Spin-coated Films Research Articles

Multi functional ionic Ru(bpy)3(PF6)2 assisted preparation of perovskite solar cell with over 19% and superior stability

Abstract The global community is striving to advance the development of emerging perovskite solar cells (PSCs). It has been demonstrated that the utilization of passivators is an effective approach to enhance the photoelectric conversion efficiency and long-term stability of PSCs, thus attracting increasing attention to organic passivators. All-inorganic CsPbI3 PSCs play a crucial role in the next-generation photovoltaic technology due to their unique optical bandgap and excellent light absorption properties. However, due to its poor stability, CsPbI3−x Br x halide hybrid perovskite has been proposed. The spin-coating film formation method leads to the presence of a large number of vacancy defects in the film, which poses a significant challenge to the commercialization of CsPbI3−x Br x perovskite films. Therefore, in this study, a novel passivator, Ru(bpy)3(PF6)2 (TRH), was introduced. By introducing the passivator, the photoelectric conversion efficiency of PSCs in air was improved, there by optimizing the device performance. After the addition of the passivator, [Ru(bpy)3]2+ filled the defects on the surface of the film, while the free PF6 - ions passivated the negatively charged halide vacancies. The fluorine atoms effectively prevented the entry of water molecules in the air. As a result, the optimized CsPbI3−x Br x film exhibited a more compact morphology, a lower defect state density, and better carrier transport performance. Eventually, the champion device achieved a photoelectric conversion efficiency of 19.47%, and even after being placed at an ambient temperature of 25 °C–30°C and a humidity of 30%–40% for 150 d, its efficiency remained above 85% of the initial efficiency of the device.

Exploring photophysical behavior and fullerene-induced quenching in difluoroboron flavanone [formula omitted]-diketonates for application in organic electronic devices: Experimental and theoretical analysis

The photophysical properties of two difluoroboron flavanone β-diketonates (DK1 and DK2) and their interaction with fullerene (C60) in toluene solution and spin-coated films were investigated using time-correlated single-photon counting, absorption spectroscopy, and steady-state fluorescence spectroscopy. In molecular crystal, the complexes exhibited red-shifted absorption and emission relative to their spectra in solution. Additionally, both complexes displayed bi-exponential decay behavior in time-resolved fluorescence measurements, indicating their capability to form both H and J types of aggregates in the solid state. The introduction of C60 resulted in significant fluorescence quenching and reduced excited-state lifetimes for both complexes. This quenching, observed in both solution and spin-coated films, was primarily driven by photo-induced electron transfer (PET) processes, underscoring the potential of these complexes as donors in fullerene-based heterojunction organic solar cells. To elucidate the process of aggregate formation and the impacts of different dimerization types within the crystalline structure of the complexes, first-principles calculations using Density Functional Theory (DFT) and time-dependent density functional theory (TD-DFT) were performed. We also employed DFT to explore various DK configurations on the fullerene surface, evaluating intermolecular distances and formation energies. These calculations highlighted the energetically favourable gap between the low-lying LUMO levels of the complexes and C60, confirming their suitability for such applications.

Solution-processed planarly oriented thin films of cholesteric liquid-crystalline semiconductors

We have successfully fabricated cholesteric liquid-crystalline (CLC) semiconductor thin films from the mixture of dimeric and monomeric compounds based on oligo(p-phenylenevinylene) units by spin-coating method. This is the first example of solution-processed planarly orientated thin film in CLC semiconductors. The mixture exhibited a CLC phase at lower temperatures than the compound alone, allowing the fabrication of spin-coated CLC thin films at room temperature. Furthermore, the dimeric compound has trifluoromethyl groups that exhibited high solubility in organic solvents such as chloroform due to its improved hydrophobicity. In addition, the high hydrophobicity of the trifluoromethyl groups lowers the surface tension of the liquid–crystal material, resulting in planar orientation.

Marangoni-Induced Honeycomb Structures in Spin-Coated Polymer Nanocomposite Films.

This study investigates Marangoni effect-induced structural changes in spin-coated polymer nanocomposite (PNC) films composed of poly(methyl methacrylate)-grafted silica nanoparticles (NPs) and poly(styrene-ran-acrylonitrile). Films cast from methyl isobutyl ketone (MIBK) solvent exhibit distinct hexagonal honeycomb cells with thickness gradients driven by surface tension variations. Atomic force microscopy reveals protruded ridges and junctions at cell intersections, where NP concentration is the highest. Upon annealing at 155 °C, NPs segregate to the surface due to their lower surface energy, and the initially protruding features flatten and eventually form depressed channels while maintaining higher NP density than surrounding areas. Time-of-flight secondary ion mass spectrometry corroborated these findings, highlighting enhanced surface segregation of NPs in MIBK films. These defects can be eliminated using methyl isoamyl ketone (MIAK) as a solvent that produces homogeneous films of uniform thickness. This study highlights the impact of the Marangoni effect on the microstructure and surface properties of PNC films, providing insights for enhancing film quality and performance.

Stepwise Construction of Supramolecular A2B4-Type Miktoarm Star Copolymers with a Cobalt Phthalocyanine Core.

Supramolecular interactions between polymers play a crucial role in the construction of three-dimensional polymer structures with unique physical and chemical properties. In this study, we have fabricated a novel supramolecular miktoarm star copolymer (μ-star) with a cobalt(II) phthalocyanine (CoPc) core using metal-ligand coordination. Axial coordination of the terminal pyridyl group of poly(methyl methacrylate) with the CoPc core of four-armed star-shaped polystyrene provided AB4- and A2B4-type μ-stars through stepwise complexation. The spin-coated polymer films from mixed solutions of CoPcPS4 and pyPMMA in 1 : 1 or 1 : 2 mass ratios exhibited phase-separated nanodomains with smooth surfaces. Supramolecular interactions in polymer systems provide a unique topology to polymers and affect their bulk morphology.

Tuning leakage current and ferroelectric properties in spin-coated BiFeO3 films through Cr doping and post-annealing atmosphere control

Effective enhancement of ferroelectric properties in BiFe1-xCrxO3 films prepared via the sol-gel method is crucial. Here, by adjusting the Cr content, BiFe1-xCrxO3 films with smooth surfaces and uniform grain structures were successfully synthesized. X-ray photoelectron spectroscopy (XPS) analyses revealed that Cr doping significantly reduces the concentrations of Fe2+ and oxygen vacancies within the BFO films, thereby mitigating leakage currents and enhancing ferroelectricity. Additionally, we investigated the microstructure and electrical characteristics of BiFe0.98Cr0.02O3 thin films subjected to post-annealing in different atmospheres (N2, Air, and O2). Notably, annealing in an O2 atmosphere notably enhanced the crystallinity and grain uniformity of BiFe0.98Cr0.02O3 thin films. This treatment resulted in superior ferroelectric polarization switching behavior, achieving the highest remanent polarization (Pr = 153.1 μC/cm2) due to reduced defect densities. Our findings underscore the critical roles of Cr3+ ions and O2 annealing atmospheres in suppressing leakage currents and boosting ferroelectric properties in BFO films.

Physical Aging of Poly(methyl methacrylate) Brushes and Spin-Coated Films.

While there is significant attention aimed at understanding how one-dimensional confinement and chain confirmations can impact the glass transition temperature (Tg) of polymer films, there remains a limited focus on similar effects on sub-Tg processes, notably, structural relaxation. Using spectroscopic ellipsometry, we investigated the combined influence of confinement and molecular packing on Tg and physical aging, i.e., the property changes that accompany structural relaxation, at select film thicknesses and aging temperatures (Ta). We used poly(methyl methacrylate) (PMMA) films in the brush and spin-coated morphologies as model systems. We found that whether a PMMA film exhibited a decrease or increase in physical aging rate with confinement was dependent on the morphology. Notably, PMMA brushes exhibited higher physical aging rates compared to similarly thick spin-coated films at all values of Ta. These intriguing findings reveal the strong effects of confinement and molecular packing on the structural relaxation of polymer films. Results from this study have the potential to aid in the design of thin-film materials with controllable long-term glassy-state properties.

Does the substrate and a buffer layer have a greater influence on poly(3-hexylthiophene) films deposited by the chronocoulometry technique?

Abstract In this study, we investigate the interface morphology and optical properties of electrochemical poly(3-hexylthiophene) (P3HT) films deposited by electrochemical synthesis using the chronocoulometry technique on tin-doped indium oxide (ITO) and fluorine-doped tin oxide (FTO) and how the substrate used influences in the deposition of the films and their optical and morphological properties, as well as the buffer layer and the interface effect, with and without spin-coating films of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). P3HT polymeric films were synthesized and deposited via the oxidation of the 3-hexylthiophene (3-HT) monomer and characterized via Raman spectroscopy. The morphology and thickness of the P3HT layer present in the samples ITO/P3HT, FTO/P3HT, ITO/PEDOT:PSS/P3HT, and FTO/PEDOT:PSS/P3HT were carried out using atomic force microscopy (AFM). The optical and electronic gap energy of P3HT were calculated from UV‒Vis spectra and cyclic voltammetry curves, respectively. The photoluminescence (PL) spectra showed broad and asymmetrical line shapes fitted by multi-Gaussian functions identifying different emission species. Emission ellipsometry spectroscopy was performed to study the energy transference between adjacent polymer chains. Our results show a higher linear polarized light emitted by ITO/PEDOT:PSS/P3HT film, ∼37%, thus demonstrating a significant decrease in the energy transfer. Based on these results, the efficiency of organic solar cells can be improved via the interaction of the polymer/polymer interface.

Enhancing zT in Organic Thermoelectric Materials through Nanoscale Local Control Crystallization.

Organic thermoelectric materials are promising for wearable heating and cooling devices, as well as near-room-temperature energy generation, due to their nontoxicity, abundance, low cost, and flexibility. However, their primary challenge preventing widespread use is their reduced figure of merit (zT) caused by low electrical conductivity. This study presents a method to enhance the thermoelectric performance of solution-processable organic materials through confined crystallization using the lithographically controlled wetting (LCW) technique. Using PEDOT as a benchmark, we demonstrate that controlled crystallization at the nanoscale improves electrical conductivity by optimizing chain packing and grain morphology. Structural characterizations reveal the formation of a highly compact PEDOT arrangement, achieved through a combination of confined crystallization and DMSO post-treatment, leading to a 4-fold increase in the power factor compared to spin-coated films. This approach also reduces the thermal conductivity dependence on electrical conductivity, improving the zT by up to 260%. The LCW technique, compatible with large-area and flexible substrates, offers a simple, green, and low-cost method to boost the performance of organic thermoelectrics, advancing the potential for sustainable energy solutions and advanced organic electronic devices.

Enhancing symmetric supercapacitor performance through spin-coated lithium trivanadate films modified with carbon

Enhancing symmetric supercapacitor performance through spin-coated lithium trivanadate films modified with carbon

A general model for spin coating on a non-axisymmetric curved substrate

We derive a generalised asymptotic model for the flow of a thin fluid film over an arbitrarily parameterised non-axisymmetric curved substrate surface based on the lubrication approximation. In addition to surface tension, gravity and centrifugal force, our model incorporates the effects of the Coriolis force and disjoining pressure, together with a non-uniform initial condition, which have not been widely considered in existing literature. We use this model to investigate the impact of the Coriolis force and fingering instability on the spreading of a non-axisymmetric spin-coated film at a range of substrate angular velocities, first on a flat substrate, and then on parabolic cylinder- and saddle-shaped curved substrates. We show that, on flat substrates, the Coriolis force has a negligible impact at low angular velocities, and at high angular velocities results in a small deflection of fingers formed at the contact line against the direction of substrate rotation. On curved substrates, we demonstrate that, as the angular velocity is increased, spin-coated films transition from being dominated by gravitational drainage with no fingering to spreading and fingering in the direction with the greatest component of centrifugal force tangent to the substrate surface. For both curved substrates and all angular velocities considered, we show that the film thickness and total wetted substrate area remain similar over time to those on a flat substrate, with the key difference being the shape of the spreading droplet.

Highly sensitive and room-temperature operable carbon dioxide gas sensor based on spin-coated Sn-doped Co3O4 thin films with advanced recovery properties

The urgency to address climate change has highlighted the need for gas sensors capable of monitoring air quality at room temperature (RT) and accurately measuring the concentrations of carbon oxides (CO2 and CO) in the environment. This study details the development of a highly sensitive CO2 gas sensor using spin-coated Sn-doped Co3O4 thin films, operating at a room temperature of 30⁰C and a relative humidity (RH%) of 43 %. Extensive characterization employing XRD, SEM, EDX, FTIR, and UV–Vis optical techniques verified the impact of Sn doping on the surface morphology, phase purity, and a notable reduction in the dual-band gap of the thin films. Gas sensing measurements were conducted at RT using varying CO2 gas concentrations. A sensor response of 796.81 % was obtained for the optimally sensitive film, 10 % Sn-doped Co3O4, at a CO2 concentration of 9990 ppm. Additionally, a range of RH % levels was examined at a constant CO2 gas concentration of 9990 ppm, revealing an optimal humidity level of 43 % at RT. Further analysis revealed that the 10 % Sn-Co3O4 sensor displayed enhanced sensitivity to CO2, surpassing its response to N2, H2, and NH3 gases. The determined limits of detection and quantification underscore the sensor's precision and reliability in quantifying CO2 gas concentrations. Our findings demonstrate the excellent potential of Sn-doped Co₃O₄ thin films as highly sensitive CO₂ gas sensors. These films provide a promising solution for detecting elevated CO₂ levels at room temperature, aiding climate change mitigation efforts.

2D versus 3D-Like Electrical Behavior of MXene Thin Films: Insights from Weak Localization in the Role of Thickness, Interflake Coupling and Defects.

MXenes stand out from other 2D materials because they combine very good electrical conductivity with hydrophilicity, allowing cost-effective processing as thin films. Therefore, there is a high fundamental interest in unraveling the electronic transport mechanisms at stake in multilayers of the most conducting MXene, Ti3C2Tx. Although weak localization (WL) has been proposed as the dominating low-temperature (LT) transport mechanism in Ti3C2Tx thin films, there have been few attempts to model it quantitatively. In this work, the role of important structural parameters - thickness, interflake coupling, defects - on the dimensionality of the LT transport mechanisms in spin-coated Ti3C2Tx thin films is investigated through LT and magnetic field dependent resistivity measurements. A dimensional crossover from 2D to 3D WL is clearly evidenced when the film thickness exceeds the dephasing length lϕ, estimated here in the 50-100 nm range. 2D WL can be restored by weakening the coupling between adjacent flakes, the intrinsic thickness of which is lower than lϕ, hence acting as parallel 2D conductors. Alternatively, lϕ can be reduced down to the 10 nm range by defects. These results clearly emphasize the ability of WL quantitative study to give deep insights in the physics of electron transport in MXene thinfilms.

Low-temperature Deposited Highly Sensitive Integrated All-Solid Electrodes for Electrochemical pH Detection

This article describes the process of fabricating an integrated all-solid electrode (IASE) by integrating thin films of titanium dioxide (TiO<i>2</i>) and silver/silver chloride (Ag/AgCl) onto an indium tin oxide (ITO) substrate. The fabrication of a pH sensing electrode (SE) involved utilizing a spin-coated thin film composed of TiO<i>2</i>. Thermally produced thin films of Ag/AgCl were used to develop solid reference electrodes (RE). The present work examined the impact of the drying process on the pH sensitivity and linearity of the low-temperature deposited IASE. The drying procedure was carried out within a temperature range from room temperature to 100°C. The investigation involved the examination of crystallinity, surface morphology, and thin film composition through the utilization of field effect scanning electron microscopy (FESEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) methods. In addition, a comparison was made between the pH sensing performance of the IASE and a commercially available Ag/AgCl RE. The findings of this research demonstrate that the IASE sample, which underwent a drying process at a temperature of 100°C, exhibited remarkable sensitivity and linearity values of 66.7 mV/pH and 0.9827, separately, when compared to the commercially available RE.

Design of a Novel Peptide with Esterolytic Activity toward PET by Mimicking the Catalytic Motif of Serine Hydrolases.

Serine hydrolases have become increasingly important for recycling PET plastics. However, their properties are inherently constrained by their 3D structure, which in turn limits the conditions for their application. Considering peptides as catalysts for industrial depolymerization processes can help us to escape some of these limitations. In this article, a 25 amino acid thermostable peptide, HSH-25, was designed to depolymerize PET. The peptide incorporates a His-Ser-His motif, inspired by the catalytic triad found in the serine hydrolase family, into a β-hairpin fold. Stability of the fold was investigated by molecular dynamics simulations. Esterolytic activity of the peptide toward model substrates was detected within a pH range from pH 7 to pH 9.5. Degradation of polymeric PET substrates was confirmed by atomic force microscopy imaging on spin-coated PET thin films.

Sustainable Production of Biomass-Derived Graphite and Graphene Conductive Inks from Biochar.

Graphite is a commonly used raw material across many industries and the demand for high-quality graphite has been increasing in recent years, especially as a primary component for lithium-ion batteries. However, graphite production is currently limited by production shortages, uneven geographical distribution, and significant environmental impacts incurred from conventional processing. Here, an efficient method of synthesizing biomass-derived graphite from biochar is presented as a sustainable alternative to natural and synthetic graphite. The resulting bio-graphite equals or exceeds quantitative quality metrics of spheroidized natural graphite, achieving a Raman ID/IG ratio of 0.051 and crystallite size parallel to the graphene layers (La) of 2.08 µm. This bio-graphite is directly applied as a raw input to liquid-phase exfoliation of graphene for the scalable production of conductive inks. The spin-coated films from the bio-graphene ink exhibit the highest conductivity among all biomass-derived graphene or carbon materials, reaching 3.58 ± 0.16 × 104 Sm-1. Life cycle assessment demonstrates that this bio-graphite requires less fossil fuel and produces reduced greenhouse gas emissions compared to incumbent methods for natural, synthesized, and other bio-derived graphitic materials. This work thus offers a sustainable, locally adaptable solution for producing state-of-the-art graphite that is suitable for bio-graphene and other high-value products.

Enhancing low-temperature sensor applications: Synergistic effects of Ni doping and SnO2 interlayer on spin-coated ZnO thin films on glass substrate

This study investigates the effects of Nickel doping and a SnO2 interlayer on the structural, morphological, optical, and electrical properties of ZnO thin films. Undoped and Ni-doped ZnO films were fabricated on glass substrates, with and without an SnO2 interlayer, using the sol-gel spin coating method. The samples—denoted as ZG (undoped ZnO), NZG (Ni-doped ZnO), ZSG (undoped ZnO with SnO2 interlayer), and NZSG (Ni-doped ZnO with SnO2 interlayer)—underwent comprehensive characterization via XRD, AFM, PL, UV–Vis spectroscopy, Hall effect measurements, Hot probe, and Two-point method. XRD analysis confirmed successful Ni incorporation and enhanced ZnO crystallinity, particularly in the presence of the SnO2 interlayer. AFM analysis revealed improved grain distribution and size due to the synergistic effects of Ni doping and the SnO2 interlayer. UV–Vis results indicated significant impacts on transparency and the Urbach energy, with Ni doping alone broadening the bandgap. PL measurements showed that the synergistic effects quenched UV luminescence associated with the glass substrate, enhancing visible luminescence. Chromaticity analysis suggested that ZSG and NZSG samples are suitable for warm blue region applications. Electrical measurements revealed n-type conductivity across all films except NZG, with Ni doping increasing resistivity. Additionally, the ZSG (PTC) sensor exhibited a slightly higher sensitivity (0.3852 Ω/°C) compared to the NZSG sensor (0.3782 Ω/°C), with a similar trend observed in NTC sensors. These findings suggest that Ni-doped ZnO films with SnO2 interlayers could potentially serve as thermistors and RTDs, offering promising applications in temperature sensing and optoelectronics.

Highly Alternating Copolymer of [1.1.1]Propellane and Perfluoro Vinyl Ether: Forming a Hydrophobic and Oleophobic Surface with

Utilizing the unique properties of fluorine substitution is an effective strategy for constructing highly functional materials. Here, we synthesized a novel copolymer composed of [1.1.1]propellane and perfluoro(propyl vinyl ether) (PPVE), rich in alternating sequences. The spin-coated copolymer film was amorphous, and its surface exhibited an extremely low surface free energy (γ). The γ value was lower than that of polytetrafluoroethylene despite containing only 40 mol % PPVE units. This can be attributed to the cancellation of the C-F dipole moments by the entirely random orientation of the fluorine units.

Effect of Al doping on the structural, optical and photocatalytic properties of sol-gel spin-coated NiO thin films

Nanostructured NiO thin films are renowned for their catalytic activity and potential for degradation of industrial effluents. In this study, Al-doped NiO (Ni1-xAlxO with x = 0, 0.02, 0.04, 0.06, and 0.08) thin films were synthesized by sol–gel spin coating, and the influence of Al doping on their physical properties, surface morphology, optical band gap, and photo-catalytic performance was investigated. X-ray diffraction (XRD) analysis confirmed the high crystallinity of the thin films and revealed a pronounced doping effect on parameters such as crystallite size, microstrain, and dislocation density. Scanning electron microscopy (SEM) revealed the formation of spherical nanoparticles with particle sizes ranging from 26 nm to 11 nm. The elemental composition was verified through energy-dispersive x-ray (EDX) analysis. The optical bandgap of the prepared films was determined through UV-visible spectroscopy. The Ni0.98Al0.02O films exhibited the lowest PL intensity, indicating a reduced recombination rate. To assess the photo-degradation capability of the prepared thin film catalysts, industrial effluent Indigo Carmine was employed as a test compound. The Ni0.98Al0.02O sample demonstrated the highest degradation efficiency, achieving about 96% degradation within 2 h of UV–vis light irradiation. Furthermore, the degradation followed pseudo-first-order kinetics.

The evolution of morphology and structure of spin-coated Zinc Acetate thin films and their impact on ZnO film morphology

The deposition of ZnO thin films using sol-gel technology is a straight forward and widely used method for fabricating ZnO films with diverse morphologies and tunable electrical and optical properties. Notably, the preparation of ZnO compact layers from a zinc acetate and monoethanolamine (ZA:MEA) solution via spin-coating has gained popularity due to its simplicity. The pretreatment of spin-coated ZA:MEA films significantly impacts the morphology and structure of the resulting ZnO films. While the effects of preheating and its rate on ZnO precursor films have been extensively studied, the morphological and structural evolution of ZA:MEA films immediately after spin-coating and its subsequent impact on the final ZnO film have not been previously explored. In this study, we present the topography and phase composition of as-grown ZA:MEA films using atomic force microscopy (AFM). We conduct an in-situ investigation of the morphological evolution of ZA:MEA films. Our results reveal that as-grown ZA:MEA films possess an inhomogeneous structure. AFM phase image shows two distinct domains in the ZA:MEA films. Over time, we observe the growth of crystals in both vertical and perpendicular directions. ZA:MEA film aged for at least 20 h develops arrays of vertically oriented crystals throughout the film covered with sheet-like crystals forming on the film surface. This temporal evolution in the morphology and structure of ZA:MEA films significantly influences the morphology of the final ZnO film.