12 research outputs found
Hot Electron-Based Solid State TiO2|Ag Solar Cells
The present work reports a simple and direct sputtering deposition to form solid state TiO2|Ag independent plasmonic solar cells. The independent plasmonic solar cells are based on a Schottky barrier between two materials, TiO2 and Ag. The Ag functions as the absorber generating âhotâ electrons, as well as the contact for the solar cell. The Ag sputtering is performed for different durations, to form Ag nanoparticles with a wide size distribution on the surface of rough spray pyrolysis deposited TiO2. Incident photon to current efficiency (IPCE) measurements show photovoltaic activity below the TiO2 bandgap, which is caused by the silver nanoparticles that have a wide plasmonic band, leading to the generation of âhotâ electrons. X-ray photoelectron spectroscopy analysis supports the âhotâ electron injection mechanism by following the Ag plasmon band and detecting local photovoltages. The measurements show that electrons are formed in the Ag upon illumination and are injected into the TiO2, producing photovoltaic activity. JâV measurements show photocurrents up to 1.18 mA cmâ2 and photovoltages up to 430 mV are achieved, with overall efficiencies of 0.2%. This is, to our knowledge, the highest performance reported for such independent plasmonic solar cells
Preparation and Application of Electrodes in Capacitive Deionization (CDI): a State-of-Art Review
As a promising desalination technology, capacitive deionization (CDI) have shown practicality and cost-effectiveness in brackish water treatment. Developing more efficient electrode materials is the key to improving salt removal performance. This work reviewed current progress on electrode fabrication in application of CDI. Fundamental principal (e.g. EDL theory and adsorption isotherms) and process factors (e.g. pore distribution, potential, salt type and concentration) of CDI performance were presented first. It was then followed by in-depth discussion and comparison on properties and fabrication technique of different electrodes, including carbon aerogel, activated carbon, carbon nanotubes, graphene and ordered mesoporous carbon. Finally, polyaniline as conductive polymer and its potential application as CDI electrode-enhancing materials were also discussed
Quantum Efficiency and Bandgap Analysis for Combinatorial Photovoltaics: Sorting Activity of CuâO Compounds in All-Oxide Device Libraries
All-oxide-based photovoltaics (PVs)
encompass the potential for
extremely low cost solar cells, provided they can obtain an order
of magnitude improvement in their power conversion efficiencies. To
achieve this goal, we perform a combinatorial materials study of metal
oxide based light absorbers, charge transporters, junctions between
them, and PV devices. Here we report the development of a combinatorial
internal quantum efficiency (IQE) method. IQE measures the efficiency
associated with the charge separation and collection processes, and
thus is a proxy for PV activity of materials once placed into devices,
discarding optical properties that cause uncontrolled light harvesting.
The IQE is supported by high-throughput techniques for bandgap fitting,
composition analysis, and thickness mapping, which are also crucial
parameters for the combinatorial investigation cycle of photovoltaics.
As a model system we use a library of 169 solar cells with a varying
thickness of sprayed titanium dioxide (TiO<sub>2</sub>) as the window
layer, and covarying thickness and composition of binary compounds
of copper oxides (CuâO) as the light absorber, fabricated by
Pulsed Laser Deposition (PLD). The analysis on the combinatorial devices
shows the correlation between compositions and bandgap, and their
effect on PV activity within several device configurations. The analysis
suggests that the presence of Cu<sub>4</sub>O<sub>3</sub> plays a
significant role in the PV activity of binary CuâO compounds
Utilizing Pulsed Laser Deposition Lateral Inhomogeneity as a Tool in Combinatorial Material Science
Pulsed laser deposition (PLD) is
widely used in combinatorial material
science, as it enables rapid fabrication of different composite materials.
Nevertheless, this method was usually limited to small substrates,
since PLD deposition on large substrate areas results in severe lateral
inhomogeneity. A few technical solutions for this problem have been
suggested, including the use of different designs of masks, which
were meant to prevent inhomogeneity in the thickness, density, and
oxidation state of a layer, while only the composition is allowed
to be changed. In this study, a possible way to take advantage of
the large scale deposition inhomogeneity is demonstrated, choosing
an iron oxide PLD-deposited library with continuous compositional
spread (CCS) as a model system. An Fe<sub>2</sub>O<sub>3</sub>âNb<sub>2</sub>O<sub>5</sub> library was fabricated using PLD, without any
mask between the targets and the substrate. The library was measured
using high-throughput scanners for electrical, structural, and optical
properties. A decrease in electrical resistivity that is several orders
of magnitude lower than pure α-Fe<sub>2</sub>O<sub>3</sub> was
achieved at âŒ20% NbâO (measured at 47 and 267 °C)
but only at points that are distanced from the center of the PLD plasma
plume. Using hierarchical clustering analysis, we show that the PLD
inhomogeneity can be used as an additional degree of freedom, helping,
in this case, to achieve iron oxide with much lower resistivity
Electrochemistry and capacitive charging of porous electrodes in asymmetric multicomponent electrolytes
We present porous electrode theory for the general situation of electrolytes containing mixtures of mobile ions of arbitrary valencies and diffusion coefficients (mobilities). We focus on electrodes composed of primary particles that are porous themselves. The predominantly bimodal distribution of pores in the electrode consists of the interparticle or macroporosity outside the particles through which the ions are transported (transport pathways), and the intraparticle or micropores inside the particles, where electrostatic double layers (EDLs) are formed. Both types of pores are filled with electrolyte (solvent plus ions). For the micropores we make use of a novel modified-Donnan (mD) approach valid for strongly overlapped double layers. The mD-model extends the standard Donnan approach in two ways: (1) by including a Stern layer in between the electrical charge and the ions in the micropores, and (2) by including a chemical attraction energy for the ions to go from the macropores into the micropores. This is the first paper where the mD-model is used to model ion transport and electrochemical reactions in a porous electrode. Furthermore we investigate the influence of the charge transfer kinetics on the chemical charge in the electrode, i.e., a contribution to the electrode charge of an origin different from that stemming from the Faradaic reaction itself, e.g. originating from carboxylic acid surface groups as found in activated carbon electrodes. We show that the chemical charge depends on the current via a shift in local pH, i.e. âcurrent-induced charge regulation.â We present results of an example calculation where a divalent cation is reduced to a monovalent ion which electro-diffuses out of the electrode.National Science Foundation (U.S.) (NSF Contract No. DMS 0948071)Massachusetts Institute of Technology. Energy Initiative (Seed grant