Spin-coated Films Research Articles

Photo-induced oxygen vacancy formation and anomalous photoconductivity in solution-processed CoFe2O4 thin films

Designing an optoelectronic device requires adequate information about the photo-response of the active material. Here, we have studied the optical and optoelectrical properties of the solution-processed inverse spinel structured CoFe2O4 (CFO) thin film and correlated it with the photovoltaic performance of CFO active material-based all-oxide solar cell. The optical absorption spectra of spin-coated CFO films show the existence of a direct bandgap of 2.64 eV with a maximum absorption coefficient >105/cm. A simple spin-coated CFO/TiO2p–n heterojunction shows an open circuit voltage of over 0.95 V under 1 sun illumination. However, photo-induced oxygen vacancy formation and the desorption of surface oxygen lead to additional electron generation and hole capture, respectively, in the p-type CFO, resulting in an anomalous photocurrent decay under white light illumination, resulting in a low short-circuit current density. This study provides a fundamental understanding of photo-carrier dynamics in solution-processed CFO thin films and apprehends the photophysics of designing spinel-ferrite-based optoelectronic devices.

Optical analyses of spin-coated Mn3O4 thin film

In this paper, Mn3O4 thin film was deposited on a Fluorine doped Tin Oxide substrate by the spin coating technique. X-ray diffraction, Raman spectroscopy, and ultra-violet visible spectroscopy were used to explore the structural and optical properties of Mn3O4 thin film. Raman spectrum confirms the phase of Mn3O4 thin film as tetragonal. The optical band gap has been calculated by using the Tauc’s plot and Kubelka-Munk model. The optical analyses suggest that prepared Mn3O4 thin film can be used as a potential candidate for optical semiconductor devices including photovoltaic cells and optical sensors.

High-consistent optical fiber photoacoustic generator with carbon nanoparticles-PDMS composite

Optical fiber photoacoustic (PA) probe is considered to have great prospects in high resolution invasive imaging due to the advantages of flexible, miniaturized broadband ultrasonic excitation. Unfortunately, more attentions are currently focused on the fabrication of the PA probe with a high PA conversion efficiency, instead of the consistency of the developed probe that is of great importance for practical applications. In this paper, in consideration of the coating thickness and flatness closely concerned with the consistency, a number of PA probes with 15 wt.% carbon nanoparticles (CNPs) and polydimethylsiloxane (PDMS) composite were fabricated by a spin-transfer method with the help of transferring uniformly spin-coated film on the endface of an optical fiber. Underwater ultrasonic detection showed that the fabricated probes exhibited a good consistency with the corresponding lower coefficients of variation of 1.7%, 1.4% and 1.1% for the sound pressure, center frequency and bandwidth, sharply reduced by 89%, 72% and 81% in comparison with the commonly used dip-coating probes tested in this work. Also, due to the thinner film obtained through the presented fabrication method, the maximum PA pressure value of 1.04 MPa with a -6 dB bandwidth of 54.2 MHz was achieved, which further demonstrates a great potential in high-resolution ultrasound imaging utilizing multiple probes with high consistency.

Study of brush coating and spin coating on stannic oxide thin film for the electron transport layer in a perovskite solar cell

This work addresses the challenges associated with using brush coating as a cost-effective and rapid method for large-scale deposition instead of applying a spin coating for the large-scale production of solar cells. This study used brush coating and spin coating techniques to coat a 0.1 M precursor solution onto a cleaned glass substrate. Brush coating utilized a fibril brush, followed by thermal annealing at 180 °C for 1 min, while the spin coating was performed at 1000 RPM for 10 s. Compositional analysis was conducted using Electron Diffraction X-ray (EDAX), and structural analysis employed X-ray Diffraction (XRD). The EDAX analysis confirmed the presence of stannic oxide and XRD data indicated a tetragonal crystal structure of SnO 2, matched with standard data. Scanning Electron Microscopy (SEM) examination revealed that the spin-coated film surface morphology was more effective than the brush-coated film. Additionally, the brush-coated sample demonstrated superior morphology and crystallinity compared to previous research. The optical bandgap, conduction band and valence band edge potentials were determined by UV-spectroscopy. The spin-coated sample exhibited values of 4.02, −1.33 and 2.69 eV, respectively, while the brush-coated sample showed values of 3.98, −1.31 and 2.67 eV, respectively. The valence band maximum and conduction band minimum binding energies were determined using the core level binding energy in the XPS spectroscopy data. Overall, brush coating and spin coating exhibited similarities with minor differences. We may infer that the main drawback of this approach lies in the surface morphology, which can be mitigated through careful management of the coating rate and heat treatment.

Impact of solvents on doctor blade coatings and bathocuproine cathode interlayer for large-area organic solar cell modules

Efforts to commercialize organic solar cells (OSCs) by developing roll-to-roll compatible modules have encountered challenges in optimizing printing processes to attain laboratory-level performance in fully printable OSC architectures. In this study, we present efficient OSC modules fabricated solely through printing methods. We systematically evaluated the impact of processing solvents on the morphology of crucial layers, such as the hole transport, photoactive, and electron transport layers, applied using the doctor blade coating method, with a particular focus on processability. Notably, deposition of charge transport layer using printing techniques is still a challenging task, mainly due to the hydrophobic characteristic of the organic photoactive layer. To overcome this issue, we investigated the solvent effect of a well-studied cathode interlayer, bathocuproine (BCP). We were able to form a uniform thin BCP film (∼10 nm) on a non-fullerene based organic photoactive layer using the doctor bladed coating method. Our results showed that the use of volatile alcohols in the BCP processing required a delicate balance between wettability and vaporization, which contrasted with the results for spin-coated films. These findings provide important insights into improving the efficiency of printing techniques for depositing charge transport layers. The fully printed OSC modules, featuring uniform and continuous BCP layer formation, achieved an impressive power conversion efficiency of 10.8% with a total area of 10.0 cm2 and a geometrical fill factor of 86.5%.

Co-evaporated p-i-n perovskite solar cells with sputtered NiOx hole transport layer

Metal oxides have long been used as charge transport layers in thin film solar cells due to their suitable energy band levels, high charge carrier mobilities, and excellent long-term stability. One example is non-stoichiometric nickel oxide (NiOx), a hole transport material which can be deposited in a conformal, scalable, and solvent-free manner via sputtering. However, sputtered NiOx has only ever been combined with spin-coated perovskite films in perovskite solar cells (PSCs). Here we report the fabrication of the first co-evaporated PSCs with sputtered NiOx as the hole transport layer. We reveal how the amount of argon gas used during sputtering affects important physical properties such as hole conductivity, visible light transmittance, and suitability of the NiOx surface for perovskite nucleation and growth. Optimized sputtering conditions led to CH3NH3PbI3 (MAPbI3) PSCs with an 18.6% power conversion efficiency (PCE), which was further increased to 19.5% by adding a spiro-TTB interlayer between NiOx and MAPbI3. We also show that removing the NiOx annealing step only reduced the device PCE by 1%, paving the way toward low-temperature deposition of metal oxide transport layers. This work exhibits the versatility of NiOx sputtering and perovskite evaporation as a powerful combination for solvent-free and low-temperature fabrication of highly efficient PSCs.

Responsive polymer thin films

Responsive polymer thin films

Variation of Charge Carrier Dynamics for Polycrystalline Perovskite Films by One-Step Solution and Vapor-Deposition Methods.

To date, solution-processing and vapor-deposition fabrication methods have achieved huge successes in high-efficiency perovskite solar cells (PSCs) and satisfy special demanding requirements for diverse application purposes, respectively. Although people realize that the fabrication procedure is crucial in device performance, insightful studies of charge carrier dynamics in perovskite films by different methods still lack. In this work, we compare the carrier behaviors in one-step spin-coated and dual-source coevaporated MAPbI3 perovskite films by combining time-resolved photoluminescence spectroscopy and carrier dynamics simulation. We suggest that strains, lattice orientations, and defects at buried side of perovskite films, which are associated with different preparation processes, lead to variations in carrier behaviors. Hence fabrication of perovskite layers should be elaborately designed in order to satisfy the needs of different carrier behaviors in specified device configurations of PSCs such as smooth planar or textured monolithic tandem structures.

Single oscillator model assessments and dielectric loss of non-crystalline brilliant green films, and characterization of brilliant green/p-Si photodetectors

Herein, spin-coated brilliant green films (from 95 to 237 nm) were characterized by an X-ray diffractometer (XRD). The extracted cell parameters of the analyzed monoclinic unit cell are a = 14.9650 Ǻ, b = 11.7708 Ǻ, c = 10.6658 Ǻ, α=90.00 Ǻ, β=134.76 Ǻ and γ=90.00 Ǻ, and space group P2. The extracted characteristic XPS peaks for brilliant green thin films at 283.82, 531.49, 398.44 and 168 eV are assigned to C 1s, O 1s, N1 s and S 2p, respectively. All the fabricated brilliant green films exhibit noncrystalline nature with indirect bandgaps. The recorded transmittance and reflectance are used to calculate the absorption coefficient. The refractive index of the brilliant green thin films is estimated by mathematical relations, depending on the extracted optical energy gap. In the non-absorbing region, the absorption edges are overlapped for all films at >1600 nm. The rate of optical energy dissipation revealed two triggering peaks in the visible region at 1.85 and 2.87 eV and 4.1 and 5.3 eV in the ultraviolet region with a higher absorption coefficient. The Cauchy and Sellimeier models analyzed and simulated observed dispersion data. The estimated values of the ideality factor, =3.41, the reverse saturation current, Io=1.06×10−7A and =0.64 eV. The junction resistance, Rj, demonstrated reasonable rectification with low series resistance, Rs =795 Ω, and shunt resistance, Rsh =0.21 MΩ. The photodetector parameters of the brilliant green/p-Si interfaces are characterized, such as the SNR and LDR ratios, and show a linear, stable response with the photon energy ranging from 7 to 32 mW/cm2. The evaluated detectivity has values of order 1011 Jones with no detect value distortion.

Tuning Thermoelectric Properties of Spin-Coated Cu2SnS3 Thin Films by Annealing

Tuning Thermoelectric Properties of Spin-Coated Cu2SnS3 Thin Films by Annealing

Regulation of dewetting and morphology evolution in spin-coated PS/PMMA blend films via graphene-based Janus nanosheets

Spin-coated blend films with complex phase-separated morphology find broad applications while precise tailoring of the morphology is still challenging. In this study, graphene oxide (GO)-based Janus nanosheets were synthesized by interfacial polymerization in a GO nanosheet stabilized Pickering emulsion with polystyrene (PS) and poly(hydroxyethyl methacrylate) synchronously being grafted to the GO nanosheet from the oil and water sides. The Janus nanosheets make the morphology of spin-coated PS/poly(methyl methacrylate)(PMMA) blend films tunable over the full height of the film until the substrate as their preferential assembly at the PS/PMMA interface and attachment on the glass substrate drive the top PS phase to migrate towards the substrate and the bottom PMMA phase to dewet from the substrate towards the air. By varying blend composition and Janus nanosheet loading, morphologies are readily transformed from a PS network on top of PMMA to PS droplets in the PMMA matrix and from PS encapsulated by PMMA to PMMA cavities in the PS network, etc.. This enables generating thin films with various morphologies ranging from a flat surface to cavity-network structures, droplet-matrix structures or bi-continuous structures, etc. at will. Moreover, the morphologies trapped by jammed nanosheets at the interface are super stable against further evolution upon annealing.

Influence of rectangular substrate chamfer on edge bead effect of a spin-coated thin film

Spin coating is a common method for fabricating thin films. The edge bead effect is a major contributor to thin film non-uniformities. This study investigates the influence of chamfer angles and widths of a rectangular substrate on the edge bead formation mechanism in spin-coated films. Through the use of volume-of-fluid simulations and experiments, it was determined that the chamfer angle had a significant impact on the edge bead effect, while the chamfer width was not found to be a major factor. The use of a synchronous chamber in spin coating was found to negatively affect film planarization by restricting solvent evaporation and elevating its concentration, leading to a decreased film thickness. Additionally, the study concluded that the edge effect is not impacted by the Bernoulli effect or liquid accumulation along the edge if the average film thickness is below 1500 nm. The main reason for reducing the height of the edge bead was determined to be liquid fusion at the edge of the substrate, which only occurred when the chamfer width was close to the film thickness.

Enhanced Performance of Ru-Based Infrared Imaging Sensor Array With Electrospun Thermal Isolation Structure

Predicting and optimizing thermal conductivity of materials used in infrared thermal imaging sensors is an effective method to improve thermal isolation performance, which can substantially reduce the thermal crosstalk among pixels. This paper reports an electrospun P(VDF-TrFE) nanofiber film used as adiabatic support structure in thermal sensor array, and investigates its effect on imaging performance of thermal sensor. Based on solid heat transfer simulation, the thermal conductivities of electrospun P(VDF-TrFE) films with different packing ratios were theoretically calculated, showing a significant decrease compared with the spin-coated counterpart. The temperature increment of thermal sensor using nanofiber film with 43.71% packing ratio is calculated as 1.68 times higher than that using spin-coated film. An average temperature rise of 1.73 times was experimentally obtained, and the thermal response time was also reduced to half, compared with the sensor using spin-coated film. The method of improving thermal isolation performance using electrospun fibrous film could be of great advantage to high sensitivity infrared imaging sensor.

Design, synthesis, and characterization of highly photostable Pigment Yellow 74 derivatives for painting applications

The present objective of this study was develop highly photostable novel Pigment Yellow 74 (P.Y. 74) derivatives. The structures of the synthesized compounds were confirmed by NMR, IR, and HRMS spectral analysis. From the NMR, and IR spectra, pigments exist in the hydrazone tautomeric form. Irradiating pigment samples with UV light allowed us to test their photostability in liquid and spin-coated films. The results revealed that the synthesized pigments PYA, PYB, and PYC have better photostability than the commercial P.Y. 74. The higher photostability of the synthesized pigment (PYA) is mainly due to the presence of strong intramolecular hydrogen bonding. The shifting of pivaloyl carbonyl stretching frequencies towards lower wavenumbers in the FT-IR spectra, as well as the pigment exhibiting sharp reflections in the powder XRD spectra, demonstrate this. The studied results provide insight into the synthesized PYA as a possible replacement to the commercial P.Y. 74 in the color industry.

Using Different Surface Energy Models to Assess the Interactions between Antiviral Coating Films and phi6 Model Virus.

High molecular weight chitosan (HMWCh), quaternised cellulose nanofibrils (qCNF), and their mixture showed antiviral potential in liquid phase, while this effect decreased when applied to facial masks, as studied in our recent work. To gain more insight into material antiviral activity, spin-coated thin films were prepared from each suspension (HMWCh, qCNF) and their mixture with a 1:1 ratio. To understand their mechanism of action, the interactions between these model films with various polar and nonpolar liquids and bacteriophage phi6 (in liquid phase) as a viral surrogate were studied. Surface free energy (SFE) estimates were used as a tool to evaluate the potential adhesion of different polar liquid phases to these films by contact angle measurements (CA) using the sessile drop method. The Fowkes, Owens-Wendt-Rabel-Kealble (OWRK), Wu, and van Oss-Chaudhury-Good (vOGC) mathematical models were used to estimate surface free energy and its polar and dispersive contributions, as well as the Lewis acid and Lewis base contributions. In addition, the surface tension SFT of liquids was also determined. The adhesion and cohesion forces in wetting processes were also observed. The estimated SFE of spin-coated films varied between mathematical models (26-31 mJ/m2) depending on the polarity of the solvents tested, but the correlation between models clearly indicated a significant dominance of the dispersion components that hinder wettability. The poor wettability was also supported by the fact that the cohesive forces in the liquid phase were stronger than the adhesion to the contact surface. In addition, the dispersive (hydrophobic) component dominated in the phi6 dispersion, and since this was also the case in the spin-coated films, it can be assumed that weak physical van der Waals forces (dispersion forces) and hydrophobic interactions occurred between phi6 and the polysaccharide films, resulting in the virus not being in sufficient contact with the tested material during antiviral testing of the material to be inactivated by the active coatings of the polysaccharides used. Regarding the contact killing mechanism, this is a disadvantage that can be overcome by changing the previous material surface (activation). In this way, HMWCh, qCNF, and their mixture can attach to the material surface with better adhesion, thickness, and different shape and orientation, resulting in a more dominant polar fraction of SFE and thus enabling the interactions within the polar part of phi6 dispersion.

High-efficiency Sb2Se3 thin-film solar cells based on Cd(S,O) buffer layers prepared via spin-coating

CdS films prepared via chemical bath deposition exhibit extremely good performance as a buffer layer of chalcogenide solar cells. However, their commercial application is very limited because of the production of a large amount of wastewater containing cadmium. In this study, we develop an efficient way to prepare CdS films using the spin-coating technique. The spin solution is anhydrous, and the oxygen content can be well controlled by changing the Cd/S content ratio in the solution. The crystal structure, morphology, and optical and electrical properties of CdS films with different Cd/S content ratios are characterized. The effect of the oxygen content on the device performance is investigated. We find that the introduction of an appropriate amount of oxygen can improve the carrier transport efficiency by decreasing the interface recombination. The spin-coated CdS films have good coverage of the substrate for film thicknesses below 50 nm. By the optimizing of Cd/S content ratio, we achieve an improved efficiency of 5.76% for the Sb2Se3 solar cells. This preparation technique is sufficiently simple for large-scale processing and produces much less wastewater containing cadmium; thus, it is promising for application to future large-scale solar cell production.

Electrically Amplified Circularly Polarized Luminescence by a Chiral Anion Strategy.

The development of circularly polarized electroluminescence (CPEL) is currently hampered by the high difficulty and cost in the syntheses of suitable chiral materials and the notorious chirality diminishment issue in electrical devices. Herein, diastereomeric IrIII and RuII complexes with chiral (±)-camphorsulfonate counteranions are readily synthesized and used as the active materials in circularly polarized light-emitting electrochemical cells to generate promising CPELs. The addition of the chiral ionic liquid (±)-1-butyl-3-methylimidazole camphorsulfonate into the active layer significantly improves the device performance and the electroluminescence dissymmetry factors (≈10-3 ), in stark contrast to the very weak circularly polarized photoluminescence of the spin-coated films of these diastereomeric complexes. Control experiments with enantiopure IrIII complexes suggest that the chiral anions play a dominant role in the electrically-induced amplification of CPELs.

Synthesis and Study of the Optical Properties of a Conjugated Polymer with Configurational Isomerism for Optoelectronics.

A π-conjugated polymer (PBQT) containing bis-(2-ethylhexyloxy)-benzo [1,2-b'] bithiophene (BDT) units alternated with a quinoline-vinylene trimer was obtained by the Stille reaction. The chemical structure of the polymer was verified by nuclear magnetic resonance (1H NMR), Fourier transform infrared (FT-IR), and mass spectroscopy (MALDI-TOF). The intrinsic photophysical properties of the solution were evaluated by absorption and (static and dynamic) fluorescence. The polymer PBQT exhibits photochromism with a change in absorption from blue (449 nm) to burgundy (545 nm) and a change in fluorescence emission from green (513 nm) to orange (605 nm) due to conformational photoisomerization from the trans to the cis isomer, which was supported by theoretical calculations DFT and TD-DFT. This optical response can be used in optical sensors, security elements, or optical switches. Furthermore, the polymer forms spin-coated films with absorption properties that cover the entire visible range, with a maximum near the solar emission maximum. The frontier molecular orbitals, HOMO and LUMO, were calculated by cyclic voltammetry, and values of -5.29 eV and -3.69, respectively, and a bandgap of 1.6 eV were obtained, making this material a semiconductor with a good energetic match. These properties could suggest its use in photovoltaic applications.

Production of hydrogen gas sensors based on sol–gel spin-coated Nb2O5 thin films

Production of hydrogen gas sensors based on sol–gel spin-coated Nb2O5 thin films

Multilevel resistive switching in solution-processed CuFe2O4/TiO2 heterostructure

Low-cost, stable, and easy-to-fabricate resistive switching memory (RSM) devices are highly desirable for next-generation nonvolatile memories. Spinel-structured CuFe2O4 (CFO), composed of earth-abundant, environmentally friendly elements, is a multifunctional material mainly featuring super-paramagnetism. This work explores the potential of spin-coated CFO thin films as an active material in RSM. A simple fluorine-doped tin oxide (FTO)/CFO/Ag device shows a bipolar resistive switching behavior with the problems like scattered SET and RESET voltages and endurance deterioration. Adding a TiO2 layer in the conventional device, we overcame the above limitations and achieved additional advantages of multilevel switching and improved temperature stability. The solution-processed FTO/TiO2/CFO/Ag bilayer device shows stable endurance with a maximum ON/OFF ratio of 100 with the ability to have multiple high resistance states and exhibits excellent temperature stability up to 250 °C. Our results further enhance the multifunctionality of CFO with the potential of being low-cost multilevel RSM.