Spin-coating Process Research Articles

Ultraviolet-Visible-Near Infrared Broadband Photodetector Based on Electronspun Disorder ZnO Nanowires/Ge Quantum Dots Hybrid Structure

Ultraviolet-visible-near infrared broadband photodetectors have significant prospects in many fields such as image sensing, communication, chemical sensing, and day and nighttime surveillance. Hybrid one-dimensional (1D) and zero-dimensional (0D) materials are attractive for broadband-responsive photodetectors since its unique charges transfer characteristics and facile fabrication processes. Herein, a Si/ZnO nanowires/Ge quantum dots photodetector has been constructed via processes that combined electrospinning and spin-coating methods. A broadband response behavior from ultraviolet to near-infrared (from 250 to 1550 nm) is observed. The responsivity of the hybrid structure increases around three times from 550 to 1100 nm compared with the pure Si photodetector. Moreover, when the photodetector is illuminated by a light source exceeding 1100 nm, such as 1310 and 1550 nm, there is also a significant photoresponse. Additionally, the ZnO NWs/Ge quantum dots heterostructure is expected to be used in flexible substrates, which benefits from electrospinning and spin-coating processes. The strategy that combines 1D ZnO NWs and 0D solution-processed Ge QDs nanostructures may open a new avenue for flexible and broadband photodetector.

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.

Role of solution concentration in formation kinetics of bromide perovskite thin films during spin-coating monitored by optical in situ metrology.

Optoelectronic devices based on metal halide perovskites continue to show a improved performance, and solution-based coating techniques pave the way for large-area applications. However, not all parameters influencing the thin film formation process of metal halide perovskites are identified and entirely rationalised over their full compositional range, thus hampering optimised thin film fabrication. Furthermore, while the perovskite deposition via spin-coating and annealing is an easily accessible technique, more profound insights into the chemical formation process are still lacking. Varying the precursor solution concentration is commonly used to vary the resulting thin film thickness. This study shows that varying the precursor solution concentration also affects the thin film morphology and optoelectronic quality. Hence, we herein investigate the influence of the precursor solution concentration on the formation process of a pure bromide-based triple cation perovskite (Cs0.05MA0.10FA0.85PbBr3) by fiber-based optical in situ measurement. During the spin-coating process, in situ UV-vis and PL measurements reveal formation kinetics are strongly dependent on the concentration. Furthermore, we identify delayed nucleation and retarded growth kinetics for more concentrated precursor solutions. In addition, we quantify the shifting chemical equilibrium of colloidal pre-coordination in the precursor solution depending on concentration. Namely, colloids are pre-organised to a higher degree and higher-coordination lead-bromide complexes tend to form in more concentrated precursor solutions. Thus, the modified solution chemistry rationalises retarded perovskite formation kinetics and highlights the precursor concentration as an influential and optimisable parameter for solution-based thin film deposition.

Preparation of highly efficient and stable CsPbBr3 perovskite solar cells based on an anti-solvent rinsing strategy

CsPbBr 3 perovskite solar cell has become a hot research object due to its excellent stability. It has been proved that anti-solvent washing is a good way to improve the crystal quality of organic-inorganic hybrid perovskite materials using a one-step spin-coating method. However, it is rarely reported in the preparation of all-inorganic perovskite materials. Here, an anti-solvent rinsing strategy was introduced for the synthesis of CsPbBr 3 films via the multi-step spin-coating process. We found that the addition of anti-solvent with high boiling points could significantly improve the surface morphology and crystal quality of CsPbBr 3 films by optimizing the nucleation and crystallization of PbBr 2 films. By virtue of the anti-solvent rinsing strategy, the highest efficiency of 9.6% and long-term stability over 800 h in ambient air without encapsulation were achieved. Our conclusions provide a certain reference value for the preparation of highly efficient and stable CsPbBr 3 perovskite solar cells. ● An anti-solvent rinsing strategy was introduced for the synthesis of CsPbBr 3 films via the multi-step spin-coating process. ● We found that the addition of anti-solvents with high boiling points could significantly improve the surface morphology and crystal quality of CsPbBr 3 films by optimizing the nucleation and crystallization of PbBr 2 films. ● By virtue of the anti-solvent rinsing strategy, a highest power conversion efficiency of 9.6% and long-term stability over 800 h in ambient air without encapsulation were achieved.

Robust transfer-printing method for perovskite films and nanostructures

Metal halide perovskites, as a promising semiconductor material, have been successfully used in electroluminescent devices because of their desirable characteristics, such as good conductivity, high color purity, tunable bandgap, low cost and solution process ability. In the past few years, significant progress has been made in the development of high-efficiency perovskite light-emitting diodes (PeLEDs). These efficient PeLEDs are mainly achieved by sophisticated spin-coating methods, which can easily control the perovskite's composition, film thickness, morphology and crystallinity. However, with the continuous development of PeLEDs, commercial production problems have to be solved, such as large area production, high resolution patterning and substrate diversity, which are difficult for the current spin-coating process.

Formation mechanism of CsPbBr<sub>3</sub> in multi-step spin-coating process

The quality of perovskite films plays a crucial role in solar cell, which can affect the stability and power conversion efficiency (PCE). As one of inorganic perovskites with excellent stability, CsPbBr<sub>3</sub> perovskite is usually prepared by multi-step method due to the large difference in solubility between its precursor salts (PbBr<sub>2</sub> and CsBr). The main reason is that the formation mechanism of CsPbBr<sub>3</sub> film is not thoroughly studied. The incomplete reaction of PbBr<sub>2</sub> and emergence of Cs<sub>4</sub>PbBr<sub>6</sub> when the CsBr is excessive become problems that need to be solved urgently. In this paper, the phase transition of films during spin coating is observed in detail. In the process of film formation, the CsBr diffuses into the predeposited PbBr<sub>2</sub> film to complete the reaction. The short reaction time results in insufficient reactions inside the film but overreaction on the surface of film. The CsPb<sub>2</sub>Br<sub>5</sub> and Cs<sub>4</sub>PbBr<sub>6</sub> appear with CsPbBr<sub>3</sub> perovskite, and the film formed by repetitively annealing blocks the diffusion of CsBr. Methanol has an etching effect on the perovskite film which can eliminate the blocking effect. By extending the reaction time of CsBr solution on the film surface, the PbBr<sub>2</sub> in the bottom layer is fully reacted, and after being annealed, the perovskite film will recrystallize to form a compact film. With the reaction time controlled appropriately, the CsPb<sub>2</sub>Br<sub>5</sub> in the film can be effectively reduced and Cs<sub>4</sub>PbBr<sub>6</sub> will not appear. The film grain size increases, grain boundary decreases, and the recombination is effectively inhibited, which ensures the improvement of the photoelectric performance of the solar cell. Under the condition of spin-coating four times and reaction time of 30 s, the solar cell has 6.30% PCE, <i>V</i><sub>oc</sub> = 1.28 V, <i>J</i><sub>sc</sub> = 8.40 mA/cm<sup>2</sup>, <i>FF</i> = 0.59 . Comparing with the solar cells with no extended reaction time, the PCE improves more than 18%. This work will provide an important insight into the growth mechanism of perovskite film toward high crystallinity and less defects.

Wafer-scale nanocracks enable single-molecule detection and on-site analysis

Large-area surface-enhanced Raman spectroscopy (SERS) sensing platforms displaying ultrahigh sensitivity and signal uniformity have potentially enormous sensing applicability, but they are still challenging to prepare in a scalable manner. In this study, silver nanopaste (AgNPA) was employed to prepare a wafer-scale, ultrasensitive SERS substrate. The self-generated, high-density Ag nanocracks (NCKs) with small gaps could be created on Si wafers via a spin-coating process, and provided extremely abundant hotspots for SERS analyses with ultrahigh sensitivity—down to the level of single molecules (enhancement factor: ca. 1010; detection limit: ca. 10–18 M)—and great signal reproducibility (variation: ca. 3.6%). Moreover, the Ag NCK arrays demonstrated broad applicability and practicability for on-site detection when combined with a portable 785 Raman spectrometer. This method allowed the highly sensitive detection of a diverse range of analytes (benzo[a]pyrene, di-2-ethylhexyl phthalate, aflatoxins B1, zearalenone, ractopamine, salbutamol, sildenafil, thiram, dimethoate, and methamidophos). In particular, pesticides are used extensively in agricultural production. Unfortunately, they can affect the environment and human health as a result of acute toxicity. Therefore, the simultaneous label-free detection of three different pesticides was demonstrated. Finally, the SERS substrates are fabricated through a simple, efficient, and scalable process that offers new opportunities for mass production.

Enhancing the Luminance Efficiency of Formamidinium-Based Dion-Jacobson Perovskite Light-Emitting Diodes via Compositional Engineering.

In this paper, the phase formation mechanism of formamidinium (FA)-based Dion-Jacobson (DJ) perovskites is uncovered for the first time, which includes the formation of the n1 domain (n = 1 perovskite phase) and a trace amount of the large n domain in the spin-coating process and the growth of the n2 domain and the large n domain during the thermal annealing stage. The phase formation mechanism clearly reveals the different phase distributions between FA-based Ruddlesden-Popper (RP) and FA-based DJ perovskite films at different stages of film preparation due to the larger formation energy of the DJ perovskites. According to this phase formation mechanism, we put forward an effective strategy of the small A-site cation compositional engineering. Then, excess perovskitizer cations (FA+) are introduced to increase the crystallinity, modulate the phase distribution and passivate defects without disturbing the structure of DJ perovskites simultaneously. The final green-light DJ PeLED devices show a maximum luminance of 41 520 cd/m2 and a maximum current efficiency of 31.1 cd/A (EQE: 8.5%), which are the record values so far. The final DJ PeLEDs show an improved operational lifetime of ca. 15 min at an initial luminance of ca. 800 cd/m2. Our results suggest that DJ perovskites can be promising for light-emitting applications.

Efficient Ag-Doped Perovskite Solar Cells Fabricated in Ambient Air

So far, it is still a great challenge to prepare high efficiency organic–inorganic perovskite solar cells in ambient air. Specifically, moisture is easily combined with the perovskite material during the spin-coating process, which result in porous perovskite films with poor surface morphology. In this study, we investigated crystalline Ag-doped perovskite films by a one-step spin-coating method in air with 30–40% relative humidity (RH), in which ethyl acetate (EA) was used as antisolvent can absorb moisture in air to reduced nucleation density. More significantly, EA is a feasible and environmentally friendly solvent to replace highly toxic solvent. Moreover, 1.0% Ag-doped device shows a highest power conversion efficiency (PCE) of 14.36%. The improved performance is not only ascribed to the superior CH3NH3PbI3 film with high crystallinity but to the versatile tunability of energy band structure.

Strategies for chemical vapor deposition of two-dimensional organic-inorganic halide perovskites

SummaryTwo-dimensional (2D) organic-inorganic halide perovskites (OIHPs) with an alternating stacked structure of an organic layer and an inorganic layer draw significant attention for photovoltaics, multiple quantum-well, and passivation of three-dimensional perovskites. Although the low-cost and simple spin-coating process of these materials offers a vast platform to study fundamental properties and help them achieve rapid progress in electronics and optoelectronics, chemical vapor deposition (CVD) growth is also necessary for large-area, epitaxial, selective, and conformal growth. Here, one-step CVD strategies for 2D OIHP growth are proposed, and the growth trends depending on the precursor and substrate conditions are discussed. We report a CVD-grown nontoxic, lead-free 2D tin-OIHP flake to show the system offering a universal route to synthesize perovskite crystals based on arbitrary organic and inorganic components.

Implementing an intermittent spin-coating strategy to enable bottom-up crystallization in layered halide perovskites

Two-dimensional halide perovskites (2D PVSKs) have drawn tremendous attentions owing to their outstanding ambient stability. However, the random orientation of layered crystals severely impedes the out-of-plane carrier transport and limits the solar cell performance. An in-depth understanding coupled with an effective control of the crystallization in 2D PVSKs is the crux for highly efficient and durable devices. In this contribution, we accidentally discovered that the crystallization of 2D PVSKs can be effectively regulated by so-called ′intermittent spin-coating (ISC)′ process. Combined analyses of in(ex)-situ grazing-incidence wide-angle X-ray scattering with time-of-flight secondary ion mass spectrometry distinguish the interface initialized bottom-up crystallization upon ISC treatment from the bi-directional one in the conventional spin-coating process, which results in significantly enhanced crystal orientation and thus facilitated carrier transport as confirmed by both electrical measurements and ultrafast spectroscopies. As a result, the p-i-n architecture planar solar cells based on ISC fabricated paradigm PEA2MA3Pb4I13 deliver a respectable efficiency of 11.2% without any treatment, which is three-fold improvement over their spin-coated counterparts and can be further boosted up to 14.0% by NH4Cl addition, demonstrating the compatibility of ISC method with other film optimization strategies.

Strategy for Crystallization Management of Perovskite: Incorporation of FAI in a PbI2 Precursor for a Two-Step Spin-Coating Process

Strategy for Crystallization Management of Perovskite: Incorporation of FAI in a PbI₂ Precursor for a Two-Step Spin-Coating Process

MXene Coatings: Novel Hydrogen Permeation Barriers for Pipe Steels.

MXenes are a new class of two-dimensional (2D) materials with promising applications in many fields because of their layered structure and unique performance. In particular, the physical barrier properties of two-dimensional nanosheets make them suitable as barriers against hydrogen. Herein, MXene coatings were prepared on pipe steel by a simple spin-coating process with a colloidal suspension. The hydrogen resistance was evaluated by electrochemical hydrogen permeation tests and slow strain rate tests, and the corrosion resistance was assessed by potentiodynamic polarization. The results reveal that MXene coatings offer excellent hydrogen resistance and corrosion protection by forming a barrier against diffusion. Experimentally, the hydrogen permeability of the MXene coating is one third of the substrate, and the diffusion coefficient decreases as well. The mechanistic study indicates that the hydrogen resistance of the MXene coatings is affected by the number of spin-coated layers, while the concentration of the d-MXene colloidal suspension determines the thickness of a single coating. However, damage to the sample surface caused by the colloidal suspension that contains H+ and F− may limit the improvement of the hydrogen resistance. This paper reveals a new application of 2D MXene materials as a novel efficient barrier against hydrogen permeation and the subsequent alleviation of hydrogen embrittlement in the steel substrate.

Antifouling Fibrous Membrane Enables High Efficiency and High-Flux Microfiltration for Water Treatment.

Membrane biofouling has long been a major obstacle to highly efficient water treatment. The modification of the membrane surface with hydrophilic materials can effectively enhance biofouling resistance. However, the water flux of the membranes is often compromised for the improvement of antifouling properties. In this work, a composite membrane composed of a zwitterionic hydrogel and electrospinning fibers was prepared by a spin-coating and UV cross-linking process. At the optimum conditions, the composite membrane could effectively resist the biofouling contaminations, as well as purify polluted water containing bacteria or diatoms with a high flux (1349.2 ± 85.5 L m-2 h-1 for 106 CFU mL-1 of an Escherichia coli solution). Moreover, compared with the commercial poly(ether sulfone) (PES) membrane, the membrane displayed an outstanding long-term filtration performance with a lower water flux decline. Therefore, findings in this work provide an effective antifouling modification strategy for microfiltration membranes and hold great potential for developing antifouling membranes for water treatment.

Enhancing the performance of CsPbIBr2 solar cells through zinc halides doping

B-site doping is an effective strategy to improve the performance of inorganic perovskite solar cells. Zinc halides (ZnX2, XI, Br, Cl) doped CsPbIBr2 solar cells were prepared by simply introducing ZnX2 salts into the precursor solution for one step spin-coating process. The doped inorganic perovskite films exhibit enhanced crystallinity and improved surface morphology. More over, the photoluminescence and single-carrier device characterizations confirm that the internal defect density of CsPbIBr2 films decreases remarkably after ZnX2 doping and the non-radiative recombination is suppressed. The CsPbIBr2 solar cells based on the ZnI2 doped films achieve a champion efficiency of 8.15%, outperforming that (6.93%) of the pristine counterpart.

Nature-inspired slippery polymer thin film for ice-repellent applications

In this study, the authors investigated the anti-icing performance of a hierarchical slippery polymer thin film that is inspired by structures of the lotus leaf and Nepenthes pitcher plant. The polymer solution was mixed with the lubricant at the appropriate concentration to achieve slippery properties. The dry etching method followed by the spin-coating process was used to generate a uniform polymer microstructure on the thin film. The polymer nanostructure was then yielded by an additional plasma-etching method using carbon tetrafluoride (CF4) gas. The anti-icing efficiency was then compared with that of the non-functional samples to demonstrate the advantages of combination in all criteria. Moreover, a theoretical prediction based on the free-energy approach was used to measure the nucleation time at the interface and illustrated good agreement with real-time measurement. The results propose a new and facile approach for outdoor anti-icing applications.

Construction of Multilayer Films and Superlattice- and Mosaic-like Heterostructures of 2D Metal Oxide Nanosheets via a Facile Spin-Coating Process.

This study reports a design of a variety of nanostructured films of 2D oxide nanosheets. We systematically examined the deposition of perovskite-type Ca2Nb3O10- nanosheets by spin-coating their dimethyl sulfoxide dispersion. Neat and homogeneous monolayer tiling was attained on various substrates by selecting an optimum rotation speed, which was dependent on the nanosheet concentration. Repeating the optimized spin-coating process allowed for layer-by-layer deposition of the nanosheets into multilayer films with a designed layer number. Vertical superlattice heterostructures could also be assembled by alternately spin-coating the suspensions of Ca2Nb3O10- and Ti0.87O20.52- nanosheets. Furthermore, spin-coating of a mixed suspension of Ca2Nb3O10- and Ti0.87O20.52- nanosheets led to a mixed mosaic-like monolayer of these two nanosheets. The present study thus demonstrated spin-coating as a facile and powerful route to construct various nanostructures based on 2D oxide nanosheets.

The structural and optical properties of GO: Temperature-dependent analysis of the electrical properties of Al/GO/p-type Si semiconductor structures

A spin-coating process has been used to generate graphene oxide (GO) thin films on p-type silicon. The temperature-dependent basic electrical characteristics of Al/GO/p-type Si metal–semiconductor structures have been examined through current–voltage (I–V) measurements in the temperature range 80–420 K by increments of 20 K based on thermionic emission (TE) theory. At each temperature, the main electrical parameters, such as ideality factor (n), rectification ratio (RR), saturation current (I0), barrier height (Φbo), and series resistance (RS), were determined. With increasing temperature, the values of n, I0, RR, and RS decreased, whereas the value of Φbo increased. These unusual temperature fluctuations in Φbo and n may be rationalized in terms of twofold Gaussian distributions at 80–200 K and 220–420 K. For the high- and low-temperature regions, evaluation of these two Gaussian distributions of the I–V curves for the Al/GO/p-type Si structure yielded mean barrier heights of 1.676 and 0.555 eV with standard deviations (σ0) of 166 mV and 76 mV, respectively. Modified ln(I0/T2)−(q2σs2)/(2k2T2) vs. q/(kT) plots, which correspond to these two separate temperature regions, further corroborated these barrier height values. The value of the Richardson constant (A*), 3.567 × 10−6 A K−2 cm−2, is substantially lower than the known value for p-Si. However, for the distribution in the 220–420 K region, the Richardson constant of 48.069 A K−2 cm−2 is near to the known theoretical value of 32 A K−2 cm−2 for p-type Si.

Fully-covered slot-die-coated ZnO thin films for reproducible carbon-based perovskite solar cells

The spin-coating process is generally used for depositing the electron transporting layer (ETL) of a perovskite solar cell (PSC). However, this technique is not compatible for potential large-scale and high-throughput manufacturing. Herein, the deposition of ZnO thin films was developed via a homemade slot-die coater setup on a 3-axis CNC platform to achieve high-quality ETLs. It was found that the deposition parameters play an important role on morphology control. By carefully optimising the process parameters, fully-covered and compact ZnO thin films were achieved. With the optimised ZnO ETL, carbon-based PSC offered the highest power conversion efficiency (PCE) of 10.81%. Moreover, PSCs with slot-die-coated ZnO films showed much better reproducibility and superior storage stability over 500 h than those with spin-coated ones. The particular reason for performance improvement was the enhancement in surface properties of ZnO ETLs, resulting in the reduction of interfacial charge recombination. This work facilitates the opportunity for high-quality and cost-effective thin film deposition on large-scale production applicable for photovoltaics as well as other optoelectronic applications.

High-Performance Transparent PEDOT: PSS/CNT Films for OLEDs.

Improved OLED systems have great potential for next-generation display applications. Carbon nanotubes (CNTs) and the conductive polymers poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) have attracted great interest for advanced applications, such as optoelectronic products. In this paper, the simultaneous enhancement of the conductivity, roughness, and adhesion properties of transparent conductive films with PEDOT: PSS/CNTs is reported. These films prepared by a simple spin-coating process were successfully used to produce high-performance organic light-emitting diodes (OLEDs) with an improved lifetime. Addition of PEDOT: PSS lowered the film sheet resistance and CNTs helped to enhance the stability and maintain the lifetime of the OLEDs. In addition, treatment with methanol and nitric acid changed the morphology of the polymer film, which led to greatly reduced sheet resistance, enhanced substrate adhesion, and reduced film roughness. The best performance of the film (PEDOT: PSS: CNT = 110: 1, W/W) was 100.34 Ω/sq.@ 90.1 T%. High transmittance, low sheet resistance, excellent adhesion, and low roughness (3.11 nm) were achieved synchronously. The fabricated OLED demonstrated a low minimum operating voltage (3 V) and could endure high voltage (20 V), at which its luminance reached 2973 cd/m2. Thus, the incorporation of CNTs within PEDOT: PSS electrodes has great potential for the improvement of the performance of OLED devices.