A5013763651- Quantum Dots Synthesis And Properties
- TiO2 Photocatalysis and Solar Cells
- Organic Electronics and Photovoltaics
- Perovskite Materials and Applications
- Conducting polymers and applications
- Advanced Photocatalysis Techniques
- Chalcogenide Semiconductor Thin Films
- Plasmonic and Surface Plasmon Research
- 2D Materials and Applications
- Photonic Crystals and Applications
- Nanowire Synthesis and Applications
- Gold and Silver Nanoparticles Synthesis and Applications
- Molecular Junctions and Nanostructures
- Electrochemical Analysis and Applications
- Thin-Film Transistor Technologies
- Photonic and Optical Devices
- Silicon Nanostructures and Photoluminescence
- Copper-based nanomaterials and applications
- Advanced MEMS and NEMS Technologies
- Silicon and Solar Cell Technologies
- Transition Metal Oxide Nanomaterials
- Strong Light-Matter Interactions
- Carbon Nanotubes in Composites
- Semiconductor materials and interfaces
- Liquid Crystal Research Advancements
University of Colorado Boulder
2012-2024
National Renewable Energy Laboratory
2014-2024
École Polytechnique Fédérale de Lausanne
2005
University of Reading
2000-2004
Eneos (Japan)
2003
American University of Beirut
2003
Utrecht University
1996-2002
Ghent University
1999
Crack-free nanocrystalline rutile TiO2 films with thicknesses of up to 12 μm were prepared and characterized in connection their application dye-sensitized solar cells. The photoelectrochemical properties the rutile-based cell are compared those anatase-based cell. Scanning electron microscopy (SEM) shows that consist homogeneously distributed rod-shaped particles an average dimension 20 × 80 nm. Both thickness morphology have a strong influence on Measurements incident monochromatic...
The role of electrical potential, charge transport, and recombination in determining the photopotential photocurrent conversion efficiency (IPCE) dye-sensitized nanocrystalline solar cells was studied. Electrostatic arguments impedance spectroscopy (EIS) are used to obtain information on electrochemical potential distribution cell. It is shown that macroscopic level, no significant drop exists within porous TiO2 when it contacts electrolyte at transparent conducting oxide substrate...
The light harvesting efficiency of dye-sensitized photoelectrodes was enhanced by coupling a TiO(2) photonic crystal layer to conventional film nanoparticles. In addition acting as dielectric mirror, the inverse opal caused significant change in dye absorbance which depended on position stop band. Absorbance suppressed at wavelengths shorter than band maximum and longer wavelengths. This effect arises from slow group velocity vicinity band, consequent localization intensity voids (to blue)...
Plasmon-active silver nanoparticle layers were included in solution-processed bulk-heterojunction solar cells. Nanoparticle fabricated using vapor-phase deposition on indium tin oxide electrodes. Owing to the increase optical electrical field inside photoactive layer, inclusion of such particle films lead increased absorption and consequently photoconversion at solar-conversion relevant wavelengths. The resulting energy conversion efficiency for a bulk heterojunction photovoltaic device...
Percolation theory is applied to understand the influence of network geometry on electron transport dynamics in dye-sensitized nanocrystalline TiO2 solar cells, and predicted results are compared with those measured by transient photocurrent. The porosity films was varied experimentally from 52 71%. Electron modeled using simulated mesoporous films, consisting a random nanoparticle network, random-walk approach. pathway through correlated film coordination numbers particles film....
A random-walk approach is developed to model the electron-transport dynamics in dye-sensitized TiO2 solar cells within a multiple-trapping framework, and predicted results are compared with those measured by transient photocurrent. The illumination geometry wavelength of probe light used create certain initial spatial distributions photoinjected electrons films. Both have dramatic effect on shape photocurrent transient. Cells probed incident from either collecting (substrate) electrode side...
Improving costs and scale reflect looming opportunities
The effect of lithium intercalation on the transport dynamics and recombination kinetics in dye-sensitized nanoparticle TiO2 solar cells at levels below 5 atom % was investigated by photocurrent photovoltage transient spectroelectrochemical techniques. Titanium dioxide films were doped electrochemically dark under illumination. It discovered that when Li+ is present electrolyte, intercalates irreversibly into open circuit (ca. −0.7 V) normal light intensities. Photocurrent transients...
We report two viable organic excitonic solar cell structures where the conventional In2O3:Sn (ITO) hole-collecting electrode was replaced by a thin single-walled carbon nanotube layer. The first structure includes poly(3,4-ethylenedioxythiophene) (PEDOT) and gave nonoptimized device efficiency of 1.5%. second did not use PEDOT as hole selective contact had an 0.47%. strong rectifying behavior shows that nanotubes are for holes efficient recombination sites. reported cell, produced without...
Organometal–halide perovskite solar cells have greatly improved in just a few years to power conversion efficiency exceeding 20%. This technology shows unprecedented promise for terawatt-scale deployment of energy because its low-cost, solution-based processing and earth-abundant materials. We studied charge separation transport cells—which are the fundamental mechanisms device operation critical factors output—by determining junction structure across using nanoelectrical characterization...
The structure and photoelectrochemical properties of TiO2 films deposited onto SnO2 conducting glass from the ambient hydrolysis TiCl4 annealed at temperatures ranging 100 to 500 °C were studied by Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), intensity-modulated photovoltage spectroscopy (IMVS), photocurrent (IMPS) measurements. Analysis XRD spectra shows that TiCl4-produced have rutile structure, regardless annealing temperature. TEM reveals consist...
We report transient photocurrent measurements on solar cell structures based dye-sensitized, porous TiO2 films filled with a liquid electrolyte. The are interpreted as ambipolar diffusion; under most measurement conditions, the diffusion coefficient is dominated by electrons diffusing in matrix. strong dependence of upon photoexcitation density, has been proposed previously. coefficients vary from 10-8 cm2 s-1 at low density to 10-4 for densities 1018 cm-3. At specified measured using weak...
The mechanism by which the adsorbent chenodeoxycholate, cografted with a sensitizer onto TiO2 nanocrystals, alters open-circuit photovoltage and short-circuit current of dye-sensitized solar cells was investigated. influence tetrabutylammonium chenodeoxycholate on dye loading studied under variety conditions in films were exposed to sensitizing coadsorbent. Photocurrent−voltage measurements combined desorption studies revealed that adding reduces as much 60% while having relatively small...
Analytical expressions describing electron transport in dye-sensitized nanocrystalline TiO2 solar cells are derived and verified by intensity-modulated photocurrent spectroscopy measurements. An exponential distribution of surface states can account for the observed power law dependence electron-transport rate on population. Use an effective diffusion coefficient to describe kinetics is found be inadequate. A slope 69 meV inferred surface-state curve.
The dependence of the electron diffusion coefficient and photoinduced density on internal surface area TiO2 nanoparticle films in dye-sensitized solar cells was investigated by photocurrent transient measurements. varied altering average particle size films. traps is found to change direct proportion with area, indicating that are located predominately at particles instead bulk or interparticle grain boundaries. observed scaling suggests limit transport These results address a long-standing...
Using X-ray and ultraviolet photoelectron spectroscopy, the surface band positions of solution-processed CH3NH3PbI3 perovskite thin films deposited on an insulating substrate (Al2O3), various n-type (TiO2, ZrO2, ZnO, F:SnO2 (FTO)) substrates, p-type (PEDOT:PSS, NiO, Cu2O) substrates are studied. Many-body GW calculations valence density states, with spin–orbit interactions included, show a clear correspondence our experimental spectra used to confirm assignment maximum. These...
The dependence of the electron transport and recombination dynamics on internal surface area mesoporous nanocrystalline TiO2 films in dye-sensitized solar cells was investigated. varied by altering average particle size films. scaling photoelectron density diffusion coefficient at short circuit with confirms results a recent study (Kopidakis, N.; Neale, N. R.; Zhu, K.; van de Lagemaat, J.; Frank, A. J. Appl. Phys. Lett. 2005, 87, 202106) that transport-limiting traps are located...
Here, we examine grain boundaries (GBs) with respect to non-GB regions (grain surfaces (GSs) and interiors (GIs)) in high-quality micrometer-sized perovskite CH3NH3PbI3 (or MAPbI3) thin films using high-resolution confocal fluorescence-lifetime imaging microscopy conjunction kinetic modeling of charge-transport recombination processes. We show that, contrary previous studies, GBs our MAPbI3 do not lead increased but that these happens primarily the (i.e., GSs or GIs). also find are...
Abstract Networks made of single‐walled carbon nanotubes (SWNTs) and metallic nanowire networks, graphene, ultra‐thin metal films have all been proposed as replacements for transparent conducting oxides (TCOs) in photovoltaic other applications. However, only limited comparisons nanostructured networks TCOs are available. Several common figures merit that often used to compare the electrical optical performance contacts evaluated here, merits each method comparison discussed. Calculating...
We demonstrate a facile solvothermal approach for growing mixed halide perovskite CH<sub>3</sub>NH<sub>3</sub>Pb(Br<sub>1−x</sub>Cl<sub>x</sub>)<sub>3</sub>single crystals.
We use a high signal-to-noise X-ray photoelectron spectrum of bulk PbS, GW calculations, and model assuming parabolic bands to unravel the various ultraviolet spectral features PbS as well determine how best analyze valence band region quantum dot (QD) films. spectroscopy (XPS UPS) are commonly used probe difference between Fermi level maximum (VBM) for crystalline thin-film semiconductors. However, we find that when standard XPS/UPS analysis is results often unrealistic due low density...
We report on the effects of replacing both In2O3:Sn (ITO) and hole transport layer (HTL) in organic photovoltaic (OPV) cells with single-walled carbon nanotube (SWNT) network transparent electrodes. have produced an OPV device without HTL exhibiting NREL-certified efficiency 2.65% a short-circuit current density 11.2 mA/cm2. Our results demonstrate that SWNT networks can be used to replace ITO efficient devices serves distinctly different roles ITO- SWNT-based devices.