Two-step Deposition Process Research Articles

Self-reduction combined with photo-deposition decorating Au nanoparticles on urchin-like WO2.72 for enhancement of trimethylamine-sensing performance

Hierarchical urchin-like WO2.72 microspheres decorated by uniform Au nanoparticles were synthesized via a two-step deposition process. The two-step deposition process, including weak reduction deposition and photo-deposition, ensures uniform size and well-dispersed Au nanoparticles. The gas-sensing properties of WO2.72 and Au/WO2.72 for trimethylamine (TMA) were investigated. The results show that Au/WO2.72 has more outstanding gas-sensing performances, especially 3 wt% Au-loaded WO2.72 (A3/WO2.72). A3/WO2.72 not only has superior selectivity and response for TMA gas but also exhibits fast response and recovery time. The response of A3/WO2.72–100 ppm of TMA at 260 °C can attain 87.3, which is approximately 6.1 times of pure WO2.72. Besides, the good long-term effectiveness of A3/WO2.72-based sensor also can be observed. The mechanism of enhanced gas-sensing performances derived from the synergy of morphology, composition, and the sensitization effect of Au nanoparticles is proposed, which will facilitate the design and development of sensors decorated by noble metal.

A novel CISe/Ga-Se two–step stack approach to electrodeposit photovoltaic quality Cu-poor CuInGaSe2 thin films

In the present work, we report on the electrodeposition of CuIn1-xGaxSe2 by a novel two-step deposition process. Initially, near stoichiometric CuInSe2 thin films of [Cu/In] ratio ∼1.15 was electrodeposited by single step technique using citric acid-sodium dodecyl sulfate (SDS) electrolyte. Further, the Ga-Se thin film was deposited potentiostatically in tartrate electrolyte to obtain a CISe/Ga-Se bilayer stack. The annealed CISe, CIGSe layers were subjected to XRD, FE-SEM and Raman studies to understand the structural, morphological, compositional and phase changes. The final composition of the annealed CIGSe thin film exhibited a CuIn0.66Ga0.34Se1.66 stoichiometry.

CNC assisted spray deposition of large grain size CH3NH3PbI3 film for perovskite solar cells

This work presents a utilization of spray deposition technique in the fabrication of thin film perovskite solar cell devices with an assistance of a homemade CNC machine. An 80 nm-thick compact TiO2 was sprayed at a substrate temperature of 400 °C for electron blocking layer. Both one and two-step spray deposition technique are used to compare the quality of the perovskite absorber layer. A large grain size and voids free CH3NH3PbI3 film achieved by using the two-step spray deposition process. When such films are incorporated into a solar cell device with conductive carbon counter electrode, the maximum power conversion efficiencies of up to 9.58% are realized. This approach could pave the way to develop low-cost perovskite solar cell.

Effective two-step chemical deposition for homogeneous lead sulfide thin films on a flexible polymer substrate

Chalcogenide PbS has been extensively studied as a p-type semiconductor material for various optoelectronic devices. Here, an effective two-step chemical bath deposition process is introduced to achieve dense microstructure of PbS thin films specifically for a flexible polyethylene terephthalate (PET) substrate. Three different types of substrates, such as Cu foils, glass substrate and PET, were initially examined to compare different crystal growth behaviors of PbS thin films depending on the choice of substrate. Only the PET substrate demonstrated an unacceptable coverage of films even with the extended deposition due to a retarded growth presumably with more scattered initial distribution of nuclei. Conclusively, two-step deposition processing at a low temperature of 40 °C for the PET substrate was successful in achieving homogeneous microstructures with proper bandgap and film thickness. As a promising result, the 60 min plus 60 min-double depositions at 40 °C produced an ideal bandgap of ~1.58 eV with a proper film thickness of ~200 nm.

Evaluation of grating realized via pulse current electroplating combined with atomic layer deposition as an x-ray grating interferometer

In this work, the authors developed a simple and efficient two-step deposition process for the realization of an x-ray absorption grating: ALD (atomic layer deposition) of a conductive seed layer, followed by electroplating of the absorbing metal with a pulse current mode. An Si grating with a high aspect ratio of 1:40 was fabricated by deep reactive ion etching on an 8 in. Si wafer. In order to form a conductive seed layer on the Si grating with such a high aspect ratio over an area of 10 × 10 cm2, Ru was conformally deposited by a thermal ALD process with O2 reactant gas. The authors analyzed the results of electroplating performed in different bias modes to fill Au in a high aspect ratio Si grating structure. It was found that electroplating in the pulse current mode (duty cycle: 5%, current density: 1.7 mA/cm2) for 79 h allowed Au to uniformly fill the entire grating area, whereas in the direct current mode, severe step coverage on top of the grating was observed. The authors successfully tested the grating fabricated by the suggested two-step deposition process as an absorption grating (G2) for a high x-ray energy Talbot-Lau grating interferometer.

Barrier-free process for fluorinated silicon glass film in Cu interconnects

A dielectric barrier is required for a porous low-dielectric-constant (low-k) film used in Cu interconnects, however, resulting in an increased effective dielectric constant. In this study, a barrier-free fluorinated silicon glass (FSG) dielectric process is proposed and evaluated. Experimental results indicated that FSG films, although had a higher capacitance than p-SiCOH/SiCN stacked films, provide a higher hardness, better O2 plasma resistance, supper Cu barrier, and enhanced dielectric breakdown strength. Therefore, a barrier-free FSG dielectric process is feasible and promising strategy for back-end-of-line interconnects integrity. Moreover, the issue of Cu/FSG peeling under a thermal stress can be solved by providing a post-annealing after FSG deposition or using an in-situ two-step FSG deposition process. The mechanism is also proposed in this study.

Demonstration of on-chip quantum dot microcavity lasers in a molecularly engineered annular groove.

The on-chip quantum dot (QD) microcavity laser engineered on an annular groove made of fused silica was demonstrated based on the external quasi-cavity configuration. By incorporating an appropriate dose of polymer into QD film, the spectral purity of the lasing spectrum was significantly enhanced. In contrast to the dye microcavity laser embedded on the same trench profile, a QD laser possesses a lifetime that is over 10 times longer. We have introduced a unique two-step quantum gain deposition process that has remarkably reduced the wavelength drifts of laser emissions in an aqueous environment by approximately 400%. The reconfigurable cavity platform in combination with an appropriately engineered quantum gain medium embedded onto it promises to enable photostable chip-scale coherent light sources for various photonic, chemical, and biochemical sensing applications.

Building High Performance Li-S Batteries by Compositing Nanosized Sulfur and Conductive Adsorbent within MWCNTs

Lithium sulfur batteries (Li-S) are considered to be the next generation high energy density storage system. But the polysulfide dissolution and intrinsic insulation of sulfur cause problems such as poor rate performance, low coulombic efficiency and short cycle life. To build both high rate and long life sulfur cathodes, we combine nanosized sulfur crystals and Li+/electron conductive black phosphorus (BP) with multi-walled carbon nanotubes (MWCNTs-BP/S) through two-step deposition process. Nanosized sulfur crystals could shorten Li+/electron transport routes and the cross-linked MWCNTs skeleton supports stable and super conductivity of whole cathodes. What's more, the Li+ diffusion and reaction kinetics of sulfur cathodes are greatly promoted by BP nanoparticles due to its good electronic conductivity and high Li+ diffusion constant. Meanwhile, the polysulfide diffusion is effectively restrained through chemisorption of P-S bonds. As a result, the MWCNTs-BP/S cathode with 70 wt% sulfur exhibits a stable working state over 1000 cycles at 1 C with a fading rate as low as 0.053%. Even at an ultrahigh rate of 8 C, the specific capacity still remain 505 mA h g−1. Our research proves that applying polysulfide adsorbents with both good Li+/electronic conductivity is effective for improving reaction kinetics.

Boosting the efficiency of carbon-based planar CsPbBr3 perovskite solar cells by a modified multistep spin-coating technique and interface engineering

All-inorganic CsPbBr3 perovskite solar cells (PSCs) have attracted tremendous attentions in the photovoltaic field these days in view of their outstanding stability, especially thermal stability. However, the bromide-rich perovskite, such as CsPbBr3, always suffer from a low phase-purity and poor morphology synthesized by traditional two-step deposition route. Herein, we demonstrate a facile multistep spin-coating strategy to fabricate high-quality CsPbBr3 films on the low-temperature processed compact TiO2 (c-TiO2) electron transport layer (ETL) of the carbon-based PSCs. As-prepared films exhibit more homogeneous with higher CsPbBr3-phase purity and larger average grain sizes up to 1 µm, compared to those prepared through traditional two-step deposition process. The champion power conversion efficiency (PCE) of the planar CsPbBr3 PSC is boosted from 7.05% to 8.12%, getting an increase by 15.2%, due to the increased crystallinity and light-harvesting ability as well as reduced trap states of the CsPbBr3 film. To further enhance the device performance, a SnO2 thin layer with much higher carrier mobility than TiO2 is introduced to passivate the c-TiO2 ETL. It is found that the SnO2 layer can not only improve the surface morphology of the ETL, but also reduce the current shunting pathways in the c-TiO2. The TiO2/SnO2 bilayered ETL possesses a superior electron extraction capability, beneficial to the charge transport and suppression of the interfacial trap-assisted recombination. The best-performing TiO2/SnO2-based CsPbBr3 PSC delivers an excellent fill factor of 0.817 and a high PCE of 8.79%, which is the highest efficiency for planar CsPbBr3 PSCs reported to date. More importantly, the unencapsulated all-inorganic PSCs show a promising humidity and thermal stability with no decline in efficiency when stored in ambient air at room temperature (25 °C) for over 1000 h and 60 °C for one month, respectively. Our work pave the ways for practical applications of cost-effective, highly efficient and stable all-inorganic PSCs.

Increased luminescent efficiency of perovskite light emitting diodes based on modified two-step deposition method providing gradient concentration

We increased the luminescent efficiency of perovskite light-emitting diodes (PeLEDs) by using a modified two-step deposition method combined with an interdiffusion process without additional solvent engineering or additive molecules. Methylammonium lead bromide (MAPbBr3) polycrystalline films with nanosized grains and low electronic disorder were fabricated by a modified two-step deposition process. The as-fabricated MAPbBr3 films showed gradient concentration characteristics as a result of a gradient distribution of the MABr. Also, the MABr-gradient concentration structure was intensified by the interdiffusion process, showing improved performance of MAPbBr3 PeLEDs with maximum current efficiency CEmax = 0.861 cd A−1 and maximum luminance = 604 cd m−2 with very narrow electroluminescence spectral width. This is the highest CEmax among MAPbBr3-based PeLEDs deposited by the two-step deposition method.

Synthetic Lateral Metal-Semiconductor Heterostructures of Transition Metal Disulfides.

Lateral heterostructures with planar integrity form the basis of two-dimensional (2D) electronics and optoelectronics. Here we report that, through a two-step chemical vapor deposition (CVD) process, high-quality lateral heterostructures can be constructed between metallic and semiconducting transition metal disulfide (TMD) layers. Instead of edge epitaxy, polycrystalline monolayer MoS2 in such junctions was revealed to nucleate from the vertices of multilayered VS2 crystals, creating one-dimensional junctions with ultralow contact resistance (0.5 kΩ·μm). This lateral contact contributes to 6-fold improved field-effect mobility for monolayer MoS2, compared to the conventional on-top nickel contacts. The all-CVD strategy presented here hence opens up a new avenue for all-2D-based synthetic electronics.

Effects of the concentration of PbI2 and CH3NH3I on the perovskite films and the performance of perovskite solar cells based on ZnO-TiO2 nanorod arrays

To date the research of the effects of the concentration of PbI2 and CH3NH3I in the two-step sequential deposition process on the perovskite films and the performance of the perovskite solar cells (PSCs) based on nanorod arrays is rarely reported. In this paper, the perovskite films and the PSCs based on ZnO-TiO2 nanorod arrays were prepared by two-step sequential deposition method in ambient atmosphere. The effects of the concentration of PbI2 and CH3NH3I solution on the morphology, structure, optical absorption and luminescence properties of perovskite films and cell performance were systematically investigated by using field emission scanning electron microscope, X-ray diffractometer, UV–vis spectrophotometer, fluorophotometer, and photocurrent density-voltage (J-V) curves. The best power conversion efficiency (PCE) of perovskite solar cell reaches 10.38% by using PbI2 with a concentration of 1.0 M and CH3NH3I with a concentration of 0.063 M in ambient atmosphere with a relative humidity of about 40%. The PCE of the device may be further improved by optimizing the density and length of nanorod arrays and using glove box. These results provide valuable information for preparing more efficient all-solid-state PSC based on nanorod arrays.

Efficient Perovskite Solar Cells with Reduced Photocurrent Hysteresis through Tuned Crystallinity of Hybrid Perovskite Thin Films

Hybrid perovskite materials used for realization of efficient perovskite solar cells have drawn great attention in both academic and industrial sectors. It was reported that the crystallinity of hybrid thin-film perovskite materials plays an important role in device performance. In this study, we report a novel and simple method to tune the crystallinity of CH3NH3PbI3 thin film for device performance of perovskite solar cells. By employing tetraphenylphosphonium chloride on the top of PbI2 thin layer in the two-step perovskite deposition processes, the crystallinity of the resultant CH3NH3PbI3 thin film was tuned. As a result, perovskite solar cells by the CH3NH3PbI3 thin film with tuned crystallinity exhibit an enlarged open-circuit voltage and enhanced short-circuit current, thus boosted efficiency as well as reduced photocurrent hysteresis compared to pristine CH3NH3PbI3 thin film. These results indicate that our study provides a new simple way to boost device performance of perovskite solar cells through tuning the crystallinity of CH3NH3PbI3 thin film.

Probing photoresponse of aligned single-walled carbon nanotube doped ultrathin MoS2

We report a facile method to produce ultrathin molybdenum disulfide (MoS2) hybrids with polarized near-infrared (NIR) photoresponses, in which horizontally-aligned single-walled carbon nanotubes (SWNTs) are integrated with single- and few-layer MoS2 through a two-step chemical vapor deposition process. The photocurrent generation mechanisms in SWNT-MoS2 hybrids are systematically investigated through wavelength- and polarization-dependent scanning photocurrent measurements. When the incident photon energy is above the direct bandgap of MoS2, isotropic photocurrent signals are observed, which can be primarily attributed to the direct bandgap transition in MoS2. In contrast, if the incident photon energy in the NIR region is below the direct bandgap of MoS2, the maximum photocurrent response occurs when the incident light is polarized in the direction along the SWNTs, indicating that photocurrent signals mainly result from the anisotropic absorption of SWNTs. More importantly, these two-dimensional (2D) hybrid structures inherit the electrical transport properties from MoS2, displaying n-type characteristics at a zero gate voltage. These fundamental studies provide a new way to produce ultrathin MoS2 hybrids with inherited electrical properties and polarized NIR photoresponses, opening doors for engineering various 2D hybrid materials for future broadband optoelectronic applications.

Global Control of CH3NH3PbI3 Formation with Multifunctional Ionic Liquid for Perovskite Hybrid Photovoltaics

Here, a simple strategy using 1-butyl-3-methylimidazolium iodide (BMII) as a multifunctional additive was employed to globally modify the two-step deposition process of the perovskite film. Morphological, structural, and spectral analyses showed that the BMII additive could coordinate with PbI2 and thereby retarded the reaction of PbI2 and CH3NH3I through the ionic exchange process. Moreover, the residual BMII provided a liquid domain to promote the coarsening of the perovskite crystal during the thermal annealing process. Thus, the obtained MAPbI3 film preferred low PbI2 residue, high-quality crystallization, and large-grained microstructure. Using films prepared with BMII additives, the maximum power conversion efficiency of the solar cells was improved from 12.6% of the reference cell to 15.6%. The present study gives a reproductive and facile strategy toward high quality of perovskite thin films and efficient solar cells.

Tunable Crystallization and Nucleation of Planar CH3NH3PbI3 through Solvent-Modified Interdiffusion.

A smooth and compact light absorption perovskite layer is a highly desirable prerequisite for efficient planar perovskite solar cells. However, the rapid reaction between CH3NH3I methylammonium iodide (MAI) and PbI2 often leads to an inconsistent CH3NH3PbI3 crystal nucleation and growth rate along the film depth during the two-step sequential deposition process. Herein, a facile solvent additive strategy is reported to retard the crystallization kinetics of perovskite formation and accelerate the MAI diffusion across the PbI2 layer. It was found that the ultrasmooth perovskite thin film with narrow crystallite size variation can be achieved by introducing favorable solvent additives into the MAI solution. The effects of dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, chlorobenzene, and diethyl ether additives on the morphological properties and cross-sectional crystallite size distribution were investigated using atomic force microscopy, X-ray diffraction, and scanning electron microscopy. Furthermore, the light absorption and band structure of the as-prepared CH3NH3PbI3 films were investigated and correlated with the photovoltaic performance of the equivalent solar cell devices. Details of perovskite nucleation and crystal growth processes are presented, which opens new avenues for the fabrication of more efficient planar solar cell devices with these ultrasmooth perovskite layers.

Surface Functionalization of Two-Dimensional Vertically Aligned Semiconductor Heterojunctions

Large-scale fabrication of two-dimensional (2D) nanomaterials by vapor phase depostion enabled the establishment of vertically aligned semiconductor herterojunctions. However, the property modulation of 2D semiconductor heterojunctions remains chanlleging within such thin layers. Herein, we proposed a general strategy towards the surface functionlization of 2D semiconductor heterojunctions simply by two-step atomic layer deposition (ALD) process with following post-annealing. TiO2-WO3 heterojunction was taken as a typical case in this work and its electrochemical properties were significantly improved via the proposed strategy. This strategy may open a new pathway for facile functionalization of 2D nanomaterials for the energy conversion and storage devices.

Beyond 10% efficient CZTSSe thin-film solar cells fabricated by a two-step CdS deposition process

The CZTSSe/CdS interface qualities are vital aspects and factors that would greatly decide the photovoltaic performance of CZTSSe solar cells. High-quality CZTSSe/CdS interfaces could reduce defect density and improve CZTSSe device performance. However, due to the inhomogeneous CZTSSe grain growth in local micro-regions during selenization, void defects would emerge at the CZTSSe/CdS interfaces by traditional CdS deposition method. In order to obtain high-quality CZTSSe/CdS interfaces, a novel method of two-step CdS deposition, with which the two CdS layers were deposited before and after the selenization of CZTS absorbers, was firstly introduced in the work. The first CdS layer with a certain designed thickness was deposited onto the as-deposited CZTS thin films by CBD. Then the thin films were annealed in selenium-containing atmosphere to obtain CZTSSe thin films of large grain sizes. The second CdS layers with different thicknesses were deposited onto the annealed CZTSSe thin films by CBD again. Comparing with that by the traditional one-step CdS deposition method, the efficiencies of CZTSSe solar cells by two-step CdS deposition method show a remarkable increase from 7.25% to 10.19%. An action mechanism for improving device performance by two-step CdS deposition was proposed: The first CdS layer on CZTS precursors could consistently keep a well coverage for the CZTSSe grains on the surfaces during selenization; The second CdS layer could ensure p-n junctions in good condition, which would reduce recombination centers and shunting paths. The results suggest that the two-step CdS deposition process is an effective method to obtain high-quality CZTSSe/CdS interfaces and high-performance solar cell devices.

Two-step vapor deposition of self-catalyzed large-size PbI2 nanobelts for high-performance photodetectors

Large-size, single-crystalline and high-density PbI2 nanobelts are successfully synthesized by a two-step vapor deposition process at a slow heating rate.

Model Development of p-i-n Germanium Devices for Infrared Detection

Germanium offers many benefits over groups III-V materials when used for infrared detection. Most importantly, germanium is compatible with Complementary Metal Oxide Semiconductor (CMOS) manufacturing which allows for a low-cost, high-throughput device, and it does not require cooling, which many III-V devices do. With the deposition of germanium directly on silicon, there will be a thermally induced strain due to the difference in thermal expansion coefficients between the two materials. When a biaxial tensile strain is present, the direct bandgap of germanium is lowered to ~0.77 eV and is capable of absorbing longer wavelengths. We have used a two-step deposition process to create a strained germanium film in order to fabricate a photodetector device. Our device has a dark current of 1.35 nA and a photocurrent of 22.5 nA at 1570 nm wavelength. Next, we developed a model in order to compare theoretical results with experimental results. The results indicate that the model is in close agreement with our measured data, and we are therefore able to use it to model future devices.