Discharge Plasma Chemical Vapor Deposition Research Articles

Synthesis of multiple single crystal diamonds by DC-GD-CVD

ABSTRACTMultiple single crystal diamonds (SCDs) were first synthesised on 24 high pressure high temperature (HPHT) synthetic type Ib (100) SCD seeds by direct current glow discharge plasma chemical vapour deposition (DC-GD-CVD) system with gas mixture of CH4–H2–Ar. Owing to the increase of the formed plasma density and temperature caused by the addition of 1.2 vol.-% Ar gas, a high growth rate of 22.2 µm h−1 for diamonds deposition was achieved by the plasma with diameter of 2 inches at 900–950°C. After deposition for 50 h, diamond material with a thickness of about 1 mm was uniformly deposited on each seed. The average FWHM value, hardness and transmittance of as-obtained SCDs were 3.2 cm−1, 105 GPa and 69.4%, revealing the high quality of multiple SCDs fabricated by the DC-GD-CVD method.

Improvement of Charge Transportation in Si Quantum Dot-Sensitized Solar Cells Using Vanadium Doped TiO2.

The multiple exciton generation characteristics of quantum dots have been expected to enhance the performance of photochemical solar cells. In previous work, we first introduced Si quantum dot for sensitized solar cells. The Si quantum dots were fabricated by multi-hollow discharge plasma chemical vapor deposition, and were characterized optically and morphologically. The Si quantum dot-sensitized solar cells had poor performance due to significant electron loss by charge recombination. Although the large Si particle size resulted in the exposure of a large TiO2 surface area, there was a limit to ho much the particle size could be decreased due to the reduced absorbance of small particles. Therefore, this work focused on decreasing the internal impedance to improve charge transfer. TiO2 was electronically modified by doping with vanadium, which can improve electron transfer in the TiO2 network, and which is stable in the redox electrolyte. Photogenerated electrons can more easily arrive at the conductive electrode due to the decreased internal impedance. The dark photovoltaic properties confirmed the reduction of charge recombination, and the photon-to-current conversion efficiency reflected the improved electron transfer. Impedance analysis confirmed a decrease in internal impedance and an increased electron lifetime. Consequently, these improvements by vanadium doping enhanced the overall performance of Si quantum dot-sensitized solar cells.

Quantum Characterization of Si Nano-Particles Fabricated by Multi-Hollow Discharge Plasma Chemical Vapor Deposition

Quantum Characterization of Si Nano-Particles Fabricated by Multi-Hollow Discharge Plasma Chemical Vapor Deposition

Effects of cluster incorporation into hydrogenated amorphous silicon films in initial discharge phase on film stability

We studied the effects of incorporation of hydrogenated amorphous silicon (a-Si:H) nanoparticles (clusters) generated in the initial discharge phase on light induced degradation of a-Si:H films. The amount of clusters incorporated into the films in the initial discharge phase is 15 times larger than that in the steady state. To evaluate the effects of such initial cluster incorporation on stability of a-Si:H films, we fabricated a-Si:H Schottky cells with and without initial cluster incorporation using a multi-hollow discharge plasma chemical vapor deposition method with a shutter and compared cell stability against light exposure. The degradation ratio of the cell without initial cluster incorporation is less than 1% even after 100hour light soaking of 2.7 suns. Our results show that suppressing initial cluster incorporation into a-Si:H films is a key to stable a-Si:H cells. Moreover, Si–H2 bonds in films can be reduced down to 1/10 using a cluster eliminating filter.

Photovoltaic application of Si nanoparticles fabricated by multihollow plasma discharge CVD: Dye and Si co-sensitized solar cells

Dye-sensitized solar cells (DSCs) still need wider absorption range despite their stable and good performance. This work proposed the co-sensitization of Si quantum dot (QD) and N749 dye for better photo-generation. Si QD was chemically stable with regard to all DSC components and its stability enabled to co-sensitize with dye. Si QDs were fabricated by multihollow discharge plasma chemical vapor deposition and applied for the co-sensitization. Si and dye co-sensitization led to the increase of incident photon to current conversion efficiency and decrease of internal impedance as compared with a standard DSC. As a result, short-circuit current density was increased over 1 mA/cm2 and the performance was enhanced with co-sensitization from 4.36 to 5.10%. Si and dye co-sensitization was very effective because the enhancement was much larger than the performance of Si QDSC without dye sensitization.

Nanostructure Control of Si and Ge Quantum Dots Based Solar Cells Using Plasma Processes

We report characteristics of quantum dot (QD) sensitized solar cells using Si nanoparticles and Ge nanoparticles. Si nanoparticles were synthesized by multi-hollow discharge plasma chemical vapor deposition, whereas Ge nanoparticles were done by a radio frequency magnetron sputtering using Ar+H2 under high pressure conditions. The electrical power generation from Si QDs and Ge QDs was confirmed. Si QD sensitized solar cells show an efficiency of 0.024%, fill factor of 0.32, short-circuit current of 0.75 mA/cm2 and open-circuit voltage of 0.10 V, while Ge QD sensitized solar cells show an efficiency of 0.036%, fill factor of 0.38, short-circuit current of 0.64 mA/cm2 and open-circuit voltage of 0.15 V.

Synthesis of carbon fibers with branched nanographene sheets for electrochemical double layer capacitor application.

We demonstrate a one step technique to synthesis the carbon fibers (CNFs) with branched nanographene sheets by the pulsed discharge (PD) plasma chemical vapor deposition (CVD) process. Highly crystalline branched nanographene sheets were directly grown from the surface of the carbon fibers to obtain a three dimensional (3D) nanostructure. The growth process can be explained from the catalyst support growth of the CNFs, and subsequently nucleation and growth of the nanographene sheets from the crystalline surface of the CNF. The deposited nanostructured films with different pulse discharge were used as an electrode for electrochemical double-layer capacitors (EDLC). It is observed that the capacitance is dependent on the morphology of the electrode materials and an optimum capacitance is obtained with the branched nanographene on CNFs.

SiC Nanoparticle Composite Anode for Li-Ion Batteries

ABSTRACTWe present here performance of Li ion batteries with SiC nanoparticle-film anode, which is fabricated by a double multi-hollow discharge plasma chemical vapor deposition (CVD) method. The first cycle of charge/discharge property of the Li ion battery with the SiC nanoparticle-film anode shows a high capacity of over 4,000 mAh/g, which is 12 times higher than the Li ion battery with the conventional graphite anode. The discharge capacity shows high stability for first 10th cycle, and is 3750 mAh/g for the 10th cycle.

Characteristics of Crystalline Silicon/Si Quantum Dot/Poly(3,4-ethylenedioxythiophene) Hybrid Solar Cells

Here, we report the characteristics of a novel organic/inorganic hybrid photovoltaic device using a Si quantum dot (QD) layer synthesized by multi-hollow discharge plasma chemical vapor deposition. The hybrid device has a p–i–n structure, which consists of a crystalline Si (c-Si) substrate, a Si QD layer, and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). We have examined the absorption coefficient and photoconductivity of Si QD layers, and confirmed electricity generation from Si QD layers. We have measured the current–voltage characteristics and incident photon-to-current conversion efficiency (IPCE) of c-Si/Si QD/poly(3,4-ethylenedioxythiophene) (PEDOT) hybrid solar cells. This hybrid device shows an energy conversion efficiency of 2.84%, a short-circuit current of 6.84 mA/cm2, an open-circuit voltage of 0.73 V, and a fill factor of 0.58. A high IPCE value of 82.8% is obtained at a short wavelength of 460 nm.

Study on the Fabrication of Paint-Type Si Quantum Dot-Sensitized Solar Cells

Quantum dots (QDs) have attracted much attention with their quantum characteristics in the research field of photochemical solar cells. Si QD was introduced as one of alternatives to conventional QD materials. However, their large particles could not penetrate inside TiO2 layer. Therefore, this work proposed the paint-type Si QD-sensitized solar cell. Its heat durability was suitable for the fabrication of paint-type solar cell. Si QDs were fabricated by multihollow discharge plasma chemical vapor deposition and characterized. The paste type, sintering temperature, and Si ratio were controlled and analyzed for better performance. Finally, its performance was enhanced by ZnS surface modification and the whole process was much simplified without sensitizing process.

The improvement on the performance of quantum dot-sensitized solar cells with functionalized Si

Quantum dots (QDs) have been attractive recently with their multiple exciton generation characteristics. QD solar cells can more effectively use the incident energy because one or more electrons are generated with the photon of high energy. They have less heat loss and higher theoretical efficiency (44%) than single exciton generation solar cells (33%). This work focused on Si as alternative to conventional QD materials. Si has QD's unique characteristics such as the quantum size effect and quantum confinement with non-toxicity and abundance. Si QDs were fabricated by the multi-hollow discharge plasma chemical vapor deposition and applied to QD-sensitized solar cells (QDSCs). Contrary to the good characteristics of Si QDs, Si QDSCs had poor performance as compared with conventional QDSCs because of the weak combination between Si QDs and TiO2. Small amounts of adsorbed Si QD on TiO2 made low photocurrent and TiO2 surface widely exposed to redox electrolyte caused charge recombination, the decrease of open-circuit voltage, and low fill factor. For improving their combination, Si QDs were functionalized. The electron transfer from Si to TiO2 and the bonding with TiO2 were improved and more Si QDs were adsorbed by the functionalization. In the functionalization process, the linking source is one of the key parameters. Therefore, 4-vinylbenzoic acid was controlled and its effect was analyzed. The change in the photovoltaic parameters according to the concentration of 4-vinylbenzoic acid and the performance dependence were investigated. In order to verify their characteristics, the effects in terms of the photovoltaic performance, electrochemical impedance, and optical properties were examined.

Characteristics of photocurrent generation in the near-ultraviolet region in Si quantum-dot sensitized solar cells

We have studied photocurrent generation in Si quantum-dot (QD) sensitized solar cells, where QD thin films composed of Si nanoparticles were deposited using the double multi-hollow discharge plasma chemical vapor deposition process in an SiH4/H2 and CH4 or N2 gas mixture. The short-circuit current density of the Si QD sensitized solar cells increases by a factor of 2.5 by using Si nanoparticles prepared by irradiation of CH4 or N2 plasma onto the Si nanoparticle surface. We have measured incident photon-to-current conversion efficiency (IPCE) in the near-ultraviolet range using quartz-glass front panels of the QD sensitized solar cells. With decreasing the wavelength of irradiation light, IPCE gradually increases upon light irradiation in a wavelength range less than about 600nm, and then steeply increases below 300nm, corresponding to 2.2 times the optical band-gap energy of Si QD film.

Formation of C-N-Si Film for Interlayer of Hard Material Coating by Pulsed Discharge Plasma CVD

Carbon nitride (C-N) and Si added C-N (C-N-Si) films were deposited on SKD61 steel plate by pulsed discharge (PD) plasma chemical vapour deposition (CVD). When the films were deposited with N2 and H2 diluted CH4 source gases, the deposition rate increased and the hardness decreased with increasing CH4 concentration. By means of adding mono-methyl-silane (MMS) gas to the source gases, the C-N-Si film having high hardness of 10 GPa and low Yung's modulus of 80 GPa could be deposited. The FT-IR spectrum of the films showed a peak of graphitic ring and peaks of terminating with H and N were observed. Raman spectra showed D and G peaks at around 1350 and 1590 cm−1, respectively. The intensity of D peak compared to G peak decreased when MMS was added. Ball on disk test of the C-N-Si film against SUJ2 ball showed the friction coefficient was about 0.2. These results shows that the C-N-Si film having high hardness and low Young's modulus, which is suitable for interlayer of hard film coating, can deposit by the PD plasma CVD, and suggest that the film is composed of fullerene-like structure which forms resilient and fracture tough materials.

Analysis on the effect of polysulfide electrolyte composition for higher performance of Si quantum dot-sensitized solar cells

Quantum dot-sensitized solar cell (QDSC) based on multiple exciton generation of QD has been expected to realize high efficiency. This work focused on Si QD instead of conventional QD materials because of their toxicity and scarcity. Si QDs were fabricated by multi-hollow discharge plasma chemical vapor deposition. General QDSCs use polysulfide electrolyte because it is suitable for stabilizing QDs and its redox reaction is the best as compared with other redox systems. The improvement of redox reaction which is one of the slowest reactions in the kinetic analysis is closely connected with the enhancement of performance. For the enhancement on the overall performance of Si QDSC, the performance dependence on electrolyte composition was investigated. The concentrations of Na2S and S were varied for the activation of redox reaction and KCl concentration was optimized for the improvement of electrolyte characteristics. Consequently, the best performance of Si QDSC was obtained with 1M Na2S, 2M S, and 0.4M KCl polysulfide electrolyte.

Improvement of Si Adhesion and Reduction of Electron Recombination for Si Quantum Dot-Sensitized Solar Cells

Quantum dots (QDs) based on multiple exciton generation have attracted much attention. They are capable of generating multiple electrons by single-photon absorption. Si is one of the good QD sources and its nontoxicity and abundance are advantageous for photovoltaics. In this work, Si QDs were fabricated by multihollow discharge plasma chemical vapor deposition, and they were applied to Si QD-sensitized solar cells. Their initial performance was poor because of the weak adhesion of Si and charge recombination. In this work, we solved these problems through the functionalization of Si QDs and a ZnO barrier. Functionalized Si QDs were more adsorbed on TiO2 with strengthened adhesion and the ZnO barrier prevented the contact between TiO2 and the redox electrolyte. Consequently, the improved adhesion and the reduced electron recombination led to the enhancement of overall photovoltaic characteristics.

The reduction of charge recombination and performance enhancement by the surface modification of Si quantum dot-sensitized solar cell

Multiple exciton generation solar cell based on quantum dots has higher theoretical efficiency than single exciton generation solar cell. In this work, Si quantum dots with the diameter of 10nm were fabricated by the multi-hollow discharge plasma chemical vapor deposition and applied to the quantum dot-sensitized solar cell. In this cell, there was considerable electron recombination with redox electrolyte in the Si–TiO2 network because of large Si particle size. For the reduction of recombination and the enhancement of performance, a barrier layer was introduced. Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and zinc acetate dihydrate (Zn(CH3COO)2·H2O) were employed as precursors for surface modification. Consequently, short circuit current and open circuit voltage of the cells were increased by the surface modification with both precursors. The improvement was ascribed to the inhibition of electrons back transfer from TiO2 to the electrolyte by the barrier layer. This result clearly demonstrated that the surface modification with ZnO was advantageous for the performance enhancement.

Effects of crystalline nanoparticle incorporation on growth, structure, and properties of microcrystalline silicon films deposited by plasma chemical vapor deposition

We investigated effects of incorporation of Si crystalline nanoparticles into microcrystalline Si films during their deposition on their growth, structure and properties using multi-hollow discharge plasma chemical vapor deposition. The films with nanoparticles show a lower (220) orientation ratio than those without nanoparticles, whereas both the films have nearly the same film thickness and crystallinity. The films with nanoparticles have inverted conical growth, while the films without nanoparticles have columnar growth. Nucleation density of the films with nanoparticles is higher than that of the films without nanoparticles. Both photo and dark conductivities of the films with nanoparticles tend to be lower than those without nanoparticles. Thus, incorporation of small amount of nanoparticles into microcrystalline Si film affects growth, structure and properties of the films.

Deposition of Cluster-Free B-doped Hydrogenated Amorphous Silicon Films Using SiH4+B10H14Multi-Hollow Discharge Plasma Chemical Vapor Deposition

We have deposited cluster-free B-doped hydrogenated amorphous silicon (a-Si:H) films using a SiH4+B10H14 multi-hollow discharge plasma chemical vapor deposition (CVD) method. We have studied the dependence of the deposition rate, band gap, and conductivity of the films on the gas flow rate ratio R=[B10H14]/[SiH4]. The deposition rate for SiH4+B10H14 plasmas is 2–3 times as high as that for pure SiH4 plasmas. Optical emission spectroscopy (OES) measurements indicate that SiH3 radical generation rate remains nearly constant regardless of R. These results suggest that BxHy radicals enhance the surface reaction probability and/or sticking probability of SiH3, being the predominant deposition precursor. Cluster-free B-doped a-Si:H films have a wide band-gap energy of 1.8–2.0 eV and a conductivity as high as 5.0×10-6 S/cm. These results demonstrate that cluster-free B-doped a-Si:H films deposited using SiH4+B10H14 multi-hollow discharge plasma CVD are promising as a p-layer of pin a-Si:H solar cells.

The Optical Analysis and Application of Size-controllable Si Quantum Dots Fabricated by Multi-hollow Discharge Plasma Chemical Vapor Deposition

ABSTRACTQuantum dot-sensitized solar cells (QDSCs) based on the multiple exciton generation (MEG) of QD are attractive in the field of photochemical cells because the improvement of conventional sensitized solar cells has been stagnant recently. The distinctive characteristics of QDs are their strong photo-response in the visible region and quantum confinement effects. Its theoretical efficiency is much higher than that of solar cell based on the single exciton generation (SEG). Moreover, QDs have tunable optical properties and band-gaps depending on the particle size. But QD materials widely used for QDSC have some disadvantages of toxicity and scarcity. On the other hand, Si as one of good QD materials is abundant and not toxic. Also, Si QD has high stability against light soaking and a high optical absorption coefficient due to quantum size effects. However, the research on Si QD is rare although the quantum effect of Si was already verified. It is one of reasons that the fabrication and collection of Si nano-particles are too difficult. Therefore, this work proposed multi-hollow plasma discharge chemical vapor deposition (CVD). It is possible to collect Si particles unlike conventional CVD and solve the problems of the wet process. The optical properties of Si particles were controlled by varying experimental conditions. In this work, Si particles were fabricated with various sizes and their characteristics were analyzed. Based on the results, Si QD was applied to Si QDSC.

Effect of Nitridation of Si Nanoparticles on the Performance of Quantum-Dot Sensitized Solar Cells

We developed Si quantum-dot (QD) sensitized solar cells using nitridated Si nanoparticle films. The Si/N content ratio of the Si nanoparticle films was combinatorially controlled in double multi-hollow discharge plasma chemical vapor deposition (CVD) process in a SiH4/H2 and N2 gas mixture. The short-circuit current density of Si QD sensitized solar cells increases by a factor of 1.3 with the nitridation of Si nanoparticles, and a high photon-to-current conversion efficiency of 40% was achieved at a short wavelength of 350 nm.