Hybrid organic on inorganic semiconductor heterojunction

Hybrid organic on inorganic semiconductor heterojunctions with a sandwich structure have been fabricated and studied using conjugated polymers. The inorganic semiconductor was n-type silicon substrate. The conjugated polymers used include poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) containing polyhedral oligomeric silsesquioxanes (MEH-PPV POSS), regioregular poly(3-hexylthiophene) (RR-P3HT) and poly(3,4-ethylenedioxythiophene) (PEDOT). Current density–voltage and capacitance–voltage measurements were performed. All of the devices displayed a rectifying characteristic. Among these devices, the first ever reported PEDOT doped with BF₃ on n-Si heterojunction devices showed the best performance with a rectification ratio around 5.7 × 10⁵ at ± 2 V and an ideality factor of 2.3. The results showed better device performance with decreased potential barrier height at the organic–inorganic interface. Results also suggested that smaller energy level offset between the HOMO of the conjugated polymer and the work function of anode metal will improve device performance.     

Synthesis, characterization, and electrical properties of regioregular alkyl-substituted PEDOTt

The regioregular hexyl-substituted poly(3,4-ethylenedioxy-2-thiophenylthiophene) (PEDOTt), structurally alternating copolymer of EDOT and thiophene, was synthesized via the Grignard Metathesis (GRIM) using catalytic amounts of Ni(dppp)Cl2. The products were characterized by 1H NMR spectroscopy, UV-vis spectroscopy and XRD. The alkyl-substituted conjugated polymer showed an enhancement of solubility in common organic solvents. Based on XRD data, the regioregular hexyl-substituted poly(3,4-ethylenedioxy-2-thiophenylthiophene) (PEDOTt) shows better crystallinity than the regiorandom hexyl-substituted PEDOTt owing to self-ordering. In addition, regioregular hexyl-PEDOTt has a conductivity of 0.788 S/cm by iodine doping.     

Electrorheological properties and creep behavior of polyindole/poly(vinyl acetate) composite suspensions

In this study, electrorheological (ER) properties of polyindole (PIN) and polyindole/poly (vinyl acetate), (PIN/PVAc) conducting composites having different compositions were investigated. Conductivities and dielectric properties of these composites were determined. The particle sizes of the composites were determined by dynamic light scattering method. Suspensions of PIN and PIN/PVAc composites were prepared in silicone oil, at several concentrations (c = 5–25%, m/m) and their sedimentation stabilities were determined. Then the effects of dispersed particle concentration, shear rate, electric field strength, frequency, and temperature onto ER activities of suspensions were investigated. The flow times of these suspensions at various dc electric field strengths were measured. Further, creep tests were applied to the composite suspensions and a reversible viscoelastic deformation was observed.     

Synthesis and properties of diblock copolymers containing poly(3-hexylthiophene) and poly(fluorooctyl methacrylate)

This study reports the synthesis of regioregular poly(3-hexylthiophene)-b-poly(1H,1H-dihydro perfluorooctyl methacrylate) (P3HT-b-PFOMA) block copolymers by atom transfer radical polymerization of FOMA using P3HT macroinitiators. The P3HT macroinitiator was previously prepared by chemical modification of hydroxy terminated P3HT The block copolymers were characterized by 1H-NMR, 13C-NMR, GPC, DSC, TGA and TEM. The block copolymers are able to self-assemble into phase separated micellar thin film morphology from chloroform.     

合成方法对聚(3-己基噻吩)立构规整度的影响

采用化学氧化法、格式反应法、GRIM (Grignard Metathesis Method)法和超声辅助GRIM法、合成了不同立构规整度的聚3-己基噻吩(P3HT).用GPC、紫外-可见光谱、红外光谱(FT-IR)和核磁共振谱(1 H-NMR)对P3HT的分子结构和立构规整度进行了表征.结果表明,GRIM法合成的P3...     

Fourier transform photocurrent spectroscopy applied to a broad variety of electronically active thin films (silicon, carbon, organics)

Steady state and low frequency photocurrent spectroscopies have proved as a valuable tool for investigation of many different semiconductors, used for example as an absorber in photovoltaic solar cells or in the large area sensors. Fourier transform photocurrent spectroscopy (FTPS), described here, exhibits advantages as a high sensitivity (we demonstrate dynamical range up to 9 orders of magnitude of the optical absorption coefficient, connected with the absorption process leading to free carriers; or sensitivity for dopant detection better than 1 part-per-billion), fast acquisition of data (it can be of the order of seconds) or high resolution (under more lengthy acquisition of data). Results on amorphous silicon, microcrystalline silicon, diamond layers, nanocrystalline diamond and very thin organic films, as poly(2-methoxy-5-(3′,7′-dimethyl-octyloxy))-p-phenylene-vinylene (MDMO-PPV), regioregular poly(3-hexylthiophene (P3HT) and their blends with (6,6)-phenyl-C61-butyric-acid (PCBM) are reported, together with the results measured on various thin film silicon or polymer solar cells.     

Investigation of P3HT/n-Si heterojunction using surface photovoltage spectroscopy

Surface photovoltage spectroscopy (SPS) was used to investigate the interactions of the interface between regioregular poly(3-hexylthiophene) (P3HT) and n-type single crystalline silicon. The SPS responses of silicon and the P3HT/n-Si heterojunction caused by band to band transition of silicon are 30 mV and 160 mV respectively. The band-bending in the silicon side of the P3HT/n-Si structure is larger than that of bare n-Si. The density of the interface states of the P3HT/n-Si heterojunction increased significantly after the deposition of P3HT. Based on the contact potential difference (CPD) transient results, charge transport and separation processes are fast in the silicon substrate and slow in the P3HT layer respectively.     

新型聚2,4-二乙烯基3-十二烷基噻吩-1,3,4-噁二唑交替共聚物的合成、表征及性能研究

采用Heck偶合法首次合成了新型的含有空穴传输单元3-十二烷基噻吩和电子传输单元1,3,4-噁二唑的低带隙能的聚2,4-二乙烯基-3-十二烷基噻吩-1,3,4-噁二唑共轭聚合物(P3DDTV-OXD).并且通过1H-NMR、FT-IR、凝胶色谱(GPC)、UV-vis光谱、荧光光谱(PL)、循环伏安(CV)法对所合成的共聚物进行了分析表征.与规整的聚3-十二烷基噻吩均聚物(P3DDT)相比,共聚物的UV最大吸收波长和Pl最大发射波长明显蓝移,具有强烈的蓝色荧光,且电子亲和势较高,同时拥有空穴和电子传输能力,实现了电荷在分子内的双向传输.     

Time-temperature superposition and the controlling role of solvation in the viscoelastic properties of polyaniline thin films

Comprehensive exploration of the viscoelastic properties of polyaniline films exposed to aqueous perchloric acid has been made as a function of applied potential (E), temperature (T), and mechanical oscillation frequency (f = ω/2π) using high-frequency acoustic wave resonators. The outcomes are expressed in terms of storage and loss shear modulus signatures, G'(E, T, ω) and G″(E, T, ω). Surprisingly, these are barely sensitive to potential, through which both polymer charge and solvation are manipulated, and only modestly sensitive to temperature. In contrast, the response to timescale is dramatic. Using the principle of time-temperature superposition, G' and G″ at different temperatures and frequencies (time scales) can each be placed on master relaxation curves. Models developed for mechanical properties of bulk polymers at low frequency were applied to these thin film responses at high frequency. These include the Williams-Landel-Ferry model, the activation model, and the Rouse-Zimm model based, respectively, on concepts of free volume, thermal activation, and relaxation. Each of the models could be applied with physically reasonable outcomes in terms of the relevant parameters (thermal expansion coefficient, glass transition temperature, and activation enthalpy). G' and G″ values are correlated with solvent content. The enthalpy change for solvent entry is small, positive and relatively independent of polymer charge state, all of which contrast sharply with the behavior of thiophene-based conducting polymers in organic solvents.     

SnO2掺杂对BMN陶瓷结构及介电性能的影响

采用固相烧结法制备Ba(Mg_(1/3)Nb_(2/3))O_3+x(x=0~8)%SnO_2(BMSN,x为质量分数)微波介质陶瓷,并研究SnO_2掺杂对Ba(Mg_(1/3)Nb_(2/3))O_3(BMN)微波介质陶瓷结构及介电性能的影响。XRD分析表明,陶瓷体系中存在两种相,主晶相Ba(Mg_(1/3)-Nb_(2/3))O_3和附加相Ba_5Nb_4O_(15)。随着x的增大,BMSN陶瓷体系的相结构逐渐由钙钛矿六方结构转变为立方结构,同时有序相逐渐由1∶2有序结构转变为1∶1有序结构。研究表明:添加适量的SnO_2可以促进液相烧结,当SnO_2掺杂质量分数为6%时,BMN陶瓷致密化烧结温度由纯相时的1 550℃以上降低至1 200℃,表观密度ρ=6.39g/cm3,相对理论密度为99.1%,此时BMSN陶瓷体系拥有优良的微波介电性能——高相对介电常数(ε_r=33.6),接近于零的谐振频率温度系数(τ_f=0.15×10~(-6)℃~(-1)),高品质因数与谐振频率的乘积(Q·f=112 300GHz(8GHz))。     

Transient photovoltage in poly(3-hexylthiophene)/n-crystalline-silicon heterojunction

Transient photovoltage (PV) phenomena in regioregular poly(3-hexylthiophene) (P3HT)/n-crystalline-silicon (n-Si) heterojunction are studied under pulsed laser illumination. The PV transients of P3HT/n-Si heterojunctions are strongly retarded in time up to about 3 μs. The PV transients of P3HT/n-Si heterojunctions with thinner P3HT layer convert from positive to negative at longer times, which is caused by the long release time of trapped electrons at the P3HT/n-Si interface. Moreover, we find that the response of transient PV is dependent on the thickness of P3HT layer, the temperature and the excitation level.     

Viscoelastic properties of low-viscosity liquids studied with thickness-shear mode resonators

The network analysis method was applied to AT cut quartz blanks (f(0) = 10 MHz), which were loaded with liquids of low and medium viscosity (water, methanol, ethanol, 1-propanol, 1-butanol, glycerol solutions). The shift of the resonance frequency Δf could be separated into a term due to rigidly coupled mass Δf(rig) and a term due to viscous damping Δf - Δf(rig). From the difference Δf - Δf(rig) and the broadening of the resonance curve, the complex shear modulus G = G' + iωη(L) was calculated. The viscosity coefficients η(L) are in good agreement with literature data. As G' > 0, it can be concluded that the examined fluids also reveal elasticity at shear frequencies in the MHz range. For the low-viscosity liquids, elastic contributions resulting from collective interactions of molecules are measurable but small and neglectable in most applications. The medium viscous liquid glycerol (98%) begins to exhibit considerable elasticity, resulting from the relaxation of separate molecules.     

Pressing effect in polymer solar cells with bulk heterojunction nanolayers

We report the effect of pressing light-absorbing layers on the performance of polymer solar cells. The light-absorbing active layer was prepared on the transparent conducting oxide coated substrates from solutions that contain a mixture of regioregular poly(3-hexylthiophene) and soluble fullerene molecules. The active layers were pressed using a home-built micro-press system by controlling temperature and pressure, followed by the top electrode deposition. The surface of the active layers pressed was examined using atomic force microscope, while the photovoltaic characteristics of devices were measured under simulated solar light illumination (air mass 1.5 G, 100 mW/cm2). Results showed that the dark current of devices was noticeably increased by pressing the active layer without respect to the pressing temperature. The highest power conversion efficiency was achieved for the device with the active layer pressed under 10 kgf at 70 degrees C. The result was explained in terms of surface morphology and thermophysical effect.     

Properties of transverse ultrasonic transducers of ferroelectricpolymers working in thickness shear modes

Shear piezoelectric properties of poly(vinylidene fluoride) (PVDF) and copolymer of vinylidene fluoride and trifluoroethylene [P(VDF/TrFE)] have been studied precisely in a wide temperature range from 10 to 400 K. It was found that these polymers have the shear electromechanical coupling factors k₁₅ and k₂₄ large enough to be utilized for transverse ultrasonic transducers operating in a wide frequency range and in a wide temperature range below 400 K. Shear mode ultrasonic transducers of P(VDF/TrFE) were fabricated and their performances were studied both experimentally and theoretically. The shear polymer transducers are useful for generation and detection of transverse ultrasonic waves     

Effect of film and device annealing in polymer:polymer solar cells with a LiF nanolayer

We report the effect of thermal annealing on the performance of polymer:polymer solar cells with a lithium fluoride (LiF) nanolayer inserted between active layer and electron-collecting electrode. The active layer was prepared using blend films of regioregular poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). Film annealing and device annealing were separately performed at 150 °C for 30 min to understand the influence of the existence of LiF nanolayer during thermal annealing. Results showed that both film and device annealing did considerably improve the power conversion efficiency (PCE) of P3HT:F8BT solar cells though the PCE was higher in the case of device annealing. The surface analysis suggested that the improved device performance by thermal annealing is attributed partly to the formation of planar p-n junction structure in the P3HT:F8BT blend film during thermal annealing.     

Static and dynamic mechanical properties of poly(vinyl chloride) loaded with aluminum oxide nanopowder

A series of nanocomposites from poly(vinyl chloride) loaded with different concentrations of Al₂O₃ nanopowder was prepared. The tensile mechanical properties of these composites were studied at different temperatures namely; stress–strain curves. The elastic modulus was calculated and found to decrease with increasing both filler loading and temperature. The strain at a certain stress at different temperatures was studied and the thermal activation energy for polymer chains was calculated. The complex viscosity as well as the storage modulus was found to decrease with increasing the filler loadings at different frequencies. The relaxation time of the polymer matrix was calculated and found to independent on the concentration of the filler but it decreased linearly with increasing frequency. The glass transition temperature was found to increase with increasing both filler loading and frequency.     

Novel regioregular polythiophenes containing side-chain porphyrin groups for polymeric photovoltaic cells

The paper presents a new strategy for the preparation of porphyrin-functionalized head-to-tail regioregular thiophene copolymers using a simple and effective post polymerization functionalization (PPF) procedure based on the synthesis of a regioregular and soluble polythiophene precursor followed by subsequent reaction with a suitably functionalized porphyrin derivative. Thus, thiophene copolymers poly[3-(6-bromohexyl)thiophene-co-(3-[5-(4-phenoxy)-10,15,20-triphenylporphyrinyl] hexylthiophene)]s at different porphyrin chromophore contents were prepared, obtaining, in all cases, very soluble and easily filmable derivatives. Their thermal, optical and electrochemical properties were determined and their performances as the active layer in bulk heterojunction solar cells tested.     

Long-term soft tissue reaction to various polylactides and their in vivo degradation

Cylindrical pins made from poly(L-lactide), poly(L/D-lactide) 95/5% and poly(L/DL-lactide) 95/5% were implanted in the subcutaneous tissue of sheep. The tissue reaction to the implanted materials and their in vivo degradation was investigated at 1,3,6 and 12 months. The capsule formed around the polylactide implants consisted of fibroblasts, fibrocytes, phagocytes, a few foreign body giant cells and polymorphonuclear cells. For all three polylactides used, the cellular response was most intensive during the first 6 months of implantation and significantly subsided at 1 year. The thickness of the capsule was 200 m at 1 month, increased to 200–600 m at 6 months, and decreased to 100 to 200 m at 1 year, depending on the material used. The tissue reaction was more intense for poly(L/D-lactide) than for poly(L/DL-lactide) and poly(L-lactide). The drop in molecular weight of the implants was highest after 1 month of implantation (70 to 95%). Irrespective of the extensive reduction of the molecular weight at 1 month, none of the polymers used was completely resorbed at 1 year. The most advanced resorption was observed for poly(L/D-lactide). Despite molecular weight reduction, the poly(L-lactide) implants had maintained 70% of their initial bending strength and 95% of their shear strength at 3 months. The poly (L/D-lactide) and poly(L/DL-lactide) had maintained only 26 to 27% of their initial bending strength and 26 to 31% of the initial shear strength, respectively. The crystallinity of all the materials increased after implantation as compared with nonimplanted materials. The overall crystallinity increase and the final crystallinity reached by the materials at 1 year was, however, lowest for poly(L/DL-lactide) as compared with the other two polylactides.     

Control of self organization in conjugated polymer fibers

We propose new strategy to facilitate the fabrication of conjugated polymer fiber with higher oriented structures, which focused on electrospinning of a blend solution of regioregular poly(3-hexylthiophene) (rr-P3HT) and poly(vinyl pyrrolidone) (PVP). SEM observation revealed that the blend system forms homogeneous composite nanofibers. This system exhibits the specific feature of strong interchain contribution of P3HT from UV-vis absorption, fluorescence spectroscopic, XRD, and photoelectron spectrometric (for HOMO levels) investigations. We also demonstrate the removal of the PVP component from the P3HT/PVP composite fibers through the selective extraction and such strong interchain stacking of pristine P3HT fiber mat can be remarkably maintained.     

Evaluation of molecular orientation and alignment of poly(3-hexylthiophene) on Au (111) and on poly(4-vinylphenol) surfaces

The orientation and alignment of regioregular poly(3-hexylthiophene) (P3HT) molecules on Au (111) surface and on poly(4-vinylphenol) (PVP) thin film were investigated. The P3HT molecules on the smooth Au (111) are oriented with both the backbones and the side chains parallel to the substrate (plane-on orientation) as revealed by the scanning tunneling microscope (STM) images. However, the P3HT molecules on the PVP thin films are preferably oriented with side chains perpendicular to the surface (edge-on orientation). Surface modification of the PVP by hexamethyldisilazane (HMDS) can increase the crystalline size in the P3HT semicrystalline films. The performance of an all-polymer organic field-effect transistor (OFET) with the drop-cast P3HT semiconductor layer and the crosslinked PVP gate insulator on poly(ethylene naphthalate) (PEN) substrate was evaluated.