Spin Casting Research Articles

Irreversible Adsorption Governs the Equilibration of Thin Polymer Films.

We demonstrate that the enhanced segmental motion commonly observed in spin cast thin polymer films is a nonequilibrium phenomenon. In the presence of nonrepulsive interfaces, prolonged annealing in the liquid state allows, in fact, recovering bulk segmental mobility. Our measurements prove that, while the fraction of unrelaxed chains increases upon nanoconfinement, the dynamics of equilibration is almost unaffected by the film thickness. We show that the rate of equilibration of nanoconfined chains does not depend on the structural relaxation process but on the feasibility to form an adsorbed layer. We propose that the equilibration of the thin polymer melts is driven by the slow relaxation of interfacial chains upon irreversible adsorption on the confining walls.

Monomolecular films of arborescent polystyrene–graft–poly(2-vinylpyridine) copolymers: Precursors to nanostructured carbon materials

An arborescent polystyrene (PS)–graft–poly(2-vinylpyridine) (P2VP) copolymer of overall generation number G2, consisting of side chains with Mn ∼5000, served as template for the preparation of nanostructured carbon films. Spin casting of arborescent PS–graf–P2VP copolymers yielded monomolecular films of uniform thickness. The uniformity of the copolymer films was influenced by the casting solvent selected. Methanol solutions of the copolymers led to non-uniform layers consisting of large aggregates and voids. Homogeneous monolayer films were attained from copolymer solutions in tetrahydrofuran, which is a good solvent for both the PS and P2VP components. The copolymer molecules in the film were strongly flattened by adsorption forces, but recovered a spherical geometry after annealing in water. The water-annealed films could be directly converted into their analogous carbon films having nanodots on the surface by UV irradiation with concurrent pyrolysis. The pyrolyzed nanomaterials exhibited the characteristics of partially graphitic carbon with nitrogen.

Solution based–spin cast processed LPG sensor at room temperature

Liquefied petroleum gas (LPG) sensor was fabricated by solution based-spin casting of thin films of polyaniline-niobium pentoxide (PANI-Nb2O5) composite onto glass substrate at room temperature. The PANI-Nb2O5 composite was synthesized by relatively simple method of in-situ chemical polymerization at room temperature and was structurally characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite was then chemically processed and coated on an easily available glass substrate to obtain a film of the composite by cost effective spin coating technique. The sensing response of 45.21% was observed at 500ppm of LPG at room temperature with a response time of 30s and recovery time of 50s, respectively. The composite showed stable sensing ability over a period of two months with a small degradation of 3.26%.

Utilization of down-shifting photoluminescent ZnO quantum dots on solar cells

We report on the synthesis of photo luminescent zinc oxide (ZnO) quantum dots, their deployment on the window side of photovoltaic structures and the measured influence on the power conversion efficiency. Down-shifting effects were characterized by exciting the synthesized nanostructures with photons in the 340–350 nm range, and measuring the wavelength of the emitted photons observed to be ~500 nm. The colloidal ZnO quantum dots were synthesized in an ethanol-based solution, obtaining different sized nanostructures centered at 4 nm, optically recognizable by their emission in various colors. Subsequently, different concentrations of zinc oxide quantum dots were prepared and dispersed in poly-methyl-methacrylate (PMMA) to be spin cast on the window side of previously characterized solar cells. The observations made to date indicate an improvement of ~4.8% in the PCE. In this work, we discuss the results obtained and suggest pathways to further increase the power conversion efficiency of photovoltaic devices employing quantum dots.

Conductive nonwetting flexible substrate

In this paper an easy method to prepare flexible conductive substrates has been demonstrated. The substrates are mainly PET (PolyEthyleneTerephthalate), on which AgNW (silver nanowire) were deposited by spin casting method. For adhesion purpose a common cosmetic material has been utilized. The material provides versatile features to these coated substrates, including robustness, hydrophobicity with transparent bracing of nanowires (NW) with the flexible substrate. Four probe conductivity measurement shows the resistivity is 12 Ω/cm and is comparable to that of commercially available indium tin oxide (ITO) coated substrates. This method is cheap, easy and can be used for different objectives like flexible thin film photovoltaic, light emitting diodes, photosensors etc.

Organic-inorganic hybrid fluorescent sensor thin films of rhodamine B embedded Ag-SBA15 for selective recognition of Hg (II) ions in water

Nowadays, the rapid and effective detection of low doses of heavy metal pollutants in contaminated water is a timely challenge in environmental pollution research. In this study, a rapid and highly sensitive assay for the detection of Hg2+ based on quenching of metal-enhanced fluorescence of rhodamine B (RB) has been fabricated. RB and silver nanoparticle were incorporated into the mesoporous siliceous framework spin cast on a quartz glass through post-synthetic incorporation method. The morphology and crystallinity of mesoporous structure and Ag nanoparticle were characterized by transmission electron microscopy and X-ray diffraction analyses. Photoluminescence assays on the hybrid thin film of RB-Ag-SBA15 showed a high enhancement when compared to the intensity of silver free SBA15-RB in the wavelength of 575nm. The fluorescence of RB-Ag-SBA15 thin film decreased gradually with the increase in the concentration of Hg2+ and the detection limits were 10.54nmol/L. Furthermore, the fluorescence intensity increased linearly with the concentration of Hg2+ in the range from 1.0×10−8mol/L to 10×10−8mol/L, with a response time of a few seconds. In addition, this system offers a high selectivity over interfering cations such as Cd2+and Pb2+. Overall, we have developed an optical assay having a well-ordered mesoporous SBA15 containing Ag-RBfor selective detection of Hg2+ in aqueous solution. The scheme combines the advantages of specific binding interactions between Hg2+ and RB molecule and optical emission properties of RB. The method is suitable for a single-shot and irreversible analytical assay in a quartz glass/microtiter plate.

Highly dispersible edge-selectively oxidized graphene with improved electrical performance.

We prepared liquid phase exfoliated edge-selectively oxidized graphene (LPEOG) with a high concentration in water (∼14.7 mg ml-1) and a high ratio of a single layer (70%). The edge of graphite was selectively oxidized by step II oxidation of the modified Hummers method, and we subsequently exfoliated the edge-selectively oxidized graphite (EOG) into LPEOG. The edge selective oxidation of the LPEOG was confirmed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), zeta-potentiometry, Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The highly concentrated LPEOG ink can be used in solution processing such as simple drawing or spin casting. Reduced LPEOG showed a higher conductivity (120 000 S m-1) than that of reduced graphene oxide (68 800 S m-1) despite the small lateral size. A transparent conducting film prepared from the LPEOG ink showed a lower surface resistance (∼2.97 kΩ sq-1) at a higher transmittance (>83.0 %T) compared to those of the graphene oxide based film. These results indicate that preservation of π-conjugation of the basal plane of graphene is critical for electrical performance of graphene. Our method facilitates solution processing of graphene for a wide range of applications.

Convective self-assembly of π-conjugated oligomers and polymers

AFM images depicting the morphology of two films of TH13 oligomers deposited by spin casting (left) and CSA (right).

Panchromatic Sequentially Cast Ternary Polymer Solar Cells.

A sequential-casting ternary method is developed to create stratified bulk heterojunction (BHJ) solar cells, in which the two BHJ layers are spin cast sequentially without the need of adopting a middle electrode and orthogonal solvents. This method is found to be particularly useful for polymers that form a mechanically alloyed morphology due to the high degree of miscibility in the blend.

Fabrication of selenization-free superstrate-type CuInS2 solar cells based on all-spin-coated layers

Today manufacturing of high efficiency chalcogenide thin film solar cells is based on high cost vacuum-based deposition processes at high temperature (>500 °C) and in chalcogen -containing atmosphere. In this paper, we introduce a simple vacuum-free and selenization-free, solution processing for fabricating a superstrate-type CuInS2 (CIS) solar cell. The absorber, buffer and blocking layers were all deposited by spin coating of molecular precursor inks. We demonstrate the deposition of In2S3 buffer layer by sol-gel spin casting for the first time. The rapid sintering process of CIS layer was carried out at 250 °C that is considered a very low temperature in CIGS thin-film technologies. A novel molecular-ink route to deposit In2S3 type buffer layer is presented. For the back contact we employed carbon, deposited by simple knife coating method. Different parameters including type of buffer, thickness of absorber layer, CIS and In2S3 annealing temperature and morphology were optimized. Our air stable simple device structure consisting of <Glass/FTO/TiO2/In2S3/CIS/Carbon > showed promising power conversion efficiency (PCE) of 2.67%.

Solution processed n-In2S3/p-P3HT planar hybrid solar cell

In2S3 is one of the widely used semiconductors in optoelectronic applications. It has already been used as an n-type buffer layer instead of highly toxic CdS semiconductor in copper indium sulfide based inorganic thin film solar cells. In this work, thin films of In2S3 were prepared on ITO coated glass and glass substrates by a solution based spin casting process. The optical, morphological, and structural characterizations of the In2S3 thin film were studied by Uv-vis spectroscopy, X-ray diffraction, and scanning electron microscopy. According to the X-ray diffraction result the thin film exhibited tetragonal β-phase. The Uv-vis study showed that the In2S3 film exhibited optical band gap of ~2.42 eV. Furthermore, a thin film of In2S3 has also been applied as an inorganic electron accepting semiconductor layer for preparing the planar inorganic/organic hybrid solar cell. The hybrid device with the In2S3 layer exhibited performance with an open-circuit voltage (Voc) of ~0.343 V, short-circuit current density (Jsc) of ~0.528 mA/cm2, fill factor of ~0.53, and power conversion efficiency (η) of ~0.12 %.

Photovoltaic properties of low temperature solution processed earth abundant CuO nanocrystal‐based hybrid solar cells

p‐type copper oxide (CuO) nanocrystals were prepared by a wet chemical method and are used to make thin films by spin casting. CuO nanocrystals were characterised using XRD, Raman, TEM and XPS. Low temperature solution processed thin films of CuO crystals showed a hole mobility of 4.57 × 10−4 cm2 V−1 s−1 perpendicular to the plane of the film and is measured using space charge limited current method. Due to the difficulty in making solution processed homo p–n junction and n‐doping of CuO, a planar hybrid heterojunction solar cell is fabricated using solution processed CuO and a n‐type organic material, [6,6]‐phenyl‐C70 butyric acid methyl ester (PCBM). A power conversion efficiency of 0.23% is obtained for hybrid solar cell comprising CuO as active layer where all the device fabrications were carried out at temperature ≤100 °C. Analysis of the current density–voltage (J–V) characteristics at different light intensities is carried out to unravel the recombination mechanism occurring at the interface. Further, effect of annealing the active layer on the photovoltaic performance is investigated.

Laser cladding strategies for producing WC reinforced NiCr coatings inside twin barrels

Abstract Thick and hard coatings are widely applied in a substantial number of heavy-duty industrial applications to improve wear and corrosion resistance. The techniques that allow producing depositions of metallic, ceramic or metallic-ceramic mixtures in zones with difficult access, like inner walls of a cylinder, are quite limited. Methods like spin casting, for instance, are successfully applied in parts with cylindrical symmetry. Nevertheless, when parts with more complex geometries have to be coated, new solutions must be applied. The use of laser cladding as a possible alternative for these applications is studied in the present work. Coatings of a NiCr matrix reinforced with hard tungsten carbide particles were produced in internal walls. Carbides with different shape and size were employed in order to find the most suitable candidate for producing defect free coatings with maximum thickness. In order to achieve this goal, the effect of different processing parameters was investigated. The use of preheating and a soft buffer layer were also considered for minimizing the thermal stresses produced during the rapid cooling of the coating, from the melting point to the solid state.

Radiative recombination kinetics in electroluminescent spin cast pristine α-4T

Many experimental studies have established the substantial impact of the sound structure of the organic thin films on optoelectronic device performances. This study is a collection of experimental and theoretical investigation of the radiative recombination kinetics in an organic light emitting diode based on spin cast α-4T. The structural properties of the organic thin films (α-4T) deposited by the spin coating technique are discussed. The electrical characterization of the diode-like samples (ITO/α-4T/Al) have revealed a very low effective mobility of charge carriers in the spin cast α-4Tand the radiative recombination current was extracted. The luminescence-current characterization of the diode-like samples (ITO/α-4T/Al) was investigated and modeled.

Dithienopyrrole-benzodithiophene based donor materials for small molecular BHJSCs: Impact of side chain and annealing treatment on their photovoltaic properties

Two small molecular organic materials denoted as ICT1 and ICT2 with A-D1-D2-D1-A architecture have been synthesized and their thermal, photo-physical, electrochemical and photovoltaic properties are explored. Synthesized materials have n-butylrhodanine acceptor (A), dithienopyrrole (DTP) (D1) and benzodithiophene (BDT) (D2) (Alkoxy BDT and alkylthiophene BDT, respectively for ICT1 and ICT2) donor moieties. Both the materials have good solubility (up to 25 mg/mL) in most common organic solvents and have excellent thermal stability with the decomposition temperature (Td) as 348 and 382 °C, respectively for ICT1 and ICT2. Both ICT1 and ICT2 have broad and intense visible region absorption (molar excitation coefficient is 1.71 × 105 and 1.65 × 105 mol−1 cm−1, respectively for ICT1 and ICT2) and have suitable HOMO and LUMO energy levels for PC71BM acceptor. Bulk heterojunction solar cells with ITO/PEDOT:PSS/blend/Al structure are fabricated using these materials. The BHJSCs fabricated by spin cast of ICT1:PC71BM and ICT2:PC71BM (1:2 wt ratio) blend from chloroform showed power conversion efficiency (PCE) of 2.77% (Jsc = 6.84 mA/cm2, Voc = 0.92 V and FF = 0.44) and 3.27% (Jsc = 7.26 mA/cm2, Voc = 0.96 V and FF = 0.47), respectively. Annealing the active layer significantly improved the PCE of these BHJSCs to 5.12% (Jsc = 10.15 mA/cm2, Voc = 0.87 V and FF = 0.58) and 5.90% (Jsc = 10.68 mA/cm2, Voc = 0.92 V and FF = 0.60), respectively for ICT1 and ICT2 donors. The enhancement in the PCE is due to higher light harvesting ability of the active layer, better nanoscale morphology for efficient and balanced charge transport and effective exciton dissociation at the donor-acceptor interface.

ОПТИМИЗАЦИЯ ТЕХНОЛОГИИ ИЗГОТОВЛЕНИЯ ЦЕНТРОБЕЖНОЛИТЫХ ВАЛКОВ

This paper reports the sheet roll spun casting. It is shown that sheet rolls of required quality and with minimum production costs are manufactured through a method of spun casting on a machine with a vertical axis of a mould rotation. It is defined that at spun casting a more intensive foundry cooling occurs as a result of which a blank is characterized with a denser and more even structure of a working layer. It is revealed that the stability of such a process depends to a considerable degree upon a spin casting system functioning a significant property of which is a speed of rotation. In the paper there is analyzed a rotation speed influence upon a grain size, a quantitative ratio of structural constituents in a working layer composed of nickel-chromium cast iron and also upon the level of its properties. The analysis of the rotation speed influence of a casting mold upon a structure and a property level of a roll working surface was based on experimental investigations of foundries under industrial conditions. The microstructure (the size of primary grains, their composition) of products analyzed was estimated with the aid of a common metallographic procedure. On the basis of experiments carried out it is determined that even an insignificant increase (by 7%) of mould rotation speed during roll casting allows without expensive processing of liquid melt of a work-ing layer increasing its structure uniformity. As a result of this the level of its properties increases (hardness – by 3 units). Consequently, the increase of rolling tool efficiency is expected. The presented results of investigations are basic for works on servicing characteristics increase of spin-cast rolls.

Solution-based Spin Cast Processed Polypyrrole/Niobium Pentoxide Nanocomposite as Room Temperature Liquefied Petroleum Gas Sensor

In the present work, fabrication of polypyrrole (PPy)/niobium pentoxide (Nb2O5) nanocomposite as room temperature liquefied petroleum gas (LPG) sensing device is reported. Nb2O5 nanoparticles were combined with PPy via chemical polymerization to obtain PPy/Nb2O5 nanocomposite structure and was characterized for structural and morphological studies by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. Then, the nanocomposites were chemically processed and coated on easily available glass substrate to obtain a film of the composite by cost-effective spin coating technique and a sensing response of 38.125% was observed at 500 ppm of LPG at room temperature with a response time of 75 s and recovery time of 98 s. The sensing mechanism is discussed with the help of energy band diagram.

Investigation of wettability and moisture sorption property of electrospun poly(N-isopropylacrylamide) nanofibers

ABSTRACTPoly(N-isopropylacrylamide) (PNIPAM) has been used extensively for numerous biomedical applications. However, there is not enough information in the literature on the wettability and hygroscopic properties of electrospun PNIPAM fibers, relevant for water harvesting applications. This study focuses on investigating the wettability and hygroscopic properties of electrospun PNIPAM fibers at room temperature and elevated temperature. The wettability properties of electrospun PNIPAM fibers were compared to spin-coated PNIPAM thin films. The wettability properties of the electrospun fibers were enhanced by 56% compared to spin-coated films. Water contact angle (WCA) measured on electrospun fibers was determined to be 137° at elevated temperatures while WCA on spin cast PNIPAM film was determined to be 81° at elevated temperatures. Furthermore, hygroscopic properties of the electrospun PNIPAM fibers were studied using thermogravimetric analysis (TGA). The PNIPAM fibers are seen to exhibit moisture absorption capacity of about 16.6 wt. % under humid conditions.

Solar heat reflective coating formed of polystyrene chains bearing 4-vinylpyridine-rich end segments

Incorporation of a minor dose of 4-vinylpyridine (4-VP) into an end segment of polystyrene (PS) chain by emulsion copolymerization yields a copolymer molecule P(4-VP/S) with weak surface-activity. The spin cast thin films of P(4-VP/S) display enhanced solar light reflectance of R = 80–90% compared with its PS homopolymer counterpart. It is imperative to use dimethylformamide (DMF) as casting solvent because the hydrophilic nature of DMF induces core-to-grain assembling while dried in humid air, leading to a nodular film matrix. A rise of 4-VP dose in P(4-VP/S) causes a breath-figure patterned matrix instead and consequently an obvious reduction of reflectance in the near-infrared region. Mechanistically, P(4-VP/S) chains that bear a short end-segment with rich 4-VP units constitute tiny hydrophilic cores because of entrapment of moisture during drying, surrounding which the long PS tails thus undergo chain coiling to form nanoparticles. They then aggregate to form submicron grains in rosette and the partial coalescence of adjacent grains results in micron lumps. Such hierarchical evolution finally constructs a matrix exhibiting an enhanced solar reflectance.

Effect of Drying Time on Morphology and Photovoltaic Characteristics of Polymer Solar Cells of Bis-PCBM/P3HT Composites

Slow drying has been proposed as a way to improve the performance of polymer solar cells (PSCs) where the drying time for the coated films is increased using a condensed solvent vapor atmosphere. This work investigated the slow drying mechanism by using PSCs consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and bis-[6,6]-phenyl-C61-butyric acid methyl ester (bis-PCBM) and focusing on the phase-separated morphology of bulk heterojunction films. With conventional spin casting, the power conversion efficiency (PCE) of the cells was very low (0.83%). The application of slow drying resulted in notable improvements in the short-circuit current density (5.85 → 8.07 mA/cm2) and fill factor (0.12 → 0.55). Optimization of the thermal annealing and cathode interfacial conditions resulted in a high PCE of 4.05%. As the drying time was increased, the P3HT domains changed from connected band-like shapes to small separated ball-like shapes. The mechanism for this effect of slow drying on the bis-PCBM/P3HT cell characteristics is understood as follows: The slow drying causes the P3HT domains to separate into small pieces, which causes the area of the p−n interfaces to increase, resulting in an increase in free carrier generation and increased the short-circuit current density of PSCs.