Hybrid Chemical Vapor Deposition Research Articles

Insight into the Defect Chemistry and Ion Migration in Perovskite Fabricated by Hybrid Chemical Vapor Deposition

Insight into the Defect Chemistry and Ion Migration in Perovskite Fabricated by Hybrid Chemical Vapor Deposition

Holistic Strategies Lead to Enhanced Efficiency and Stability of Hybrid Chemical Vapor Deposition Based Perovskite Solar Cells and Modules

AbstractHybrid chemical vapor deposition (HCVD) is a promising method for the up‐scalable fabrication of perovskite solar cells/modules (PSCs/PSMs). However, the efficiency of the HCVD‐based perovskite solar cells still lags behind the solution‐processed PSCs/PSMs. In this work, the oxygen loss of the electron transport layer of SnO2 in the HCVD process and its negative impact on solar cell device performance are revealed. As the counter‐measure, potassium sulfamate (H2KNO3S) is introduced as the passivation layer to both mitigate the oxygen loss issue of SnO2 and passivate the uncoordinated Pb2+ in the perovskite film. In parallel, N‐methylpyrrolidone (NMP) is used as the solvent to dissolve PbI2 by forming the intermediate phase of PbI2•NMP, which can greatly lower the energy barrier for perovskite nucleation in the HCVD process. The perovskite seed is employed to further modulate the kinetics of perovskite crystal growth and improve the grain size. The resultant solar cells yield a champion power conversion efficiency (PCE) of 21.98% (0.09 cm2) with a stable output performance of 21.15%, and the PCEs of the mini‐modules are 16.16% (22.4 cm2, stable output performance of 14.72%) and 12.12% (91.8 cm2). Furthermore, the unencapsulated small area device shows an outstanding operational stability with a T80 lifetime exceeding 4000 h.

Thermodynamic Analysis of Group-III-Nitride Alloying with Yttrium by Hybrid Chemical Vapor Deposition.

Group-IIIb-transition-metal-alloyed wurtzite Group-IIIa-nitride (IIIb-IIIa-N) thin films have higher piezoelectric characteristics than binary IIIa-N for a broad range of applications in photonic, electronic, sensing, and energy harvesting systems. We perform theoretical thermodynamic analysis for the deposition and epitaxial growth of Y-alloyed GaN and AlN films by a newly introduced growth technique of hybrid chemical vapor deposition (HybCVD), which can overcome the limitations of the conventional techniques. We investigate the equilibrium vapor pressures in the source zones to determine the dominant precursors of cations for the input of the mixing zone. Then, we study the driving force for the vapor-solid phase reactions of cation precursors in the growth zone to calculate the relationship between the solid composition of YxGa1-xN and YxAl1-xN and the relative amount of input precursors (Y vs. GaCl and AlCl3) in different deposition conditions, such as temperature, V/III precursor input ratio, and H2/inert-gas mixture ratio in the carrier gas. The xY composition in YAlN changes nearly linearly with the input ratio of cation precursors regardless of the growth conditions. However, YGaN composition changes non-linearly and is also substantially affected by the conditions. The thermodynamic analysis provides insight into the chemistry involved in the epitaxial growth of IIIa-IIIb-N by the HybCVD, as well as the information for suitable growth conditions, which will guide the way for ongoing experimental efforts on the improvement of piezoelectricity of the lead-free piezoelectric materials.

A modified hybrid chemical vapor deposition method for the fabrication of efficient CsPbBr3 perovskite solar cells

Due to its outstanding stability, all-inorganic cesium lead bromide (CsPbBr3) perovskite is gaining increasing attention as a functional material in photovoltaics and other optoelectronic applications. However, the preparation of high-quality CsPbBr3 films via solution processing remains a significant challenge due to the cesium precursor’s low solubility in common solvents. As a result, developing viable evaporation deposition strategies is critical for increasing the photovoltaic performance of perovskite solar cells (PSCs) based on CsPbBr3. In this paper, a modified hybrid chemical vapor deposition is applied to fabricate CsPbBr3 films, and the effects of reaction temperature and reaction time on the crystallinity, morphology, and photo-electric properties of the films are investigated. By optimizing the reaction conditions, high-quality CsPbBr3 films with good crystallinity and uniformity are successfully obtained. Based on these films, CsPbBr3 PSCs with a device configuration of fluorine-doped tin oxide/compact-TiO2/CsPbBr3/carbon attained impressive power conversion efficiency of 4.41% with an ultra-high open-circuit voltage (V OC) of 1.39 V. This demonstration suggests that the modified hybrid chemical vapor deposition strategy enables a promising fabrication route suitable for all-inorganic perovskite thin films in photovoltaic application.

Rapid hybrid chemical vapor deposition for efficient and hysteresis-free perovskite solar modules with an operation lifetime exceeding 800 hours

Rapid hybrid chemical vapor deposition is developed to fabricate perovskite solar modules with a markedly reduced time while maintaining high performance.

Characterization of Hydrophobic Silane Film Deposited on AISI 304 Stainless Steel for Corrosion Protection

This present study was conducted to determine the aptitude of hydrophobic silane coating in corrosion resistance of AISI 304 stainless steel substrate at the nanoscale. Three newly developed hydrophobic silane-based compounds of compositions, namely [tris(trimethylsiloxy)silyethyl]dimethylchlorosilane (alkyl); tridecafloro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS); and henicosyl-1,1,2,2-tetrahydrododecyltricholrosilane (FDDTS), were used as precursors to coat AISI 304 stainless steel surfaces. Prior to deposition, the substrate surfaces were pretreated with plasma oxide via a multi-step treatment to serve as adhesion. The plasma oxide and the silane precursors were deposited by using a hybrid atomic layer deposition and chemical vapor deposition process. The structural, chemical and electrochemical stabilities were investigated using SEM, AFM, XRD, ATR-FTIR, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that the microstructures and morphology of the coated samples were similar, due to the chlorosilane functionalization. The FTIR indicated complete hydrolysis at the nanoscale while the polarization results showed that nano-coating can hamper the corrosion propagation mechanisms. Furthermore, the EIS results revealed that all the precursors acted as a barrier to AISI 304 dissolution into the electrolyte. The electrochemical effect was observed in the microstructural transformation of the coatings. Although all the precursors were shown to have been effective at few nanoscales, the stability of the FDDTS showed to have superseded that of alkyl and FOTS.

Characterization of Low-Frequency Excess Noise in CH3NH3PbI3-Based Solar Cells Grown by Solution and Hybrid Chemical Vapor Deposition Techniques.

In this study, detailed investigations of low-frequency noise (LFN) characteristics of hybrid chemical vapor deposition (HCVD)- and solution-grown CH3NH3PbI3 (MAPI) solar cells are reported. It has been shown that LFN is a ubiquitous phenomenon observed in all semiconductor devices. It is the smallest signal that can be measured from the device; hence, systematic characterization of the LFN properties can be utilized as a highly sensitive nondestructive tool for the characterization of material defects in the device. It has been demonstrated that the noise power spectral densities of the devices are critically dependent on the parameters of the fabrication process, including the growth ambient of the perovskite layer and the incorporation of the mesoscopic structures in the devices. Our experimental results indicated that the LFN arises from a thermally activated trapping and detrapping process, resulting in the corresponding fluctuations in the conductance of the device. The results show that the presence of oxygen in the growth ambient of the HCVD process and the inclusion of an mp-TiO2 layer in the device structure are two important factors contributing to the substantial reduction in the density of the localized states in the MAPI devices. Furthermore, the lifetimes of the MAPI perovskite-based solar cells are strongly dependent on the material defect concentration. The degradation process is substantially more rapid for the devices with higher initial defect density compared to the devices prepared under optimized conditions and structure that exhibit substantially lower initial trap density.

Combination of Hybrid CVD and Cation Exchange for Upscaling Cs‐Substituted Mixed Cation Perovskite Solar Cells with High Efficiency and Stability

AbstractMixed cation hybrid perovskites such as CsxFA1−xPbI3 are promising materials for solar cell applications, due to their excellent photoelectronic properties and improved stability. Although power conversion efficiencies (PCEs) as high as 18.16% have been reported, devices are mostly processed by the anti‐solvent method, which is difficult for further scaling‐up. Here, a method to fabricate CsxFA1−xPbI3 by performing Cs cation exchange on hybrid chemical vapor deposition grown FAPbI3 with the Cs+ ratio adjustable from 0 to 24% is reported. The champion perovskite module based on Cs0.07FA0.93PbI3 with an active area of 12.0 cm2 shows a module PCE of 14.6% and PCE loss/area of 0.17% cm−2, demonstrating the significant advantage of this method toward scaling‐up. This in‐depth study shows that when the perovskite films prepared by this method contain 6.6% Cs+ in bulk and 15.0% at the surface, that is, Cs0.07FA0.93PbI3, solar cell devices show not only significantly increased PCEs but also substantially improved stability, due to favorable energy level alignment with TiO2 electron transport layer and spiro‐MeOTAD hole transport layer, increased grain size, and improved perovskite phase stability.

Exploiting the Properties of Ti‐Doped CVD‐Grown Diamonds for the Assembling of Electrodes

A hybrid chemical vapor deposition (CVD)‐powder flowing technique specifically developed in lab has been employed to produce high‐quality polycrystalline diamond layers containing Ti inclusions. Morphology, structural features, and surface composition of nanocomposite diamond‐based samples produced by different growth times have been analyzed by scanning electron microscopy, Raman and Auger spectroscopy, respectively. The CVD methodology adopted for the Ti incorporation in the diamond lattice does not perturb the crystalline quality of the diamond matrix, therefore maintaining the outstanding properties of the C‐sp3 phase. The functional properties of the nanocomposite layers have been tested by nanoindentation and I–V measurements. The electrochemical performance of the diamond/Ti electrodes is evaluated by performing cyclic voltammetry in different media, namely, acidic, neutral, and basic aqueous solutions, and by estimating the rate constant of heterogeneous electron transfer to diamond surface for the ferro/ferricyanide redox couple. The rather good electrochemical performances, the mechanical strength, and the chemical inertness of the Ti‐doped diamond electrodes produced by the CVD approach, comply with the whole set of technological requirements, such as robustness, long durability, and biocompatibility, required for use in hostile environments or in biological systems.

Crystal Engineering for Low Defect Density and High Efficiency Hybrid Chemical Vapor Deposition Grown Perovskite Solar Cells

Synthesis of high quality perovskite absorber is a key factor in determining the performance of the solar cells. We demonstrate that hybrid chemical vapor deposition (HCVD) growth technique can provide high level of versatility and repeatability to ensure the optimal conditions for the growth of the perovskite films as well as potential for batch processing. It is found that the growth ambient and degree of crystallization of CH3NH3PbI3 (MAPI) have strong impact on the defect density of MAPI. We demonstrate that HCVD process with slow postdeposition cooling rate can significantly reduce the density of shallow and deep traps in the MAPI due to enhanced material crystallization, while a mixed O2/N2 carrier gas is effective in passivating both shallow and deep traps. By careful control of the perovskite growth process, a champion device with power conversion efficiency of 17.6% is achieved. Our work complements the existing theoretical studies on different types of trap states in MAPI and fills the gap on the theoretical analysis of the interaction between deep levels and oxygen. The experimental results are consistent with the theoretical predictions.

Fe2O3-WO3 nanosystems synthesized by a hybrid CVD/sputtering route, and analyzed by X-ray photoelectron spectroscopy

Fe2O3-WO3nanosystems have been grown on metallic Ti substrates by a hybrid chemical vapor deposition(CVD) / Radio Frequency (RF)-sputtering route. The obtained specimens have been characterized in their structure, morphology and chemical composition by means of X-ray diffraction(XRD), field emission-scanning electron microscopy (FE-SEM), secondary ion mass spectrometry(SIMS) and X-ray photoelectron spectroscopy(XPS). Herein, a detailed XPS investigation of a representative sample is proposed. In addition to the wide scan spectrum, particular attention is dedicated to the analysis of O 1s, Fe 2p, W 4f, and W 4d core levels. The obtained results suggested the formation of pure Fe2O3-WO3composites, in which each oxide maintained its chemical identity.

Low‐Pressure Hybrid Chemical Vapor Growth for Efficient Perovskite Solar Cells and Large‐Area Module

Vapor‐based deposition technique is considered as a promising approach for preparing a high‐quality and uniform perovskite thin film. With evolution from coevaporation deposition to a low‐pressure vapor‐assisted solution process, both energy budget and reaction yield for perovskite film fabrications are improved. In this paper, a low‐pressure hybrid chemical vapor deposition (LPHCVD) method is applied to fabricate CH3NH3PbI3 perovskite films. The crucial dependence of working pressure on the perovskite formation is revealed. Moreover, the reaction time plays an important role in controlling the quality of the synthesized perovskite film. Efficient perovskite solar cells of 14.99% (mesoscopic), 15.37% (planar), and perovskite modules (active area of 8.4 cm2) of 6.22% are achieved by this LPHCVD method.

High performance perovskite solar cells by hybrid chemical vapor deposition

Organometal halide based perovskites are promising materials for solar cell applications and are rapidly developing with current devices reaching ∼19% efficiency. In this work we introduce a new method of perovskite synthesis by hybrid chemical vapor deposition (HCVD), and demonstrate efficiencies as high as 11.8%. These cells were found to be stable with time, and retained almost the same efficiency after approximately 1100 h storage in dry N2 gas. This method is particularly attractive because of its ability to scale up to industrial levels and the ability to precisely control gas flow rate, temperature, and pressure with high reproducibility. This is the first demonstration of a perovskite solar cell using chemical vapor deposition and there is likely still room for significant optimization in efficiency.

Low-temperature synthesis of thin graphite sheets using plasma-assisted thermal chemical vapor deposition system

We report the low-temperature synthesis of thin graphite sheets using a hybrid chemical vapor deposition (HCVD) system that combines plasma and thermal CVD (TCVD). Electron beam deposited Ni films were used as catalytic substrates, and methane was used as a carbon feedstock. The quartz tube was into two regions: core plasma region for efficient dissociation of methane and a TCVD region for thermal synthesis, respectively. After the syntheses at different TCVD temperatures from 550 °C to 900 °C, as-grown films were transferred to transparent polymeric substrates to apply as flexible conductive electrodes. Finally, it was found that thin graphite sheets consisting of ~ 15 graphene layers were synthesized at 600 °C using the HCVD system and could be applicable as transparent conductive films.

Cr-diamondlike carbon nanocomposite films: Synthesis, characterization and properties

Diamondlike carbon (DLC) films, known for exhibiting attractive combination of properties, have been extensively studied in the recent past. The inherent, internal compressive stresses affecting their adhesion and their relatively low thermal stability above 400 °C are two major drawbacks preventing wide usage of these films. Carbide formers incorporated into the carbon network have the potential to stabilize the film structure, relax internal stresses and improve their performance. The present work focuses on the synthesis, structure and mechanical and tribological property characterization of Cr-containing nanocomposite DLC films. The films were synthesized using a plasma-enhanced hybrid chemical vapor and physical vapor deposition process in a discharge composed of a mixture of CH 4 and Ar gases. The Cr content in the films varied up to 18 at.%. The film morphology and composition were characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and nuclear reaction analysis. The mechanical and tribological behavior of the films was studied as a function of Cr concentration by conducting nanoindentation and pin-on-disc experiments, respectively. The results showed that the films can be either amorphous with dispersed metallic-like Cr (at low Cr content) or nanocomposite consisting of face-centered cubic metastable CrC nanoparticles dispersed in the DLC matrix. Films with low Cr content (< 5 at.%) were found to possess similar tribological characteristics with those of pure DLC films. Incorporation of more Cr (> 12 at.%) results in larger chromium carbide particles that have an adverse effect on wear resistance. The films with the low Cr content offer the opportunity to combine the excellent tribological behavior with other desirable properties deriving from the presence of the second phase.

LaCoO&lt;SUB&gt;3&lt;/SUB&gt; Nanosystems by a Hybrid CVD/Sol–Gel Approach

LaCoO3 nanosystems are receiving increasing attention for the development of innovative fuel cells and heterogeneous catalysts. In this report, we describe the synthesis of nanophasic LaCoO3 thin films by a hybrid chemical vapor deposition (CVD)/sol-gel (SG) approach. The adopted strategy consists in the CVD of La-O-based systems on SG cobalt oxide xerogels CoOx(OH)y at temperatures as low as 200 degrees C and in the subsequent thermal treatment in air (400-800 degrees C, 2-8 h). In this context, particular attention is devoted to achieving an intimate La/Co intermixing already in the as-prepared systems, in order to favor reactions yielding a single La-Co-O phase with uniform composition. The obtained results point out to the formation of pure and structurally homogeneous LaCoO3 nanosystems after annealing at 700 degrees C, 2 h, with a typical grain-like morphology. More severe thermal treatment resulted in the thermal decomposition of LaCoO3 nanocrystallites.

Tribological Study of Microbearings for MEMS Applications

Microsleeve bearings intended for microrotational machinery were fabricated by X-ray lithography and Ni electroplating. Coated to the working surfaces of the bearings was a 900nm thick uniform tungsten hydrocarbon (W–C:H) coating using an inductively coupled plasma (ICP) assisted, hybrid chemical vapor deposition (CVD)/physical vapor deposition (PVD) tool. Tribological characteristics and mechanical properties of as-electrodeposited Ni microbearings, annealed Ni microbearings at 800°C, and W–C:H coated microbearings were investigated. Potential applications of the microbearings may involve very light contact pressure (5-30MPa) and high sliding speed, such as micromotors and microturbines. Conventional pin-on disk test methods on top flat surfaces, (001) planes, cannot effectively predict tribological characteristics because these microbearings use the sidewall (110 plane) as a working surface. A special micro wear tester and friction tester were developed. Surface morphologies of new and worn bearing surfaces were studied using SEM. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) characterized the W–C:H coated microbearings. Test results of the W–C:H coated microbearings (wear characteristics and friction) are also presented. W–C:H coated microbearings had much lower wear rate than uncoated bearings. During the wear test, a transfer layer formed on the counter steel shaft even under very small contact pressure, leading to low steady state friction and high wear resistance.

Modulation of charge transport in diamond-based layers

Doping of diamond by substitutional insertion of metallic species or production of diamond/metals nanocomposite layers has been obtained by a hybrid chemical vapor deposition based technique. The potential of such an approach makes it possible to obtain a wide class of purposely designed diamond-based structures characterized by specific properties of charge transport. Reflection high-energy electron diffraction, scanning electron microscopy and x-ray dispersive spectrometry have been used to study the structural and compositional characteristics of some Nd-, W- and Ti-containing diamond films. The peculiar electrical properties conferred to the host diamond layers by the insertion of various metals have been investigated in the range of 25–500 K by performing Hall effect and conductivity measurements. The mechanism of charge transport and the electrical properties of these materials are found to be mainly governed by organization of the metallic species, which can be in different forms, such as dispersion at the atomic scale and the distribution of isolated clusters or aggregates localized at grain boundaries. Depending on the microstructure, the resulting materials can behave as p-type semiconductors, characterized by resistivity values as low as 3.3×10−3 Ω cm and high values of Hall mobility, or show metal-like conduction, with resistivity as low as 2.2×10−1 Ω cm. The insertion of metallic species does not perturb the crystalline quality of the host diamond matrix and, consequently, the layers produced combine the outstanding properties of diamond with electrical behavior that can be modulated for specific applications.

Diamond-based composite layers as protective coatings for ion beam extraction systems

W-containing polycrystalline diamond films were produced by a hybrid chemical vapor deposition- powder flowing technique, in order to test the feasibility of using composite diamond-based materials as protective coatings for acceleration grids subjected to ion bombardment. The morphology and structure of the composite layers, deposited on Mo substrates, were investigated by scanning electron microscopy and reflection high-energy electron diffraction. It is found that W insertion substantially lowers the resistivity of the diamond-based layers (around 10−2Ω cm) but does not modify the lattice parameters of the host diamond matrix. The performance of such coatings for shielding Mo grids from ion-induced sputtering was tested using 1 keV Ar+ beams. The Auger electron spectroscopy spectra indicated that the dose of 6×1019 ions/cm2 employed was not sufficient for complete erosion of the composite layers, for which sputtering yields in the range of 0.6–0.9 atoms/ion were measured. The secondary electron emission induced by 1.5–4.0 keV Ar+ ions was investigated and compared with the emission from uncoated Mo samples.

Inductively coupled plasma assisted deposition and mechanical properties of metal-free and Ti-containing hydrocarbon coatings

Metal-free amorphous hydrocarbon (a-C:H) and Ti-containing hydrocarbon (Ti–C:H) coatings have been synthesized in a hybrid chemical vapor deposition (CVD)/physical vapor deposition (PVD) system which combines inductively coupled plasma (ICP) and sputter deposition. a-C:H coatings have been fabricated by ICP assisted CVD in inert/hydrocarbon gas mixtures while Ti–C:H coatings have been fabricated by ICP assisted magnetron sputtering of Ti in inert/hydrocarbon gas mixtures. We present results of structural characterization and mechanical property measurements on these a-C:H and Ti–C:H coatings. In particular, the influence of hydrogen on the coating mechanical properties is probed experimentally. We show that hydrogen significantly influences the mechanical properties of a-C:H and Ti–C:H coatings and needs to be considered for a full understanding of the mechanical properties of Ti–C:H coatings. Our results demonstrate that combining ICP with sputter deposition makes a versatile CVD/PVD tool capable of depositing metal-free and metal-containing hydrocarbon coatings with widely varying microstructures and mechanical properties.