Spin-coated Films Research Articles

Highly Efficient Large-Area Flexible Perovskite Solar Cells Containing Tin Oxide Vertical Nanopillars without Oxygen Vacancies

Fabrication of high-quality electron transporting layers (ETLs) on large-area flexible electrodes is necessarily required, but challenging, to improve photovoltaic performance of flexible perovskite solar cells (PSCs) that are demanded for wearable electronic devices. This work shows one-step, oxygen-assisted glancing angle deposition to facilely deposit polycrystalline SnO2 nanopillars (NPs) that are free of oxygen deficiencies and vertically protrude on large-area transparent electrodes. Functioning as ETLs, SnO2 NPs comprehensively lead to an enhancement of light harvesting in perovskites, exciton separation, electron extraction and collection, and hole blocking, as well as the prevention of perovskite decomposition and the formation of perovskite defects. Large-area (1 cm2) flexible PSCs containing the SnO2 NPs show the champion power conversion efficiency (PCE) of 14.9%, which undergoes only 10% degradation for approximately 800 h storage and 20% degradation by manual bending for around 400 times. These photovoltaic performances are remarkably superior to large-area flexible PSCs having the conventionally used spin-coated SnO2 thin films that contain oxygen vacancies. These results pave the way toward scale-up fabrication of flexible PSCs that simultaneously satisfy the commercial requirements of high photovoltaic efficiency, shelf stability, and mechanical stability.

Improving hole injection ability using a newly proposed WO3/NiOx bilayer in solution processed quantum dot light-emitting diodes

We propose a novel device structure with a WO3/NiOx bilayer to improve the hole injection ability in QLEDs fabricated mainly by a solution-based process. First, we employed a spin-coated NiOx thin film as a hole injection layer (HIL) to replace Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) PEDOT:PSS which corrodes indium tin oxide (ITO) used as an anode in QLEDs. We showed a simply optimized annealing process, instead of a rather complicated process like doping, can improve the electrical conductivity of the NiOx thin film. The reason for the dependency of conductivity on the post-metallization annealing is because of the change of the total amount of Ni vacancy in the NiOx thin film as a function of annealing temperature: The electrical conductivity of the NiOx thin film annealed at 275 °C was the best in this work. Second, we inserted the WO3 thin film in between ITO electrode and NiOx HIL to form an ITO/WO3/NiOx structure which reduces the hole injection barrier to 0.35 eV, resulting in the excellent characteristic in view of charge balance. Finally, we measured the properties of QLEDs with the WO3/NiOx bilayer to check the effects of the proposed device structure and showed the substantial improvement of the electrical conductivity of NiOx, the luminance, and the current efficiency of the QLEDs.

Quenching Fluorescence of Quantum Dots by Using Gold Nanocrystals in Quantum and Classical Size Regime

This paper investigates the factors which can influence the quenching effect from the perspective of energy transfer. The quenched fluorescence of the CdSe semiconductor quantum dots (SQDs) by using plasmonic Au nanocrystals (p-AuNCs) and molecule-like Au nanocrystals (m-AuNCs) in aqueous suspensions and spin-coated films is comparatively investigated. In the aqueous suspensions, the p-AuNCs have larger quenching effect than the m-AuNCs. In the spin-coated films, the p-AuNCs and m-AuNCs have comparable quenching factor. Furthermore, the experiments show that the p-AuNCs simultaneously enhance the radiative and nonradiative rates. But the m-AuNCs only enhance the nonradiative rate of the SQDs, which reveals the difference of quenching process between the p-AuNCs and m-AuNCs. This result of the research has guiding significance for the detection technique based on the fluorescence quenching.

Substrate Effects on the Random Lasing Performance of Solution-Processed Hybrid-Perovskite Multicrystal Film

We report dependence of random lasing performance of directly spin-coated multicrystalline thin films of an organic–inorganic hybrid, halide perovskite CH3NH3PbBr3 (MAPbBr3), on different substrates. It was discovered that random lasing performance is strongly dependent on the surface energy properties of the substrate, which determine the morphology and crystallization properties of the spin-coated film, and will consequently determine its optical scattering and emission properties. Using indium–tin oxide (ITO)-coated glass, fused silica, and tricyclo[5.2.1.02,6] decanedimethanol diacrylate (ADCP)-coated fused silica as the substrate materials, we compared the spectroscopic response of the random lasers and thus justified the photophysical mechanisms involved. The modification of the surface properties of the substrate enables controlling of the MAPbBr3 crystallization and leads to the changing of the random lasing properties. The discoveries herein are also important for the construction of other types of laser devices, where the substrate effects should be considered during the design and preparation of the micro-/nano structures.

Fabrication of Cu2ZnSnS4 Light Absorber Using a Cost-Effective Mechanochemical Method for Photovoltaic Applications.

In the present study, we adopt an easy and cost-effective route for preparing Cu2ZnSnS4 (CZTS)-absorber nanoparticles by a mechanochemical method using non-toxic and environmentally benign solvents (butanol, methyl ethyl ketone, and ethanol). The gram-scale synthesis of absorber nanoparticles was achieved in a non-hazardous, zero-waste process without using high-vacuum equipment. The effects of annealing and Na incorporation on the properties of spin-coated CZTS thin films were scrutinized. The deposited samples showed kesterite crystal structure and single phase. The morphological results revealed an improvement in the surface morphology after annealing. The optical bandgaps of the thin films lied in the range of 1.50–1.57 eV with p-type nature. Finally, photovoltaic devices were fabricated, and their cell performance parameters were studied. An efficiency of 0.16% was observed. The present study provides a potential route for the cost-effective fabrication of CZTS-based photovoltaic devices.

Inverted Circularly Polarized Luminescence Behavior Induced by Helical Nanofibers through Chiral Co-Assembly from Achiral Liquid Crystal Polymers and Chiral Inducers.

Chiral supramolecular assembly can provide a powerful strategy for developing circularly polarized luminescence (CPL)-active materials by forming helices or superhelices into single or multiple components. Herein, we chose three achiral liquid crystal polymers (LC-P1/P2/P3) and chiral binaphthyl-based inducers (R/S-M) with anchored dihedral angles to construct chiral co-assemblies and explore the induced CPL behavior from pyrenyl (Py) emitters in achiral LC polymers through the regulation of helical nanofibers during the supramolecular co-assembly process. Most interestingly, chiral co-assembly (R/S-M)0.1-(P3)0.9 emitted an inverted blue-colored CPL signal during thermal annealing treatment at the glass transition temperature due to the flexible main chain of the LC polymer (LC-P3). The strongest blue-colored CPL emission for the (R/S-M)0.1-(P3)0.9 spin-coated film (λem = 455 nm, |gem| = 6.47 × 10-2, ΦF = 48.5%) could be detected by using thermal annealing treatment at 105 °C.

Precise Tuning and Characterization of Viscoelastic Interfaces for the Study of Early Epithelial-Mesenchymal Transition Behaviors.

There is growing evidence that cellular functions are regulated by the viscoelastic nature of surrounding matrices. This study aimed to investigate the impact of interfacial viscoelasticity on adhesion and epithelial-mesenchymal transition (EMT) behaviors of epithelial cells. The interfacial viscoelasticity was manipulated using spin-coated thin films composed of copolymers of ε-caprolactone and d,l-lactide photo-cross-linked with benzophenone, whose mechanical properties were characterized using atomic force microscopy and a rheometer. The critical range for the morphological transition of epithelial Madin-Darby canine kidney (MDCK) cells was of the order of 102 ms relaxation time, which was 1-2 orders of magnitude smaller than the relaxation times reported (10-102 s). An analysis of strain rate-dependent viscoelastic properties revealed that the difference was caused by the different strain rate/frequency used for the mechanical characterization of the interface and bulk. Furthermore, decoupling of the interfacial viscous and elastic terms demonstrated that E/N-cadherin expression levels were regulated differently by interfacial relaxation and elasticity. These results confirm the significance of precise manipulation and characterization of interfacial viscoelasticity in mechanobiology studies on EMT progression.

Multi – wavelength photodetectors based on porous spin-coated and compact RF-sputtered NiO films grown over Si substrate: Effect of surface morphology

Spin-coated and RF-sputtered NiO films were grown over Si substrate. FESEM analysis showed porous morphology for spin-coated NiO film and compact surface morphology for RF-sputtered NiO film. The photodetection properties were explored in metal-semiconductor-metal (MSM) configuration and were found to be greatly affected by the surface morphology of NiO. The responsivity of spin-coated NiO/Si PD was measured as 6.90, 3.68 and 4.39 A/W, whereas it was measured as 1.73, 1.81 and 2.07 A/W for RF-sputtered NiO/Si photodetector (PD), under exposure to 365, 625 and 850 nm lights, respectively. The photo-to-dark current ratio (PDCR) was calculated as 303, 172, 206 and 31, 35, 41 for spin-coated and RF-sputtered NiO/Si PDs, respectively. The higher photoresponse of spin-coated NiO/Si PD over RF-sputtered NiO/Si PD, especially at 365 nm wavelength, resulted from the larger surface area of porous structured spin-coated NiO film. Both PDs exhibited stable and repeatable photoresponse at different switching frequencies of the illumination source. The rise/fall time were estimated as 1.96/9.76 and 3.49/7.68 ms for spin-coated and RF-sputtered NiO/Si PDs, respectively.

Controllable β-phase formation in poly(9,9-dioctylfluorene) by dip-coating for blue polymer light-emitting diodes

The performance of polymer light-emitting diodes based on poly(9,9-dioctylfluorene) (PFO) is strongly affected by the presence of β-phase in the polymer films. In this work, β-phase PFO films were developed by a facile method dip-coating in one step. Absorption spectra with an additional peak at 435 nm and red-shifted emission spectra demonstrate the formation of β-phase in the dip-coated films. Notably, β-phase content in the PFO films can be tailored by controlling the withdrawal speed. The experimental results show that the content of β-phase in PFO films increases from 1.4 % to 23.2 % with the decreasing of the withdrawal speed from 60 mm/min to 5 mm/min, and the device efficiency and color purity for the blue emission get improved due to the formation of β-phase. When the withdrawal speed is 5 mm/min, the devices possess the optimal performance with a current efficiency of 2.47 cd/A, which is 3.6 times as high as that of the device with the spin-coated PFO film as emitting layer. These results demonstrate that as a simple methodology, the dip-coating technology can effectively induce the molecular chain orientation in the film to regulate the optoelectronic properties for applications in efficient optoelectronic devices.

Ferroelectric perovskite‐type films with robust in‐plane polarization toward efficient room-temperature chemiresistive sensing

Ferroelectric materials have become key components for versatile device applications, and their thin films are highly desirable for integrating the miniaturized devices. Despite substantial endeavors, it is still challenging to achieve effective chemiresistive sensing in the ferroelectric films. Here, for the first time, we have exploited ferroelectric thin films of 2D hybrid perovskite BA2EA2Pb3I10 (1), to fabricate the high-performance chemiresistor gas sensors. The spin-coated films of 1 exhibit high orientation and good crystallinity, thus preserving robust in-plane spontaneous polarization (Ps ∼2.0 μC/cm2) and low electric coercivity. Notably, such ferroelectric film-based sensors after electric poling enable the dramatic room-temperature sensing responses to NO2 gas, including high sensitivity (0.05 ppm−1), extremely low detection limit (1 ppm) and fast responding rate (∼6 s). Besides, the chemiresistive responses are remarkably enhanced by threefold (up to 320%) through electric poling. It is proposed that this behavior closely involves with strong in-plane ferroelectric polarization of 1 that generates a built-in electric field inhibiting the recombination of charge carriers. As far as we know, this ferroelectric-based film chemiresisor is one of the best room-temperature sensors for NO2 gas among all the existing candidate materials. These findings highlight great potential of ferroelectrics toward effective chemiresistive performances, and also establish a bright direction to explore their future device applications.

Electrohydrodynamic-Jet-Printed Phthalimide-Derived Conjugated Polymers for Organic Field-Effect Transistors and Logic Gates.

A π-conjugated polymer semiconductor, PBDTTTffPI, was synthesized for use as an organic semiconductor suitable for electrohydrodynamic (EHD) jet printing technology. Bulky alkylation of the polymer gave PBDTTTffPI good solubility in several organic solvents. EHD jet printing using PBDTTTffPI ink produced direct patterns of polymer semiconductors while maintaining smooth surface morphologies and crystal structures similar to those of spin-coated PBDTTTffPI films. EHD-jet-printed PBDTTTffPI was appropriate for use as a semiconductor layer in organic field-effect transistors (OFETs) and logic gates. OFETs that used EHD-jet-printed PBDTTTffPI had better electrical characteristics than devices that used spin-coated semiconductor films. When a dielectric material (Al2O3) with a high dielectric constant was introduced, the jet-printed PBDTTTffPI operated well at low voltages. Integrated devices such as inverters, NAND gates, and NOR gates were fabricated by printing PBDTTTffPI patterns and showed good switching behaviors. Therefore, the use of printable PBDTTTffPI provides an advance toward fabrication of practical integrated arrays in next-generation devices.

The effect of hydrothermal grown zinc oxide nanoparticles as seeds on the properties of nanoripples in zinc oxide thin films

This work reports on a simple approach to improving the optoelectronic properties of Wurtzite ZnO nanoripples by means of incorporating hydrothermally synthesised ZnO nanoparticles under controlled synthesis temperature. Initially, ZnO nanoparticles were investigated and subsequently utilised as seeds to induce ripple growth in spin-coated ZnO thin films. TEM images illustrated the development of nanospheres at 140°C. The yield of ZnO NPs at 180°C increased and consisted of a combination of nanorods and nanospheres. Morphologically, seedless ZnO nanoripples showed rugged ends of the nanoripple structures. The SEM images illustrated that the layers uniformly formed on the substrates, and seeding the ZnO nanoripples caused the nanoripples to elongate. The thickness of the nanoripples thin films showed a decrease with the incorporation of hydrothermally synthesised ZnO seeds from 134 nm for unseeded ZnO nanoripples to 96 nm at 180°C. The incorporation of ZnO NPs seeding treatment increased the transmission of ZnO nanoripples from 82% to 92%, leading to untreated ZnO nanoripples exhibiting a direct band gap of 3.19 eV that increased after seeding to 3.36 eV. The change in the band gap to a higher value(s) and increased transparency confirms the progressive improvement of the thin films due to incorporating ZnO seeding for optoelectronic and photovoltaic applications.

Intrinsically Viscoelastic Supramolecular Conjugated Polymer toward Suppressing Coffee-Ring Effect

Intrinsically Viscoelastic Supramolecular Conjugated Polymer toward Suppressing Coffee-Ring Effect

Impact of thickness of spin-coated P3HT thin films, over their optical and electronic properties

Impact of thickness of spin-coated P3HT thin films, over their optical and electronic properties

Tunable induced circular dichroism in gels.

The ICD phenomenon has drawn a lot of attention in recent years in applicable fields such as chiral sensing and chiroptical devices. In this work, we first gaze at the issues of thin spin-coated films not being able to deliver consistent ICD signals. A hypothesis of the underlying problem is proposed through a brief elucidation of the spin-coating process. To confirm and eliminate the uncontrollable dynamic factors with spin coating, we then dedicate our efforts to develop a new gel system based on chiral L-/D-N',N'-Dibenzoyl-cystine. Achiral dye molecules are intercalated in a DBC gel through a "one-step" preparation procedure. Compared to the former spin-coating system, significantly improved reproducibility of the new gel system is demonstrated. Besides, the ICD signals can be customized in a broad spectral range (wavelength tunability) by substituting dye molecules. Finally, we discuss the potential applications of this interesting system.

A nickel metal-organic-decomposition ink of nickel-ethanolamine complex leading to highly conductive nickel patterns for printed electronic applications

Conductive inks are key materials for the wide application of printed electronics. A metal-organic-decomposition (MOD) ink of nickel was prepared via a simple and high-yield complexation reaction pathway between nickel formate dihydrate and ethanolamine in a mixed solvent containing ethanol and ethylene glycol. The well-designed non-particulate ink shows long-term storage stability. The decomposition process of the ink and the microstructure evolution of the spin-coated films during sintering were investigated. The observed increase in conductivity can be ascribed to the establishment of a continuous conductive path between particles due to sintering and particle growth and more thorough removal of residual organics after increasing the sintering temperature from 300 to 400 °C. A low resistivity of 20.6 µΩ cm (3.0 times that of bulk nickel) was obtained. The inkjet printing performance of the Ni MOD ink was demonstrated. Our systematic work provides a fundamental understanding of the synthesis scenario of nickel organic decomposition ink. The good inkjet-printing performance and excellent conductivity of Ni MOD ink provide a wide range of possibilities for its broader applications in the field of printed electronics.

On the optical anisotropy in 2D metal-halide perovskites.

Two-dimensional metal-halide perovskites (MHPs) are versatile solution-processed organic/inorganic quantum wells where the structural anisotropy creates profound anisotropy in their electronic and excitonic properties and associated optical constants. We here employ a wholistic framework, based on semiempirical modeling (k·p/effective mass theory calculations) informed by hybrid density functional theory (DFT) and multimodal spectroscopic ellipsometry on (C6H5(CH2)2NH3)2PbI4 films and crystals, that allows us to link the observed optical properties and anisotropy precisely to the underlying physical parameters that shape the electronic structure of a layered MHP. We find substantial frequency-dependent anisotropy in the optical constants and close correspondence between experiment and theory, demonstrating a high degree of in-plane alignment of the two-dimensional planes in both spin-coated thin films and cleaved single crystals made in this study. Hybrid DFT results elucidate the degree to which organic and inorganic frontier orbitals contribute to optical transitions polarized along a particular axis. The combined experimental and theoretical approach enables us to estimate the fundamental electronic bandgap of 2.65-2.68 eV in this prototypical 2D perovskite and to determine the spin-orbit coupling (ΔSO = 1.20 eV) and effective crystal field (δ = -1.36 eV) which break the degeneracy of the frontier conduction band states and determine the exciton fine structure. The methods and results described here afford a better understanding of the connection between structure and induced optical anisotropy in quantum-confined MHPs, an important structure-property relationship for optoelectronic applications and devices.

AI modelling and evaluation of process parameters of spin coated PVDF thin film

A study was conducted to evaluate the effect of spinning speed, weight % of poly (vinylidene fluoride) (PVDF), annealing temperature on percentage of β-phase formation in spin-coated PVDF films. β-phase is a polymorph of PVDF film which exhibits strong piezoelectric properties. PVDF films were characterized using X-ray diffraction to determine the β-phase content in the PVDF film for different spin coating process parameter. L9 orthogonal array was used to determine the process parameters for different experiments. ANOVA analysis was made based on the experimental results and a regression equation was obtained to determine the β-phase content for a given process parameter setting. A fuzzy model was also built to determine the β-phase content for different process parameters. It was concluded that fuzzy model is more accurate than regression model.

Development of Highly Sensitive, Stable and Selective Hydrogen Gas Sensors Based on Sol-Gel Spin-Coated Nb2o5 Thin Films

Development of Highly Sensitive, Stable and Selective Hydrogen Gas Sensors Based on Sol-Gel Spin-Coated Nb2o5 Thin Films

High Dielectric Performance of Heterojunction Structures Based on Spin-Coated Graphene-PVP Thin Film on Silicon With Gold Contacts for Organic Electronics

The letter reports that frequency response of heterojunction structure based on a spin-coated graphene-PVP thin film on silicon with gold Schottky contacts and the electronic properties obtained by using capacitance (C) and conductance (G/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\omega $ </tex-math></inline-formula> ) versus voltage characteristics in the frequency range from 5 to 5 MHz. Furthermore, the electronic magnitudes were calculated. The accumulation capacitance observed at 3 V changes from 920 to 1094 pF. Here, empirically, the C and G/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\omega $ </tex-math></inline-formula> values increased with a decreasing frequency, while increasing in depletion and accumulation regions with increasing voltages. However, particularly, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{s}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}$ </tex-math></inline-formula> curves have peaks in low frequency values in the accumulation and depletion regions, these peaks decreased at high frequencies. Besides, an interface trap state density of 5.6– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.58\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> .eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> with a relaxation time constant of 157– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$31.5 ~\mu \text{s}$ </tex-math></inline-formula> was deduced. Additionally, the frequency and dc bias voltage-dependent dielectric characteristics show a huge dispersion, at room temperature. Experimentally, the high dielectric constant ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon '_{max}$ </tex-math></inline-formula> ) is 111 which is very higher than the maximum value of the conventional materials (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (3.8), SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (7.5), and so on) and appropriate doped materials to PVP. The results indicate that the graphene-PVP thin film with the high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon '_{max}$ </tex-math></inline-formula> value has a potential in metal-organic-semiconductors device technologies instead of a conventional device.