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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Influences of alcoholic solvents on spray pyrolysis deposition of TiO{sub 2} blocking layer films for solid-state dye-sensitized solar cells

Influences of alcoholic solvents for titanium diisopropoxide bis(acetylacetonate) (TPA) precursor solutions on the spray pyrolysis deposited TiO{sub 2} films and the photovoltaic performance of the solid-state dye-sensitized solar cells (SDSCs) using these TiO{sub 2} films as the blocking layers were investigated. Smooth TiO{sub 2} films were obtained by spray pyrolysis deposition of a TPA solution in isopropanol (IPA) at a relatively low temperature of 260 Degree-Sign C. On the other hand, when ethanol was used as solvent, the TiO{sub 2} films fabricated at the same temperature showed much rougher surfaces with many pinholes. Our results showed that ethanol reacts with TPA to form titanium diethoxide bis(acetylacetonate) (TEA), which requires a higher thermal decomposition temperature than that of TPA. SDSCs with TiO{sub 2} blocking layer films fabricated using a TPA solution in IPA showed higher power conversion efficiencies with smaller variations. - Graphical abstract: Alcoholic solvents used for the TiO{sub 2} precursor play a critical role in determining the surface morphology of blocking layers and thus the photovoltaic performance of the SDSCs. Highlights: Black-Right-Pointing-Pointer Solvent influences morphology of spray pyrolysis deposited TiO{sub 2} blocking layer. Black-Right-Pointing-Pointer Ethanol reacts with TPA, resulting poor quality of blocking layer. Black-Right-Pointing-Pointer Isopropanol is better than ethanol for obtaining smooth blocking layer. Black-Right-Pointing-Pointer SDSC with blocking layer made with isopropanol showed better performance.

36 MATERIALS SCIENCE↗
DOE OSTI2015

High performance dye-sensitized solar cells using graphene modified fluorine-doped tin oxide glass by Langmuir–Blodgett technique

Since the introduction of dye-sensitized solar cells (DSSCs) with low fabrication cost and high power conversion efficiency, extensive studies have been carried out to improve the charge transfer rate and performance of DSSCs. In this paper, we present DSSCs that use surface modified fluorine-doped tin oxide (FTO) substrates with reduced graphene oxide (r-GO) sheets prepared using the Langmuir–Blodgett (LB) technique to decrease the charge recombination at the TiO{sub 2}/FTO interface. R-GO sheets were excellently attached on FTO surface without physical deformations such as wrinkles; effects of the surface coverage of r-GO on the DSSC performance were also investigated. By using graphene modified FTO substrates, the resistance at the interface of TiO{sub 2}/FTO was reduced and the power conversion efficiency was increased to 8.44%. - Graphical abstract: DSSCs with graphene modified FTO glass were fabricated with the Langmuir Blodgett technique. GO sheets were transferred to FTO at various surface pressures in order to change the surface density of graphene and the highest power conversion efficiency of the DSSC was 8.44%. - Highlights: • By LB technique, r-GO sheets were coated on FTO without physical deformation. • DSSCs were fabricated with, r-GO modified FTO substrates. • With surface modification by r-GO, the interface resistance of DSSC decreased. • Maximum PCE of the DSSC was increased up to 8.44%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Morphology control of ZnO nanostructures for high efficient dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated based on different ZnO nanostructures with controllable morphologies synthesized via capping agent-assisted hydrothermal method. The capping agent hindered the growth along (001) direction, so the morphology evolved from rods to nanosheets with increasing the amounts of capping agents. The kinetics of the photoelectrochemical properties in DSSCs were also evaluated via electrochemical impedance spectroscopy with focusing on exploring the electron lifetime, electron diffusion coefficient and effective diffusion length of the cells in a quantitative manner based on an equivalent circuit model. The physical properties, such as specific surface area, photoluminescence and ultraviolet–vis diffuse reflectance spectra (DRS), were also extensively characterized in detail. DSSCs fabricated with ZnO nanosheets/rod hierarchical structures as photoanodes showed significantly improved photovoltaic performance with open-circuit voltage increasing from 0.45 V to 0.73 V, as well as the overall conversion efficiency 5.69 times better than that of ZnO rod. It was attributed to higher surface area (21.96 m{sup 2}·g{sup −1}) and more efficient light absorption, as well as more efficient electron transfer process. - Highlights: • Controlled morphologies from rods to nanosheets were manipulated by hydrothermal method. • Different ZnO morphologies based DSSCs were investigated by IV and EIS with forward biases. • DSSCs based on nano hierarchical structures yield 5.67 times higher of power conversion efficiency than that of rods.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Enhancement of the efficiency of dye-sensitized solar cell with multi-wall carbon nanotubes/polypyrrole composite counter electrodes prepared by electrophoresis/electrochemical polymerization

Graphical abstract: The overall energy conversion efficiency of the DSSC employing the MWCNT/PPy CE reached 3.78%. Compared with a reference DSSC using single MWCNT film CE with efficiency of 2.68%, the energy conversion efficiency was increased by 41.04%. Highlights: ► MWCNT/PPy composite film prepared by electrodeposition layer by layer was used as counter electrode in DSSC. ► The overall energy conversion efficiency of the DSSC was 3.78% by employing the composite film. ► The energy conversion efficiency increased by 41.04% compared with efficiency of 2.68% by using the single MWCNT film. ► We analyzed the mechanism and influence factor of electron transfer in the composite electrode by EIS. - Abstract: For the purpose of replacing the precious Pt counter electrode in dye-sensitized solar cells (DSSCs) with higher energy conversion efficiency, multi-wall carbon nanotube (MWCNT)/polypyrrole (PPy) double layers film counter electrode (CE) was fabricated by electrophoresis and cyclic voltammetry (CV) layer by layer. Atom force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscope (TEM) demonstrated the morphologies of the composite electrode and Raman spectroscopy verified the PPy had come into being. The overall energy conversion efficiency of the DSSC employing the MWCNT/PPy CE reached 3.78%. Compared with a reference DSSC using single MWCNT film CE with efficiency of 2.68%, the energy conversion efficiency was increased by 41.04%. The result of impedance showed that the charge transfer resistance R{sub ct} of the MWCNT/PPy CE had the lowest value compared to that of MWCNT or PPy electrode. These results indicate that the composite film with high conductivity, high active surface area, and good catalytic properties for I{sub 3}{sup −} reduction can potentially be used as the CE in a high-performance DSSC.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effects of hydrochloric acid treatment of TiO{sub 2} nanoparticles/nanofibers bilayer film on the photovoltaic properties of dye-sensitized solar cells

Highlights: ► The TiO{sub 2} nanoparticles/TiO{sub 2} nanofibers bilayer film was fabricated for DSSC. ► The effects of HCl treated TiO{sub 2} on the performance of DSSC were investigated. ► The potential methods of improving conversion efficiency are suggested. - Abstract: The TiO{sub 2} nanoparticles/nanofibers bilayer film has been fabricated via spin coating and electrospinning followed by calcination. The TiO{sub 2} bilayer film with thickness of about 6.0 μm is composed of anatase TiO{sub 2} phase. Dye-sensitized solar cells (DSSC) were assembled by hydrochloric acid (HCl) treated TiO{sub 2} film. The results of the photocurrent action spectra, electrochemical impedance spectroscopy (EIS), and I–V curves showed that each photovoltaic parameter of DSSC increased with the concentration of HCl increasing, and reached a maximum value and afterwards decreased. The maximum incident monochromatic photo-to-electron conversion efficiency (at 350 nm) and maximum overall conversion efficiency (η) of 0.05 M HCl treated TiO{sub 2} based DSSC were enhanced to 48.0% and 4.75%, which were respectively increased by 14% and 6.3% than those of DSSC based on untreated TiO{sub 2} film.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Highly efficient dye-sensitized solar cell with GNS/MWCNT/PANI as a counter electrode

Highlights: • High-performance PANI/MWCNT-CE was incorporated in a Pt-CE in DSSCs. • GNS/MWCNT/PANI-CE exhibits a high power conversion efficiency (PCE) of 7.52%. • GNS/MWCNT/PANI composite has a high catalytic activity for the reduction of I{sub 3}{sup −}. • GNS/MWCNT/PANI composite has a low R{sub CT} on the electrolyte/CE interface. - Abstract: A graphene-based nanosheet composite/multiwalled carbon nanotube/polyaniline (GNS/MWCNT/PANI) was synthesized via an in situ polymerization technique and applied by the spin-coating method as a counter electrode (CE) in dye-sensitized solar cells (DSSCs). The combination of the high catalytic activity of PANI and outstanding conductivity of GNS/MWCNT improved the photovoltaic performance of the hybrid CE. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that the GNS/MWCNT/PANI composite has high catalytic activity for the reduction of triiodide to iodide and low charge-transfer resistance at the electrolyte/electrode interface. Transmission electron microscopy (TEM) images showed that the GNS/MWCNT/PANI-CE has a rough and porous structure and X-ray diffraction analysis confirmed the formation of PANI coating on the surface of the GNS/CNT. In particular, current–voltage measurements showed the superior power conversion efficiency (PCE) of 7.52% of the DSSC based on GNS/MWCNT/PANI-CE compared to the PCE of 6.69% of the DSSC based on Pt-CE.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Light scattering management of dye-sensitized solar cells based on double-layered photoanodes aided by uniform TiO{sub 2} aggregates

Highlights: • A new architecture of double-layered TiO{sub 2} electrodes is presented. • The electrode contains two alternate layers of TiO{sub 2} nanoparticles and aggregates. • The aggregates layers are deposited onto the nanocrystalline layer. • The new design showed improved efficiency compared to conventional cells. - Abstract: This study presents a new double-layered TiO{sub 2} film containing a nanocrystalline under-layer and a uniform, sponge-like light scattering over-layer for dye-sensitized solar cells (DSCs) application. The over-layer is composed of 2-μm-diameter uniform aggregates, containing small nanoparticles with the average grain size of 20 nm. X-ray diffraction reveals that the light scattering layer has a mixture of anatase and rutile phases, whereas the nanocrystalline layer has a pure anatase phase. Ultraviolet–visible (UV–vis) spectra show that the light scattering layer has lower band gap energy than the nanocrystalline under-layer, extending the absorption of TiO{sub 2} into visible region. Diffuse reflectance spectroscopy demonstrates that the double-layered electrode enjoyed better light scattering ability. The double-layered DSC shows the highest power conversion efficiency of 7.69% and incident photon-to-current efficiency of 88% as a result of higher light harvesting and less recombination which is demonstrated by electrochemical impedance spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Improvement on the catalytic activity of the flexible PEDOT counter electrode in dye-sensitized solar cells

Highlights: • The catalytic activity of PEDOT electrode can be tuned by varying deposited time. • A highly effective Pt/PEDOT electrode was also prepared. • The DSSCs using Pt/PEDOT counter electrode shows high efficiency of 7.90%. - Abstract: A flexible Poly (3, 4-ethylenedioxythiophene) (PEDOT) electrode on indium-doped tin oxide coated polyethylene naphthalate (ITO-PEN) substrate is prepared by electrochemical methods for dye-sensitized solar cells (DSSCs) as counter electrode. The impact of deposition time on the catalytic activities of the flexible PEDOT electrode towards the iodide redox couple has been investigated by cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and Tafel polarization curve measurements. After optimization, the DSSCs using PEDOT counter electrode deposited 80 s shows power conversion efficiency (PCE) of 7.18%, close to than the Pt counter electrode based counterpart (7.56%). To further improve the catalytic activity of PEDOT, Pt/PDEOT composite catalyst is synthesized. And the DSSCs with the Pt/PDEOT composite CE generates a high PCE of 7.90%.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Acid-free approach towards the growth of vertically aligned TiO2 nanorods as an efficient photoanode for dye-sensitized solar cells

Highlights: • Vertically aligned TiO{sub 2} NRs are fabricated by an acid-free hydrothermal approach. • Study the effect of TiO{sub 2} NRs growth parameters on its structural/optical properties. • The optimized TiO{sub 2} NRs were employed as an efficient photoanode for DSSCs. • An optimal PCE of 2.45% was achived by DSSC with TiO{sub 2} NRs with heights of ∼1.56 μm. - Abstract: We synthesized the closely packed titanium dioxide nanorods (TiO{sub 2} NRs) on fluorine-doped tin oxide (FTO) glass by a facile and cost-effective hydrothermal method. The TiO{sub 2} NRs were further utilized as a photoanode for dye-sensitized solar cells (DSSCs). For hydrothermal growth of TiO{sub 2} NRs, we utilized an acid-free reaction medium instead of a strong acidic medium, which can reduce the equipment cost as well as the environmental damages. Before employing these TiO{sub 2} NRs for DSSCs as a photoanode, the effects of hydrothermal growth parameters on the structural and optical characteristics of TiO{sub 2} NRs/FTO glass were investigated. Eventually, the TiO{sub 2} NRs with optimized height and diameter were employed to DSSCs and their photovoltaic characteristics were examined.

14 SOLAR ENERGY↗
DOE OSTI2018

Enhancing the efficiency of quasi-solid-state dye-sensitized solar cells by adding bis(trifluoromethane)sulfonimide lithium salt and camphorsulfonic acid to gel-based electrolytes

Highlights: • Bis(trifluoromethane)sulfonimide lithium salt and camphorsulfonic acid were added to the gel-based electrolytes for DSSCs. • Lithium salt and camphorsulfonic acid can enhance the conductivity of the electrolytes. • Adding lithium salt and camphorsulfonic acid to the gel-based electrolytes effectively enhanced the DSSC efficiency. • The DSSC devices with the gel-based electrolytes exhibited a longer stability. - Abstract: In this study, gel-based electrolytes were produced by mixing a liquid-based electrolyte with poly(methyl methacrylate) (PMMA), which served as a gelator to enhance the stability of the electrolytes and dye-sensitized solar cells (DSSCs). Furthermore, bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and camphorsulfonic acid (C{sub 10}H{sub 16}O{sub 4}S) were separately added to the gel-based electrolytes. The results indicate that adding LiTFSI and C{sub 10}H{sub 16}O{sub 4}S to the gel-based electrolytes effectively enhanced the device efficiency. In particular, the device with the 1:1 + 0.1 M LiTFSI gel-based electrolyte exhibited the optimal efficiency (7.33%), which was higher than that observed in the device with the liquid-based electrolyte. The results also proved that the DSSC devices with the gel-based electrolytes exhibited a longer stability. Therefore, using optimized gel-based electrolytes can enhance the power conversion efficiency and stability of DSSC devices.

14 SOLAR ENERGY↗
DOE OSTI2018

The dye-sensitized solar cells based on the interconnected ternary cobalt diindium sulfide nanosheet array counter electrode

Highlights: • The ternary CoIn{sub 2}S{sub 4} CE was fabricated by in situ solvothermal synthesis. • The CoIn{sub 2}S{sub 4} CE displays an interconnected nanosheet array structure. • The solvent and In{sub 2.77}S{sub 4} intermediate play key roles on the formation of CoIn{sub 2}S{sub 4}. • DSSC based on the CoIn{sub 2}S{sub 4} CE gives an efficiency of 8.83%. - Abstract: The ternary cobalt diindium sulfide (CoIn{sub 2}S{sub 4}) counter electrode (CE) with interconnected nanosheet array structure is fabricated on the fluorine-doped tin oxide (FTO) substrate by in situ ethanol solvothermal synthesis. The ethanol solvent and In{sub 2.77}S{sub 4} intermediate play important roles on the formation of the interconnected nanosheet array structure. The dye-sensitized solar cell (DSSC) with the optimized ternary CoIn{sub 2}S{sub 4} CE gives an energy conversion efficiency of 8.83%, which is much higher than that of DSSCs based on the binary CoS{sub 2} (6.47%), and In{sub 2.77}S{sub 4} (0.46%) CEs and can be comparable with that of Pt CE (8.19%) under full sunlight illumination (100 mW cm{sup −2}, AM 1.5 G). Except for the intrinsically electrocatalytic activity from the CoIn{sub 2}S{sub 4}, the higher conversion efficiency of CoIn{sub 2}S{sub 4} based DSSC can be attributed to that the interconnected nanosheet array structure provides plentiful catalytic active sites, abundant electron transport channels, and fast electrolyte diffusion.

14 SOLAR ENERGY↗
DOE OSTI2022

Enhanced ZIF-8-enabled colorimetric CO 2 sensing through dye-precursor synthesis

The accumulation of carbon dioxide (CO 2 ) within enclosed spaces, along with volatile organic compounds, under certain humidity, temperature, and ventilation conditions is associated with detrimental human health symptoms such as fatigue. Color-based chemical sensing is a promising approach to detect CO 2 levels relevant to indoor air quality through producing fast, quantifiable output visible to the naked eye. In a prior work, a colorimetric gas sensor was fabricated through synthesizing the metal-organic framework, ZIF-8, as the adsorbent, followed by post-synthetic mixing with a dye, phenol red (PSP), and primary amine, ethylenediamine (ED). While this sensor (termed PSP-ED/ZIF-8) maintained its structural integrity in atmospheric conditions and exhibited an increasing fuchsia-to-yellow color change with increasing CO 2 levels in dry environment, the colorimetric response greatly suffered in the presence of humid CO 2 . Here in this work, a significantly improved colorimetric CO 2 sensor (referred to as ED/PSP:ZIF-8) is accomplished through directly incorporating phenol red in the ZIF-8 metal and linker precursor solutions and then blending with ethylenediamine. MATLAB-generated color distributions and in-situ ultraviolet-visible (UV-Vis) spectroscopic studies quantitatively demonstrate an enhanced colorimetric gas response of ED/PSP:ZIF-8 compared to that of PSP-ED/ZIF-8 across an important range of CO 2 for indoor air quality monitoring (500 – 3500 ppm) and across a range of humidity. The new sensor also exhibits high selectivity to CO 2 compared to select volatile organic compounds, such as acetone and ethanol, which contribute to human health symptoms experienced indoors. The enhanced performance is attributed to the proposed incorporation of phenol red within ZIF-8, while maintaining the chemical stability of the MOF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Crucial role of nuclear dynamics for electron injection in a dye–semiconductor complex

In this study, we investigate the electron injection from a terrylene-based chromophore to the TiO 2 semiconductor bridged by a recently proposed phenyl-amide-phenyl molecular rectifier. The mechanism of electron transfer is studied by means of quantum dynamics simulations using an extended Hückel Hamiltonian. It is found that the inclusion of the nuclear motion is necessary to observe the photoinduced electron transfer. In particular, the fluctuations of the dihedral angle between the terrylene and the phenyl ring modulate the localization and thus the electronic coupling between the donor and acceptor states involved in the injection process. The electron propagation shows characteristic oscillatory features that correlate with interatomic distance fluctuations in the bridge, which are associated with the vibrational modes driving the process. The understanding of such effects is important for the design of functional dyes with optimal injection and rectification properties.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Growth and Post-Deposition Treatments of SrTiO 3 Films for Dye-Sensitized Photoelectrosynthesis Cell Applications

Sensitized SrTiO 3 films were observed as potential photoanodes for dye-sensitized photoelectrosynthesis cells (DSPECs). The SrTiO 3 films were grown via pulsed laser deposition (PLD) on a transparent conducting oxide (fluorine-doped tin oxide, FTO) substrate, annealed, and then loaded with zinc(II) 5,10,15-tris(mesityl)-20-[(dihydroxyphosphoryl)phenyl] porphyrin (MPZnP). When paired with a platinum wire counter electrode and an Ag/AgCl reference electrode these sensitized films exhibited photocurrent densities on the order of 350 nA/cm 2 under 0 V applied bias conditions versus a normal hydrogen electrode (NHE) and 75 mW/cm 2 illumination at a wavelength of 445 nm. The conditions of the post-deposition annealing step—namely, a high-temperature reducing atmosphere—proved to be the most vital growth parameters for increasing photocurrent in these electrodes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Improving Light Harvesting in Dye-Sensitized Solar Cells Using Hybrid Bimetallic Nanostructures

In this paper, we demonstrate improved light trapping in dye-sensitized solar cells (DSSCs) with hybrid bimetallic gold core/silver shell nanostructures. Silica-coated bimetallic nanostructures (Au/Ag/SiO 2 NSs) integrated in the active layer of DSSCs resulted in 7.51% power conversion efficiency relative to 5.97% for reference DSSCs, giving rise to 26% enhancement in device performance. DSSC efficiencies were governed by the particle density of Au/Ag/SiO 2 NSs with best performing devices utilizing only 0.44 wt % of nanostructures. We performed transient absorption spectroscopy of DSSCs with variable concentrations of Au/Ag/SiO 2 NSs and observed an increase in amplitude and decrease in lifetime with increasing particle density relative to reference. Finally, we attributed this trend to plasmon resonant energy transfer and population of the singlet excited states of the sensitizer molecules at the optimum concentration of NSs promoting enhanced exciton generation and rapid charge transfer into TiO 2 .

14 SOLAR ENERGY↗
DOE OSTI2010

A note on the visualization of wetting film structures and a nonwetting immiscible fluid in a pore network micromodel using a solvatochromic dye

Nile Red is demonstrated as a single dye whose solvatochromism enables selective visualization of two immiscible liquid fluids in a micromodel containing a homogeneous array of pillars creating a porous network. Nile Red dissolves in and partitions between hexadecane as a nonwetting fluid and PEG200 as a hydrophilic fluid that wets the silicon oxide surfaces in the micromodel. Both the absorption spectra and fluorescence emission spectra are sensitive to the solvent environment, such that the two phases can be distinguished by the observed color or the fluorescence emission band. Bright field, hyperspectral, epifluorescence, and confocal fluorescence methods were used to image the micromodel after displacing PEG200 in the model with hexadecane. The use of Nile Red with these imaging methods facilitates visualization of phase identity at specific locations; the interfaces between the two immiscible liquid phases; wetting behavior of the wetting phase within the porous structure; and retention of the wetting phase as thin films around pillars and as bridges across the pore throats. The pillars and wetting phase bridges create a network of obstacles defining a tortuous preferential flow path for the nonwetting phase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Thermally exfoliated graphene based counter electrode for low cost dye sensitized solar cells

Graphene obtained from thermal exfoliation of graphite oxide are highly wrinkled and have large surface area. Their wrinkled nature is expected to give them excellent catalytic activity. Herein, we demonstrate the use of thermally exfoliated graphene (TEG) as cost effective electrocatalyst for the tri-iodide reduction in dye sensitized solar cells (DSSCs). X-ray diffraction, Raman and Infra red spectroscopy and electron microscopy studies confirm the defective and wrinkled nature of TEG. BET surface area measurement show a large surface area of {approx} 470 m{sup 2}/g. The counter electrode was fabricated by drop casting a slurry of TEG dispersed in a Nafion:Ethanol solution on fluorine doped tin oxide (FTO) substrates. The use of Nafion prevented film ''peel off,'' thus ensuring a good substrate adhesion. Electrochemical impedance spectroscopy reveals that TEG had a catalytic performance comparable to that of Pt, suggesting its use as counter electrode material. As expected, the DSSC fabricated with Nafion solubilized TEG/FTO as counter electrode shows an efficiency of about 2.8%, comparable to Pt counter electrode based DSSC which has an efficiency of about 3.4%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗