Large Area Deposition Research Articles

Inorganic metal iodide mediated solution phase surface passivation for quantum dot solar cell

The recent advancements in solution phase surface passivation of quantum dots (QDs) enable the development of production compatible QD ink for their large-area deposition, of a single coating. Surface passivation and colloidal stability of the QDs in polar solvents have been achieved using inorganic–organic hybrid halometallate ligands. The inorganic halometallate anions bind to the unsaturated metal sites of the QD surface, while the organic counter cations provide the colloidal stability and charge balance to the QDs. Organic ligands is a reason for concern though for the stability of the QD solar cells processed from solution-phase ligand exchange. Here, we report a solution-phase ligand exchange strategy using alkali metal halides as a substitution for the organic counterpart to facilitate solution-phase ligand exchange using all-inorganic halometallate ligands. Considering the limited solubility of the alkali halides in organic solvents a two-stage ligand-exchanged process has been commenced to help remove the excess ligands, preserve the electronic purity and allow the formation of highly passivated QD films from solution-phase deposition. A twofold increase in solar cell performance is shown with the help of the modified ligand exchange approach. The solar cell properties are further analysed through detailed characterizations of the QD solar cells.

The controllable deposition of large area roll-to-roll sputtered ito thin films for photovoltaic applications

In the present study, using a large area roll-to-roll DC magnetron sputtering system deposition of ITO thin films on polyethylene terephthalate (PET) substrates were achieved. In order to investigate the effect of growth conditions on the film properties all through the deposition process, optical emission spectroscopy (OES) analysis have been accomplished in a governable way. The consequences of Oxygen partial pressure and film thickness on electrical, and optical properties of the films were determined. It was shown that the intensity of optical emission peaks are subjected to the discharge power and as well as the O2/Ar flow ratio. Large area, uniform ITO films with relatively high transparency and low electrical resistivity (Rs˂50 Ω/sqr) were succesfully deposited on PET substrates. The significance of both the figure of merit (FOM) and the optical band gap values on the performance of different TCO thin films were addressed. In this work, the obtained results suggest that the overall performance is sufficient to implement the ITO films in photovoltaic and OLED applications.

Efficient combination of Roll-to-Roll compatible techniques towards the large area deposition of a polymer dielectric film and the solution-processing of an organic semiconductor for the field-effect transistors fabrication on plastic substrate

Abstract Flexible Organic Field-Effect Transistors (OFETs) constitute nowadays a highly promising field of the organic and printed electronics due to their multiple applications (flexible displays, sensors etc.). However, their cost-effective fabrication by large area Roll-to-Roll compatible printing methods still remains a challenge for their integration to commercial products. In this work, the moderate speed (1 m/min) process of the flexible cross-linked Poly(4-vinyl phenol) (PVP) polymer gate dielectric layer was carried out by integrating a slot-die method that mimics the Roll-to-Roll (R2R) coating conditions, in combination to an airbrush spray method for the solution-processing of the 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-PEN) organic semiconductor. Particularly, the PVP dielectric was slot-die-coated over a 90 × 15 cm2 substrate, while subsequently the TIPS-PEN semiconductor was sprayed onto the 15 × 20 mm2 cPVP-patterned plastic substrates. Α surface investigation study on the well-formed slot-die-coated cPVP strips was conducted, revealing desirable dielectric film topography as a result of the good control over the coating process. A detailed analysis of the cPVP thickness evolution along the 90 × 1.3 cm2 patterned stripe, was carried out. The morphological analysis of the sprayed TIPS-PEN layer over the cPVP film revealed well-organized large crystalline domains across the channel area, as a result of the sufficient crystallization time and the excellent cPVP surface morphology. The fabricated bottom gate/top contact flexible OFETs exhibited excellent I-V electrical characteristics with a maximum mobility of 0.21 cm2/V, negligible hysteresis, low threshold voltages (average value of −0.1 V) and on/off current ratios in the range of 103 to >104. These results demonstrate the potentiality of the proposed scalable methods for the large scale fabrication of high performance low-cost OFET devices.

Facile deposition and characterization of large area highly conducting and transparent Sb-doped SnO2 thin film

We have deposited a large area (10 × 10 cm2) Sb-doped SnO2 (ATO) thin film transparent conducting electrode (TCE) using chemical spray pyrolysis method. The XRD analysis confirms tetragonal crystal structure of ATO thin film with significant preferred orientation. The XPS analysis clearly indicates the presence of Sb in +5 charge state when substituted into the SnO2 lattice. The UV–Vis transmittance spectra of the film showed average transmittance of 77.5% at 550 nm and the calculated direct band gap value was 3.82 eV. As-deposited ATO film exhibited lowest sheet resistivity and resistance of 6.715 × 10−4 Ω cm and 31.91 Ω/□ respectively due to Sb-dopant effect into the Sn lattice. Doping with Sb into SnO2 exhibits high carrier concentration of 7.899 × 1020 cm−3 and mobility of 28.45 cm2/Vs resulting in enhanced electrical transport properties. The variation of the sheet resistance of the large area deposited film is estimated across every 1 × 1 cm2 surface area. Variation of sheet resistance of the ATO film as a function of annealing temperature and duration was found to be appreciably stable. Kelvin probe study yielded a surface work function of 5.14 eV for the ATO film indicating the suitability to serve as an indium-free alternate TCE for optoelectronic device applications.

Lead Iodide and Perovskite Films Obtained by Iodination of PbS Thin Films

Here we demonstrate a low-temperature process for the synthesis of pinhole-free lead iodide and perovskite (CH3NH3PbI3) films. The approach consists in converting amorphous sputtered lead sulfide films onto lead iodide (PbI2) films through an iodination process. The following step consists of the conversion of PbI2 into CH3NH3PbI3 through dipping into methylammonium iodide (CH3NH3I) solution. The effectiveness of this new route was investigated through X-ray diffraction, optical transmittance, scanning electron microscopy and X-ray photoelectron spectroscopy. This method is comprehensibly compatible with large-scale and large-area deposition and provides a convenient and highly reproducible route for the preparation of perovskite thin films.

Transfer-Medium-Free Nanofiber-Reinforced Graphene Film and Applications in Wearable Transparent Pressure Sensors.

Graphene exhibits properties of atomic thickness, high transparency, and high carrier mobility, which is highly desirable for a flexible transparent conductive material. However, the electronic properties of large-area chemical vapor deposition grown graphene film suffer from insulated polymer contaminations introduced by the transfer process and the easily cracked nature. Here, we report a preparation method of a transfer-medium-free large-area nanofiber-reinforced graphene (a-PAN/G) film simply by annealing the electrostatically spun polyacrylonitrile (PAN) nanofibers on the graphene film. The film could be free-standing on water and suspended in air with high transparency and enhanced electrical and mechanical properties compared to that of a monolayer graphene film. The flexible transparent a-PAN/G films were demonstrated as active materials for sensitive pressure sensors. The obtained pressure sensors demonstrate high sensitivity (44.5 kPa-1 within 1.2 kPa), low operating voltage (0.01-0.5 V), and excellent stability for 5500 loading-unloading cycles, revealing promising potential applications in wearable electronics.

Wind tunnel tests to estimate PM10 and PM2.5-emissions from complex substrates of open-cast strip mines in Germany

Abstract Open-cast lignite mines are sources of PM- emissions, caused by mining activities and wind erosion on the large bare deposition areas. PM10- and PM2.5-emissions of these technogenic materials have not been determined in detail so far, but are needed for emission cadastres or in dispersion models at the local scale In wind tunnel experiments substrates from the four active mines in Lower Lusatia in eastern Germany were investigated to estimate PM10- and PM2.5-emissions. The substrates include the cover layers and the lignite seams. Two experimental approaches were compared to relate the PM- emissions of the substrates to the main releasing mechanisms and substrate characteristics. The results show that lignite and lignite containing substrates emit distinctly higher amounts of PM10 and PM2.5 than mineral substrates, regardless of the releasing process. The estimated PM-emission potentials (PM-EP) ranged between 5 and 650 µg g−1 for PM10 and between 2 and 44 µg g−1 for PM2.5 and are correlated to the dry sieving fraction The highest PM- emissions per m2 occur together with the highest transport rates, although the materials themselves have low PM-EP. A distinct higher rate is emitted from lignite samples and substrates permeated with lignite. Wind erosion increases the PM10- emissions to 360 per cent and the PM2.5-emissions to 270 per cent of the PM-EP. The PM10- emissions of the mineral substrates are close to the potentials and heterogeneity of the materials has also an increasing effect.

Parametric study and residual gas analysis of large-area silicon-nitride thin-film deposition by plasma-enhanced chemical vapor deposition

Large-area silicon-nitride thin films deposited from silane and ammonia by plasma-enhanced chemical vapor deposition are investigated experimentally in a 300 mm apparatus with a vertical showerhead. The responses of deposition rate and refractive index to the process parameters are found and discussed. The effects of showerhead configuration on the full-wafer deposition rate and refractive index are further examined, and the inherent non-uniformity is improved by using a proper convex showerhead. The residual gases are analyzed online, and a good correlation between the partial pressure of hydrogen and the deposition rate is found.

Enhanced absorption of CVD grown molybdenum disulfide monolayers via surface plasmon resonance with silver nano-triangles

Transient reflection was performed on large-area chemical vapor deposition (CVD) grown monolayer MoS2 flakes with silver nano-triangles coated on the surface to characterize its modifications to the optical properties of MoS2. Broadband transient reflection was carried out over a range of different pump wavelengths to tune in and out of the plasmonic resonance band of the nano-triangles. Large enhancement in transient reflectivity was observed, which approximately followed the plasmon resonance spectrum of the nano-triangles. Finite-difference time-domain simulations were performed to verify that there is an increased absorption due to local surface plasmon-induced near-field enhancements. We also report observation of the dynamics of the MoS2 exciton bleaching bands, which showed subtle differences in recombination dynamics related to the exciton-plasmon coupling strength for excitation on-resonance and off-resonance at the silver nano-triangles plasmonic band.

Horizontal-to-Vertical Transition of 2D Layer Orientation in Low-Temperature Chemical Vapor Deposition-Grown PtSe2 and Its Influences on Electrical Properties and Device Applications.

Two-dimensional (2D) transition-metal dichalcogenides (2D TMDs) in the form of MX2 (M: transition metal, X: chalcogen) exhibit intrinsically anisotropic layered crystallinity wherein their material properties are determined by constituting M and X elements. 2D platinum diselenide (2D PtSe2) is a relatively unexplored class of 2D TMDs with noble-metal Pt as M, offering distinct advantages over conventional 2D TMDs such as higher carrier mobility and lower growth temperatures. Despite the projected promise, much of its fundamental structural and electrical properties and their interrelation have not been clarified, and so its full technological potential remains mostly unexplored. In this work, we investigate the structural evolution of large-area chemical vapor deposition (CVD)-grown 2D PtSe2 layers of tailored morphology and clarify its influence on resulting electrical properties. Specifically, we unveil the coupled transition of structural-electrical properties in 2D PtSe2 layers grown at a low temperature (i.e., 400 °C). The layer orientation of 2D PtSe2 grown by the CVD selenization of seed Pt films exhibits horizontal-to-vertical transition with increasing Pt thickness. While vertically aligned 2D PtSe2 layers present metallic transports, field-effect-transistor gate responses were observed with thin horizontally aligned 2D PtSe2 layers prepared with Pt of small thickness. Density functional theory calculation identifies the electronic structures of 2D PtSe2 layers undergoing the transition of horizontal-to-vertical layer orientation, further confirming the presence of this uniquely coupled structural-electrical transition. The advantage of low-temperature growth was further demonstrated by directly growing 2D PtSe2 layers of controlled orientation on polyimide polymeric substrates and fabricating their Kirigami structures, further strengthening the application potential of this material. Discussions on the growth mechanism behind the horizontal-to-vertical 2D layer transition are also presented.

Template deposition of Sb2S3 for solid-state sensitized solar cells

Unavoidable impurities form in Sb2S3 absorber fabricated by conventional chemical bath deposition method which is harmful to the photovoltaic performance of Sb2S3-sensitized solar cells. To obtain high quality Sb2S3 absorber, a two-step template method is introduced to deposit Sb2S3 on mesoporous TiO2 film. This template method is performed by dipping ZnS-coated TiO2 films in a Sb source solution for several minutes. This low temperature method with short operation time allows large area deposition of Sb2S3. Properties of ZnS and Sb2S3 are systematically studied. X-ray photoelectron spectroscopy confirms the absence of impurities. The optimized Sb2S3 device exhibits a power conversion efficiency (PCE) of 3.69%, with an open-circuit voltage of 0.514 V, a short-circuit current-density of 12.14 mA/cm2, and a fill factor of 59.1% under AM 1.5G illumination which is better than the device fabricated by chemical bath deposition. The PCE of our Sb2S3 devices showed an obvious increase after 1–2 months storage which may be caused by reconstruction of the ZnS/Sb2S3 coating fabricated by partial cation exchange.

Controlled deposition of large-area and highly-ordered thin films: effect of dip-coating-induced morphological evolution on resistive memory performance

A scalable dip-coating technique is reported to precisely control nano-patterned films and resistive memory devices with a record reproducibility of 96%.

Scalable Fabrication of Stable High Efficiency Perovskite Solar Cells and Modules Utilizing Room Temperature Sputtered SnO2 Electron Transport Layer

AbstractStability and scalability have become the two main challenges for perovskite solar cells (PSCs) with the research focus in the field advancing toward commercialization. One of the prerequisites to solve these challenges is to develop a cost‐effective, uniform, and high quality electron transport layer that is compatible with stable PSCs. Sputtering deposition is widely employed for large area deposition of high quality thin films in the industry. Here the composition, structure, and electronic properties of room temperature sputtered SnO2 are systematically studied. Ar and O2 are used as the sputtering and reactive gas, respectively, and it is found that a highly oxidizing environment is essential for the formation of high quality SnO2 films. With the optimized structure, SnO2 films with high quality have been prepared. It is demonstrated that PSCs based on the sputtered SnO2 electron transport layer show an efficiency up to 20.2% (stabilized power output of 19.8%) and a T80 operational lifetime of 625 h. Furthermore, the uniform and thin sputtered SnO2 film with high conductivity is promising for large area solar modules, which show efficiencies over 12% with an aperture area of 22.8 cm2 fabricated on 5 × 5 cm2 substrates (geometry fill factor = 91%), and a T80 operational lifetime of 515 h.

Raman spectroscopy on 3-D acid-functional single-walled carbon nanotubes for flexible transparent-conducting films deposited with vacuum-filtration and dip-coating

This research investigated the Raman spectra on 3-D functional single-walled carbon nanotubes (SWCNTs) which were deposited on polycarbonate (PC) with dip-coating as flexible transparent-conducting film for fast and large area deposition. The pre-acidification was done by using of sulfuric acid to form the 3-D carboxylic acid (COOH) functionalization on the SWCNTs collected by vacuum filtration. The analysis of Raman spectra could explicate the pre-purity saturation of sulfuric by the area ratios of G/D. Simultaneously the G+ peak appeared the blue shift with the acid functionalization inside SWCNTs and G− peak suggested the good dispersion of SWCNTs by its vibration along the circumferential direction, so the area ratio of the G+/G− could explain the dispersion level of the acid-functional SWCNTs. However, the best pre-acid temperature and time were 120 °C and 24 h, respectively, and the sheet resistance of SWCNTs/PC flexible film could be <500 Ω/sq at transmittance above 70%.

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Photon counting performance of amorphous selenium and its dependence on detector structure.

Photon counting detectors (PCD) have the potential to improve x-ray imaging; however, they are still hindered by high costs and performance limitations. By using amorphous selenium (a-Se), the cost of PCDs can be significantly reduced compared with modern crystalline semiconductors, and enable large-area deposition. We are developing a direct conversion field-shaping multiwell avalanche detector (SWAD) to overcome the limitation of low carrier mobility and low charge conversion gain in a-Se. SWAD's dual-grid design creates separate nonavalanche interaction (bulk) and avalanche sensing (well) regions, achieving depth-independent avalanche gain. Unipolar time differential (UTD) charge sensing, combined with tunable avalanche gain in the well region allows for fast response and high charge gain. We developed a probability-based numerical simulation to investigate the impact of UTD charge sensing and avalanche gain on the photon counting performance of different a-Se detector configurations. Pulse height spectra (PHS) for 59.5 and 30keV photons were simulated. We observed excellent agreement between our model and previously published PHS measurements for a planar detector. The energy resolution significantly improved from 33keV for the planar detector to for SWAD. SWAD was found to have a linear response approaching .

Graphene-engineered automated sprayed mesoscopic structure for perovskite device scaling-up

One of the most thrilling developments in the photovoltaic field over recent years has been the use of organic–inorganic lead halide perovskite, such as CH3NH3PbI3 (MAPbI3), as a promising new material for low-cost and highly efficient solar cells. Despite the impressive power conversion efficiency (PCE) exceeding 22% demonstrated on lab-scale devices, large-area material deposition procedures and automatized device fabrication protocols are still challenging to achieve high-throughput serial manufacturing of modules and panels. In this work, we demonstrate that spray coating is an effective technique for the production of mesoscopic small- and large-area perovskite solar cells (PSCs). In particular, we report a sprayed graphene-doped mesoporous TiO2 (mTiO2) scaffold for mesoscopic PSCs. By successfully combining the spray coating technique with the insertion of graphene additive into the sprayed mTiO2 scaffold, a uniform film deposition and a significant enhancement of the electron transport/injection at the mTiO2/perovskite electrode is achieved. The use of graphene flakes on the sprayed scaffold boosts the PCE of small-area cells up to 17.5% that corresponds to an increase of more than 15% compared to standard cells. For large-area (1.1 cm2) cells, a PCE up to 14.96% is achieved. Moreover, graphene-doped mTiO2 layer enhances the stability of the PSCs compared to standard devices. The feasibility of PSC fabrication by spray coating deposition of the mesoporous film on large-area 21 × 24 cm2 provides a viable and low-cost route to scale up the manufacturing of low-cost, stable and high-efficiency PSCs.

TiO2 Thin Films by Solution Technique for Solar Cells

Titanium dioxide has a number of applications in solar cells. In this study, TiO 2 thin films were synthesized using a simple but less expensive, low temperature and large area deposition method referred to as chemical bath deposition. Their electrical and optical properties were examined at various temperatures where it was observed that the films exhibited low reflectance which increased with increase in wavelength with refractive indices of 2.2–2.5 in the visible spectra. Sheet resistivity ranged between 13.54±0.095 Ω/m to 17.27±0.209 Ω/m. They were use to fabricate photovoltaic cell which exhibited the following parameters: a short circuit current, I sc =0.002445 A, open voltage, V oc = 0.04731 V, a fill factor, FF=0.551 and an efficiency, η=0.531 %. They were recommended for diode applications.

Electrochemical Performance of Few-Layer Graphene Nano-Flake Supercapacitors Prepared by the Vacuum Kinetic Spray Method

A few-layer graphene nano-flake thin film was prepared by an affordable vacuum kinetic spray method at room temperature and modest low vacuum conditions. In this economical approach, graphite microparticles, a few layers thick, are deposited on a stainless-steel substrate to form few-layer graphene nano-flakes using a nanoparticle deposition system (NPDS). The NPDS allows for a large area deposition at a low cost and can deposit various metal oxides at room temperature and low vacuum conditions. The morphology and structure of the deposited thin films are alterable by changing the scan speed of the deposition. These changes were verified by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The electrochemical performances of the supercapacitors, fabricated using the deposited films and H3PO4–PVA gel electrolytes with different concentrations, were measured using a 2-electrode cell. The electrochemical performance was evaluated by cyclic voltammetry, galvanostatic Charge–discharge, and electrochemical impedance spectroscopy. The proposed affordable fabricated supercapacitors show a high areal capacitance and a small equivalent series resistance.

(Invited) Sputter Growth of Chalcogenide Superlattice Films for Future Phase Change Memory Application

Ge-Sb-Te ternary alloys are key materials for phase-change random access memory (PCRAM). In PCRAM, data recording relies on reversible switching between amorphous and crystalline phases by electrical pulse induced Joule heating. We have proposed and developed GeTe/Sb2Te3 superlattice phase change memory, which is known as interfacial phase change memory (iPCM), and have demonstrated a significant reduction in switching energy and much longer endurance compared to conventional alloy-type phase change memory. Since this superlattice is composed of atomically aligned GeTe and Sb2Te3 multilayers, fabricating a highly-oriented film is crucial. Furthermore, in order to utilize such material for novel devices in an industrial setting, reliable processes that allow large area deposition of uniform films is critical. Sputtering is one of the most useful, technologically friendly, and reliable methods for thin film fabrication. In this work, the growth mechanism of layered chalcogenide films is discussed. The superlattice films were grown on various substrate materials by radio-frequency magnetron sputtering. Ge-Te and Sb-Te alloy targets were used. Before the growth of the film, Ar sputter cleaning was carried out to remove a native oxide from the substrate surface. An Sb2Te3 seed layer was grown initially at room temperature followed by alternate deposition of GeTe and Sb2Te3 layers at high temperature. The crystal structure of the films as well as the degree of orientation were evaluated by x-ray diffraction (XRD) while the microstructure was observed by transmission electron microscopy (TEM). We found there is a strong dependency on substrate materials in terms of out-of-plane orientation of the superlattice film. On the basis of the obtained results, we will discuss the growth mechanisms of layered chalcogenide films and propose optimal growth conditions for future phase change memory applications. This work was supported by JST-CREST (JPMJCR14F1).