Toward high-performance polymer solar cells: The importance of morphology control

Polymer solar cells have the potential to become a major electrical power generating tool in the 21st century. R&D endeavors are focusing on continuous roll-to-roll printing of polymeric or organic compounds from solution-like newspapers-to produce flexible and lightweight devices at low cost. It is recognized, though, that besides the functional properties of the compounds the organization of structures on the nanometer level-forced and controlled mainly by the processing conditions applied-determines the performance of state-of-the-art polymer solar cells. In such devices the photoactive layer is composed of at least two functional materials that form nanoscale interpenetrating phases with specific functionalities, a so-called bulk heterojunction. In this perspective article, our current knowledge on the main factors determining the morphology formation and evolution is introduced, and gaps of our understanding on nanoscale structure-property relations in the field of high-performance polymer solar cells are addressed. Finally, promising routes toward formation of tailored morphologies are presented.

Sugars-grafted aliphatic biodegradable poly(L-lactide-co-carbonate)s by click reaction and their specific interaction with lectin molecules

A novel biodegradable aliphatic poly(L-lactide-co-carbonate) bearing pendant acetylene groups was successfully prepared by ring-opening copolymerization of L-lactide (LA) with 5-methyl-5-propargyloxycarbonyl-1,3-dioxan-2-one (PC) in the presence of benzyl alcohol as initiator with ZnEt2 as catalyst in bulk at 100 degrees C and subsequently used for grafting 2-azidoethyl beta-D-glucopyranoside and 2-azidoethyl beta-lactoside by the typical "click reaction," that is Cu(I)-catalyzed cycloaddition of azide and alkyne. The density of acetylene groups in the copolymer can be tailored by the molar ratio of PC to LA during the copolymerization. The aliphatic copolymers grafted with sugars showed low cytotoxicity to L929 cells, improved hydrophilic properties and specific recognition and binding ability with lectins, that is Concanavalin A (Con A) and Ricinus communis agglutinin (RCA). Therefore, this kind of sugar-grafted copolymer could be a good candidate in variety of biomedical applications.

Formation and photoluminescence of silver nanoparticles stabilized by a two-armed polymer with a crown ether core

Silver nanoparticles were synthesized by the use of a two-armed polymer with a crown ether core [poly(styrene)]-dibenzo-18-crown-6-[poly(styrene)] based on the flexibility of the polymer chains and the complex effect of crown ether with Ag+ and Ag. The size of silver nanoparticles could be tailored by controlling the initial concentrations of the polymer and Ag+, and the molecular weight of the polymer. The emission of silver nanoparticles was blue-shifted, and the intensity of the photoluminescence of silver nanoparticles stabilized by the polymer was significantly increased due to the complex effect between the crown ether embedded in the polymer and the silver nanoparticles.

Composition dependence of the crystallization behavior and morphology of the poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior and morphology of the crystalline-crystalline poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer (PEO-b-PCL) was studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and hot-stage polarized optical microscope (POM). The mutual effects between the PEO and PCL blocks were significant, leading to the obvious composition dependence of the crystallization behavior and morphology of PEO-b-PCL. In this study, the PEO block length was fixed (M-n = 5000) and the weight ratio of PCL/PEO was tailored by changing the PCL block length. Both blocks could crystallize in PEO-b-PCL with the PCL weight fraction (WFPCL) of 0.23-0.87. For the sample with the WFPCL of 0.36 or less, the PEO block crystallized first, resulting in the obvious confinement of the PCL block and vice versa for the sample with WFPCL of 0.43 or more. With increasing WFPCL, the crystallinity of PEO reduced continuously while the variation of the PCL crystallinity exhibited a maximum. The long period of PEO-b-PCL increased with increasing WFPCL from 0.16 to 0.50 but then decreased with the further increase of WFPCL due to the interaction of the respective variation of the thicknesses of the PEO and PCL crystalline lamellae.

Fabrication and photoluminescence properties of core-shell structured spherical SiO2@Gd2Ti2O7 : Eu3+ phosphors

A sol-gel technique was used to prepare Gd2Ti2O7:Eu3+-coated submicron silica spheres (SiO2@Gd2Ti2O7:Eu3+). The resulted SiO2@Gd2Ti2O7:Eu3+ core-shell particles were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive x-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, as well as kinetic decays. The XRD results demonstrate that the Gd2Ti2O7:Eu3+ layers begin to crystallize on the SiO2 spheres after annealing at 800 degrees C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size similar to 620 nm), non-agglomeration, and smooth surface. The thickness of the Gd2Ti2O7:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (60 nm for four deposition cycles). Under the irradiation of 310 nm ultraviolet, the SiO2@GdTi2O7:Eu3+ samples show strong emission of Eu3+.

Sol-gel growth of Gd2MoO6 : Eu3+ nanocrystalline layers on SiO2 spheres (SiO2@Gd2MoO6 : Eu3+) and their luminescent properties

SiO2@Gd2MoO6:EU3+ core-shell phosphors were prepared by the sol-gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy ITEM), photoluminescence (PL) spectra as well as kinetic decays were used to characterize the resulting SiO2@Gd2MoO6:Eu3+ core-shell phosphors. The XRD results demonstrate that the Gd2MoO6:Eu3+ layers on the SiO2 spheres begin to crystallize after annealing at 600 degrees C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have a near perfect spherical shape with narrow size distribution (average size ca. 600 nm), are not agglomerated, and have a smooth surface. The thickness of the Gd2MoO6:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). The Eu3+ shows a strong PL luminescence (dominated by D-5(0)-F-7(2) red emission at 613 nm) under the excitation of 307 nm UV light.

Fabrication and optical properties of core-shell structured spherical SiO2@GdVO4 : Eu3+ phosphor via sol-gel process

Europium-doped nanocrystalline GdVO4 phosphor layers were coated on the surface of preformed submicron silica spheres by sol-gel method. The resulted SiO2@Gd0.95Eu0.05VO4 core-shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, low voltage cathodoluminescence (CL), time resolved PL spectra and kinetic decays. The XRD results demonstrate that the Gd0.95Eu0.05VO4 layers begin to crystallize on the SiO2 spheres after annealing at 600 C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have spherical shape, narrow size distribution (average size ca. 600 nm), non-agglomeration. The thickness of the Gd0.95Eu0.05VO4 shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). PL and CL show that the emissions are dominated by D-5(0)-F-7(2) transition of Eu3+ (618 nm, red).

Morphology and structures of self-assembled symmetric poly(di-n-alkylsilanes)

The self-assembly of poly(di-n-butylsilane) (PDBS) and poly(di-n-hexylsilane) (PDHS) on the surfaces of amorphous carbon and highly oriented pyrolytic graphite (HOPG) have been investigated, respectively. The morphology and structures of these self-assembled thin films were studied by using atomic force microscopy, transmission electronic microscopy, and wide-angle X-ray diffraction. In the case of weak van der Waals interactions between absorbed molecules and substrate, i.e., on amorphous carbon, the self-assembly process was driven by absorbate-absorbate intermolecular interactions. For PDBS with weak absorbate-absorbate intermolecular interactions, the thin film showed organization lacking any measurable preferred orientation on the surface of amorphous carbon. While for PDHS with rigid backbone and strong intermolecular interactions, flat-on lamellae with silicon backbones perpendicular to the surface of amorphous carbon were formed. However, in the case of strong van der Waals interactions between absorbed molecules and substrate, i.e., on HOPG, the self-assembly process was tailored by the balance of absorbate-absorbate intermolecular interactions and molecule-substrate interactions. Both PDHS and PDBS thin films grew into edge-on lamellae on the surface of HOPG, which aligned according to a Mold symmetry.

Electrochemical Synthesis of Barium Tungstate Crystallites with Different Morphologies: Effect of Electrolyte Components

Barium tungstate crystallites with different sizes and morphologies were successfully synthesized using a simple electro-chemical technique by varying the components of electrolyte solutions. XRD analysis evidenced that the as-prepared samples were a pure tetragonal-phase of BaWO4 with a scheelite structure. Scanning electron microscopy images and PL spectra of BaWO4 crystallites revealed that the presence of OH- ions and the incorporation of absolute ethanol into the electrolyte solution would have important effects on their particle sizes, morphologies, and optical properties.

激光拼焊生产线定位误差分析及其控制

对激光拼焊生产线板材定位精度进行了分析与研究。详细介绍了该系统定位装置的组成及定位原理。通过对板材自身直线度误差、定位销定位误差和对中运动误差的分析,建立了激光拼焊生产线板材定位误差模型。根据系统定位机构特点提出了过盈量作用机制来提高定位精度,通过对前后侧压紧力F1、F2以及过盈量I这3个主要参数的优化,在全自动激光拼焊生产线上实现良好的板材定位精度。对比试验验证了采用过盈量作用机制能有效减小板材定位误差,提高焊接质量。

激光拼焊错边产生与预测建模方法

错边是评定激光拼焊质量的一个非常重要的指标,薄板构件错边的控制是激光拼焊中一个难题。针对国内首条全自动激光拼焊设备,对错边的产生以及控制方法进行了深入研究,经过大量试验确定了影响错边大小的几个主要因素,板材自身物理变形、压紧力大小与均匀性、压紧横梁变形、支撑底板平面度误差以及焊接变形的影响。通过分析以上因素对错边的影响以及各个因素之间相互关系,建立了错边预测的数学模型。试验验证了模型的正确性,从而为确定错边产生原因,提高焊接质量提供了一个有效的理论指导。

一种快速获取激光拼焊焊缝错配的新算法

本文讨论了基于视觉和结构光的焊缝形貌视觉检测系统的组成原理,针对拼板激光焊接工程中对焊缝检测的实时性要求高的特点,创新性地提出了一种快速获得焊缝错配缺陷的算法,主要步骤为:首先基于有关标准的检测指标阈值的设定,再次,针对在线提取到的图像进行预处理,主要是加窗和中值滤波;最后为Radon变换与错配检测。该算法能减少计算任务,从而快速获得错配检测指标。实验给出了不等厚板拼焊时的线性错配的数值和分布,同时验证了该算法的有效性。

PLC在长焊缝激光拼焊系统中的应用

介绍了长焊缝激光拼焊系统的工作原理和控制要求。针对长焊缝激光拼焊的难点,提出了焊缝塑性成形原理,采用碾压轮对板材焊缝进行碾压预处理提高定位精度。阐述了牵引电机同步控制原理和碾压轮力控制原理。详细介绍了该系统的组成和工作原理,确定了以三菱PLC为核心的长焊缝激光拼焊的控制系统,说明了其硬件组成、软件设计和控制系统的抗干扰措施。

基于PLC的激光拼焊生产线控制系统设计

本文介绍了基于PLC的激光拼焊生产线控制系统。分析了激光拼焊生产工艺过程,针对激光拼焊生产过程中多工作单元相互协调和工业过程复杂等特点,开发了基于三菱PLC的控制系统,介绍了系统的软硬件设计方法。该系统能够完成上料、定位、压紧、焊接、检测、下料以及废料处理功能,实现了激光拼焊生产线的全自动化,具有较高的安全性和稳定性。

基于三坐标测量机激光拼焊板材直线度研究

利用高精度三坐标测量机扫描功能,充分获得焊接板材端面线性三维数据坐标值,采用基于最小二乘法而建立的理想直线数学模型来评定直线度误差,并与实际采用塞尺法进行对比,结果发现采用三坐标测量更能详尽地反应整个焊接边缘直线度真实情况,节省大量的数据处理时间,且数据更加准确可靠,并在实际激光焊接中获得良好激光焊缝,同时直观地给出了焊接板材边缘线性特征,为剪板机刀具调整提供了方向与位置。