Evaluation of poly(3-hexylthiophene)/polymeric insulator interface by charge modulation spectroscopy technique

We have investigated the sub-band gap states behaviors in P3HT MIS diodes and P3HT Schottky diode by the combination of C–V characteristics and the charge modulation spectroscopy (CMS) measurements. Single-layered heat-treated P3HT film sandwiched by ITO and Al electrodes behaves as a dielectric film, whereas it behaves as Schottky diode when oxygen molecules were doped. The thickness of depletion layer at Al/P3HT interface is controlled by external voltage, and there are two peaks at around 1.3 eV and 1.95 eV in CMS curves. On the other hand, P3HT MIS diodes deposited on polymeric gate insulators have three peaks in CMS curves at around 1.3, 1.6 and 1.95 eV respectively in accumulation. The first peak observed was attributed to the optical transition of polarons in isolated (1D) P3HT chain, and it was related to the field effect mobility and conjugation length in lamellae chains. The second peak observed was attributed to the optical transition of delocalized polarons in π-stacked (2D) P3HT chains, and the peak intensity became strong for highly crystallized P3HT film. The third peak was attributed to the deeply trapped charges in amorphous P3HT region, respectively.     

High mobility top-gated poly(3-hexylthiophene) field-effect transistors with high work-function Pt electrodes

We report high-performance top-gated organic field-effect transistors (OFETs) with regio-regular poly(3-hexylthiophene) (rr-P3HT). The high charge carrier mobility in rr-P3HT FETs (0.4 cm²/Vs) was achieved due to the relatively low contact resistance and high crystallinity of rr-P3HT films. The contact resistance was controlled mainly through the use of high work-function platinum (Pt) (5.6 eV) for the charge injection electrode and a top-gate, bottom-contact geometry that enabled an enhanced current injection via current crowding in the staggered device structure. Moreover, the top-gate configuration provided improved device stability in air ambient conditions via the presence of a gate dielectric and gate electrode on top of the organic semiconductor.     

聚3-己基噻吩的光电性能研究

利用光电化学方法研究了聚3-己基噻吩的光电化学性质,其禁带宽度为1.89eV,同时确定了它的价带位置(-3.6eV)、导带位置(-5.4eV).研究发现聚3-己基噻吩属于直接跃迁型半导体,在本文条件下得到的最高IPCE值达5.2%     

Investigation of self-assembled monolayer treatment on SiO2 gate insulator of poly(3-hexylthiophene) thin-film transistors

We have investigated self-assembled monolayer (SAM) treatment on SiO₂ gate insulator of poly(3-hexylthiophene) (P3HT) thin-film transistor (TFT), and demonstrated a correlation between mobility and surface free energy of the insulator. The device with lower surface free energy shows higher mobility. The docosyltrichlorosilane (DCTS)-treated device exhibits the best performance among the various SAM-treated devices examined. Field-effect mobility, on/off ratio and threshold voltage of the DCTS-treated P3HT TFT were 0.015 cm²/Vs, >10⁵ and −14 V, respectively.     

Microwave-assisted synthesis of poly(3-hexylthiophene) via direct oxidation with FeCl3

In this work, CoolMate microwave synthesis system was employed to synthesize soluble poly(3-hexylthiophene) by direct oxidation of 3-hexylthiophene monomer with FeCl₃ as oxidant. P3HT was synthesized varying reaction time by 2 h, 1 h and 0.5 h. According to the results optimal microwave radiation time for synthesis was 1 h. On the other hand, P3HT was synthesized in two different solvents: chloroform (CHCl₃) and dichloromethane (CH₂Cl₂). The obtained yields depend on the solvent and the reaction time used in the synthesis, microwave-assisted synthesis leads to outstanding increase in yield (with dichloromethane solvent). Homogeneous thin films were prepared by spin-coating technique from toluene. Physicochemical characterization of P3HT polymers was carried out: changes in weight molecular distribution and polydispersity were obtained by HPLC (high-performance liquid chromatography); dyads and triads percent were analyzed by NMR (nuclear magnetic resonance). Surface topographical changes were obtained by atomic force microscopy (AFM). AFM images revealed that the surface morphology depends on synthesis method, reaction time and solvent used. Finally the samples were characterized by thermogravimetric analysis (TGA) and ultraviolet–visible analysis (UV–vis). Compared with the traditional method (without microwave), this method provided considerable decrease in the reaction time, both lower polydispersity and molecular weight, less volume of solvents for the synthesis, as well as more alternatives for solvent choice. The results confirmed the versatility of the procedure by microwave, which yields polymeric materials in 1 h and has no adverse effects on the polymers quality.     

A transport study on as-grown and cast films of electrogenerated poly(3-hexylthiophene)

Two kinds of poly(3-hexylthiophene) films with identical chemical compositions are prepared. One of the films is obtained by electropolymerization of 3-hexylthiophene (as-grown film) and the other is prepared by casting a solution dissolving the as-grown film (cast film). A clear difference is found in the mobility vs. doping level plots between the as-grown and cast films and its reason is discussed.     

Enhancement of carrier mobility in all-inkjet-printed organic thin-film transistors using a blend of poly(3-hexylthiophene) and carbon nanoparticles

To enhance the carrier mobility of all-inkjet-printed organic thin film transistors, we fabricated devices that incorporated poly(3-hexylthiophene) (P3HT) and carbon nanoparticles (CNPs). The fabricated devices had an on/off ratio of 10⁴, which is one order less than that of pristine organic thin-film transistors (OTFTs). The maximum carrier mobility as high as 0.053 cm²/V-s was achieved for a CNP/P3HT weight-weight ratio of 7/100. This degree of mobility is 10 times greater than average mobility of pristine P3HT-OTFTs. X-ray diffraction and scanning electron microscopy images reveal that the carrier mobility was enhanced by reducing the injection barrier and enhancing the carrier injection. This work demonstrates the feasibility of all-inkjet-printed OTFT technology.     

Microdisk laser emission and electrical properties of composite films based on poly(3-hexylthiophene)s with different stereoregularity

The optical and electrical properties of composite thin films of poly(3-hexylthiophene)s (PAT6s), processing different stereo-regularity originating from side-chain regio orders have been studied. The laser emission properties of PAT6 composite thin films in microdisk structure have been observed by pulsed photopumping. From the electrical and optical measurements, the electrical conductivity and the quantum efficiency of the PAT6 composite films were estimated. The emission and conductivity depending on the mixture ratios were discussed by taking the stereo-regularity of the molecular structure into consideration.     

Thermophysical properties of free-standing micrometer-thick Poly(3-hexylthiophene) films

The solution of Poly(3-hexylthiophene) (P3HT) in chloroform is generally adopted for fabricating P3HT thin films or nanofibers. In this work, 4 regular P3HT solution weight percentages, 2, 3, 5 and 7 wt.%, are compounded to fabricate P3HT thin films by using spin-coating technique. Raman spectrum study suggests that the density of the P3HT thin films varies with different P3HT solution weight percentages while X-ray diffraction analysis reveals that the crystal structures are identical for all P3HT thin films. The transient electrothermal technique is employed to measure the thermal diffusivity of the P3HT thin films and an efficient temperature-resistance calibration is performed to cooperatively study the thermal conductivity. When the P3HT weight percentage changes from 2% to 7%, the thermal conductivity varies from 1.29 W/m·K to 1.67 W/m·K and the thermal diffusivity goes down from around 10^− 6 m²/s to 5 × 10^− 7 m²/s. The density of P3HT thin films is also determined from the experimental data. The relationship between the density and thermophysical properties clearly demonstrates that the thermal conductivity increases with density while the thermal diffusivity decreases.     

The role of solvent and morphology on miscibility of methanofullerene and poly(3-hexylthiophene)

A bicontinuous, percolating bulk heterojunction morphology is integral to organic polymer solar cells. Understanding the factors affecting the miscibility of photovoltaic polymers with a fullerene electron acceptor molecule is a key to controlling the morphology. Starting from discreet pure phases - a poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) bilayer film - the evolution of the P3HT-PCBM interface was studied with particular attention to the role of residual solvent in P3HT on PCBM interdiffusion. This investigation shows that in the bilayer geometry PCBM can rapidly diffuse into amorphous P3HT, but phase separation is maintained if the P3HT layer is cast from a very volatile solvent or if it is annealed prior to casting the PCBM overlayer to complete the bilayer geometry.     

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...     

Dual nanostructures in poly (3-hexylthiophene) based organic photovoltaics under alternative current electric field

Two-dimensional X-ray diffraction was employed, to provide a complete understanding of the energy efficiency improvement of organic photovoltaics by AC electric field alignment. Two distinguishable poly (3-hexylthiophene) (P3HT) nanostructures were found in the form of two separated layers, one of which is highly oriented and the other randomly distributed. The finding helps to analyze the crystallite arrangements not only in the interface in the bulk heterojunction, but also those closer to the substrate. The highly oriented P3HT layer, although located near the substrate, was found to enhance the device efficiency, by increasing the short circuit current and decreasing the series resistance.     

Tuning optical properties of poly(3-hexylthiophene) nanoparticles through hydrothermal processing

Abstract

Poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) were prepared by a reprecipitation method. Hydrothermal processing applied external pressure to the pristine P3HT NPs at temperatures ranging from 60 to 150 °C. Optical absorption and photoluminescence (PL) spectra for the hydrothermally treated P3HT NPs varied markedly with the processing temperature. With increasing treatment temperature, the absorption peak broadened and the peak position shifted from 510 to 623 nm; moreover, the intensity ratio of the 0–1 to 0–0 emission varied. These changes were caused by interactions between the P3HT main chains and alkyl side groups and conformational modifications induced by the high pressure during the hydrothermal process. The evolution of the optical absorption spectra of the P3HT NPs during the hydrothermal processing was strongly correlated with the variation of PL excitation spectra and with the PL emission spectra of a single NP.     

Light illumination effects in ambipolar FETs based on poly(3-hexylthiophene) and fullerene derivative composite films

The effects of light illumination on field effect transistors based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C₆₁-butyric methyl ester (PCBM) composite films have been studied. It is found that the light illumination on pure P3HT and PCBM generally resulted in decrease of the threshold voltages and increase of the mobilities by a little. In the composite film at the PCBM contents of x = [P3HT] / ([P3HT] + [PCBM]) = 0.67 ∼ 0.9, an ambipolar field transport appeared. The light illumination effect was observed remarkably in the shift of threshold voltage for the hole generation at x = 0.75. Variations of Hole and electron mobilities and threshold voltage of electron generation upon light illumination were basically similar to those of the pure materials. The results were discussed in terms of the light assisted carrier generation in field effects.     

Tuning optical properties of poly(3-hexylthiophene) nanoparticles through hydrothermal processing

Poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) were prepared by a reprecipitation method. Hydrothermal processing applied external pressure to the pristine P3HT NPs at temperatures ranging from 60 to 150 °C. Optical absorption and photoluminescence (PL) spectra for the hydrothermally treated P3HT NPs varied markedly with the processing temperature. With increasing treatment temperature, the absorption peak broadened and the peak position shifted from 510 to 623 nm; moreover, the intensity ratio of the 0–1 to 0–0 emission varied. These changes were caused by interactions between the P3HT main chains and alkyl side groups and conformational modifications induced by the high pressure during the hydrothermal process. The evolution of the optical absorption spectra of the P3HT NPs during the hydrothermal processing was strongly correlated with the variation of PL excitation spectra and with the PL emission spectra of a single NP.     

X-ray photoelectron spectroscopy (XPS) and FTIR studies of vanadium barium phosphate glasses

Barium vanadophosphate glasses, having composition 50BaO–xV₂O₅–(50 − x)P₂O₅, (x = 0–50 mol%), were prepared by conventional melt quench method. Density, molar volume and glass transition temperature (T_g) were measured as a function of V₂O₅ content. Structural investigation was done using XPS and FTIR spectroscopy. First, substitution of the P₂O₅ by the V₂O₅ in the metaphosphate 50BaO–50P₂O₅ glass increases the density and T_g and decreases the molar volume. When the amount of V₂O₅ increases, all these properties show a reverse trend. XPS measurement found in the O1s, P2p, and V2p core level spectra indicate the presence of primarily P–O–P, P–O–V and V–O–V structural bonds, the asymmetry in the P 2p spectra indeed arises from the spin-orbit splitting of P 2p core level, and more than one valence state of V ions being present. IR spectroscopy reveals the depolymerization of the phosphate glass network by systematic conversion of metaphosphate chains into pyrophosphate groups and then orthophosphate groups. Even though metaphosphate to pyrophosphate conversion is taking place due to breaking of P–O–P linkages, formation of P–O–V and P–O–Ba linkages provide cross linking between short P-structural units, which make the glass network more rigid. Above 10–20 mol% V₂O₅ content, network is highly depolymerized due to the formation of orthophosphate units and V–O–V bridge bonds, resulting in poor cross-linking, making the glass network less rigid.     

Band bending at free Pb(Zr,Ti)O3 surfaces analyzed by X-ray photoelectron spectroscopy

This paper analyses in detail the core levels evolution of Pb(Zr,Ti)O₃, i.e. Pb 4f, Zr 3d, Ti 2p, O 1s in various conditions: absolutely freshly prepared sample, sample stored under air, and the effects of in vacuum annealing. The aim of the study is to quantify separately the chemical reactivity at the surface and the band bending effects due to the ferroelectric polarization. It is found that freshly prepared samples present mostly inwards (↓) polarization. This phenomenon is mostly revealed by the Ti 2p and O 1s spectra, manifested as a distinct component with 1.8 eV lower binding energy in the O 1s binding energy and by 1.1 eV in the Ti 2p binding energy. Sample aging under air suppresses the inwards polarization, and most signal comes from surfaces not presenting ferroelectric permanent polarization perpendicular to the sample surface. This process conducts also to the formation of Pb(CO₃)₂ on the surface. Annealing to temperatures up to 400 °C stabilizes a surface composed by a main part of surface without polarization perpendicular to the surface, and with some areas presenting outwards (↑) polarization. These areas have, most probably, different terminations, the polarized area being (Ti,Zr)O₂ terminated.     

Preparation and characterization of poly(indole-3-carboxaldehyde) film at the glassy carbon surface

Indole-3-carboxaldehyde (In3C) monomer was oxidized by electrochemical methods at the glassy carbon (GC) electrode in 0.05 M tetrabutylammonium tetrafluoroborate in acetonitrile, with the aim to prepare a modified electrode. Modification was performed using cyclic voltammetry (CV) scanning from 0.0 V to 2.0 V at a scan rate of 50 mV s^− 1 for 10 cycles in 1 mM In3C monomer solution. The modified GC surface (In3C-GC) was characterized by CV response of potassium ferricyanide and ferrocene redox probes as well as by the electrochemical impedance spectroscopy. The modified surface was analyzed by reflection-absorption infrared spectroscopy and compared with the spectrum of the monomeric In3C. Elemental composition of the surface was determined by X-ray photoelectron spectroscopy. Contact angle measurements was also performed to check the changes in hydrophobic character of the bare GC and compared to that of In3C-GC surface. Thickness of the oligomeric/polymeric film was investigated by ellipsometric measurements and a surface confined polymerization mechanism was proposed.     

Effects of catalyst loading amount on the synthesis of poly(3-hexylthiophene) via externally initiated Kumada catalyst-transfer polycondensation

A series of model polymerization are carried out via the one-pot externally initiated Kumada catalyst-transfer polycondensation (KCTP) of 2-bromo-5-chloromagnesium thiophene monomers, and the excess amount of initiators or catalysts are found no need to be isolated during the polycondensation process. Especially, the impacts of the nickel catalyst loading variation on regioregularity (rr), yield, molecular weight (M_n), polydispersity (PDI) and initiation efficiency of poly(3-hexylthiophene) (P3HT) are systematically investigated. The ¹H NMR, size-exclusion chromatography (SEC), and MALDI-TOF mass spectroscopy results indicated that an excess amount of catalyst does not influence yield, rr, M_n, and PDI of P3HT, nor the initiation efficiency. However, the PDI of the product is broad, and the M_n and rr values decreased in the absence of 1,3-bis(diphenylphosphino)propane (dppp). It can be concluded that the in-situ KCTP polymerization of P3HT is a practical and effective process. These results are especially valuable for the synthesis of all-conjugated block copolymers where macroinitiators are used.     

The use of nanoimprint lithography to improve efficiencies of bilayer organic solar cells based on P3HT and a small molecule acceptor

Nanoimprint lithography (NIL) was carried out on bilayer organic photovoltaics (OPVs) based on regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) as electron donor and 4,7-bis(2-(1-ethylhexyl-4,5-dicyano-imidazol-2-yl)vinyl)benzo[c]1,2,5-thiadiazole (EV-BT) as electron acceptor. The power conversion efficiency of the devices after nanoimprinting increased from 0.20% to 0.30%, closer to that of the bulk heterojunction device at 0.37%. As a result, NIL proved to be a feasible method for improving the bilayer OPV performance by increasing the donor/acceptor interfacial area.