Two-step Spin-coating Process Research Articles

A Perovskite Photovoltaic Mini-Module-CsPbBr3 Photoelectrochemical Cell Tandem Device for Solar-Driven Degradation of Organic Compounds.

Recently, halide perovskites have been widely explored for high-efficiency photocatalysis or photoelectrochemical (PEC) cells. Here, in order to make an efficient photoanode electrode for the degradation of pollutants, concretely 2-mercaptobenzothiazole (MBT), nanoscale cesium lead bromide (CsPbBr3) perovskite was directly formed on the surface of mesoporous titanium dioxide (meso-TiO2) film using a two-step spin-coating process. This photoelectrode recorded a photocurrent of up to 3.02 ± 0.03 mA/cm2 under standard AM 1.5G (100 mW/cm2) illumination through an optimization process such as introducing a thin aluminum oxide (Al2O3) coating layer. Furthermore, to supply high voltage for efficient oxidation of MBT without an external bias, we developed a new photovoltaic/PEC tandem system using a methylammonium lead iodide (MAPbI3) based mini-module consisting of three solar cells interconnected in series and confirmed its successful operation. This approach looks very promising due to its applicability to various PEC reactions.

Thiourea-Assisted Facile Fabrication of High-Quality CsPbBr3 Perovskite Films for High-Performance Solar Cells.

Inorganic CsPbBr3 perovskite solar cells have attracted widespread attention recently because of their decent efficiency and good ambient stability. Nevertheless, the fabrication of high-quality CsPbBr3 perovskite via the conventional solution-processing strategy still faces great challenges because the solubility of CsBr in the conventional solvent is poor. Here, we develop a facile thiourea-assisted two-step spin-coating process to fabricate a CsPbBr3 perovskite film with high phase purity and crystallinity and enlarged crystal grains. Thiourea is introduced into the PbBr2 layer during the first-step spin-coating process, which promotes the wettability of the PbBr2 layer and produces the space for growing large perovskite grains. The green high-concentration CsBr/H2O solution is adopted at the second-step spin-coating process, enabling enough CsBr to be deposited by a facile one-step process. By optimizing the content of thiourea, a compact CsPbBr3 perovskite film with a smooth surface, large grains, and high phase purity and crystallinity is formed. Consequently, the fabricated perovskite solar cell with the architecture of FTO/TiO2/CsPbBr3 film/carbon exhibits a superior performance with a high efficiency of 9.11%. In addition, the unencapsulated device preserves over 90% of its initial efficiency after storage at ambient conditions for 45 days.

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

Antibacterial peptide-modified collagen nanosheet for infected wound repair

Dressing materials with wet adhesive and antibacterial features are in high demand for the healing of infected wounds. Here, we report the development of an antibacterial peptide (KRWWKWWRRC)-modified collagen nanosheet (KCN) by a two-step spin-coating process. The two-dimensional nanosheet demonstrates promising mechanical strength of ~31 ​MPa at a thickness of 87 ​nm, which is comparable to human skin tissue. The KCN with high transparency and flexibility could firmly adhere to the complex surface of biological tissues in wet environments. In vitro cytotoxicity and antibacterial experiments showed that the KCN is biocompatible and has high antibacterial activity (over 99%). Moreover, a rat skin infection wound model demonstrated that the KCN showed rapid wound closure and low inflammation, and wound closure could be achieved on day 14 after surgery with good re-epithelialization. Our findings reveal a promising nanosheet-based strategy for treating bacteria-infected soft-tissue wounds.

Effect of Processing Technique Factors on Structure and Photophysical Properties of Perovskite Absorption Layer by Using Two-Step Spin-Coating Method

The investigation of crystal growth is crucial for us to improve the film quality and photophysical properties of CH3NH3PbI3 (MAPbI3). In the two-step spin-coating process, the crystal structure could be modulated by controlling the growth conditions of PbI2 and CH3NH3I (MAI) layers. In this paper, the PbI2 layer was treated with annealing under different times. A liquid–liquid diffusion (LLD) mechanism is proposed to modify the deposition of MAI precursor solution and enhance the flatness of organic–inorganic hybrid perovskite film. Furthermore, the perovskite films are prepared using different concentrations of MAI. The evolution process of perovskite structure is observed by modulating the concentration of MAI. The spin-coating of moderate MAI tends to form high quality MAPbI3 films with enhanced absorption and carrier extraction capabilities. The high concentration of MAI would cause the perovskite phase transition, which provides a novel perspective to modulate the structure of organic–inorganic hybrid perovskite in the two-step spin-coating process, although it deteriorates the device performance.

ZnO/conducting polymer bilayer via sequential spin-coating for enhanced UV sensing

Zinc oxide (ZnO) has been widely investigated as an important ultraviolet (UV) sensing material in view of its wide band gap (~3.4 eV). However, the fabrication of continuous thin films of ZnO generally requires complex, time-consuming, and expensive processes, such as sputtering and atomic layer deposition. Herein, we demonstrate a bilayer film consisting of a conducting polymer and ZnO nanoparticles sequentially deposited using a simple, rapid, and inexpensive two-step spin-coating process. In this approach, it is not necessary to have a continuous ZnO nanoparticle film as the active layer, because the conducting polymer deposited under the ZnO nanoparticles acts as a conductive and continuous supporting layer for the particles. Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) is used as the auxiliary layer to promote the efficient transport of photo-carriers generated from ZnO nanoparticles under UV light. As a result, under UV light (365 nm), photocurrents obtained from a ZnO/PEDOT: PSS bilayer film are significantly higher (∼20 times) than that from a ZnO layer for a given voltage bias. The photoelectric performance can be further tuned by controlling the speed of spin-coating in the deposition of ZnO nanoparticles. The stability and photo response (rise and decay time) of the ZnO/PEDOT: PSS bilayer film under the repeated on-off condition are also reported.

Two-step processed efficient perovskite solar cells via improving perovskite/PTAA interface using solvent engineering in PbI2 precursor**Project supported by the National Natural Science Foundation of China (Grant No. 51673214) and the National Key Research and Development Program of China (Grant No. 2017YFA0206600).

The morphology and interface of perovskite film are very important for the performance of perovskite solar cells (PSCs). The quality of perovskite film, fabricated via two-step spin-coating process, is significantly influenced by the morphology and crystallinity of PbI2 film. With the addition of additive dimethyl sulfoxide (DMSO) into the PbI2 precursor, the roughness and trap-state density of perovskite film have been significantly reduced, leading to the excellent contact between perovskite layer and subsequent deposited carrier transport layer. Accordingly, the planar heterojunction PSCs with an architecture of ITO/SnO2/perovskite/PTAA/Ag show an efficiency up to 19.02%. Furthermore, PSCs exhibit promising stability in air with a humidity of ∼ 45%, and retain 80% of initial efficiency after being exposed to air for 400 h without any encapsulation.

Correlation between the Morphology of ZnO Layers and the Electroluminescence of Quantum Dot Light-Emitting Diodes

The present work shows the effect of the ZnO layer morphology on inverted quantum dot light-emitting diodes (QLEDs) using different spin-coating processes. In the inverted structure of ITO/ZnO/QDs/CBP/MoO3/Al, ZnO nanoparticles were used as the electron transport layer. The utilization of a two-step spin-coating process to deposit a ZnO layer on a patterned ITO glass substrate resulted in an increase in the surface roughness of the ZnO layer and a decrease in the luminance of the QLEDs. However, the current efficiency of the device was enhanced by more than two-fold due to the reduced current density. Optimization of the ZnO spin-coating process can efficiently improve the optical and electrical properties of QLEDs.

High-performance pseudo-halide perovskite nanowire networks for stable and fast-response photodetector

Perovskite-based photodetectors show a great promise thanks to the material's excellent photogeneration and broadband device operation. Amongst the fundamental limitations of halide perovskites, humidity-induced degradation arises as the main impediment towards viable commercial-grade perovskite-based technologies. Here, we report a stable, reproducible and reliable pseudo halide perovskite nanowire network-based photodetector with superior performances. The perovskite nanowire network is deposited using a two-step spin-coating process atop patterned substrates under ambient conditions with relative humidity (RH%), higher than 50%. Because of the particular 1D perovskite nanowire morphology, our devices require no charge collectors, which reduces fabrication steps and costs. Most importantly, we demonstrate that incorporation of lead thiocyanate (Pb(SCN)2) directly in the precursor solution promotes the synthesis of stable hybrid perovskite nanowire networks in ambient conditions. These devices exhibit response time as fast as 50 µs and responsivities up-to ~0.23 A W−1 at 2 V bias. Also, the optimum photodetector exhibited high specific detectivity of 7.1 × 1011 cm Hz1/2 W−1. This novel and yet simple device architecture brings fabrication challenges to a minimum by allowing synthesis of perovskite nanowires under high humidity conditions.

High-Switching-Ratio Photodetectors Based on Perovskite CH₃NH₃PbI₃ Nanowires.

Hybrid organic-inorganic perovskite materials have attracted extensive attention due to their impressive performance in photovoltaic devices. One-dimensional perovskite CH3NH3PbI3 nanomaterials, possessing unique structural features such as large surface-to-volume ratio, anisotropic geometry and quantum confinement, may have excellent optoelectronic properties, which could be utilized to fabricate high-performance photodetectors. However, in comparison to CH3NH3PbI3 thin films, reports on the fabrication of CH3NH3PbI3 nanowires for optoelectrical application are rather limited. Herein, a two-step spin-coating process has been utilized to fabricate pure-phase and single-crystalline CH3NH3PbI3 nanowires on a substrate without mesoporous TiO2 or Al2O3. The size and density of CH3NH3PbI3 nanowires can be easily controlled by changing the PbI2 precursor concentration. The as-prepared CH3NH3PbI3 nanowires are utilized to fabricate photodetectors, which exhibit a fairly high switching ratio of ~600, a responsivity of 55 mA/W, and a normalized detectivity of 0.5 × 1011 jones under 532 nm light illumination (40 mW/cm2) at a very low bias voltage of 0.1 V. The as-prepared perovskite CH3NH3PbI3 nanowires with excellent optoelectronic properties are regarded to be a potential candidate for high-performance photodetector application.

Influence of Charge Transport Layers on Open-Circuit Voltage and Hysteresis in Perovskite Solar Cells

Summary Perovskite materials have experienced an impressive improvement in photovoltaic performance due to their unique combination of optoelectronic properties. Their remarkable progression, facilitated by the use of different device architectures, compositional engineering, and processing methodologies, contrasts with the lack of understanding of the materials properties and interface phenomena. Here we directly target the interplay between the charge-transporting layers (CTLs) and open-circuit potential ( V OC ) in the operation mechanism of the state-of-the-art CH 3 NH 3 PbI 3 solar cells. Our results suggest that the V OC is controlled by the splitting of quasi-Fermi levels and recombination inside the perovskite, rather than being governed by any internal electric field established by the difference in the CTL work functions. In addition, we provide novel insights into the hysteretic origin in perovskite solar cells, identifying the nature of the contacts as a critical factor in defining the charge accumulation at its interface, leading to either ionic, electronic, or mixed ionic-electronic accumulation.

Electroluminescence from perovskite LEDs with the structure of Ag/Spiro-OMeTAD/CH3NH3PbI3/TiO2/FTO

The perovskite light-emitting diodes (Pe-LEDs) with the structure of Ag/Spiro-OMeTAD/CH3NH3PbI3/TiO2/FTO were synthesized, where the CH3NH3PbI3 perovskite layer was deposited by a two-step spin-coating process. A dominant near-infrared electroluminescence (EL) at 773nm was detected from the Pe-LEDs under forward bias at room temperature. The origin and mechanism of the EL were discussed in comparison with the photoluminescence (PL) spectra, and it was attributed to the radiative recombination of electrons and holes confined in the CH3NH3PbI3 emissive layer. Moreover, the corresponding energy band diagrams was proposed to illustrate the carrier transport mechanism in the Pe-LED device.

Improvement of electron/hole injection balance based on nanowire/nanocube hybrid perovskite

The methyl ammonium lead iodide perovskite nanowire/nanocube can be fabricated with an improved two-step spin-coating process by adjusting the amount of dimethyl formamide. The hybrid structure enhanced the efficiency of electron/hole separation and charge transfer at the electron transport layer/perovskite/hole transport layer interfaces, benefiting from the improvement of electron/hole injection balance. The dynamic time parameters based on the half-baked cells, only containing electron transport layer or the hole transport layer, could assert rationality of the hypothesis by photoluminescence decays.

A Novel Two-Step Spin-Coating Process for Preparing PEDOT/PSS thin Films and Review of Recent Advances in Spin Coating

We systematically investigated the influence of surfactant on processing PEDOT/PSS thin films by spin-coating technique. As a result, the conductivity of the PEDOT/PSS thin films prepared by the two-step spin-coating method was to be averagely ca. 400Scm-1 which was calculated with sheet resistance and thickness. On the other hand, the conductivity of the PEDOT/PSS thin films prepared by the one-step spin-coating method should be much lower than that of two-step one if assuming that the thickness is the same for the two methods. It is considerable that in the one-step spin-coating method, aggregation of PEDOT/PSS colloidal particles easily occurs before spin-coating, resulting in inhomogeneous coating film. Such inhomogeneous film would show lower conductivity. The two-step spin-coating method can avoid the aggregation and then result in homogeneous film and higher conductivity. Reviews of recent patents on wet-process techniques reported by other research groups are also reported. Keywords: Conducting polymers, PEDOT/PSS, spin-coating, surfactants, transparent electrodes, wet-process.

Ultrathin polycrystalline 6,13-Bis(triisopropylsilylethynyl)-pentacene films

Ultrathin (<6 nm) polycrystalline films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-P) are deposited with a two-step spin-coating process. The influence of spin-coating conditions on morphology of the resulting film was examined by atomic force microscopy. Film thickness and RMS surface roughness were in the range of 4.0–6.1 and 0.6–1.1 nm, respectively, except for small holes. Polycrystalline structure was confirmed by grazing incidence x-ray diffraction measurements. Near-edge x-ray absorption fine structure measurements suggested that the plane through aromatic rings of TIPS-P molecules was perpendicular to the substrate surface.

Planar heterojunction perovskite/PC71BM solar cells with enhanced open-circuit voltage via a (2/1)-step spin-coating process

A two-step spin-coating process was used to synthesize perovskite films at ambient conditions. Combining a PEDOT:PSS hole-transport layer and a PC71BM acceptor, the device achieves a power conversion efficiency of 16.31% with a remarkably highVocof 1.05 V and FF of 0.78.

Effect of spin-coating process on the performance of passive-matrix organic light-emitting display

By improving the spin-coating process during the deposition of hole transport layer poly(3,4-ethylenedioxythiophene)-poly(styrene-sulfonate)(PEDOT:PSS), high efficient monochrome passive-matrix organic light-emitting display is fabricated. The PEDOT:PSS film is spin-coated with a two-step spin-coating process, in which the substrate is turned 180° during the spin-coating, forcing the piled-up materials to move reversely. By introducing the second spin-coating step, the film thickness difference between single and double lines significantly reduces, leading to a more uniform light emission and a larger fill factor for the 3.81 cm monochrome polymer light-emitting diode display. Green light-emitting display with a peak current efficiency of 17 cd/A is successfully fabricated, and the efficiency is improved by 40 percent compared with that made by traditional spin-coating method. A 3.81 cm 96×64 full color display with a current efficiency of 1.25 cd/A is also successfully made.

Formation of extended ordered monolayers of FePt nanoparticles

The formation of an extended ordered layer of monodisperse Fe 66Pt 34 nanoparticles on a 5 cm diameter silicon wafer is accessible through a two-step spin-coating process. An exchange process in the organic shell of the FePt nanoparticles allows to regulate the distance between the nanoparticles in ordered layers.