Spin-coating Approach Research Articles

Arbitrary Construction of Versatile NIR-Driven Microrobots.

Emerging light-driven micro/nanorobots (LMNRs) showcase profound potential for sophisticated manipulation and various applications. However, the realization of a versatile and straightforward fabrication technique remains a challenging pursuit. This study introduces an innovative bulk heterojunction organic semiconductor solar cell (OSC)-based spin-coating approach, aiming to facilitate the arbitrary construction of LMNRs. Leveraging the distinctive properties of a near-infrared (NIR)-responsive organic semiconductor heterojunction solution, this technique enables uniform coating across various dimensional structures (0D, 1D, 2D, 3D) to be LMNRs, denoted as "motorization." The film, with a slender profile measuring ≈140nm in thickness, effectively preserves the original morphology of objects while imparting actuation capabilities exceeding hundreds of times their own weight. The propelled motion of these microrobots is realized through NIR-driven photoelectrochemical reaction-induced self-diffusiophoresis, showcasing a versatile array of controllable motion profiles. The strategic customization of arbitrary microrobot construction addresses specific applications, ranging from 0D microrobots inducing living crystal formation to intricate, multidimensional structures designed for tasks such as microplastic extraction, cargo delivery, and phototactic precise maneuvers. This study advances user-friendly and versatile LMNR technologies, unlocking new possibilities for various applications, signaling a transformative era in multifunctional micro/nanorobot technologies.

Efficient non-doped cluster light-emitting diodes based on semiconducting copper iodide hybrids

Copper iodide hybrid clusters have attracted lots of interest in solution-processed light-emitting diodes (LEDs) for solid-state lighting and display in recent years, benefiting from their simple synthesis, structural diversity, high photoluminescence quantum yield (PLQY), and non-toxicity. However, most efficient copper iodide cluster LEDs are made by host-guest doped emitters and thus suffer from cumbersome synthesis and increased costs from the expensive hosts. Here, we report a non-doped cluster LED based on a novel copper iodine hybrid [35DPPy]4Cu2I2 (35DPPy: 3,5-diphenylpyridine) with high PLQY and decent charge transport characteristic. The non-doped [35DPPy]4Cu2I2 film synthesized by a one-step spin-coating approach possess the flat and compact morphology, high PLQY of 59.6%, and excellent heat/ultraviolet (UV) light/moisture/oxygen stability. The efficient green PL of [35DPPy]4Cu2I2 is proved to originate from the synergistic contribution from thermally activated delayed fluorescence and phosphorescence. A non-doped green LED based on [35DPPy]4Cu2I2 emitters is fabricated, achieving a peak external quantum efficiency of 4.8% and a maximum luminance of 3895 cd/m2. More importantly, large-area LEDs with an emitting area of 4.00 cm2 are realized with homogeneous and bright electroluminescence, showing their attractive potentials as novel electroluminescent emitters in the application of non-doped cluster LEDs.

Amplifying bactericidal activity: Surfactant-mediated AgBr thin film coating over two-dimensional vertically aligned ZnO nanorods for dark-light dual mode disinfection

Thin film coatings with potent antibacterial properties find critical applications in diverse domains such as medical devices, frequently touched surfaces, and food packaging for combating microbial proliferation across diverse scenarios. Two-dimensional photocatalytic antimicrobial coatings, offering a substantial actual-to-apparent surface ratio, hold immense potential for achieving this objective. However, realizing antibacterial performance not just under light but also in dark conditions remains a challenge. To address this, we present AgBr-coated vertically aligned ZnO nanorods (NRs) thin film architecture, employing a unique surfactant-mediated solution-phase spin-coating approach for achieving uniform deposition of AgBr onto ZnO NRs. The resulting ZnO NRs/AgBr heterojunction architectures have been characterized for their microstructural, morphological, elemental, optical, and wettability attributes. The studies have ascertained the tunability of AgBr content by modulating the concentration of its surfactant-based precursor solution. Further, valence band (VB) analyses revealed an increase in the electron density near to the VB edge. The dual role of AgBr as an antimicrobial agent and a photosensitizer, effectively enhancing the visible-light photodisinfection efficacy of ZnO NRs, has been evident through the dark-light dual mode antibacterial studies. Electron paramagnetic resonance measurements have shown hydroxyl radicals being majorly responsible for the visible-light photodisinfection performance. Encouragingly, reusability assessments showcase significant promise, while artificial sweat-wiping studies on the structures unveil heightened photodisinfection efficacy. This enhancement could be attributed to components like urea and lactic acid, speculated to augment the photocatalytic efficiency by minimizing charge recombination.

Fabrication and Characterization of Eco-Friendly Thin Films as Potential Optical Absorbers for Efficient Multi-Functional Opto-(Electronic) and Solar Cell Applications.

The necessity for reliable and efficient multifunctional optical and optoelectronic devices is always calling for the exploration of new fertile materials for this purpose. This study leverages the exploitation of dyed environmentally friendly biopolymeric thin films as a potential optical absorber in the development of multifunctional opto-(electronic) and solar cell applications. Uniform, stable thin films of dyed chitosan were prepared using a spin-coating approach. The molecular interactivity between the chitosan matrix and all the additive organic dyes was evaluated using FTIR measurements. The color variations were assessed using chromaticity (CIE) measurements. The optical properties of films were inspected using the measured UV-vis-NIR transmission and reflection spectra. The values of the energy gap and Urbach energy as well as the electronic parameters and nonlinear optical parameters of films were estimated. The prepared films were exploited for laser shielding as an attenuated laser cut-off material. In addition, the performance of the prepared thin films as an absorbing organic layer with silicon in an organic/inorganic heterojunction architecture for photosensing and solar energy conversion applicability was studied. The current-voltage relation under dark and illumination declared the suitability of this architecture in terms of responsivity and specific detectivity values for efficient light sensing applications. The suitability of such films for solar cell fabrications is due to some dyed films achieving open-circuit voltage and short-circuit current values, where Saf-dyed films achieved the highest Voc (302 mV) while MV-dyed films achieved the highest Jsc (0.005 mA/cm2). Finally, based on all the obtained characterization results, the engineered natural cost-effective dyed films are considered potential active materials for a wide range of optical and optoelectronic applications.

Two-Dimensional Layered Simple Aliphatic Monoammonium Tin Perovskite Thin Films and Potential Applications in Field-Effect Transistors.

Two-dimensional (2D) layered organic-inorganic perovskites have great potential for fabricating field-effect transistors due to their unique structure that enables the horizontal transport of charge carriers in metal-halide octahedra, resembling the transport behavior in semiconducting channels. Their electronic band structures are mainly dominated by the metal-halide octahedra, which eventually determine the optical and electrical characteristics, whereas organic cations have no direct contributions but would impact the electronic structures via distorting the octahedra. So far, high performance has been achieved in 2D Sn perovskites compared to their Pb counterparts because the intrinsic differences of Sn promote transport properties. The champion hole mobility has been obtained in single-ring aromatic phenylethylammonium tin iodide perovskite [(PEA)2SnI4]. However, simple aliphatic monoammonium tin perovskites and their device applications have rarely been reported. Herein, 2D layered n-butylammonium tin iodide perovskite [(BA)2SnI4] thin films have been synthesized by a spin-coating approach. A structural phase transition occurs at about 225 K in the films, accompanied by the changes in the photoluminescence peak and exciton binding energy. Longitudinal optical (LO) phonons are found to govern the scattering of charge carriers and excitons via the Fröhlich interactions in the temperature range 77-300 K. The first-principles calculations predict that the perovskite has excellent transport characteristics comparable to those of molybdenum disulfide (MoS2) and methylammonium lead iodide perovskite (MAPbI3). The (BA)2SnI4 thin film field-effect transistors constructed on polymer dielectrics with a maximum hole mobility of 0.03 cm2 V-1 s-1 in ambient conditions have been successfully demonstrated for the first time. Our findings not only offer a deep insight into the physical properties of 2D layered aliphatic monoammonium tin perovskite thin films but also provide important experimental and theoretical guidance for their potential applications in lateral-type flexible optoelectronic devices.

A method to improve the performance of all-inorganic halide perovskite CsPbBr3 memory

All-inorganic perovskite has been generally used in memristor due to its outstanding characteristics such as superior optical performance, superior stability, tunable and highly effective photoluminescence. We have proved the use of all-inorganic halide perovskite as a medium in memristor. In this paper, the memristor with construction of Au/CsPbBr3/FTO, Au/CsPbBr3/ZnO/FTO and Au/ZnO/CsPbBr3/FTO were manufactured by one-step spin-coating approach to observe representative bipolar resistance switching behaviors in different construction of resistance random access memory devices. Results show that the memristor based on ZnO/CsPbBr3 heterojunction having excellent resistance switching effect with low resetting, setting voltages and and high environmental stability. Moreover, a model of filaments through the CsPbBr3 layer was raised to interpret the resistive switching effect.

Ternary Electrical Memory Devices Based on Polycarbazole: SnO2 Nanoparticles Composite Material.

In this paper, a D–A polymer (PIB) containing carbazole as the donor group in the main chain and benzimidazole benzisoindolinone as the acceptor group was synthesized by Suzuki reaction. The Suzuki reaction, also known as the Suzuki coupling reaction, is a relatively new organic coupling reaction in which aryl or alkenyl boronic acids or boronic acid esters react with chlorine, bromine, iodoaromatic hydrocarbons or alkenes under the catalysis of zerovalent palladium complexes cross-coupling. A series of devices were fabricated by a spin-coating approach, and the devices all exhibited ternary resistance switching storage behavior. Among them, the composite device with the mass fraction of SnO2 NPs of 5 wt% has the best storage performance, with a threshold voltage of −0.4 V and a switching current ratio of 1:101.5:104.5. At the same time, the current of the device remained stable after a 3-h test. Furthermore, after 103 cycles, the current has no obvious attenuation. The device has good stability and continuity. Moreover, the conduction mechanism is further revealed. Inorganic nanoparticle composite devices have splendid memory performances and exhibit underlying application significance in storing data.

Flexible, Transparent and Highly Conductive Polymer Film Electrodes for All-Solid-State Transparent Supercapacitor Applications.

Lightweight energy storage devices with high mechanical flexibility, superior electrochemical properties and good optical transparency are highly desired for next-generation smart wearable electronics. The development of high-performance flexible and transparent electrodes for supercapacitor applications is thus attracting great attention. In this work, we successfully developed flexible, transparent and highly conductive film electrodes based on a conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The PEDOT:PSS film electrodes were prepared via a simple spin-coating approach followed by a post-treatment with a salt solution. After treatment, the film electrodes achieved a high areal specific capacitance (3.92 mF/cm2 at 1 mA/cm2) and long cycling lifetime (capacitance retention >90% after 3000 cycles) with high transmittance (>60% at 550 nm). Owing to their good optoelectronic and electrochemical properties, the as-assembled all-solid-state device for which the PEDOT:PSS film electrodes were utilized as both the active electrode materials and current collectors also exhibited superior energy storage performance over other PEDOT-based flexible and transparent symmetric supercapacitors in the literature. This work provides an effective approach for producing high-performance, flexible and transparent polymer electrodes for supercapacitor applications. The as-obtained polymer film electrodes can also be highly promising for future flexible transparent portable electronics.

Solution processed AgSbS2 film for efficient planar heterojunction solar cells

AgSbS2 is a promising absorber material for photovoltaic cells because of its optimum bandgap, strong optical absorption, and excellent stability. Here, we report a spin-coating and annealing approach for the fabrication of AgSbS2 solar cells, where Ag-Sb-thiourea complex solution was prepared as the precursor solution. We identified that the annealing temperature crucially affected the phase composition, crystallinity, and surface morphology of the AgSbS2 film. We also probed the electronic structures and established a FTO/TiO2/AgSbS2/Spiro-OMeTAD/Au device structure. This device finally achieved an encouraging power conversion efficiency of 2.25%, which is highest efficiency in AgSbS2 solar cells. Our research opens up another prospect for pursuing high performance AgSbS2 thin film solar cells by adopting a solution processing method and planar heterojunction device structure.

Tuning of Optical Band Gap: Genesis of Thickness Regulated Al Doped ZnO Nano-Crystalline Thin Films Formulated by Sol–Gel Spin Coating Approach

Tuning of Optical Band Gap: Genesis of Thickness Regulated Al Doped ZnO Nano-Crystalline Thin Films Formulated by Sol–Gel Spin Coating Approach

A novel CMOS hexaferrite circulator with 25 GHz operating frequency

A novel CMOS hexaferrite circulator with a Y-junction structure is designed and fabricated, which is compatible with standard CMOS technology. The spin-coating approach is adopted during the fabrication, in which the photoresist is mixed with nano-hexaferrite powder for preparation of a magnetic thin film in the device. Compared with the traditional circulator with an external permanent magnet for operation, the novel circulator can utilize the spin-coating magnetic film and is compatible with CMOS technology. The remanent magnetization of the adopted hexaferrite thin film can provide the required magnetic field for reciprocity properties. The optimization of impedance matching and the improvements in the related parameters are demonstrated on the novel CMOS circulator. The CMOS circulator exhibits the merits of small volume and easy integration while keeping its promising non-reciprocity properties. The fabrication is conducted based on the standard 180-nm CMOS technology. S-parameter measurements on the circulator show that the device has an isolation of 20 dB over 520 MHz bandwidth at 26.2 GHz. The minimum insertion loss is 1.81 dB. The novel CMOS-compatible circulator has potential application in 5G wireless communication systems.

Ultrafast In Situ Synthesis of Large-Area Conductive Metal–Organic Frameworks on Substrates for Flexible Chemiresistive Sensing

The widespread use of electrically conductive metal-organic frameworks (EC-MOFs) in high-performance devices is limited by the lack of facile methods for synthesizing large-area thin films on the desired substrates. Herein, we propose a spin-coating interfacial self-assembly approach to in situ synthesize high-quality centimeter-sized copper benzenehexathiol (Cu-BHT) MOFs on diverse substrates in only 5 s. The film thickness (ranging from 5 to 35 nm) and surface morphology can be precisely tuned by controlling the reaction time. The gas sensor based on the 10 nm thick Cu-BHT film exhibits a low limit of detection (0.23 ppm) and high selectivity value (>30) in sensing NH3 at ultralow driving voltages (0.01 V). Moreover, the Cu-BHT films retain their initial sensor performance after 1000 repetitive bending cycles at a bending radius of 3 mm. Density functional theory calculations suggest that Cu2c sites induced by crystal particles on the film surface can improve the sensing performance. This facile and ultrafast approach for in situ synthesis of large-area EC-MOF films on diverse substrates with tunable thickness on a nanometer scale should facilitate application of EC-MOFs in flexible electronic device arrays.

Efficient All-Inorganic Perovskite Light-Emitting Diodes with Improved Operation Stability.

Stability is becoming a main issue for perovskite light-emitting diodes (PeLEDs), as their external quantum efficiency (EQE) has been boosted to above 20%. An all-inorganic perovskite, cesium lead iodide (CsPbI3), has better stability than organic-inorganic hybrid perovskites but suffers from a transition to yellow δ-CsPbI3 phase at room temperature. Herein, we report stabilization of the α-CsPbI3 phase by in situ formation of perovskite nanocrystals (NCs). By incorporation of a proper ratio of bulky organoammonium halides, 4-fluoro-phenylmethylammonium iodide (4-F-PMAI), stable α-CsPbI3 films with nanometer-sized crystals can be obtained using a one-step spin-coating approach. The PeLEDs using α-CsPbI3 NC films as emitters show a pure red emission at 692 nm and a high EQE of 14.8%. The EQE is further boosted to 18.6% using CsPbI2.8Br0.2 as the emissive layer. Furthermore, the PeLEDs show a very decent half-lifetime of over 1200 min and a shelf stability of over 2 months, much longer than that of hybrid PeLEDs.

Efficient strain modulation of 2D materials via polymer encapsulation

Strain engineering is a promising method to manipulate the electronic and optical properties of two-dimensional (2D) materials. However, with weak van der Waals interaction, severe slippage between 2D material and substrate could dominate the bending or stretching processes, leading to inefficiency strain transfer. To overcome this limitation, we report a simple strain engineering method by encapsulating the monolayer 2D material in the flexible PVA substrate through spin-coating approach. The strong interaction force between spin-coated PVA and 2D material ensures the mechanical strain can be effectively transferred with negligible slippage or decoupling. By applying uniaxial strain to monolayer MoS2, we observe a higher bandgap modulation up to ~300 meV and a highest modulation rate of ~136 meV/%, which is approximate two times improvement compared to previous results achieved. Moreover, this simple strategy could be well extended to other 2D materials such as WS2 or WSe2, leading to enhanced bandgap modulation.

High-Intensity CsPbBr3 Perovskite LED using Poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) as Hole Transport and Electron-Blocking Layer

The majority of highly efficient perovskite light-emitting diodes (PeLED) contain PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrenesulfonate) as hole transport layer (HTL). However, the hygroscopic and acidic nature of PEDOT:PSS may lead to deterioration of PeLED performance. Moreover, due to its inferior electron-blocking properties, an additional electron-blocking layer (EBL) is required to establish charge balance and consequently obtain superior emission characteristics in typically electron-rich PeLED structures. In this work, PTAA (poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)) serving both as HTL and EBL is employed to substitute PEDOT:PSS in PeLED. The perovskite CsPbBr3 is chosen as emissive layer (EML) material due to its high color purity and photoluminescence (PL) quantum yield. Dense CsPbBr3 films are fabricated on PTAA-coated ITO substrates by employing a one-step spin-coating approach based on nonstoichiometric perovskite precursor solutions. To suppress non-radiative recombination, a small amount of methylammonium bromide (MABr) is incorporated in the CsPbBr3 lattice. The resulting films exhibit excellent coverage and PL intensity. PeLED containing pure CsPbBr3 films as EML show a green emission with a peak at 520 nm, maximum luminance of 11,000 cd/m2, an external quantum efficiency (EQE) of 3.3 % and a current efficiency (CE) of 10.3 cd/A. Further enhancement to 21,000 cd/m2, 7.5 % and 27.0 cd/A is demonstrated by PeLED with MABr-doped CsPbBr3 layers.

Constructing “hillocks”-like random-textured absorber for efficient planar perovskite solar cells

Efficient planar heterojunction perovskite solar cells (PSCs) with high-quality absorbers are promising for flexible-, semitransparent-, and tandem- photovoltaic applications. However, compared to mesoporous PSCs, planar perovskite absorbers tend to suffer from additional optical losses due to insufficient light harvesting. Accordingly, the design and fabrication of high-quality textured perovskite absorbers are promising to improve device performance. We developed a “hillocks”-like random-textured perovskite (HRT-perovskite) absorber using a facile chlorobenzene (CB) anti-solvent assisted spin-coating approach. The crystallization kinetics and formation mechanisms of CB-induced HRT-perovskite absorbers have been systematically explored, allowing us to gain insights into the role of CB, i.e. an appropriate volume of CB promotes the formation of a porous MAI-PbI2-DMSO intermediate structure. We show that the porous nature of the intermediate film provides sufficient space for lattice reconstruction and structure expansion during crystal growth, thus effectively improving the film and surface/interface quality, and, ultimately, the optoelectronic properties of the perovskite absorber. Moreover, the HRT-perovskite absorber exhibits excellent light-trapping capability and carrier mobility, due to its optimized surface roughness and longitudinally ordered grain boundary distribution. As a result, we obtained efficiencies of up to 20.03% from planar heterojunction PSCs fabricated using ~400 nm thick HRT-perovskite absorbers. The process exhibits very high reproducibility with 20 individual devices fabricated in one batch, achieving an average power conversion efficiency (PCE) of 19.00%. Finally, the whole fabrication process was conducted below 150 ℃, which is appropriate for a wide range of applications, such as flexible- and tandem- photovoltaic devices.

Optical properties of ZnO/Black Phosphorus/ZnO sandwich structures

ZnO/black phosphorus (BP)/ZnO sandwich structures are prepared via a combination of atomic layer deposition (ALD) technique and spin-coating approach. The thickness of the ZnO layers is controlled to be about 40 nm via tuning the number of ALD cycles, while the amount of BP nanosheets can be tuned during the spin coating process. The obtained ZnO/BP/ZnO are characterized by X-ray diffractometer, X-ray photoelectron spectroscopy (XPS), Atomic Force Microscope (AFM), Raman, and optical spectroscopy. It is found that there are strong interactions between the BP nanosheets and ZnO layers, as confirmed by XPS and Raman spectra, which thus affects the optical properties of ZnO. To be specific, the synthesized samples show an enhancement of the near-band edge emission and a reduction of the deep level emission with good long-term stability, due to the passivation of the defects in the formed BP-ZnO interface.

Flexible films derived from PIM-1 with ultralow dielectric constants

High hydrophobicity, non-polar structure and large pore volume are among the main criteria demanded breakthrough when designing or selecting materials with ultralow dielectric constants of k. Herein we proved the feasibility of PIM-1 films, a constitutive porous polymer with high free volume, as a rising ultra-low-k material in the field of microelectronics. An ultrathin PIM-1 film of approximate 60 nm in thickness was easily obtained by the spin-coating approach. Thermal treatment on the PIM-1 film (denoted as sPIM-1) enhanced its dielectric performance and the incorporation of cyanopropyltriethoxysilane (CPTES) to sPIM-1 improved the mechanical strength of the film significantly. The sPIM-1 films exhibited an ultralow dielectric constant (k = 1.5 at 10 kHz), substantial mechanical strength, and ability to withstand high humidity (soaking in water for 30 min) without losing their dielectric properties. The easy curing process and extremely stable performances even under the harsh conditions of practical application make it one of the most competitive candidates of low dielectric materials at present.

Functional Nanostructured Perovskite Oxides from Radical Polymer Precursors.

In the present work, nanostructured perovskite oxides with improved reactivity, tunable morphology, and different forms (powder, thin films) were prepared using acrylic molecules such as acrylamide, acrylic acid, and methacrylic acid as novel chelating agents in a straightforward fashion. The approach, developed for LaCoO3, was also applied to oxides of the type LaMO3 (M = Fe, Ni), SrTiO3, and solid solutions thereof. The polymer-to-oxide evolution followed by XRD and IR showed merely a minimal amount of carbonate residuals even at temperatures as low as 600 °C. The different cross-linking degree of the polymeric compounds influenced the material crystallization leading to oxides with different grain sizes at the same calcination temperature. Among the prepared perovskites, acrylamide-derived LaCoO3 exhibited the highest oxygen surface reactivity as demonstrated by XPS and TPD measurements. As a result, the materials showed enhanced catalytic performance, leading to complete oxidation of CO at approximately 200 °C, which was almost 100 °C lower than for citric-acid-based samples. Finally, by exploiting the UV photopolymerization of the acrylic group, homogeneous, crystalline perovskite thin films of optical quality were successfully prepared through a straightforward spin-coating approach. The findings of this work demonstrate that this novel synthesis route is a better alternative to state-of-the-art citrate-based methods for the preparation of prospective catalysis, sensing, and energy conversion materials of high purity, activity, and tunable form.

Titanium mesh-supported “TiO2 nanowire arrays/Yb-Er-F tri-doped TiO2 up-conversion nanoparticles” composite structure: Designation for high efficient flexible dye-sensitized solar cells

Titanium (Ti) mesh-supported “TiO2 nanowire arrays (TNWAs)/Yb-Er-F tri-doped TiO2 up-conversion nanoparticles (YEF-TiO2-UCNPs)” composite structures were prepared as photoanodes of the flexible dye-sensitized solar cells (DSSCs) by using hydrothermal and spin-coating approaches. The as-synthesized YEF-TiO2-UCNPs which could enhance the absorption of N719 dyes by converting the near-infrared light to visible light exhibited better up-conversion luminescence properties than the YbEr co-doped TiO2 up-conversion nanoparticles (YE-TiO2-UCNPs). Moreover, the appropriate YEF-TiO2-UCNPs could enlarge light harvesting range of the formed flexible photoanode and improved the photovoltaic performance of the DSSCs. Under the simulated solar irradiation of 100 mW cm−2 (AM 1.5G), the flexible DSSC with a Ti mesh-supported “TNWAs/YEF-TiO2-UCNPs60%P2540%” composite structure achieved a short-circuit current density (Jsc) of 12.81 mA cm−2 and a power conversion efficiency (PCE) of 5.54%, showing improvements of 45.7% and 37.8% as compared with TNWAs/P25100% (8.79 mA cm−2, 4.02%), respectively.