Uniformity Of Layer Research Articles

Improving the performance of perovskite solar cells by adding 1,8-diiodooctane in the CH3NH3PbI3 perovskite layer

In this study, different ratios of 1,8-diiodooctane (DIO) were added in the CH3NH3PbI3 perovskite layer of perovskite solar cells (PSCs). The effects of different ratios of DIO on the surface morphology of the perovskite layer were observed using an optical microscope (OM) and scanning electron microscope (SEM), whereas the surface roughness, crystal structure, and surface element bonding of the perovskite layer were observed using an atomic force microscope (AFM), X-ray diffractometer (XRD), and X-ray photoelectron spectroscope (XPS), respectively. The absorption spectrum of the perovskite layer was investigated using an ultraviolet–visible (UV/VIS) spectrometer, and the band gap of the perovskite layer was calculated. Furthermore, the PSCs with various ratios of DIO in the perovskite layer were analyzed using current density–voltage (J–V), external quantum efficiency (EQE), and electrochemical impedance spectrum (EIS) measurements. The results showed that adding DIO to the perovskite layer can reduce the nucleation rate of the perovskite through coordination, thereby enhancing the crystallinity, uniformity, and coverage of the perovskite layer and reducing its surface roughness to yield PSC device performance that is superior to a device without DIO. The resulting power conversion efficiency (PCE) increased from 10.77% without DIO to 12.86% with 1% DIO, which was a 19.4% increase, thus verifying that adding 1% DIO to the perovskite layer facilitated increasing the device performance of the PSC.

Gas-Dynamic Specifications of Glow Discharge During Ion Nitriding Process

Ion-plasma nitriding in glow discharge is a widely used method of surface hardening in the industrialized countries of the world and it is the most modern and technological type of surface hardening of machine parts, molds, dies and cutting tools. However there is no detailed review in the literature of technical characteristics and operation of a gas-vacuum part in ion nitriding units and it does not allow estimating electric power consumption for operation of a gas-vacuum system while assessing efficiency of the given equipment. The paper considers problems pertaining to relationship of gas-dynamic parameters of the nitriding process (pressure and gas flow rate) and energy characteristics of the glow discharge (current density, discharge voltage) during ion nitriding at industrial plants and their impact on the process. Calculation-practical modeling of a vacuum system for an ion nitriding installation shows that it is advisable to use vacuum units which represent consistently connected forevacuum and two-rotor pumps in order to ensure independent control of a pumping speed and flow rate of the gas mixture. Such approach makes it possible to carry out nitriding processes in a wide range of pressures with the possibility to provide high plasma gas rates at a low pressure, in particular, when processing large areas. The paper has revealed temperature interrelations, chamber pressure and glow discharge current density that ensure its existence in the abnormal form. It has been shown that at lower operational pressure during the process, higher degree of discharge abnormality can be provided at uniform temperature of the batch. Due to this it is possible to attain higher temperature similarity which ensures uniformity of a nitrided layer on all parts of the batch.

Nanoscale Insight into Performance Loss Mechanisms in P3HT:ZnO Nanorod Solar Cells

Hybrid solar cells based on semiconducting polymers and metal oxides offer the possibility of combining the best attributes of both constituents to achieve efficient and low-cost solar energy harvesting. Active layers consisting of ZnO nanorods and semiconducting polymer poly(3-hexylthiophene), P3HT, have been studied extensively over the past decade. This type of solar cell, however, still exhibits a relatively low performance and poor device-to-device reproducibility. For insight into the performance bottlenecks in P3HT:ZnO nanorod solar cells, we employ a point-by-point current–voltage mapping method using conductive atomic force microscopy to probe the local photovoltaic properties of hybrid P3HT:ZnO nanorod active layers with nanoscale spatial resolution. We observe that the short-circuit current density, open-circuit voltage, fill factor, and power conversion efficiency are highly heterogeneous and sensitive to the local thickness of the P3HT hole transport layer that sits atop the active layer, with local power conversion efficiencies reaching as high as double those seen in macroscopic devices. We further demonstrate that this hybrid system exhibits a high charge photogeneration rate, which approaches that in high-performance organic solar cells; however, photocurrent is limited by a low charge collection probability under short-circuit conditions. These experiments suggest the potential for significant performance gains in hybrid organic–inorganic nanorod solar cells through improvements in active layer uniformity and charge extraction efficiency.

High performance perovskite solar cells fabricated from porous PbI2-xBrx prepared with mixture solvent pore generation treatment

Power conversion efficiencies of perovskite solar cells depend heavily on the uniformity, coverage, grain size, and thickness of the perovskite layer. In this study, hybrid perovskite CH3NH3PbI3-xBrx thin films were fabricated from porous PbI2-xBrx layers prepared with a mixture solvent pore generation treatment process. The mixture solvent is composed of two anti-solvents of PbI2-xBrx to promote its crystallization, one with a low boiling point to accelerate the evaporative removal of the solvents of PbI2-xBrx, dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), and the other with a high boiling point to modulate the evaporative removal of DMF and DMSO to achieve a suitably configured porous structure for the PbI2-xBrx layer. With this fast pore generation treatment, uniform porous PbI2-xBrx layers were obtained within minutes, far more efficient than previously reported pore generation processes. The uniform porous PbI2-xBrx layer enabled formation of hybrid perovskite CH3NH3PbI3-xBrx thin films of low PbI2-xBrx residue, good crystallinity, low defect concentrations, and long charge carrier life times. The champion cell, assembled from the optimal hybrid perovskite thin films fabricated from optimized pore generation treatments, exhibited significantly superior power conversion performances of 19.26 mA/cm2 for the short circuit current density, 1.01 V for the open circuit voltage, 0.68 for the fill factor, and 13.16% for the power conversion efficiency, as compared to the average power conversion efficiency of 10.03% for non-porous PbI2-xBrx layer based cells.

Characterization of porous anodic alumina with AC-incorporated silver

The present research is dedicated to the description of the effects of AC electrochemical incorporation of silver on the compositional, morphological and structural characteristics of the obtained modified anodic aluminum oxide (AAO) layers. The AC electrochemical Ag-incorporation was performed on preliminary galvanostatically anodized technically pure (AA1050) aluminum alloy for different durations (up to 900 s). The obtained Al-O-Ag combined layers were submitted to systematic characterizations in order to determine the incorporation efficiency and the respective process mechanism. The performed analyses comprised subsequent determination of: (i) chemical composition, (ii) surface topology and roughness, (iii) layer thickness and uniformity, and (iv) electrochemical behavior in 3.5% NaCl model corrosive medium. The Ag content and the respective incorporation efficiency were estimated by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The topological and morphological modifications of the films were determined by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), respectively. The morphological characterizations were completed by surface and cross-sectional Energy Dispersion X-ray (EDX) analyses thus determining the film thicknesses and elements distribution. All characterizations using these analytical methods were finalized by studying the performance of these films in a model corrosive medium by Electrochemical Impedance Spectroscopy (EIS) and Linear Sweep Voltammetry (LSV).The further comprehensive data analysis of the obtained results has enabled to create a conceptual model for the description of the correlations between the Ag-incorporation duration and the resulting compositional, topological and structural features, and the resulting film properties and performance.The AC electrochemical Ag-incorporation has a relatively low efficiency and proceeds with gradual silver deposition in the bottoms of the pores and its further accumulation in an upward direction. The cause for the observed low efficiency is related to the simultaneous occurrence of AAO layer growth and dissolution during the AC polarization, which result in topological and roughness variations, as well.

Focusing of Terahertz Radiation With Laser-Ablated Antireflective Structures

Numerical simulations and experimental characterization of laser-ablated focusing antireflective and phase-shifting structures for terahertz frequencies are presented. More than 10% shift of reflectance minimum to lower frequencies was predicted by simulations for relatively coarse structures with the period of 100 $\mu$ m in comparison with that of a substantially smaller period and with results of the model used for the design of antireflective surfaces in the terahertz range. Such a shift of the resonance frequency can be employed to optimize the thickness of antireflective layers simultaneously obtaining additional means of more precise control of layer properties due to ablation of larger structures. Nearly 90% transmittance of silicon wafers within 0.5–0.6 THz frequencies was confirmed experimentally. Optical path differences equivalent to a half period at 0.53 THz, suitable for applications in high-efficiency zone plates, were demonstrated with high transmittance simultaneously. Possibilities of delay adjustment up to one wavelength were illustrated by numerical simulations. A focusing binary zone plate for 0.6 THz was produced employing phase-shift differences of the dual-function antireflective layer. Its close to diffraction-limited focusing performance was evaluated, further confirming sufficient uniformity of the structured layer.

An Experimental Study of Fracture Toughness for Nano/Ultrafine Grained Al5052/Cu Multilayered Composite Processed by Accumulative Roll Bonding

In this study, ultrafine grained Al5052/Cu multilayered composite has been produced by accumulative roll bonding (ARB) and fracture properties have been studied using plane stress fracture toughness. The fracture toughness has been investigated for the unprocessed specimens, primary sandwich and first, second, and third cycles of ARB process by ASTM E561 and compact tension (CT) specimens. Also, the microstructure and mechanical properties have been investigated using optical microscopy, scanning electron microscopy, uniaxial tensile tests, and microhardness measurements. The value of plane stress fracture toughness for the ultrafine grained Al5052/Cu composite increased by increasing the number of ARB cycles, continuously from the primary sandwich to end of the third cycle. The maximum value of 59.1 MPa m1/2 has been obtained that it is about 2.77 and 4.05 more than Al5052 and pure Cu (unprocessed specimens). This phenomenon indicated that ARB process and the addition of copper to aluminum alloy could increase the value of fracture toughness to more than three times. The results showed that by increasing the ARB cycles, the thickness of copper layers reduced and after the fifth cycle, the excellent uniformity of Cu layers achieved. By increasing the number of ARB cycles, the microhardness of both aluminum and copper layers have been significantly increased. The tensile strength of the sandwich has been enhanced continually, and the maximum value of 566.5 MPa has been achieved.

Technology and application of in-situ AlOx layers on III-V semiconductors

This work describes the preparation of a passivation AlOx layer grown in-situ in an MOVPE reactor immediately after the growth of a III-V semiconductor structure. Aluminum layers were deposited on GaAs surface at temperatures of 650, 600, 500, and 450 °C, and AlOx layers were formed spontaneously from the Al layers upon exposing the surface to the air outside the reactor. The best thickness uniformity of the AlOx layers was observed for a deposition temperature of 450 °C. Significantly higher drain current densities were achieved for high electron-mobility transistors (HEMTs) prepared on structures with the AlOx layers. We attribute this to a better surface stability of the structures during device processing.

4-tert-Butylpyridine Free Hole Transport Materials for Efficient Perovskite Solar Cells: A New Strategy to Enhance the Environmental and Thermal Stability

Organic semiconductors as hole transport materials (HTMs) often require additives, such as LiTFSI and tert-butylpyridine (TBP), in order to enhance their hole conductivities. However, the combination of lithium salts and TBP leads to significant HTM morphological deformation and poor device stability. Here we have successfully applied tetrabutylammonium (TBA) salts to replace both LiTFSI and TBP. A high power conversion efficiency of 18.4% has been achieved for the devices with TBATFSI, which is higher than the control devices with LiTFSI and TBP (18.1%). We also found that the anions in the TBA salts play important roles in the hole conductivity and uniformity of the HTM layer, as well as the hysteresis of the devices. More importantly, the devices with TBATFSI and TBAPF6 demonstrated significantly enhanced environmental and thermal stability. This new strategy of using TBA salts is promising for developing stable organic HTM thin films for solar cell applications.

Enhanced performance of LiNi0.03Mo0.01Mn1.96O4 cathode materials coated with biomass-derived carbon layer

A high-performance Ni/Mo co-doped lithium manganate composite material, LiNi0.03Mo0.01Mn1.96O4, is prepared by a solid-state method, then a biomass-derived carbon layer with ethyl cellulose as the carbon source is applied to the surface of the composite particles. We find that carbon layer with the proper loading can significantly enhance the material’s cyclic stability and capacity at high discharge rates. At rates of 5C and 10C, our optimal sample (LNMMO-3wt%C), with 3 wt% carbon layer loading, has discharge capacities up to 114 and 98 mAh g−1, respectively, which are 10 and 8% higher than those of the uncoated co-doped material. Further, the carbon layer coating significantly improves the material’s stability at high discharge rates: the capacity retention of LNMMO-3wt%C after 400 cycles at discharge rates of 5C and 10C is high reaching 93.6 and 88.1%, respectively, compared with 91.4 and 74.3% for uncoated LNMMO. Based on our experimental results and analysis, we attribute the enhanced stability and capacity at high discharge rates to two factors: (i) enhanced conductivity and (ii) reduced Mn3+ dissolution, combined with significantly decreased resistance from Li+ ion intercalation/de-intercalation, due to the uniformity of the carbon layer coating.

Surface processes at the first stage of magnetron cathode Pd-Pd5Ba activation

The electron emission of palladium-barium cathodes is highly effective due to the active BaO substance formation of low work function on the cathode surface (2.3 eV). The work function is a universal parameter characterizing the emission capacity of material. The degree of cathode surface coverage with the emission-active layer and distribution uniformity specificate such important parameters as the emission current and homogeneity of the cathode surface. The active metal – barium – is part of the activation phase – Pd5Ba intermetallic compound. The active substance layer is formed during the activation by vacuum cathode heat treatment. At thermal Pd5Ba dissociation, diffusing Ba atoms flux through the defects in the crystal structure of a palladium matrix to be oxidized by the residual oxygen locked in a device. This article is a first attempt to analyze the correlation of emission-active substance distribution over the cathode surface with the mechanisms of barium diffusion in the emitter. At the first stages of thermal activation, BaO active substance was locatized on the palladium-barium cathode surface by scanning electron microscopy (SEM) and high spatial resolution electron probe microanalysis. The analysis reveals that Ba atoms fluxing through grain boundaries form a line of the emission-active substance along the grain boundaries. The line width is in the region of several microns. In places of triple joints, BaO formations are mostly sizeable. BaO nanoparticles are formed on the surface of individual grains due to Ba diffusion through dislocation tubes. The series of vacuum cathode annealing showed that at T = 750 °C, BaO reproduction from diffusing Ba atoms does not compensate for the BaO evaporation rate. The annealing process, carried out for 30 min at T = 900 °C, has led to the active layer formation along the grain boundaries and to the formation of BaO nanoparticles on the surface of some grains. We introduce an original technique for assessing the surface coverage degree of a cathode covered with an emission-active substance. The technique implies using electronic microimages processed with the ImageMagick.

Chip-scale pattern modification method for equalizing residual layer thickness in nanoimprint lithography

A software program for modifying a mold design to obtain a uniform residual layer thickness (RLT) distribution has been developed and its validity was verified by UV-nanoimprint lithography (UV-NIL) simulation. First, the effects of granularity (G) on both residual layer uniformity and filling characteristics were characterized. For a constant complementary pattern depth and a granularity that was sufficiently larger than the minimum pattern width, filling time decreased with the decrease in granularity. For a pattern design with a wide density range and an irregular distribution, the choice of a small granularity was not always a good strategy since the etching depth required for a complementary pattern occasionally exceptionally increased with the decrease in granularity. On basis of the results obtained, the automated method was applied to a chip-scale pattern modification. Simulation results showed a marked improvement in residual layer thickness uniformity for a capacity-equalized (CE) mold. For the given conditions, the standard deviation of RLT decreased in the range from 1/3 to 1/5 in accordance with pattern designs.

Scale-up of zeolite-Y/polyethersulfone substrate for composite membrane fabrication in CO2 separation

A vacuum-assisted deposition setup was developed in pilot scale to scale up and continuously deposit zeolite-Y (ZY) nanoparticles on 14-in wide nanoporous polyethersulfone (PES) substrate. The deposited substrate was used for composite membrane fabrication for carbon capture from flue gas. The effects of operating parameters, including ZY dispersion concentration, pressure differential, and web speed, on the ZY layer thickness and uniformity were studied. A ZY dispersion concentration of 0.08 wt%, a pressure differential of 3.7 in Hg, and a web speed of 3 ft/min were identified as the optimal operating conditions for depositing a thin and uniform ZY layer with a thickness of approximately 160 nm. A mathematical model with two adjustable parameters was derived from Darcy's law to correlate the operating parameters to the ZY layer thickness. After coating a polymeric amine-containing selective layer on the deposited substrate, the formed composite membrane showed a CO2 permeance of 800 GPU with a CO2/N2 selectivity over 150 at the typical flue gas temperature of 57 °C, which was superior to the performance of the membrane coated on the bare PES substrate. This improvement was due to the reduced selective layer penetration and effective diffusional length from the deposited substrate.

Thermal conductivity and thermal boundary resistance of atomic layer deposited high-k dielectric aluminum oxide, hafnium oxide, and titanium oxide thin films on silicon

The need for increased control of layer thickness and uniformity as device dimensions shrink has spurred increased use of atomic layer deposition (ALD) for thin film growth. The ability to deposit high dielectric constant (high-k) films via ALD has allowed for their widespread use in a swath of optical, optoelectronic, and electronic devices, including integration into CMOS compatible platforms. As the thickness of these dielectric layers is reduced, the interfacial thermal resistance can dictate the overall thermal resistance of the material stack compared to the resistance due to the finite dielectric layer thickness. Time domain thermoreflectance is used to interrogate both the thermal conductivity and the thermal boundary resistance of aluminum oxide, hafnium oxide, and titanium oxide films on silicon. We calculate a representative design map of effective thermal resistances, including those of the dielectric layers and boundary resistances, as a function of dielectric layer thickness, which will be of great importance in predicting the thermal resistances of current and future devices.

Process Optimization of Deposition Conditions for Low Temperature Thin Film Insulators used in Thin Film Transistors Displays

Deposition process for thin insulator used in polysilicon gate dielectric of thin film transistors are optimized. Silane and N2O plasma are used to form SiO2 layers at temperatures below 150 oC. The deposition conditions as well as system operating parameters such as pressure, temperature, gas flow ratios, total flow rate and plasma power are also studied and their effects are discussed. The physical aspects of the yielded dielectrics such as layer thickness and uniformity are presented as well.

Impact of vibration compaction on the paving density and transverse uniformity of hot paving layer

The compaction performance of asphalt pavement depends upon not only the material design but also the construction procedure. This paper intends to quantitatively evaluate the impacts of material properties and paving parameters on the paving compaction quality (i.e., the density and uniformity). A vibration model of screed-paving layer interactions was built to simulate the screed vibration response and the vibration transmission to the paving layer with the vibration frequency and material stiffness. Then, the force transmitting ratio (FTR), contact force, moment transmitting ratio (MTR) and transmitting rotation moment were used to evaluate the compaction of the paving layer. Moreover, a quantized density model was proposed to quantitatively predict the paving compaction performance. In contrast to traditional analyses, the transverse amplitude uniformity of the screed was considered in this work. Finally, the simulation model was validated through a field test. The results show that the paving layer stiffness is positively associated with the initial layer density, which depends on the tamper frequency. For the case study in this paper, the optimum frequency is approximately 163 rad/s, 175 rad/s and 190 rad/s when the tamper frequency is 19 rad/s, 57 rad/s and 95 rad/s, respectively. Larger variation coefficient (CV) and density ratio (DR) indicate that the uniformity of the paving layer density distribution and the pavement roughness are worse. Therefore, it is recommended that the screed vibration frequency and mixture stiffness, which both affect the paving layer density and compaction uniformity, should be considered for future construction procedures.

Growth of Highly Crystalline and Large Scale Monolayer MoS2 by CVD: The Role of substrate Position

AbstractMonolayer (ML) molybdenum disulphide (MoS2) is of great interest for the scientific community due to its attractive electronic, optoelectronic and mechanical properties. Synthesis of high quality and large size ML MoS2 at low cost is still a challenge. Here, the growth of large area (≈5 × 1 mm2) ML MoS2 on SiO2/Si substrate via chemical vapor deposition (CVD) method is reported. It is shown by changing the substrate position w.r.t. MoO3 precursor, that the quality and size of the ML MoS2 can be drastically tuned. Raman spectroscopy and transmission electron microscopy are performed in order to ascertain the growth and high crystallinity of MoS2. Uniformity of MoS2 layer is adjudged by Raman mapping while atomic force microscopy is performed to determine the thickness of the layer. Kelvin probe force microscopy is performed on ML MoS2 to draw the band line up of the material.

Effect of annealing time and NH3 flow on GaN films deposited on amorphous SiO2 by MOCVD

GaN polycrystalline films were successfully grown on amorphous SiO2 by metal–organic chemical vapour deposition to fabricate transferable devices using inorganic films. Field-emission scanning electron microscopy images show that by prolonging the annealing time, re-evaporation is enhanced, which reduced the uniformity of the nucleation layer and GaN films. X-ray diffraction patterns indicate that the decomposition rate of the nucleation layer increases when the annealing flow rate of NH3 is 500 sccm, which makes the unstable plane and amorphous domains decompose rapidly, thereby improving the crystallinity of the GaN films. Photoluminescence spectra also indicate the presence of fewer defects when the annealing flow rate of NH3 is 500 sccm. The excellent crystal structure of the GaN films grown under optimized conditions was revealed by transmission electron microscopy analysis. More importantly, the crystal structure and orientation of GaN grown on SiO2 are the same as that of GaN grown on conventional sapphire substrate when a buffer layer is used. This work can aid in the development of transferable devices using GaN films.

Investigation of Hole-Transporting Poly(triarylamine) on Aggregation and Charge Transport for Hysteresisless Scalable Planar Perovskite Solar Cells.

Organometallic halide perovskite solar cells (PSCs) have unique photovoltaic properties for use in next-generation solar energy harvesting systems. The highest efficiency of PSCs reached 22.1% on a laboratory scale of <0.1 cm2 device area. Thus, scaling up is the next step toward commercialization, but the difficulty in controlling the quality of large-area perovskite thin films remains a fundamental challenge. It has also been frequently reported that the J- V hysteresis is intensified in PSCs with areas larger than 1 cm2. In this study, we have fabricated a large-area perovskite layer using PbICl films, providing an intrinsic porous layer and enhancing the uniformity of the perovskite layer at areas larger than 1 cm2. Furthermore, we have investigated the polymeric properties of the prevalent hole-transporting material poly(triarylamine) (PTAA) with its photovoltaic performance. Two types of PTAAs, poly[bis(4-phenyl)(2,4-dimethylphenyl)amine] and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], were compared. A series of PTAAs with different molecular weights ( Mw) and polydispersity indices were studied, as the molecular weight of the PTAA is a key factor in determining the electrical properties and photovoltaic performance of the system. The fabricated PSCs with an aperture area of 1 cm2 based on a high-molecular-weight PTAA achieved a power conversion efficiency of 16.47% with negligible hysteresis and excellent reproducibility.

Layer-controlled synthesis of wafer-scale MoSe2 nanosheets for photodetector arrays

Despite huge efforts have been devoted to investigating ultrathin layers of two-dimensional (2D) transition-metal dichalcogenides (TMDs), their realistic applications in electronics and optoelectronics are hindered by limited scalability and uniformity of 2D thin layers. In this work, a two-step synthesis method was adopted to produce wafer-scale molybdenum diselenide (MoSe2) nanosheets. Molybdenum oxide (MoO3) thin film was initially prepared via atomic layer deposition (ALD) and followed by a selenization process in chemical vapor deposition (CVD) tube furnace. MoSe2 nanosheets with desired thickness can be obtained by tuning ALD cycles in preparing MoO3 layers. The synthesized MoSe2 films exhibited excellent layer controllability, homogeneity and wafer-scale uniformity. Few-layer structure of our MoSe2 with a polycrystalline crystal structure was verified by means of Raman and transmission electron microscopy (TEM) measurements. Moreover, arrays of MoSe2-based photodetectors with different device dimension were fabricated and the photo-responses of the devices were studied. The device exhibited a fast photo-response time of 50 ms, a high on/off ratio of ~ 24 and a good photo-responsivity of 11.7 mA/W, and it is found that the effective illumination area was a critical factor for application. The work opens up an attractive approach to realize the application of wafer-scale 2D materials in integrated optoelectronic-systems.