New insights into Hansen's solubility parameters

Correlations among the three components, δ_d² (dispersion), δ_h² (hydrogen‐bonding), and δ_p² (polar) that make up the Hansen solubility parameter equation, δ_o² = δ_d² + δ_h² + δ_p², have been analyzed for a large number of organic solvents. A relationship is found that enables δ_h and δ_p to be estimated if δ_o and δ_d are known. This relationship is applied to a variety of common polymers and remarkably good agreement is obtained with tabulated values for δ_h and δ_p. Additional correlations are found that can be expressed in approximate functional form. The analysis also reveals relationships, expressed as inequalities, among the parameters that limit their range of possible values. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4337–4343, 2004     

Molecular solubility and hansen solubility parameters for the analysis of phase separation in bulk heterojunctions

Although the fabrication procedures for bulk heterojunction (BHJ) solar cells are routinely optimized to accommodate new organic materials, the influence of solvent properties and cohesive forces on the film‐forming process and the self‐assembly of donor and acceptor molecules on the nanoscale are poorly understood. In this study, we measure the solubility of a variety of organic semiconductors in a range of solvents and calculate cohesive forces including dispersion forces, dipole interactions, and hydrogen bonding via Hansen Solubility Parameters (HSPs). HSPs were calculated by measuring the solubilities of various organic semiconductors in 27 solvents and the influence of solvent identity on film morphology of different BHJ mixtures was explored via atomic force microscopy (AFM). The possibility of correlations between HSPs and film morphology was considered; however, it is apparent that the HSP values alone do not play a critical role in determining the morphology of the films of conjugated polymers and molecules. This collection of solubility data constitutes the first of its type for organic semiconducting materials, and may act as a useful reference for the organic semiconductor community to aid in the understanding and selection of solvents for donor–acceptor BHJ mixtures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Techniques for characterization of charge carrier mobility in organic semiconductors

The charge transport characteristics of organic semiconductors are one of the key attributes that impacts the performance of organic electronic and optoelectronic devices in which they are utilized. For improved performance in organic photovoltaic cells, light-emitting diodes, and field-effect transistors (FETs), efficient transport of the charge carriers within the organic semiconductor is especially critical. Characterization of charge transport in these organic semiconductors is important both from scientific and technological perspectives. In this review, we shall mainly discuss the techniques for measuring the charge carrier mobility and not the theoretical underpinnings of the mechanism of charge transport. Mobility measurements in organic semiconductors and particularly in conjugated polymers, using space-charge-limited current, time of flight, carrier extraction by linearly increasing voltage, double injection, FETs, and impedance spectroscopy are discussed. The relative merits, as well as limitations for each of these techniques are reviewed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Optimization of direct arylation polymerization conditions for the synthesis of poly(3‐hexylthiophene)

Direct arylation polymerization (DArP) is an emerging alternative to Stille and Suzuki polymerizations. This method is attractive as it allows preparation of high‐molecular‐weight conjugated polymers in good yield without the need to metallate monomers. Despite this promise, for poly(3‐hexylthiophene) (P3HT) and related polymers that have β‐protons on the thiophene ring, DArP is known to produce β‐defects, which make the polymer properties different from polymers produced by traditional methods. Here, we demonstrate that DArP conditions based on simple, inexpensive, and bench‐stable reagents can be tuned to limit the amount of defects and produce P3HT with properties remarkably similar to Stille P3HT. Specifically, lowering the reaction temperature, lowering the amount of catalyst, and using a bulkier carboxylate ligand is critical. Optimized conditions include reacting 2‐bromo‐3‐hexylthiophene with 0.25 mol % of Pd(OAc)₂, 1.5 equivalents of K₂CO₃, and 0.3 equivalents of neodecanoic acid in N,N‐dimethylacetamide at 70 °C and give DArP P3HT with ～60% yield, regioregularity of 93.5%, molecular weight of 20 kDa, polydispersity of 2.8, and melting point of 217 °C, providing a very close match to Stille P3HT, which is obtained with 70–80% yield, 91–94% regioregularity, molecular weight of 15–25 kDa, polydispersity of 2.5–2.8, and melting point of 214–221 °C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2660–2668     

Synthesis and characterization of all‐conjugated copolymers of 3‐hexyl‐thiophene and EDOT by grignard metathesis polymerization

Random regioregular copolymers of 3‐hexylthiophene and 3,4‐ethylenedioxythiophene were synthesized by grignard metathesis polymerization. Soluble copolymers were obtained with a high degree of regioregularity and with a monomer ratio close to the feed ratio. A comparison between the optical properties and the thin film morphologies of these copolymers and poly(3‐hexylthiophene) is also presented. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Evaluation of solubility parameters during polymerisation of amine‐cured epoxy resins

A new procedure for the calculation of solubility parameter evolution during polymerisation has been developed for amine‐cured epoxy systems, which allows quantitative thermodynamic modelling of chemically induced phase separation (CIPS). Solubility parameters calculation, chemical analysis based on near infrared spectroscopy and curing kinetics results obtained by differential scanning calorimetry will allow to model the evolution of the Flory–Huggins interaction parameter in amine‐cured epoxy blends. The resin system investigated was based on a diglycidyl ether bisphenol A (DGEBA) epoxy resin cured with isophorone diamine (IPD) blended with various reactive epoxydised dendritic hyperbranched polymer modifiers (HBP), yielding a CIPS‐controlled morphology. The analysis showed the evolution of the different contributions to the solubility parameters to follow the polymerisation kinetics. The dispersive contribution had the highest value at all stages of polymerisation, but the hydrogen and polar contributions showed the largest variation. By evaluating the dynamic evolution of the solubility parameter components, the Flory–Huggins interaction parameter in the epoxy resin‐hyperbranched polymer blends has been modelled as a function of time. This procedure, combined with thermodynamic modelling, will enable to predict phase diagrams in CIPS thermosetting blends quantitatively. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1883–1892, 2000     

Effect of solvent additives on bulk heterojunction morphology of organic photovoltaics and their impact on device performance

Morphology of the active layer in an organic photovoltaic (OPV) device is known to have a significant impact on the device performance. It is, however, difficult to characterize nanoscale morphologies in detail, especially at the ensemble level. Herein, we report the utilization of small angle neutron scattering (SANS) to investigate variations in the nanoscale morphologies of the active layer of poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction OPV depending on the composition of casting solvent. Both the power law and the poly hard sphere model were utilized to characterize the state of the donor and acceptor components, respectively, from the obtained SANS data. Furthermore, the relationship between the nanoscale morphology and device performance is outlined. It was found that the use of 2-chlorophenol, a poor solvent for P3HT and, at the same time, a very good solvent for PCBM, leads to nanomorphology featuring ordered, highly crystalline P3HT and small (15.2 nm) PCBM domains. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 128–134     

Thermal stability of P3HT and P3HT:PCBM blends in the molten state

The thermal stability of poly(3-hexylthiophene) (P3HT) in its molten state was investigated in air and nitrogen atmospheres under no illumination conditions, with the aim of testing the feasibility of processing it using polymer melt techniques. A large set of different experimental characterization techniques was used including thermogravimetric analysis (TGA), rotational rheometry, infrared spectroscopy (FTIR-ATR), proton nuclear magnetic resonance spectroscopy (¹H-NMR), gel permeation chromatography (GPC), UV-Vis and fluorescence spectroscopy. The results obtained strongly suggest that the processing of P3HT in its molten state is possible, without noticeable degradation, if carried out under nitrogen atmosphere and if the processing (residence) times are relatively short. Conversely, as expected, in a normal air atmosphere P3HT degrades rapidly at temperatures above its melting point. The effect of PCBM on the thermal stability of P3HT:PCBM blends in the molten state was also studied using TGA, and in air atmosphere PCBM is shown to delay oxidation.     

Increasing the Open‐Circuit Voltage in High‐Performance Organic Photovoltaic Devices through Conformational Twisting of an Indacenodithiophene‐Based Conjugated Polymer

A fused ladder indacenodithiophene (IDT)‐based donor–acceptor (D–A)‐type alternating conjugated polymer, PIDTHT‐BT, presenting n‐hexylthiophene conjugated side chains is prepared. By extending the degree of intramolecular repulsion through the conjugated side chain moieties, an energy level for the highest occupied molecular orbital (HOMO) of –5.46 eV – a value approximately 0.27 eV lower than that of its counterpart PIDTDT‐BT – is obtained, subsequently providing a fabricated solar cell with a high open‐circuit voltage of approximately 0.947 V. The hole mobility (determined using the space charge‐limited current model) in a blend film containing 20 wt% PIDTHT‐BT) and 80 wt% [6,6]‐phenyl‐C₇₁ butyric acid methyl ester (PC₇₁BM) is 2.2 × 10^–9 m² V^–1 s^–1, which is within the range of reasonable values for applications in organic photovoltaics. The power conversion efficiency is 4.5% under simulated solar illumination (AM 1.5G, 100 mW cm^–2).

     

Novel enhanced applications of QSPR models: Temperature dependence of aqueous solubility

A model developed to predict aqueous solubility at different temperatures has been proposed based on quantitative structure–property relationships (QSPR) methodology. The prediction consists of two steps. The first one predicts the value of k parameter in the linear equation , where S_w is the value of solubility and T is the value of temperature. The second step uses Random Forest technique to create high‐efficiency QSPR model. The performance of the model is assessed using cross‐validation and external test set prediction. Predictive capacity of developed model is compared with COSMO‐RS approximation, which has quantum chemical and thermodynamic foundations. The comparison shows slightly better prediction ability for the QSPR model presented in this publication. © 2016 Wiley Periodicals, Inc.     

Microstructural behavior and failure mechanisms of organic semicrystalline thin film blends

Organic thin film blends of P3HT semiconducting polymers and PCBM fullerenes have enabled large‐scale semiconductor fabrication pertaining to flexible and stretchable electronics. However, molecular packing and film morphologies can significantly alter mechanical stability and failure behavior. To further understand and identify the fundamental mechanisms affecting failure, a multiphase microstructurally based formulation and nonlinear finite‐element fracture methodology were used to investigate the heterogeneous deformation and failure modes of organic semicrystalline thin film blends. The multiphase formulation accounts for the crystalline and amorphous behavior, polymer tie‐chains, and the PCBM aggregates. Face‐on packing orientations resulted in extensive inelastic deformation and crystalline rotation, and this was characterized by ductile failure modes and interfacial delamination. For edge‐on packing orientations, brittle failure modes and film cracking were due to lower inelastic deformation and higher film stress in comparison with the face‐on orientations. The higher crystallinity of P3HT and larger PCBM aggregates associated with larger domain sizes, strengthened the film and resulted in extensive film cracking. These predictions of ductile and brittle failure are consistent with experimental observations for P3HT:PCBM films. The proposed predictive framework can be used to improve organic film ductility and strength through the control of molecular packing orientations and microstructural mechanisms. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 896–907     

Monte Carlo morphological modelling of a P3HT:PCBM bulk heterojunction organic solar cell

To deepen the understanding of morphology evolution in bulk heterojunction P3HT:PCBM organic photovoltaics system by thermal treatment, domain‐size‐dependent interfacial energies were first determined by coarse‐grained molecular dynamics modelling and then used in Monte Carlo simulations of the morphology evolution. Thereby initial conditions associated with optimal interfacial surface area, continuous volume, as well as domain sizes, and spatial distributions of the phase separated domains were identified. In line with earlier studies, a 1:1 P3HT:PCBM blend ratio is found to exhibit the most efficient morphology for exciton dissociation and charge transport. Our simulations reveal that preseeding of P3HT crystal at the anode side prior to the annealing process will be instrumental to pin the formation of P3HT at the favorable electrode especially when seeding exceeds a threshold of 10% surface coverage, whereas denser seeding patterns beyond the threshold did not improve the active layer morphology further. The observed trilayer depth profile (in the absence of preseeded P3HT crystals) implies that the commonly used thickness 100 nm of the active layer is not ideal for ensuring that donor and acceptor phases dominate at opposite ends of the active layer. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 270–279     

Fast annealing and patterning of polymer solar cells by means of vapor printing

The viability of vapor printing as a fast annealing treatment for the processing of polymer solar cells is demonstrated. In this method, a carrier gas transporting vapor solvent is delivered through a nozzle promoting self‐assembly of polymer chains. Devices based on poly(3‐hexylthiophene) blended with soluble fullerene are locally exposed during different annealing times to chlorobenzene vapor in a nitrogen flow. This enables finding an optimal nanostructure in promisingly short time‐scales (<5 s of exposure to vapor solvent), which yields a twofold increase in efficiency with respect to as‐cast samples. Moreover, a combined Raman, photometric, and ellipsometric characterization allows to understand why overexposure to vapor solvent reduces the performance. Finally, toluene and 1,2,3,4‐tetrahydronaphthalene are also tested using this method, showing different printing efficiencies corresponding to their specific vapor pressures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

喷涂法制备大面积倒置聚合物光伏器件

采用喷涂工艺制备了结构为ITO/ZnO/P3HT∶PCBM/V2O5/Ag(P3HT:聚噻吩;PCBM:6,6-苯基-C61-丁酸甲酯)的大面积倒置光伏器件,有效面积为1.0×1.1 cm2。 光谱测试结果表明,退火处理后,P3HT∶PCBM薄膜吸收显著增强,并且产生一定程度的红移。 采用ZnO和V2O5代替LiF和PEDOT∶PSS(聚(3,4-乙撑二氧噻吩)∶聚苯乙烯磺酸盐)作为器件修饰层,避免了PEDOT∶PSS对ITO的腐蚀和LiF潮解,采用Ag代替Al作为金属背电极避免了Al被氧化。 经过后退火处理器件的效率从1.1%提升至1.65%。 器件的稳定性相对于传统结构有了大幅提升,8周后器件效率只衰减10%。     

Correlation of charge transport with structural order in highly ordered melt‐crystallized poly(3‐hexylthiophene) thin films

A series of well‐defined poly(3‐hexylthiophene)s (P3HT) of different molecular weight (MW) and high regioregularity was investigated for charge transport properties in as‐cast and melt‐crystallized films. The semicrystalline structure of the P3HT was characterized by X‐ray scattering and Atomic force microscopy. Crystallization by cooling from the melt led to a substantial increase in crystallinity and a stronger alignment of the crystals in comparison to as‐cast films. The increase in crystallinity went along with an increase in hole mobility of up to an order of magnitude as measured by the space charge limited current method. Additionally, the hole mobility depended on the long period of P3HT lamellae and consequently on the MW. In compliance with the long period, the charge carrier mobility first increased with the MW before decreasing again at the onset of chain folding. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 943–951     

不同有机溶剂中C~6~0溶解度与温度的关系

本文测定了温度280K以上C~6~0在一些有机溶剂中的溶解度与温度的依赖关系,发出280K以上C~6~0在正己烷、甲苯、二甲苯中溶解度随温度上升而减小, 表现出放热的溶解过程。与此相反, 在环己烷中C~6~0的溶解度却有所不同, 随着温度的升高而增大, 表现出吸热的溶解过程。     

反相气相色谱法测定高密度聚乙烯溶解度参数

采用反相气相色谱(IGC)技术测定了高密度聚乙烯(HDPE)在303.15～343.15 K温度范围内的溶解度参数(δ2)及相关指标。以正己烷(n-C6)、正庚烷(n-C7)、正辛烷(n-C8)、正壬烷(n-C9)、三氯甲烷(CHCl3)及乙酸乙酯(EtAc)作为探针分子溶剂,经计算获得了探针溶剂的比保留体积(V0g)、摩尔吸收焓(ΔHS1)、无限稀释摩尔混合焓(ΔH∞l)、摩尔蒸发焓(ΔHv)、无限稀释活度系数(Ω∞1)以及探针溶剂与HDPE的Flory-Huggins相互作用参数(χ∞1,2)等指标。结果表明,上述6种探针溶剂在测定温度范围内均为HDPE的不良溶剂。此外,还推导出了HDPE在室温(298.15 K)下的溶解度参数δ2为19.00 (J/cm3)0.5。