Spin-coating Speed Research Articles

Improving Light Extraction of Organic Light-Emitting Devices by Attaching Nanostructures with Self-Assembled Photonic Crystal Patterns

A single-monolayered hexagonal self-assembled photonic crystal (PC) pattern fabricated onto polyethylene terephthalate (PET) films by using simple nanosphere lithography (NSL) method has been demonstrated in this research work. The patterned nanostructures acted as a scattering medium to extract the trapped photons from substrate mode of optical-electronic device for improving the overall external quantum efficiency of the organic light-emitting diodes (OLEDs). With an optimum latex concentration, the distribution of self-assembled polystyrene (PS) nanosphere patterns on PET films can be easily controlled by adjusting the rotation speed of spin-coater. After attaching the PS nanosphere array brightness enhancement film (BEF) sheet as a photonic crystal pattern onto the device, the luminous intensity of OLEDs in the normal viewing direction is 161% higher than the one without any BEF attachment. The electroluminescent (EL) spectrum of OLEDs with PS patterned BEF attachment also showed minor color offset and superior color stabilization characteristics, and thus it possessed the potential applications in all kinds of display technology and solid-state optical-electronic devices.

Characterization of ProTEX<sup>®</sup> PSB Thin Film as a Photosensitive Layer for MEMS Capacitive Pressure Sensor Diaphragm Based on SiC-on-Si Wafer

The ProTEX® PSB thin film as a photosensitive layer has been released in the market as an alternative replacement for silicon nitride or silicon oxide wet etch masks. In this work, this film has been deposited on SiC-on-Si wafer for the back-etching of the bulk Si to leave SiC thin film to be used as a pressure sensor diaphragm. This paper will discuss the process flow to estimate the optimized ProTEX® PSB thin film thickness for the sufficient back-etching of the 300um bulk Si. This thickness is defined by the following parameters: spin-coating rotational speed, final cure temperature and hard bake time of coating. Several samples of ProTEX® PSB thin films have been preliminary characterized by infinite focus microscopy (IFM) and scanning electron microscopy (SEM) to examine the substrate surface conditions and the effects of undercut edges structure. Based on these data, it was determined that the optimum thickness of ProTEX® PSB for this project is 2.133 μm with the spin speed of 3000 rpm, the first bake temperature of 110 °C in 120 seconds and the second bake temperature of 240 °C in 60 seconds. We conclude that ProTEX® PSB can withstand the etch mask with etch rate of 1.28 μm/min for 8 hours and gives good quality effect of undercut edge on the SiC-on-Si wafer.

Conducting polymer/in-situ generated platinum nanoparticle nanocomposite electrodes for low-cost dye-sensitized solar cells

Here we report new low-cost nanocomposite counter electrodes for dye-sensitized solar cells (DSSCs), which were prepared by in-situ generation of platinum (Pt) nanoparticles inside poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solutions at room temperature. The Pt nanoparticles (Ptnp) were evenly dispersed in the PEDOT:PSS films and their size was 20∼40nm. The PEDOT:PSS-Ptnp films were well coated on substrates, and their optical transmittance was slightly better than conventional thermally-reduced Pt electrode. The short circuit current density of DSSCs with the PEDOT:PSS-Ptnp films was almost comparable to that with the conventional Pt film. The thickness control experiment disclosed that the series resistance of the PEDOT:PSS-Ptnp films is mainly responsible for the low fill factor. We found that the Ptnp was enriched on the surface of the nanocomposite films when the spin-coating speed was high, which has been assigned as an additional reason for the improved device performance. Hence further improvement in device performance is expected by employing high conductivity PEDOT:PSS materials. Finally, we expect that the present method can contribute to the fabrication of low-cost DSSCs using flexible plastic film substrates at low temperatures.

A comprehensive study of the reaction parameters involved in the synthesis of Silica thin films with well-ordered uni-directional mesopores

Ordered mesoporous thin films with well-orientated channels are an important feature in a series of applications including sensors, optics, photocatalysis, and solar cells. However, their preparation remains a great challenge. The structural optimization of highly organized mesoporous silica thin films, with channels perpendicularly orientated to the surface and prepared by a spin-coating technique, is reported. A large series of reaction parameters were revisited with a deep investigation such as the template, solvent, aging time, pH, rotation speed, and duration of spin-coating. The best conditions for each of these different parameters were subsequently used together to control the pore size and channel orientation of the well-organized films. Characterization of the films performed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the films had homogeneous pores with a uni-directional orientation. Atomic force microscopy (AFM) and ellipsometric porosimetry analysis (EP) were employed to determine the orientation of the channels, pore size distribution, specific surface, thickness, and the accessible porosity. The present work constitutes an overall view of the different parameters which influence the formation of silica thin films, such as the thickness and the pore size distribution of a film which can be tailored to suit a potential application. The wettability properties of thin films have been studied by measuring the contact angle with different solvents such as water, isopropanol, and toluene.

Correlation of SiO x layer thickness and properties of BOPP/SiO x composite films with spin coating process parameters

The effects of the spin coating process parameters on the thickness of the SiO x layer of the BOPP/SiO x composite film were investigated. When the concentration of tetraethoxysilane (TEOS) increased from 12.5 vol% to 55% vol%, the SiO x thickness increased from about 80 nm to 470 nm. In the sol time range of 1.5 h to 5 h the SiO x layer thickness reached a maximum at about 4 h and the change of the thickness roughly matched the change of the silica colloidal sphere sizes in sol. When the spin-coating speed of the dispensing stage increased from 450 r/min to 500 r/min, the SiO x layer thickness drastically decreased from about 1.67 μm to 400 nm. While the spin-coating speed of the thinning and drying stage went up to 1200 r/min, the SiO x layer thickness was in the range of 330 nm to 390 nm. It was also found that the SiO x layer thickness was almost increased linearly from about 500 nm to 1.02 μm with the ratio of the commercial silica colloidal to the TEOS from 0.2 to 1.0. The water contact angles decreased to about 23.0° for the BOPP/Si-Sol composite film with 1.67 μm SiO x layer and about 4.0° for the BOPP/mixing Si-Sol composite film with 1.02 μm SiO x layer. Compared to BOPP, the light transparency of the BOPP/Si-Sol composite films decreased by about 5.5% with the SiO x layer from about 80 nm to 1.67 μm and by 7.0% for the BOPP/mixing Si-Sol composite film with the SiO x layer from about 350 nm to 1.02 μm respectively.

High-efficiency ITO-free polymer solar cells using highly conductive PEDOT:PSS/surfactant bilayer transparent anodes

By spin-coating a surfactant layer, glycerol monostearate (GMS) atop poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film, a PEDOT:PSS/surfactant bilayer film was prepared facilely for the first time and applied as the transparent anode for high-efficiency ITO-free bulk heterojunction polymer solar cell (BHJ-PSC) devices. A significant improvement of the conductivity of PEDOT:PSS films (from ∼1 S cm−1 to more than 1000 S cm−1) was achieved by GMS modification and the highest conductivity reaches 1019 S cm−1 for Clevios PH 1000 under an optimized spin-coating speed of GMS layer. The Clevios PH 1000/GMS bilayer film exhibits a sheet resistance of 98 Ω sq−1 and a transparency of around 80% in the visible range, which are comparable to those of ITO, fulfilling its function as the transparent anode. The conductivity improvement by GMS modification is proposed to result from the GMS-induced segregation of PSS chains and the conformational change of the conductive PEDOT chains within PEDOT:PSS. While the highly hydrophobic –(CH2)16CH3 groups of GMS preferentially interact with the hydrophobic PEDOT of PEDOT:PSS, the highly hydrophilic –COOCH2–CHOH–CH2OH groups preferentially interact with the hydrophilic PSS chains with the hydroxyl groups playing an important role on the consequent phase separation between PEDOT and PSS chains. Using Clevios PH 1000/GMS bilayer films as the transparent anodes replacing ITO, high-efficiency ITO-free BHJ-PSC devices based on poly[N-9′′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT) blended with [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) (PCDTBT:PC71BM) and thieno[3,4-b]-thiophene/benzodithiophene (PTB7):PC71BM systems exhibit power conversion efficiencies (PCE) of 5.90% and 7.06%, respectively, which are comparable to the corresponding devices based on the traditional ITO anode.

Efficiency Enhancement of Polymer Solar Cells by Applying Poly(vinylpyrrolidone) as a Cathode Buffer Layer via Spin Coating or Self-Assembly

A non-conjugated polymer poly(vinylpyrrolidone) (PVP) was applied as a new cathode buffer layer in P3HT:PCBM bulk heterojunction polymer solar cells (BHJ-PSCs), by means of either spin coating or self-assembly, resulting in significant efficiency enhancement. For the case of incorporation of PVP by spin coating, power conversion efficiency (PCE) of the ITO/PEDOT:PSS/P3HT:PCBM/PVP/Al BHJ-PSC device (3.90%) is enhanced by 29% under the optimum PVP spin-coating speed of 3000 rpm, which leads to the optimum thickness of PVP layer of ~3 nm. Such an efficiency enhancement is found to be primarily due to the increase of the short-circuit current (J(sc)) (31% enhancement), suggesting that the charge collection increases upon the incorporation of a PVP cathode buffer layer, which originates from the conjunct effects of the formation of a dipole layer between P3HT:PCBM active layer and Al electrodes, the chemical reactions of PVP molecules with Al atoms, and the increase of the roughness of the top Al film. Incorporation of PVP layer by doping PVP directly into the P3HT:PCBM active layer leads to an enhancement of PCE by 13% under the optimum PVP doping ratio of 3%, and this is interpreted by the migration of PVP molecules to the surface of the active layer via self-assembly, resulting in the formation of the PVP cathode buffer layer. While the formation of the PVP cathode buffer layer is fulfilled by both fabrication methods (spin coating and self-assembly), the dependence of the enhancement of the device performance on the thickness of the PVP cathode buffer layer formed by self-assembly or spin coating is different, because of the different aggregation microstructures of the PVP interlayer.

Optimization of thermally reduced graphene oxide for an efficient hole transport layer in polymer solar cells

In this work, graphene oxide (GO) reduced by thermal annealing was employed as a hole transport layer (HTL) in bulk heterojunction (BHJ) solar cells. Considering the insulating property of nonreduced GO, the annealing temperature plays an important role in recovering the conjugated structure of the graphene sheet, and thereby the conductivity of GO. BHJ solar cells with high-temperature (e.g., 230°C) reduced GO as the HTL showed much larger fill factor (FF) than devices with low-temperature (e.g., 130°C) reduced GO as the HTL, indicating the better conductivity of GO annealed at an elevated temperature due to the removal of oxygen functional groups from the graphene sheet to a much-higher level. On the other hand, the work function of GO may be lowered toward that of graphene (4.5eV) with increasing the reduction temperature, which results in a decreased open-circuit voltage (Voc) for the high-temperature reduced GO devices. By further optimizing the concentration and spin-coating speed of GO dispersion, we achieved a power conversion efficiency (PCE) that is 26% higher than devices without any HTL. This is mainly attributed to the increase in FF as a result of the decreased series resistance (Rs). In addition, the PCE of the optimized GO device was ∼85% of the PCE of the conventional device with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL. We anticipate that further optimization of the reduction conditions (e.g., using chemical reductants) will lead to the better performance of GO solar cells.

Nano-fibrils formation of pBTTT via adding alkylthiol into solutions: Control of morphology and crystalline structure

A large amount of dispersed pBTTT12 nano-fibrils formed easily by adding the additives to its o-dichlorobenzene solution to change the solution aggregation. It is found that a proper solubility parameter difference between polymer and additives (as large as 4 J1/2 cm−3/2) and a high boiling point of the additives are two important parameters for choosing the additives. 1-dodecanethiol is a promising additive for pBTTT12 o-dichlorobenzene solution, which can decrease the aggregation size distribution and disentangle unimer chains which are the building blocks of nano-fibrils. Under a slow spin-coating speed, coils tend to form dispersed nano-fibrils in terms of both thermodynamics and kinetics. Moreover, 1-dodecanethiol molecules intercalated into the free volume of adjacent alkyl side-chains of pBTTT molecules and change the crystalline structure. It was found that the distance between (100) crystalline planes became larger when the content of 1-dodecanethiol increased.

Parametric Study and Thickness Evaluation of Photoresist Development for the Formation of Microgap Electrodes Using Surface Nanoprofiler

A compact nanolaboratory on single chip is one of the challenging tasks for future reproductively of sensitive and selective lab-on-chip. This paper reports a simple and controllable technique for patterning microgap structures on (PR-1 2000A) positive photoresist. For the pattern transformation conventional lithography technique was used integrated with precise resolution mask namely chrome mask. This technique provides an especially simple method for the formation of micro features sizes of gaps onto the photoresist. The thickness of developed microgap structures on photoresist directly relates with the coating speed of spin coater.

Flexible White Organic Light-Emitting Devices with a Porous Red Polymer Layer and a Blue Small Molecular Layer Utilizing a Phase Separation of Blended Polymer

Flexible white organic light-emitting devices (WOLEDs) with an emitting layer consisting of a porous red poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) polymer layer and a blue 4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl (DPVBi) small molecular layer were fabricated on polyethylene terephthalate substrates. The current density of the flexible WOLEDs fabricated with a blend layer formed with a higher spincoating speed was significantly higher than that of a device fabricated with a lower spincoating speed, due to the higher pore density. The ratio between the red and the blue color peak intensities of the electroluminescence spectra for the flexible WOLEDs with a porous red MEH-PPV polymer layer and a blue DPVBi small molecular layer was controlled by the spincoating speed of the blend layer.

Corrugated structure through a spin-coating process for enhanced light extraction from organic light-emitting diodes

We have demonstrated a simple fabrication method for an out-coupling structure to enhance light extraction from organic light-emitting diodes (OLEDs). Spin-coating of SiO2 and TiOx sol mixture solution develops corrugated film. The structural evolution of the corrugation was explained by the localization of surface tension during the solvent evaporation. The structural parameters of the corrugated structure were characterized by varying the spin-coating speed and the mixing ratio of the solution. Compared to conventional devices, OLEDs with a corrugated structure at the backside of the glass substrate showed increased external quantum efficiency without change in the electroluminescence spectrum. The light extraction enhancement is attributed to the decreased incidence angle at the interface of glass substrate and air.

Thickness Control over Ionomer Coatings on Nano Patterned Three-Phase Zones for a Highly Efficient Electrode

In the present study, a carbon nanotube supported platinum (Pt/CNT) electrode with a thin and uniform ionomer layer as the proton-conducting electrolyte on a nano patterned three-phase zone (TPZ) was fabricated, aiming at high electrocatalytic activity and high charge transfer rate for methanol oxidation reaction (MOR). Unlike conventional paste or spray methods that produced thick and non-uniform ionomer layers to form TPZs within the catalyst layers (50–100 μm) of electrodes, thin and uniform ionomer layers (5-10 nm) on the hydrophilic-treated Pt/CNT catalyst electrodes (8 μm) were harvested by spin-coating. The thickness of the ionomer layer was controlled by altering the spin-coating speed, and the effect of the ionomer thickness on the surface of the catalyst layer and on the electrochemical properties of the electrodes for MOR was studied (mass activity, MA and charge transfer resistance, Rct). Compared to the electrode fabricated by spraying (MA: 355 A g−1, Rct: 48 Ω cm2), the ionomer-coated electrode spin-coated at 4000 rpm exhibited superior properties for MOR (MA: 381 A g−1, Rct: 15 Ω cm2). The outcome renders this new electrode to embrace potential applications in micro direct methanol fuel cells (μDMFCs) with the design of a thin and uniform TPZ.

Self-assembled structures of colloidal silver nanoparticles on solid substrates

With a two-phase method, well-dispersed 5.2 nm Ag nanoparticles with narrow size distribution (±0.5 nm) are synthesized. The assembled structures of colloidal Ag nanoparticles on highly oriented pyrolytic graphite (HOPG), silicon chip and microscopic glass have been investigated by atomic force microscopy (AFM). With different spin-coating speeds and concentrations of colloidal silver nanoparticles, various assembly structures could form on those substrates. On HOPG, Ag nanoparticles were absorbed and aligned along single-atom-height step edges to form a linear one-layer structure. And on silicon chip and microscopic glass, one-layer closed packing fractal structure and two-layer closed packing ring were observed respectively.

Multilayered Poly(vinylidene fluoride) Composite Membranes with Improved Interfacial Compatibility: Correlating Pervaporation Performance with Free Volume Properties

A spin-coating process integrated with an ozone-induced graft polymerization technique was applied in this study. The purpose was to improve the poor interfacial compatibility between a selective layer of poly(2-hydroxyethyl methacrylate) (PHEMA) and the surface of a poly(vinylidene fluoride) (PVDF) substrate. The composite membranes thus fabricated were tested for their pervaporation performance in dehydrating an ethyl acetate/water mixture. Furthermore, the composite membranes were characterized by field emission scanning electron microscopy (FE-SEM) for morphological change observation and by Fourier transform infrared spectroscopy equipped with attenuated total reflectance (ATR-FTIR) for surface chemical composition analysis. Effects of grafting density and spin-coating speed on pervaporation performance were examined. The composite membrane pervaporation performance was elucidated by means of free volume and depth profile data obtained with the use of a variable monoenergy slow positron beam (VMSPB). Results indicated that a smaller free volume was correlated with a higher pervaporation performance of a composite membrane consisting of a selective layer of spin-coated PHEMA on a PHEMA-grafted PVDF substrate (S-PHEMA/PHEMA-g-PVDF). The composite membrane depth profile illustrated that an S-PHEMA layer spin-coated at a higher revolutions per minute (rpm) was thinner and denser than that at a lower rpm.

Efficiency Improvement of Organic Solar Cells by Slow Growth and Changing Spin-Coating Parameters for Active Layers

The derivatives of C60, [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and 3-hexylthiophene (P3HT) were dissolved in o-dichlorobenzene (DCB) solvent, and then spin-coated as an active layer for polymer solar cells. The experimental parameters including the spin-coating speed and drying conditions for the active layer, were studied carefully to obtain the optimum power conversion efficiency (PCE). In the active layer drying procedure, the DCB solvent saturated/unsaturated vapor pressure was adjusted by controlling the amount of solvent at a half-open capacity. The DCB solution was used to enhance the self-organization of the active layer of P3HT and to reduce the number of pure PCBM clusters. In the DCB optimum solution, the PCE of a polymer solar cell can be increased from 1.36 to 1.79%. The structure corresponds to a nano-to-micron scale ordering in the unsaturation-treatment films. In the optimum unsaturation procedure, the PCE of a polymer solar cell can be increased from 1.79 to 2.53%. Using two steps with optimum rotation speeds in the active layer spin-coating, the surface uniformity can be improved, with the PCE increased from 2.53 to 3.13%.

Electrical and Optical Properties of WOLEDs with a Hybrid EML Consisting of Small Molecules

White organic light-emitting devices (WOLEDs) with a hybrid emitting layer (EML) consisting of blue-emitting small molecules and porous red-emitting polymers formed in a blended polymer layer by utilizing a phase separation process were fabricated. The hole injection efficiency from the hole injection layer to the blue EML was improved due to the formation of a partially connected junction between the hole injection layer and the blue EML. The spin-coating speed for the formation of a porous red-emitting polymer layer was optimized on the basis of the electroluminescence spectra for the WOLEDs and the atomic force microscopy images for the surface of the porous polymer layer.

Effect of Spin Speed and Solution Concentration on the Directed Assembly of Polymer Blends

Directed assembly of polymer blends using chemically heterogeneous patterns during spin-coating can be used to produce nanopatterned polymer structures. Well-ordered morphologies are obtained when the characteristic length of a polymer blend is commensurate with pattern periodicity. In this paper, spin-coating speed and solution concentration were used to control the characteristic length of a polystyrene (PS)/poly(acrylic acid) (PAA) blend. With increasing spin speed or reducing solution concentration, the characteristic length decreased. Critical spin speeds or solution concentrations that produced the required characteristic length commensurate with the given pattern periodicity were predicted. Well-ordered morphologies were obtained when spin speed or solution concentration was close to the critical value. A new method of image analysis was introduced to quantitatively evaluate the quality of replication of the underlying pattern. The range of commensurability between characteristic length and pattern...

습식공정 기반 ITO 기판 위 산화아연 나노로드 모폴로지 제어

We report growth of vertically well-aligned zinc oxide (ZnO) nanorods on indium-tin oxide (ITO)/glass substrates using a simple aqueous solution method at low temperature via control of the ZnO seed layer morphology. ZnO nanoparticles acting as seeds are pre-coated on ITO-coated glass substrates. by spin coating to control distribution and density of the ZnO seed nanoparticles. ZnO nanorods were synthesized on the seed-coated substrates in a dipping process into a main growth solution. It was found that the alignment of ZnO nanorods can be effectively manipulated by the spin-coating speed of the seed layer. A grazing incidence X-ray diffraction pattern shows that the ZnO seed layer prepared using the higher spin-coating speed is of uniform seed distribution and a flat surface, resulting in the vertical growth of ZnO nanorods aligned toward the [0001] direction in the main growth process.

Nanochannel Design by Molecular Imprinting on a Free-Standing Ultrathin Titania Membrane

A free-standing ultrathin film of a poly(vinyl alcohol) (PVA)/titania (TiO2) composite was prepared by spin coating. The thickness of the film was adjusted to 30-50 nm by changing the spin-coating speed and the concentrations of PVA and the TiO2 precursor. A template molecule, (4-phenylazo)benzoic acid (4PABA), was introduced into the film as a mixture in the TiO2 precursor and was removed after film formation by dipping the film in aq NH3 (1%). Aqueous solutions of tetraphenylporphyrin tetrasulfonic acid (TPPS), 4PABA, and sodium benzoate (SB) were filtered through this film, and the concentrations of these compounds in the filtered solution were monitored by UV-vis absorption measurements. The filtered TPPS solution was colorless, and its absorbance at 413 nm was 8% that of the original solution. In contrast, almost 100% of SB and 28.4% of 4PABA were passed through the film. The ultrathin TiO2/PVA film obtained without imprinting with 4PABA had no cavities, and aqueous solutions did not pass through this film. Therefore, it was concluded that the nonimprinted film was defect free and that imprinting of the template molecule in the film resulted in the formation of a size-selective channel across a 40 nm thickness.