and crystal structure

Surface properties are critical to assess effects of titanium dioxide (TiO2) primary nanoparticles on the immune function of pulmonary alveolar macrophage (PAMs). In this study the immune toxicity of TiO2 primary nanoparticles on PAMs relies on their surface area and crystal structure were determined. The primary PAMs of rats exposed to different sizes and crystal structure of TiO2 particles at different dosages for 24 hrs were evaluated for cytokines, phagocytosis, chemotaxis and surface molecules expression. Nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) level of PAMs significantly increased when exposed to TiO2 primary particles and there were significant association with the exposure total surface area and crystal structure of TiO2 particles in the former. TiO2 particles showed significant inhibiting effects on phagocytotic ability, chemotactic ability, Fc receptors and MHC-II molecular expression of macrophages compared with control. Exposure dosage and crystal structure of TiO2 particles play effects on phagocytotic ability and chemotactic ability of PAMs. These results suggested that TiO2 nanoparticles could induce the release of inflammatory mediators, initiate the inflammation development and inhibit the immune function of PAMs associated with non-specific immunity and specific immunity relies on surface area and crystal structure. NO activity might be a candidate marker indicating the TiO2 exposure burden and cell damage in PAMs.     

The two-dimensional hybrid surface plasma micro-cavity

A hybrid surface plasma micro-cavity structure with a defect cavity is formed based on the two-dimensional surface plasmon resonance photonic crystal waveguide structure. A cell defect is introduced in the centre of the photonic crystal layer to build the hybrid surface plasma micro-cavity structure. This work is numerical based on the finite-difference time-domain method. The photon energy is confined to the micro-cavity and the photon energy is strongest at the interface between the insulating layer and the metal layer. The micro-cavity structure has a very small mode volume of sub-wavelength scale in the 1550 nm communication band. The value of Q/V is up to 7132.08 λ/n^?3.     

锂掺杂二氧化钛致密层对染料敏化太阳电池性能的影响

利用脉冲激光沉积(PLD), 在纳米多孔二氧化钛层(np-TiO₂)与透明导电玻璃之间分别沉积了二氧化钛致密层(d-TiO₂)和掺锂二氧化钛致密层(d-Li-TiO₂), XRD衍射结果显示该致密层具有锐钛矿结构. 电池开路电压随时间的衰减实验结果表明, 该结构可以有效减慢开路电压的衰减, 抑制透明导电玻璃上的电子向电解质逆向传输并进行电子复合的几率; 同时, 掺入锂后, 致密TiO₂层(d-TiO₂)能带宽度变窄, 降低了np-TiO₂层与透明导电玻璃之间的界面电阻, 使得np-TiO₂层导带上的光生电子更容易地向透明导电玻璃传输, 进而使得具有d-Li-TiO₂层的染料敏化太阳电池比无致密层的染料敏化太阳电池光电转换效率提高了42%.     

Nanofabrication of organic/inorganic hybrids of TiO2 with substituted phthalocyanine or polythiophene

Organic photovoltaic cells, similar to Gr?tzel type, have been widely investigated in recent years. In the case of Gr?tzel-type cells, TiO2 colloids are usually spin-coated onto an electrode and then sintered. Later, such electrodes are immersed in dye solution to sensitize the TiO2 layer for fabrication of photovoltaic cells. In the current study, an attempt was made to fabricate photovoltaic cells using a layer-by-layer technique. Based on such a method, ordered substituted phthalocyanine or conducting polythiophene-sensitized TiO2 multilayers were fabricated at the molecular level. Buildup of multilayer films of copper phthalocyanine-capped TiO2 and poly(thiophene-3-acetic acid)/TiO2 was monitored by increments in the UV-visible absorption and the frequency decrease of quartz crystal microbalance. The ordered multilayers were further characterized by infrared spectroscopy, and electrochemical and photoelectrochemical measurements.     

Fabrication of two-dimensional superposed microstructure by interference lithography

In this paper, we report the basic theory and method of single exposure interference lithography (IL) to fabricate two-dimensional (2D) superposed microstructures. Distribution of six-beam interference intensities with different azimuth angle is discussed, and 2D superposed microstructures with different periodic constants are obtained by computer simulations. The experiment results using CHP-C positive photoresist show a 2D superposed photonic crystal composed of a periodically repeated hexagonal pattern of hexagonal lattice cells, which is in close agreement with the computer simulation. Fabrication of a superposed structure by single exposure IL paves the way for studying 2D photonic crystal fabrication, surface lasing, optical waveguides, and so on.     

Highly active nanocrystalline TiO(2) photoelectrodes

A simple method for the fabrication of highly photoactive nanocrystalline two-layer TiO(2) electrodes for solar cell applications is presented. Diluted titanium acetylacetonate has been used as a precursor for covering SnO(2):F (FTO) films with dense packed TiO(2) nanocrystallites. The nanoporous thick TiO(2) film follows the dense packed thin TiO(2) film as a second layer. For the latter, amorphous TiO(2) nanoparticles have been successfully synthesized by a sol-gel technique in an acidic environment with pH<1 and hydrothermal growth at a temperature of 200?°C. The acidic nanoparticle gel was neutralized by basic ammonia and a TiO(2) gel of pH?5 was obtained; this pH value is higher than the recently reported value of 3.1 (Park et al 2005 Adv. Mater. 17 2349-53). Highly interconnected, nanoporous, transparent and active TiO(2) films have been fabricated from the pH?5 gel. SEM, AFM and XRD analyses have been carried out for investigation of the crystal structure and the size of nanoparticles as well as the surface morphology of the films. Investigation of the photocurrent-voltage characteristics has shown improvement in cell performance along with the modification of the surface morphology, depending on pH of the TiO(2) gel. Increasing the pH of the gel from 2.1 to 5 enhanced the overall conversion efficiency of the dye-sensitized solar cells by approximately 30%. An energy conversion efficiency of 8.83% has been achieved for the cell (AM1.5, 100 mWcm(-2) simulated sunlight) compared to 6.61% efficiency in the absence of ammonia in the TiO(2) gel.     

Fabrication of a multi-scale nanostructure of TiO(2) for application in dye-sensitized solar cells

We propose a highly ordered multi-scale nanostructure of TiO(2) for applications as an anode in dye-sensitized solar cells (DSSCs). The structure is composed of a TiO(2) blocking layer, a TiO(2) inverse opal main body, regularly arranged transport channels between contacting spherical voids of the TiO(2) inverse opal, and TiO(2) nanoparticles coated on the spherical surfaces of the voids. The ordered and continuous backbone of the inverse opal serves as the fast electron transport pathways while the regularly arranged transport channels enable easy transport of dye and electrolyte within the structure. A multi-cycle procedure was developed to enable fabrication of thick inverse opals and easy adjustment of the inverse opal thickness. An example structure was constructed, involving a blocking layer of 90?nm thickness, an inverse opal of 100?nm voids, transport channels of 30-50?nm openings, and nanoparticles 10-15?nm in size. An open-circuit voltage decay investigation showed a significant improvement in electron lifetime for the proposed multi-scale TiO(2) nanostructure based DSSC than that of a TiO(2) nanoparticle film based DSSC, revealing the superior electron recombination characteristic offered by the proposed TiO(2) nanostructure. The conversion efficiency of the DSSC assembled from such an anode structure can reach 4% with a short-circuit current density (J(sc)) of 8.7?mA?cm(-2) and open-circuit potential (V(oc)) of 0.76?V under AM 1.5 (100?mW?cm(-2)) illumination.     

Controlled growth of vertically aligned ZnO nanowires with different crystal orientation of the ZnO seed layer

A novel synthesis and growth method achieving vertically aligned zinc oxide (ZnO) nanowires on a silicon dioxide (SiO(2)) coated silicon (Si) substrate is demonstrated. The growth direction of the ZnO nanowires is determined by the crystal structure of the ZnO seed layer, which is formed by the oxidation of a DC-sputtered Zn film. The [002] crystal direction of the seed layer is dominant under optimized thickness of the Zn film and thermal treatment. Vertically aligned ZnO nanowires on SiO(2) coated Si substrate are realized from the appropriately thick oxidized Zn seed layer by a vapor-solid growth mechanism by catalyst-free thermal chemical vapor deposition (CVD). These experimental results raise the possibility of using the nanowires as functional blocks for high-density integration systems and/or photonic applications.     

可见光区一维光子晶体纳米膜偏振带通滤波器的设计

应用一维时域有限差分方法研究各种条件下一维二元光子晶体的偏振带通滤波特性,具体数值分析了掺杂层位置、厚度、电磁参数、入射角度四种因素对偏振滤波特性的影响.数值结果表明传统意义上的光学多层膜是一维二元光子晶体在光学厚度满足四分之一波长时的特例;可见光区的偏振滤波器的窄带滤波特性与掺杂层的位置有关,掺杂层在整个膜中间位置时偏振分离效果好,掺杂层的厚度与周期层厚度相差越大则分离效果越好,两组元折射率相差越大越易形成禁带,入射角越大禁带越窄,偏振的分离度越好.特别是P偏振局域模更多;在线度参数相同的情况下介质电磁参数对禁带有较大影响,禁带只有在两组元折射率相差越大才能形成,介质损耗同样是不可忽略的因素;光源的入射角对禁带有重大影响.本文的研究对光子器件的设计有一定的指导作用.     

Polarization characteristics of phase retardation defect mode lasing in polymeric cholesteric liquid crystals

We have studied the lasing characteristics of a dye-doped nematic layer sandwiched by two polymeric cholesteric liquid crystal (CLC) films as photonic band gap (PBG) materials. The nematic layer acts as a defect layer, the anisotropy of which brings about the following remarkable optical characteristics: (1) reflectance in the PBG region exceeds 50% due to the retardation effect, being unpredictable from a single CLC film; (2) efficient lasing occurs either at the defect mode wavelength or at the photonic band edge; and (3) the lasing emission due to both the defect mode and the photonic band edge mode contains both right- and left-circular polarizations, while the lasing emission from a dye-doped single CLC layer with a left-handed helix is left-circularly polarized.     

采用光子晶体的行波管慢波结构高频特性研究

提出了一种采用光子晶体作为行波管慢波结构屏蔽筒的新方案,论证了方案的可行性,并进行了模式分析。在充分研究光子晶体禁带特性的基础上,计算了光子晶体慢波结构的色散特性和耦合阻抗,对计算结果的分析表明,光子晶体在行波管慢波结构中起到了定向选模的作用,为行波管实现高次模式工作奠定了基础。