Organic Polymer Thin Films Research Articles

Ultrafast electron dynamics in excited states of conjugated thiophene-fluorene organic polymer (pF8T2) thin films.

The electronic states of poly(9,9-dioctylfluorenyl-alt-bithiophene) pF8T2 on H/Si(100) substrates, prototypical for organic photovoltaics, were investigated by ultrafast photoelectron spectroscopy and by time-resolved fluorescence studies. Occupied and unoccupied electronic states were analysed by ultraviolet photoelectron spectroscopy (UPS), static and dynamic femtosecond two-photon photoemission (2PPE), and time-correlated single photon counting (TCSPC). Time-resolved measurements allow assessment of population lifetimes of intermediate states. The combination of time-resolved photoelectron spectroscopy and fluorescence excitation allows following the electronic dynamics in excited states from the femtosecond to the nanosecond time scale. For this prototypical material the electron kinetic energy resolved lifetimes range from about a few tens of femtoseconds up to hundreds of picoseconds. After annealing these types of organic thin films the efficiency of organic solar cells usually increases. We show that annealing does not influence the initial ultrafast charge generation processes, but the long-lived states. However, the nanosecond scale fluorescence lifetimes measured by TCSPC are prolonged after annealing, which therefore is identified as the cause of a greater exciton diffusion range and thus is beneficial for charge carrier extraction.

Preparation of a triazine porous organic polymer thin film by nanoparticle-polymer reticulation for high-efficient molecule/ion separation

Triazine porous organic polymer thin film constructed using nanoparticle-polymer reticulation strategy exhibits high perm-selectivity and good anti-fouling/-bacterial property.

Control of Molecular Orientation and Carrier Transport of Thiophene-Based Semiconducting Polymer via Superparamagnetic Nanoparticles Fe3O4@C-Assisted Magnetic Alignment Method

Realizing the high molecular orientation and structurally ordered microstructure of organic semiconductor polymer thin films is beneficial for enhancing the charge transport of conjugated polymers and achieving high-performance organic electronic devices. In this work, we successfully developed large-area highly aligned films of a thiophene-based polymer, namely poly(2,5-bis(3-alkylthiophen-2-yl) thieno [3,2-b] thiophene) (PBTTT), using the magnetic alignment method at a low magnetic field (0.12 T), which was assisted by superparamagnetic nanoparticles Fe3O4@C. The aligned microstructure of the composite films is confirmed by systematic analysis that includes polarized optical microscopy, polarized UV–visible absorption spectroscopy, and an atomic force microscope. Organic field effect transistors based on magnetic aligned composite film exhibit a 2.8-fold improvement in carrier mobility compared with the unaligned films. We hold a formation mechanism that the rapid magnetically induced self-assembly property of Fe3O4@C and its intermolecular interaction with polymer chains are key to the new method of preparing oriented thin films.

In situ growth of multifunctional porous organic polymer nanofilms with molecular sieving and catalytic abilities

Porous organic polymers (POPs) have evinced a huge potential for membrane-based separations owing to their impressive surface areas, high mesopore ratio, superior chemical stabilities, and catalytic abilities. In this study, for the first time, an o-hydroxy porous organic polymer (POP) thin film was in situ generated atop a (polyacrylonitrile) HPAN membrane support via diazo-coupling reaction under mild conditions. Analysis by FT-IR, XPS and SEM confirmed the successful formation of a coherent, thin POP nanofilm. Zeta potentials and water contact angle measurements demonstrated that the resultant POP film was hydrophilic (water contact angle = 48°) and negatively charged because of the abundance of hydroxyl groups. The roles of synthesis parameters (e.g., the solution pH and the reaction time) in the membrane microstructure and separation performance were explored in detail. The best-performing composite membranes show a high pure water permeability (66.5 L m−2h−1 bar−1), superior dye retentions (RCR = 99.6%, RDR = 98.0%, RMB = 98.8%), and low divalent salt retention (<15.0%), thus promising for separation of dye/salt mixtures. In addition, the thus-obtained POP film was utilized as the catalyst to yield propylene carbonate in aqueous solution with a high conversion rate of 80% at room temperature. The significance of this study is expected to provide a useful guideline of in situ fabrication of multifunctional POP membranes for separation of dye/salt mixtures and catalysis.

The Photostability of Novel Boron Hydride Blue Emitters in Solution and Polystyrene Matrix.

In recent work, the boron hydride anti-B18H22 was announced in the literature as a new laser dye, and, along with several of its derivatives, its solutions are capable of delivering blue luminescence with quantum yields of unity. However, as a dopant in solid polymer films, its luminescent efficiencies reduce dramatically. Clarification of underlying detrimental effects is crucial for any application and, thus, this contribution makes the initial steps in the use of these inorganic compounds in electrooptical devices based on organic polymer thin films. The photoluminescence behavior of the highly luminescent boron hydrides, anti-B18H22 and 3,3′,4,4′-Et4-anti-B18H18, were therefore investigated. The quantum yields of luminescence and photostabilities of both compounds were studied in different solvents and as polymer-solvent blends. The photophysical properties of both boranes are evaluated and discussed in terms of their solvent-solute interactions using photoluminescence (PL) and NMR spectroscopies. The UV degradability of prepared thin films was studied by fluorimetric measurement. The effect of the surrounding atmosphere, dopant concentration and the molecular structure were assessed.

In-situ synthesis of covalent organic polymer thin film integrates with palladium nanoparticles for the construction of a cathodic photoelectrochemical cytosensor

Sensitive detection of cancer cells is essential to early clinic diagnosis, and the photoelectrochemical (PEC) sensors with high sensitivity and good selectivity may provide new approaches for cytosensing. Herein, we demonstrate the development of a new cathodic PEC cytosensor based on the integration of covalent organic polymer (COP) with palladium nanoparticles (PdNPs). The COP films are in-situ grown at room temperature on the transparent indium tin oxide-coated glass substrates, and they subsequently assemble with PdNPs to immobilize aptamers via palladium-sulfur chemistry. PdNPs can catalyze the oxidation of dopamine to produce aminochrome and its derivative, which may function as the electron acceptors of COP for the generation of an enhanced photocurrent. In the absence of cancer cells, the electrons on the conduction band of COP on the electrode transfer to the aminochrome and O2, while the electrons on the electrode transfer to the hole of valence band, resulting in a high cathodic photocurrent. In the presence of cancer cells, the trapped cancer cells efficiently cover the electrode to reduce the surface of COP/PdNPs, resulting in the decrease of catalytic precipitation on the electrode and consequently the generation of a low PEC signal. This PEC cytosensor exhibits high sensitivity with a detection limit of 8 cells mL−1 and a large dynamic range from 10 to 106 cells mL−1. Moreover, this PEC cytosensor has distinct advantages of high selectivity, good reproducibility and excellent stability, and it can be extended to directly detect various cancer cells through the integration with corresponding specific aptamers.

Optical and Electrical Properties of Organic Semiconductor Thin Films on Aperiodic Plasmonic Metasurfaces.

Metal electrodes are playing an increasingly important role in controlling photon absorption and in promoting optimal light management in thin-film semiconductor devices. For organic optoelectronic devices, the conventional fabrication approach is to build the device on top of a transparent electrode, with metal electrode deposition as the last step. This makes it challenging to control the surface of the metal electrode to promote good light management properties. An inverted fabrication approach that builds the device on top of a metal electrode makes it possible to control the morphology of the metal surface independently of the organic semiconductor active layer to achieve a variety of photonic and plasmonic behaviors useful for devices. However, there are few reports of inverted fabrication of organic optoelectronic devices and its impacts on device properties. Silver (Ag) is the most suitable metal for fabrication of nanostructured electrodes with plasmonic behavior (i.e., plasmonic electrodes) because of its low parasitic absorption loss and high reflectivity. In this project, we describe the facile fabrication of silver nanoparticle (AgNP) aperiodic plasmonic metasurfaces and study their physical and optical characteristics. Then, we investigate the photonic and electrical behaviors of the aperiodic plasmonic metasurfaces when interfaced with poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) organic semiconducting polymer thin films. The luminescence quantum yield of F8BT thin films increases from 29% on planar Ag up to 66% on AgNP metasurfaces due to the Purcell effect and the improved extraction of emission coupled to surface plasmon polariton modes. In particular, we show that plasmonic enhancement can overcome ohmic losses associated with metals and metal-induced exciton quenching. According to the current-voltage characteristics of hole-only devices with and without aperiodic plasmonic metasurfaces, we conclude that AgNP aperiodic plasmonic metasurfaces have comparable electrical behavior to planar metal electrodes while having superior light management capability.

Structural and optical characterization of novel [ZnKCMC]TF for optoelectronic device applications

A novel organic complex polymer thin film, Zn (Zinc)/KCMC (Keto Carboxymethyl cellulose) [ZnKCMC]TF was fabricated using Sol–Gel technique. Different characterization techniques for [ZnKCMC]TF (e.g. FTIR, UV–Vis, XRD, SEM) and optical properties were used. XRD analysis has determined the resulting structural properties of [ZnCMC]TF and CMC polymers. Molecular structure, vibrational spectrum, and optical properties have been optimized. The optimization was performed using density functional theory (DFT) by DMol3 and Cambridge Serial Total Energy Package (CASTEP) program. The two polymers chemical structure was confirmed by spectroscopic and structural properties for both KCMC and [ZnKCMC]TF, XRD results showed the same crystal structure (Monoclinic 2). KCMC has a grain size bigger than [ZnKCMC]TF. Furthermore, the Tauc’s equation results indicate clearly that the optical energy band gap values are reduced from 3.492 eV for [KCMC]TF to 3.149 eV for [ZnKCMC]TF. Optical constants (refractive index n, absorption index k, and optical conductivity) increase with photon energy. The optical properties of simulated FTIR, XRD, and CATSTEP are in significant agreement with the [KCMC]TF and [ZnKCMC]TF experimental study. The Polymer [ZnKCMC]TF presents a good candidate for optoelectronics and solar cell applications.

Topological properties and direct current electrical charge transport mechanism of plasma polymerized cyclohexane thin films

High-performance plasma polymerized organic thin films have been synthesized by employing a capacitively coupled glow discharge technique and cyclohexane is used as a precursor material. The surface of the plasma polymerized cyclohexane (PPCHex) thin films observed to be smooth, pinhole free and uniform. It is observed from thermal analysis that the rate of loss of mass is very low in air atmosphere below 510 K and the films are thermally stable. Above 510 K weight loss takes place in different stages in air. The current density of the PPCHex thin films is increased when the thicknesses is decreased and that is increased with increasing temperatures. The conduction mechanism of carrier transport operative in these PPCHex thin film is dominated by Schottky type conduction mechanism. The activation energy of the PPCHex thin films for applied voltage 10 V is found 0.14 ± 0.05 eV near room temperature region and that in the higher temperature region is 0.57 ± 0.04 eV. The activation energy in the Schottky region for the applied voltage 50 V is about 0.16 ± 0.06 eV near the room temperature region and that is 0.83 ± 0.05 eV at the higher temperature region.

IR spectroscopic and photoluminescence studies of plasma polymerized organic thin films based on tea tree oil

Plasma-assisted synthesis of transparent, environment friendly, lightweight, flexible and stable organic thin films from naturally occurring precursors were emerging as potential candidates for organic semiconductor industry. In the present study, tea tree (Malaleuca alternifolia) oil based polymer thin films were deposited on glass and silicon substrate by using radio frequency plasma polymerization technique. The polymer thin films were characterized with atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy techniques. AFM images indicate the formation of homogenous film on the substrate surface. FTIR spectra gives bands related to methyl and methylene groups which confirms the formation of chain branching in the polymer films. Relatively intense infrared (IR) bands obtained from films deposited on glass substrate reveals that glass substrate is more favourable for the growth of polymers than silicon substrate. Optical band gap of the polymerized thin film on glass substrate was estimated using Tauc plot which gives a value of 3.19 eV, indicating the semiconducting nature of the material. Photoluminescence (PL) emission in the yellow region were observed from both the samples and its CIE colour coordinates also matches with yellow emission. Broad visible emission observed in the wavelength range 465–695 nm indicates the presence of multichromophores in the polymer film. Samples also gives IR emission in the wavelength range of 850–1090 nm, upon excitation with a wavelength of 785 nm contributed to polaronic transitions.

Effect of molecular backbone structure on vapor phase coupling reaction between diiso(thio)cyanates with diamines, diols, and dithiols

Gas phase vacuum deposition processes such as chemical vapor deposition or molecular layer deposition can be used to deposit conformal thin films of organic polymers. Urea and urethane are typical products in such vacuum thin film deposition methods that are obtained from spontaneous, catalyst- and solvent-free reactions between isocyanates/isothiocyanates and amines/diols/thiols. In this work, the thermochemistry of the urea/urethane coupling reactions between homobifunctional reactants is analyzed using double-hybrid density functional theory calculations. The reactant pairs are chosen such that the molecular backbone structures are either aromatic (-C6H4-) or aliphatic (-(CH2)4-) in both reactants. It is observed that the activation energies of the reactions can be correlated with the basicity of the amines/alcohol/thiol species. Furthermore, since the chemical properties are dependent on the structure of the molecular backbone, the molecular reactivity of the aliphatic reactant pairs are suggested to be higher than aromatic ones.

Electrochemical Properties and Band Gap Variation of Polyaniline Due to the Presence of ZnO

Composite thin films of polyaniline (PAN)/ZnO are synthesized via electropolymerization (ECP) process in acidic medium on ITO (working electrode) with platinum mesh as a counter electrode and Ag/AgCl as a reference electrode. Acidic medium helps in polymerization and enhances the crystallinity of PAN. PAN films that are obtained in the presence of sulfuric acid give partial crystallinity in its high conducting form, i.e., emeraldine salt. Inorganic metal oxide–organic polymer thin film was used to get a new type of composite nanostructures. The cyclic voltammetry and chronoamperometric properties were investigated by potentiostat for different doping percentages of ZnO with a constant Molar concentration of PAN. Current conduction properties are found to be increased in the presence of ZnO particles. Optical properties were investigated using UV–Vis and photoluminescence spectroscopy. Photoluminescence shows emission in the blue, green and yellow regions. Band gap variation has also been calculated with the help of Tauc’s plot which found to be decreasing with the increase of doping percentage of ZnO.

Material gain concentration quenching in organic dye-doped polymer thin films

The optimization of material gain in optically pumped dye-doped polymer thin films is an important task in the development of organic solid-state lasers. In this work, we present a theoretical model that accommodates the influence of concentration quenching on material gain and employ it to study the novel dye molecule 2-(4-(bis(4-(tert-butyl)phenyl)amino)benzylidene)malononitrile (PMN) and the well-established dye molecule 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) embedded in poly(methyl methacrylate) (PMMA). Polycarbonate was tested as an alternative host material for PMN. The material gain in these dye-doped polymer thin films was determined by the variable stripe length method. The inclusion of concentration quenching in the material gain expression is able to significantly reduce the overestimation of the gain efficiency inherent to a linear model.

(Invited) Advances in Testing Inorganic & Hybrid Organic Thermoelectric Thin Films

In this work, a novel Si-based Lab-on-a-Chip test platform is introduced to perform in-plane ZT measurements of various classes of thermoelectric films with a complete set of thermoelectric test structures. The electrical conductivity σ, the Seebeck coefficient S, the thermal conductivity κ, and the power factor PF and the figure of merit ZT values can be experimentally determined in a single simultaneous measurement run as a function of temperature. It is shown that this Lab-on-a-Chip test system can be applied to classic inorganic thermoelectric films such as PbTe and PbSe and also to hybrid inorganic-organic films such as SURMOF films and as well as to conducting organic PEDOT:PSS films. Generally, the thermoelectric film can be deposited in the exposed test area of the chip by using a shadow mask. All the parameters can be measured in the temperature range of 300 K to 370 K with a 1 T magnet field. Applications are demonstrated for all three film material categories. Here, PbTe and PbSe thin films and double-layer PbTe/PbSe films were synthesized by Atomic Layer Deposition (ALD) technology directly on the pre-structured Si chip. A thin Al2O3 protection and diffusion barrier layer was applied to avoid oxidation and degradation of PbTe/PbSe films. The Seebeck coefficient, electrical conductivity and thermal conductivity for PbTe, PbSe and double-layer PbTe/PbSe film were measured simultaneously by applying in-pane ZT chips. Furthermore, this Lab-on-a-Chip test system can be extended to Surface Anchored Metal-organic-framework (SURMOF) films, which consist of quasi-liquid phase epitaxially grown highly ordered crystalline films. MOF films are designed scaffold-like compounds that consist of metal ions connected by organic ligands. Furthermore, the example of a complete thermoelectric characterization of a conductive organic polymer thin film material will be discussed.

Polymer Thin Films for Anti‐Reflection and Passivation on the Front Surface of Interdigitated Back Contact c‐Si Solar Cell

In this work, a polymer thin film, polystyrenesulfonate (PSS), is employed in interdigitated back contact (IBC) solar cells as an anti‐reflection (AR) coating and front surface passivation (SP) layer. It is found that PSS thin film is highly transparent and possesses a refraction index of about 1.5, and thus functions well as AR coating for Si wafer‐based solar cells. An effective minority carrier lifetime of 2.3 ms is obtained on 1–5 Ω · cm n‐type crystalline Si wafer with both sides symmetrically coated by PSS thin film, proving a good Si surface passivation by this polymer. An increase in power conversion efficiency is obtained when 150 nm‐thick PSS thin film is coated on the front surface of IBC solar cells without any AR/SP layers, resulted from the increased short circuit current density and open circuit voltage. This work opens up a new approach using organic polymer thin film deposited with low temperature and vacuum‐free technique as AR/SP multifunctional layer in Si solar cells.

水晶振動子式ニオイセンサシステムの機能設計と開発に関するレビュー

Functional design of organic polymer thin films as the molecular recognition membrane of quartz crystal microbalance (QCM)-type odor sensor system is reviewed. The organic polymer materials which are used as the molecular recognition membrane of QCM odor sensors are selected in the view of solubility parameters. It is found that the solubility parameter is very useful to choice the organic polymers as the molecular recognition membrane of the QCM gas sensors for target gas and odor. It is also found that the use of polymer films with nano-wires is effective to increase the sensitivity of the QCM odor sensors.

Polythiophene Thin Films by Surface-Initiated Polymerization: Mechanistic and Structural Studies

The ability to control nanoscale morphology and molecular organization in organic semiconducting polymer thin films is an important prerequisite for enhancing the efficiency of organic thin-film devices including organic light-emitting and photovoltaic devices. The current “top-down” paradigm for making such devices is based on utilizing solution-based processing (e.g., spin-casting) of soluble semiconducting polymers. This approach typically provides only modest control over nanoscale molecular organization and polymer chain alignment. A promising alternative to using solutions of presynthesized semiconducting polymers pursues instead a “bottom-up” approach to prepare surface-grafted semiconducting polymer thin films by surface-initiated polymerization of small-molecule monomers. Herein, we describe the development of an efficient method to prepare polythiophene thin films utilizing surface-initiated Kumada catalyst transfer polymerization. In this study, we provided evidence that the surface-initiated p...

An Investigation into the Role of Capping on Second Harmonic Generation from Nonlinear Organic Polymer and Guest-Host Thin Films by In-Situ Poling

In attempts to fabricate thermally stable second-order nonlinear polymer thin films, we have investigated the second harmonic generation (SHG) from both nonlinear polymer and guest-host thin films. We have also investigated the role of capping on the SHG, temporal stability and relaxation of dipole alignment. Corona poling techniques were employed to orient the dopants into the noncentrosymmetric structure required to obtain the SHG. The effect of capping with a polymeric encapsulant below the glass transition temperature of the polymers on the unpoled and corona poled thin films was studied. Capping of the nonlinear polymer and guest host thin films have resulted in high SHG with good temporal stability. SHG signal falls drastically during the first 8 days after poling while no further significant decay in SHG signal was observed after about 33 days. Our investigations have identified the characteristics required for a good encapsulant on a non-con-ductive surface.

Radiation damage yields across the carbon 1s excitation edge

X-rays are used as a probe in many materials analysis techniques, but they may induce changes in the sample that can invalidate the measurement. Strategies that overcome “radiation damage” are therefore desirable. Tuning the incident photon energy below a core electron excitation edge of a material (where only valence excitation takes place) rather than above it (where primarily core excitation occurs) has been theorized as a way to reduce radiation damage. To investigate this strategy, we used a scanning transmission X-ray microscope to expose thin films of organic polymers to X-rays with photon energies below and above the C 1s excitation edge. The extent of radiation damage was quantified by X-ray absorption spectroscopy and lithography. We found that the amount of radiation damage per unit absorbed dose was the same using incident photons below and above the C 1s excitation edge. We conclude that the turn on of Auger processes when C 1s holes are created does not affect the overall radiation damage outcome.

Deposition and characterization of organic polymer thin films using a dielectric barrier discharge with different C2Hm/N2 (m = 2, 4, 6) gas mixtures

Organic polymer thin films have been deposited on Si(100) and aluminum coated glass substrates by a dielectric barrier discharge (DBD) operated at medium pressure using different C2H m /N2 (m = 2, 4, 6) gas mixtures. The deposited films were characterized by various spectroscopic techniques. Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) revealed the chemical functional groups present in the films. The surface chemical compositions have been derived from X-ray photo electron spectroscopy (XPS). FT-IRRAS and XPS show the presence of sp, s p 2 and s p 3 bonds of carbon and nitrogen. Various functional groups such as NH containing, saturated and unsaturated alkyl groups have been identified. Thin films obtained from C2H2/N2 and C2H4/N2 gas mixtures revealed a higher N/C ratio when compared to thin films obtained from C2H6/N2. Thickness, refractive index and extinction coefficient were evaluated by spectroscopic ellipsometry (SE). Significant differences between the films obtained with different gas mixtures are observed.