Van-Duong Dao

Dry plasma reduction to synthesize supported platinum nanoparticles for flexible dye-sensitized solar cells

A dye-sensitized solar cell (DSC) can be a promising device as a ubiquitous power source, if it is flexible. Since the annealing step of TiO2 nanoparticles (NPs) is a major obstacle to using a thermoplastic film as a transparent photoanode (PA), a transparent counter electrode (CE) using a thermoplastic film as a photo illumination window can be a reasonable alternative for developing a flexible DSC together with a non-transparent PA using a flexible metal foil coated with TiO2 NPs. To achieve this purpose together with improving photo conversion efficiency, it is necessary to deposit highly active supported platinum (Pt) NPs with homogeneous size dispersity on the surface of a transparent conducting oxide (TCO). Various methods developed so far, however, have critical process restrictions such as high temperature, low pressure, liquid environment, and chemical toxicity, which render them difficult to develop into an economic continuous process. Here we report an excellent method of directly depositing Pt-NPs on the surface of a TCO using dry plasma reduction (DPR) under atmospheric pressure without using any toxic chemicals while keeping the temperature below 70 °C. After determining an optimum concentration of Pt precursor solution to maximize the photovoltaic performance of DSCs, we successfully demonstrate a new flexible DSC which is composed of a non-transparent PA using thin Ti foil coated with TiO2 NPs and a transparent CE, as a photo illumination window, using Pt-NPs supported on a PET/ITO film.

Pt nanoparticles immobilized on CVD-grown graphene as a transparent counter electrode material for dye-sensitized solar cells.

The dye-sensitized solar cell (DSC) has attracted considerable attention as a next-generation solar cell because of its many virtues such as low fabrication cost, environmentally benign process, glossy transparency, and relatively high energy conversion efficiency. One of the issues with DSCs is the need to improve the transfer of electrons into the redox system to activate electrolyte reduction at the counter electrode (CE). Pt is traditionally the most popular material for the CE of DSCs, and numerous substitutes, such as carbon nanotubes (CNT), CNT–TiN, and CNT–Pt materials, have been developed to replace or reduce the amount of expensive Pt used. Owing to its unique 2D structure, large specific surface area, high electrical conductivity, and robust mechanical strength, graphene is known as one of the best supports for metal nanoparticles (NPs) for applications in energy conversion/storage devices. Graphene–metal composites have mostly been synthesized through either chemical or physical methods. However, extreme conditions such as high temperature, low pressure, a liquid environment, and chemical toxicity become drawbacks for the application of graphene–metal composites in large-scale production. Recently, we developed a new process for efficiently synthesizing supported PtNPs by using dry plasma reduction (DPR) near room temperature under atmospheric pressure. The aim of this technique was to overcome the previously mentioned process restrictions. Herein, we demonstrate the use of DPR to synthesize PtNPs on chemical vapor deposition (CVD)-grown graphene under atmospheric pressure, without using any toxic chemicals, near room temperature. The aim of this study was to develop transparent and efficient DSCs, which are crucial for realizing building-integrated photovoltaics (BIPVs), through synergistically combining the high transparency of CVD-grown graphene and the low charge-transfer resistance of supported PtNPs by using methods that keep the production cost low. The synthesis of Pt NPs hybridized on CVD-grown graphene was achieved by using DPR, as shown in Scheme 1. First, a drop of precursor solution was loaded on the substrate, followed by complete drying of the solvent at 70 8C for 10 min. During this drying process, H2PtCl6.xH2O was partially reduced

Pt-NP–MWNT nanohybrid as a robust and low-cost counter electrode material for dye-sensitized solar cells

Pt-NPs hybridized inside and outside multi-walled carbon nanotubes (MWNTs) were successfully synthesized using a liquid plasma system with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide under atmospheric pressure. The Pt-NPs with a size of 3–4 nm were stably and uniformly hybridized on both inner and outer surfaces of the MWNTs. The nanohybrid materials were applied to the counter electrode of dye-sensitized solar cells (DSCs). Electrochemical impedance measurement of DSCs revealed that the charge-transfer resistance of a MWNT–Pt nanohybrid-coated electrode was less than that of Pt-sputtered and MWNT-coated electrodes. Due to the low charge-transfer resistance, the DSC exhibited fairly improved energy conversion efficiency compared to the DSCs equipped with Pt-sputtered and MWNT-coated counter electrodes.

Pt Nanourchins as Efficient and Robust Counter Electrode Materials for Dye-Sensitized Solar Cells.

This study reports on the synthesis of Pt nanourchins (PtNUs) on FTO glass surfaces and their application as an efficient and robust counter electrode (CE) in dye-sensitized solar cells (DSCs). PtNUs with sizes in the range of 100-300 nm are successfully synthesized on FTO surfaces via a simple room temperature chemical reduction of H2PtCl6 using formic acid. Note that the PtNUs have numerous Pt nanowires with 2 nm diameters and 12 nm lengths. The PtNU CE exhibits very low charge-transfer resistance for DSCs. The efficiency of DSCs fabricated with PtNU CEs is 9.39%, which is higher than that of devices assembled with Pt-sputtered CEs (8.51%).

Dry plasma synthesis of a MWNT–Pt nanohybrid as an efficient and low-cost counter electrode material for dye-sensitized solar cells

Dry plasma reduction (DPR) is an excellent approach for easily and uniformly immobilizing many platinum nanoparticles (Pt-NPs) with a size of 2-3 nm on both inner and outer surfaces of MWNTs under atmospheric pressure and at near room temperature. The MWNT-Pt nanohybrid exhibits quite low charge transfer resistance for dye-sensitized solar cells.

Highly-Efficient Plasmon-Enhanced Dye-Sensitized Solar Cells Created by Means of Dry Plasma Reduction

Plasmon-assisted energy conversion is investigated in a comparative study of dye-sensitized solar cells (DSCs) equipped with photo-anodes, which are fabricated by forming gold (Au) and silver (Ag) nanoparticles (NPs) on an fluorine-doped tin oxide (FTO) glass surface by means of dry plasma reduction (DPR) and coating TiO2 paste onto the modified FTO glass through a screen printing method. As a result, the FTO/Ag-NPs/TiO2 photo-anode showed an enhancement of its photocurrent, whereas the FTO/Au-NPs/TiO2 photo-anode showed less photocurrent than even a standard photo-anode fabricated by simply coating TiO2 paste onto the modified FTO glass through screen printing. This result stems from the small size and high areal number density of Au-NPs on FTO glass, which prevent the incident light from reaching the TiO2 layer.

Ordered SnO nanoparticles in MWCNT as a functional host material for high-rate lithium-sulfur battery cathode

Lithium-sulfur battery has become one of the most promising candidates for next generation batteries, and it is still restricted due to the low sulfur conductivity, large volume expansion and severe polysulfide shuttling. Herein, we present a novel hybrid electrode with a ternary nanomaterial based on sulfur-impregnated multiwalled carbon nanotubes filled with ordered tin-monoxide nanoparticles (MWCNT-SnO/S). Using a dry plasma reduction method, a mechanically robust material is prepared as a cathode host material for lithium-sulfur batteries. The MWCNT-SnO/S electrode exhibits high conductivity, good ability to capture polysulfides, and small volume change during a repeated charge–discharge process. In situ transmission electron microscopy and ultraviolet–visible absorption results indicate that the MWCNT-SnO host efficiently suppresses volume expansion during lithiation and reduces polysulfide dissolution into the electrolyte. Furthermore, the ordered SnO nanoparticles in the MWCNTs facilitate fast ion/electron transfer during the redox reactions by acting as connective links between the walls of the MWCNTs. The MWCNT-SnO/S cathode with a high sulfur content of 70 wt.% exhibits an initial discharge capacity of 1,682.4 mAh·g–1 at 167.5 mA·g–1 (0.1 C rate) and retains a capacity of 530.1 mAh·g–1 at 0.5 C after 1,000 cycles with nearly 100% Coulombic efficiency. Furthermore, the electrode exhibits the high capacity even at a high current rate of 20 C.

Novel dithiols as capping ligands for CdSe quantum dots: optical properties and solar cell applications

Recently, organic ligands have been shown to play a significant role in optical and electronic properties of CdSe quantum dots and also in solar cell applications. We report organic dithiols as novel capping ligands for CdSe quantum dots (QDs). The organic dithiol compounds were designed in such a way that the two thiol groups of a dithiol (acts as a bidentate ligand) can bond directly to an inorganic CdSe QD surface which passivate effectively to show high optical efficiency by promoting interfacial charge transfer. This work would offer a direct and effective pathway to synthesize CdSe QDs that attaches dithiol ligands with aromatic functionality while maintaining the size and shape control of the CdSe QDs. The structure, crystallinity, and optical properties of the dithiol-capped CdSe QDs were analyzed by XRD, TEM, and photoluminescence. The covalent immobilization of dithiols onto CdSe QDs was confirmed by XPS, FT-IR, TGA, XRD and TEM characterizations. Further, the influence of dithiol-type capping ligands on the optical properties of highly luminescent CdSe QDs was investigated. It has been found that the growth rate and the photoluminescence intensity of CdSe QDs were strongly dependent on the type of dithiol ligands. We also experimentally investigated the use of dithiol-capped CdSe QDs in solar cells. The dithiol shell allows for the electron transport from the surface of the QDs, evidenced by better performance as CdSe QDs sensitized solar cells. The power conversion efficiency (η) of CdSe QDs reached up to 0.65%.

Efficiency enhancement of dye-sensitized solar cells by use of ZrO2-doped TiO2 nanofibers photoanode.

Due to the good stability and convenient optical properties, TiO2 nanostructures still the prominent photoanode materials in the Dye Sensitized Solar Cells (DSCs). However, the well-known low bandgap energy and weak adsorption affinity for the dye distinctly constrain the wide application. This work discusses the impact of Zr-doping and nanofibrous morphology on the performance and physicochemical properties of TiO2. Zr-doped TiO2 nanofibers (NFs), with various zirconia content (0, 0.5, 1, 1.5 and 2wt%) were prepared by calcination of electrospun mats composed of polyvinyl acetate, titanium isopropoxyl and zirconium n-propoxyl. For all formulations, the results have shown that the prepared materials are continuous, randomly oriented, and good morphology nanofibers. The average diameter decreased from 353.85nm to 210.78nm after calcination without a considerable influence on the nanofibrous structure regardless the zirconia content. XRD result shows that there is no Rutile nor Brookite phases in the obtained material and the average crystallite size of the sample is affected by the presence of Zr-doping and changed from 23.01nm to 37.63nm for TiO2 and Zr-doped TiO2, respectively. Optical studies have shown Zr-doped TiO2 NFs have more absorbance in the visible region than that of pristine TiO2 NFs; the maximum absorbance is corresponding to the NFs having 1wt% zirconia. The improved spectra of Zr-doped TiO2 in the visible region is attributed to the heterostructure composition resulting from Zr-doping. The absorption bandgaps were calculated using Tauc model as 3.202 and 3.217 for pristine and Zr (1wt%)-doped TiO2 NFs, respectively. Furthermore, in Dye-sensitized Solar Cells, utilizing Zr (1wt%)-doped TiO2 nanofibers achieved higher efficiency of 4.51% compared to the 1.61% obtained from the pristine TiO2 NFs.

Shape-controlled synthesis of PtPd alloys as a low-cost and efficient counter electrode for dye-sensitized solar cells

Dry plasma reduction is an excellent approach for easy synthesis of PtPd alloys with different sizes, shapes (nanoparticles, nanorods, microrods, etc.), and distributions on fluorine-doped tin oxide (FTO) substrates through simply controlling the volume ratio of the Pt and Pd precursor solution under atmospheric pressure near room temperature. Dye-sensitized solar cells (DSCs) utilizing a bimetallic Pt0.5Pd0.5 nanorod counter electrode exhibit better performance than those of DSCs fabricated with Pt and Pd electrodes. The obtained results establish a foundation for the use of PtPd alloy CEs as well as the economic utility of Pt in efficient and low-cost DSCs.