Energy Conversion Properties Research Articles

Synthesis of PEDOT-modified graphene composite materials as flexible electrodes for energy storage and conversion applications

In this study, poly(3,4-ethylenedioxythiophene) (PEDOT)-modified graphene composite materials have been shown to exhibit excellent energy storage and conversion properties. Flexible, conducting and porous carbon cloth (CC) and graphene paper (GP)-modified CC (GP/CC) were used as substrates for comparison in all experiments. PEDOT was electrodeposited on these substrates, and their capacitance properties were measured for supercapacitor applications. Furthermore, the adsorption of size-selected Pt colloidal nanoparticles has also been performed using two substrates to form the electrode materials for fuel cell applications. We found that the PEDOT/GP/CC is the excellent flexible electrode material for both supercapacitors and fuel cells.

Preparation of 0.90Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub>-0.10BaTiO<sub>3</sub> Ferroelectric Thin Film and its Application in Pyroelectric Energy Harvesting

Ferroelectric0.90Bi0.5Na0.5TiO3-0.10BaTiO3(0.90BNT-0.10BT) thin film with single perovskite phase is prepared using an improved sol-gel spin coating method onto indium-tin-oxide (ITO) glass substrates. A new solution process is developed for the preparation of precursor solution which is stable in air, presenting a low gelation and trend to the formation of precipitates. The as-prepared thin film is crystallized into single perovskite phase and has good ferroelectric properties. It is remarkable that the thin films show excellent heat-to-electrical energy conversion properties. The results of this work for the first time demonstrate the feasibility of using lead-free BNT-BT films for pyroelectric energy harvesting.

Incorporating a stable fluorenone unit into D–A–π–A organic dyes for dye-sensitized solar cells

Two new organic dyes based on a donor–acceptor–π–bridge–acceptor/anchor (D–A–π–A) configuration, HIQF1 and HIQF2, were synthesized, characterized, and successfully employed in dye-sensitized solar cells. The incorporation of the weakly electron-withdrawing fluorenone group as an additional acceptor enhanced the dyes' properties for solar energy conversion in several ways. First, the absorption spectra of the dyes were broadened, covering a large range of sunlight. Second, the absorption spectra observed upon dye adsorption on TiO2 were only slightly blue-shifted as compared to the spectra of the dyes in solution. Third, the orbital energy levels and electron distributions of the D–A–π–A backbone were ideal for highly efficient electron transport and injection. The incorporation of long electron-donating alkoxy groups in the donor unit of HIQF1 further increased the dye's short-circuit photocurrent density (Jsc), open-circuit voltage (Voc), and overall conversion efficiency (η), but had little negative effect on the fill factor (FF). Solar cells sensitized with HIQF1 showed excellent current–voltage characteristics; the Jsc, Voc, and FF values were 12.26 mA cm−2, 0.70 V, and 0.73, corresponding to a η value of 6.26%.

Analysis of the operation of thin nanowire photoelectrodes for solar energy conversion

The solar energy conversion properties of thin Si and GaP nanowire photoelectrodes in photoelectrochemical cells have been examined through sets of finite-element simulations. A discussion describing the motivation behind nanostructured, high aspect ratio semiconductor photoelectrode designs and a brief survey of current experimental results reported for nanostructured semiconductor photoelectrodes in photoelectrochemical cells are presented first. An analysis is then shown that outlines the primary recombination pathways governing the steady-state current-potential behaviors of thin, cylindrical nanowire photoelectrodes, with explicit expressions detailing the differences between planar and cylindrical photoelectrodes arising from the solution of carrier fluxes in planar and cylindrical geometries. Results from finite-element simulations used to model the key features of thin nanowire photoelectrodes under low-level injection conditions are shown that illustrate which recombination pathway(s) is operative under various experimental conditions. Specifically, the respective effects of non-uniform doping, tapering along the length, variation in charge carrier mobilities and lifetimes, changes in nanowire radius, and changes in the density of surface defects on the observable photocurrent-potential responses are reported. These cumulative results serve as guides for future experimental work aimed at improving the attainable solar energy conversion efficiencies of doped semiconductor nanowire photoelectrodes. Lastly, separate simulations that model lightly doped nanowire photoelectrodes under high-level injection conditions are discussed. These results suggest discrete, ohmic-selective contacts may afford a way to circumvent the stringent doping requirements discussed herein for thin nanowire photoelectrodes.

Efficient n-GaAs Photoelectrodes Grown by Close-Spaced Vapor Transport from a Solid Source

n-GaAs films were grown epitaxially on n(+)-GaAs substrates by a close-spaced vapor transport method and their photoelectrochemical energy conversion properties studied. Under 100 mW cm(-2) of ELH solar simulation, conversion efficiencies up to 9.3% for CSVT n-GaAs photoanodes were measured in an unoptimized ferrocene/ferrocenium test cell. This value was significantly higher than the 5.7% measured for similarly doped commercial n-GaAs wafers. Spectral response experiments showed that the higher performance of CSVT n-GaAs films relative to the commercial wafers was due to longer minority carrier diffusion lengths (L(D)), up to 1,020 nm in the CSVT films compared to 260 nm in the commercial n-GaAs wafers. Routes to improve the performance of CSVT GaAs and the implications of these results for the development of scalable GaAs-based solar energy conversion devices are discussed.

De novodesign of molecular wires with optimal properties for solar energy conversion

The area of organic photovoltaic materials has elicited great interest in both the scientific and technological communities due to its potential to deliver cheap and highly efficient solar cells [1]. To date, however, such so-called molecular wires have typically yielded energy conversion efficiencies of only ~5-6% despite a theoretical maximum of 13% [2]. We present an approach that uses a genetic algorithm to search the space of synthetically accessible molecular wires for those with optimal electronic structures. This approach combines both cheminformatics (SMILES to 3D using OpenBabel) and computational chemistry (semi-empirical calculations using Gaussian09). Using this method, we have found hundreds of candidates with predicted efficiencies over 8% including many with efficiencies over 10%.

Highly Efficient Photoinduced Electron Transfer in a Novel Tetrakis(tetraphenylporphyrinatozinc)/Perylenetetracarboxidiimide Array and Its Application to a Photovoltaic Device

Abstract A novel donor–acceptor array consisting of four 5-(p-substituted phenyl)-10,15,20-triphenylporphyrinatozinc (POR) complexes attached to the 1,6,7,12-positions of perylene-3,4:9,10-tetracarboxidiimide (PDI) was synthesized and characterized. HOMO and LUMO values of the array were aquired by cyclic voltammetry. Photophysical properties were studied by steady-state UV–vis and fluorescence spectroscopy. The results showed that this compound absorbs strongly from 300 to 700 nm, making it an ideal system to harvest polychromatic light. After selective excitation of the POR moiety or PDI moiety, an almost complete fluorescence quenching was observed, indicating that highly efficient photoinduced electron transfer occurs in this array. The predominant quenching process for PDI–POR4 array is electron-transfer yielding POR4+–PDI−. The self-assemblies of this molecular in polar and nonpolar solvents were investigated. Intermolecular π–π interaction in cooperation with the van der Waals interaction between POR and PDI component leads to the formation of spherical nanoparticles and ribbon-like morphological structures in methanol and n-hexane, respectively. Photoelectrochemical studies exhibited prompt and steady photocurrent photovoltage response. Moreover, photovoltaic measurement on this array reveals efficient light energy conversion properties, such as a fill factor of 0.42. These results are of particular relevance for photovoltaic nanodevices and solar energy conversion applications.

Optical and thermal optimization of stationary non-evacuated CPC solar concentrator with fully illuminated wedge receivers

Stationary low concentrator collectors ( C < 2), of the CPC type, are of great interest for thermal energy supply of industrial processes, at temperatures below or equal to 100 °C. In particular, concentrators with fully illuminated V inverted absorbers have attractive properties for thermal energy conversion. Numerical analysis of the geometric and optical characteristics of different low concentration CPC’s ( C between 1 and 2) with fully inverted wedge absorbers, shows that the cavities with the minimal relationship between the length and height of the reflector surface and the aperture, ( L/ A) and ( H/ A), and the lower average number of reflections 〈 n〉 correspond to the lowest angular acceptance concentrator. If a concentration of 1.2 is desired, the smallest ratios of ( L/ A) and ( H/ A) and mean number of reflections 〈 n〉 occur for C = 2 ( θ a = 30°). However, when the annual generated thermal energy is also considered (for example, for Recife, tilt equals latitude, fluid temperature equals 50 °C, East–West orientation), a very large maximum value in the concentration region between 1.4 and 1.6 (acceptance angles of 38.68° e 45.58°) occurs. The simulation results indicate, that while the operational temperature rises, the ratio between the annual generated thermal energy by the CPC and a good quality flat-plate collector becomes greater than 1: for CPC with 1.2 concentration these ratios become 1.0 at 50 °C and 1.35 at 80 °C. The improvement in the reflectivity of the reflector surface of the CPC rises significantly this relation, i.e., if the reflectivity exceeds from 0.86 to 0.96 the CPC of the concentration relation 1.2, operating at 80 °C may generate 55% more thermal energy than flat-plate collector.

Functionalized pentacenes for dye-sensitized solar cells

Carboxylic acid functionalized pentacene-based dyes are synthesized and tested in dye-sensitized solar cells utilizing titania (rutile) nanowire arrays as the electron transporting photoanode. Functionalization on both chromophore and solubilizing substitutents leads to materials demonstrating promising light-harvesting and energy-conversion properties in these large polycyclic aromatic compounds.

Optimisation of doped amorphous silicon layers applied to heterojunction solar cells

The optimisation of amorphous silicon layers (a-Si:H) is of key importance to obtain high efficiency heterojunction (HJ) solar cells. However, since many mechanisms take place in photovoltaic energy conversion, good electrical and optical properties of a-Si:H films do not always result in high efficiency HJ devices. This is principally due to the use of very thin layers were interfaces are of capital importance and bulk properties are not always the main guideline to best results on solar cells. In this work, we focus on the doping analysis of (n) and (p) a-Si:H layers directly and their impact on solar cell results. First, we have deposited and characterized simple (p) and (n) a-Si:H layers and then we have integrated them on full heterojunction solar cells. We have correlated the solar cells characteristics (Jsc, Voc and FF) with layer properties in order to understand the main mechanisms involved in the high performance of HJ devices. Finally, we have chosen the best layers to improve the efficiency of our heterojunction solar cells on (n) c-Si 125PSQ wafers up to 20% on an industrially-compatible process.

820 mV open-circuit voltages from Cu2O/CH3CN junctions

P-Type cuprous oxide (Cu2O) photoelectrodes prepared by the thermal oxidation of Cu foils exhibited open-circuit voltages in excess of 800 mV in nonaqueous regenerative photoelectrochemical cells. In contact with the decamethylcobaltocene+/0 (Me10CoCp2+/0) redox couple, cuprous oxide yielded open-circuit voltage, Voc, values of 820 mV and short-circuit current density, Jsc, values of 3.1 mA cm−2 under simulated air mass 1.5 illumination. The energy-conversion efficiency of 1.5% was limited by solution absorption and optical reflection losses that reduced the short-circuit photocurrent density. Spectral response measurements demonstrated that the internal quantum yield approached unity in the 400–500 nm spectral range, but poor red response, attributable to bulk recombination, lowered the overall efficiency of the cell. X-Ray photoelectron spectroscopy and Auger electron spectroscopy indicated that the photoelectrodes had a high-quality cuprous oxide surface, and revealed no observable photocorrosion during operation in the nonaqueous electrolyte. The semiconductor/liquid junctions thus provide a noninvasive method to investigate the energy-conversion properties of cuprous oxide without the confounding factors of deleterious surface reactions.

Resonance Energy Transfer Improves the Biological Function of Bacteriorhodopsin within a Hybrid Material Built from Purple Membranes and Semiconductor Quantum Dots

Purple membrane (PM) from bacteria Halobacterium salinarum contains a photochromic protein bacteriorhodopsin (bR) arranged in a 2D hexagonal nanocrystalline lattice (Figure 1 ). Absorption of light by the protein-bound chromophore retinal results in pumping the protons through the PM creating an electrochemical gradient which is then used by the ATPases to energize the cellular processes. Energy conversion, photochromism, and photoelectrism are the inherent effects which are employed in many bR technical applications. bR, along with the other photosensitive proteins, is not able to deal with the excess energy of photons in UV and blue spectral region and utilizes less than 0.5% of the energy from the available incident solar light for its biological function. Here, we proceed with optimization of bR functions through the engineering of a "nanoconverter" of solar energy based on semiconductor quantum dots (QDs) tagged with the PM. These nanoconverters are able to harvest light from deep-UV to the visible region and to transfer this additionally collected energy to bR via Förster resonance energy transfer (FRET). We show that specific nanobio-optical and spatial coupling of QDs (donor) and bR retinal (acceptor) provide a means to achieve FRET with efficiency approaching 100%. We have finally demonstrated that the integration of QDs within PM significantly increases the efficiency of light-driven transmembrane proton pumping, which is the main bR biological function. This new QD-PM hybrid material will have numerous optoelectronic, photonic, and photovoltaic applications based on its energy conversion, photochromism, and photoelectrism properties.

Preparation and DSC application of the size-tuned ZnO nanoarrays

Abstract ZnO nanoarray was successfully prepared by a simple chemical bath deposition method on the glass slide deposited with a spin-coated ZnO seed crystal layer. With the measurements of SEM, XRD and UV–vis absorption spectra, the properties of the ZnO nanoarray were characterized in detail. The results show that the ZnO nanoarray is the hexagonal wurtzite structure and grow along the [0 0 1] axis. Furthermore, the energy-conversion property of the device was investigated in such ZnO nanoarray constructed dye-sensitized solar cells (DSCs), which has potential applications in the new-concept photovoltaic devices.

Preparation and Photophysical and Photoelectrochemical Properties of Supramolecular Porphyrin Nanorods Structurally Controlled by Encapsulated Fullerene Derivatives

A new class of porphyrin nanorods structurally controlled by encapsulated fullerene derivatives is prepared via a solvent mixture technique. These nanorods, composed of fullerenes (C60, C60 derivatives and C70) and zinc meso-tetra(4-pyridyl)porphyrin [ZnP(Py)4], are formed with the aid of a surfactant, cetyltrimethylammonium bromide (CTAB), in a DMF/acetonitrile mixture. In scanning electron microscopy (SEM) measurement, ZnP(Py)4 pristine hexagonal nanotubes with a large hollow structure [denoted as ZnP(Py)4 tube] are observed, whereas the hollow hole is completely closed in the case of nanorods composed of fullerenes (C60 and C70) and ZnP(Py)4 [fullerene−ZnP(Py)4 rod]. In C60 derivative−ZnP(Py)4 rods, the distorted polygonal columnar structures with large diameter and length are formed, as compared to the hexagonal structures of C60−ZnP(Py)4 and C70−ZnP(Py)4 rods. X-ray diffraction (XRD) analyses also reveals that ZnP(Py)4 alignment in the nanorod is based on the stacked assemblies of ZnP(Py)4 coordinated hexagonal formations. Elemental analysis and titration experiment by absorption measurement were also performed to quantitatively check the relative molecular ratio between porphyrins and fullerenes. Steady-state and time-resolved fluorescence spectra show efficient fluorescence quenching, suggesting the forward electron-transfer process from the singlet excited state of ZnP(Py)4 to fullerenes. Moreover, the back electron-transfer processes are detected by nanosecond transient absorption measurements. The forward and back electron-transfer rate constants are largely dependent on the structures of the nanorods. To construct photoelectrochemical solar cells, fullerene−ZnP(Py)4 rods are deposited onto nanostructured SnO2 films (OTE/SnO2). Fullerene−ZnP(Py)4 rod-modified electrodes exhibited efficient light energy conversion properties, such as a power conversion efficiency (η) of 0.63% and an incident photon to current conversion efficiency (IPCE) of 35%, which are much larger than those of ZnP(Py)4 tube.

Light Energy Conversion Properties of Supramolecular Triad and Tetrad of Fullerene Derivatives with N,N-Dimethylaniline-Flavin Dyad

not Available.

Magnetic‐Field Effects in Organic Semiconducting Materials and Devices

AbstractIt has been experimentally discovered that a low magnetic field (less than 500 mT) can substantially change the electroluminescence, photoluminescence, photocurrent, and electrical‐injection current in nonmagnetic organic semiconducting materials, leading to magnetic‐field effects (MFEs). Recently, there has been significant driving force in understanding the fundamental mechanisms of magnetic responses from nonmagnetic organic materials because of two potential impacts. First, MFEs can be powerful experimental tools in revealing and elucidating useful and non‐useful excited processes occurring in organic electronic, optical, and optoelectronic devices. Second, MFEs can lead to the development of new multifunctional organic devices with integrated electronic, optical, and magnetic properties for energy conversion, optical communication, and sensing technologies. This progress report discusses magnetically sensitive excited states and charge‐transport processes involved in MFEs. The discussions focus on both fundamental theories and tuning mechanisms of MFEs in nonmagnetic organic semiconducting materials.

Properties of Ag-doped Bi-Sb alloys as thermoelectric conversion materials for solid state refrigeration

The energy conversion properties of Bi-Sb system thermoelectric materials doped by Ag was investigated. Bi85Sb15 − xAgx (x = 0, 1, 2, 3, 4) alloys with Ag substitution for Sb were synthesized by mechanical alloying and then pressed under 5 GPa at 523 K for 30 min. The phase structure of the alloys was characterized by Xray diffraction. The electric conductivities and the Seebeck coefficients were measured at the temperature range of 80–300 K. The results reveal that the electric conductivities of the Ag-doped Bi-Sb alloys are highly improved. The power factor of Bi85Sb14Ag1 reaches a maximum value of 2.98×10−3 W/(K2·m) at 255 K, which is about three times that of the un-doped sample Bi85Sb15 at the same temperature.

Oriented Nanostructures for Energy Conversion and Storage

Recently, the role of nanostructured materials in addressing the challenges in energy and natural resources has attracted wide attention. In particular, oriented nanostructures demonstrate promising properties for energy harvesting, conversion, and storage. In this Review, we highlight the synthesis and application of oriented nanostructures in a few key areas of energy technologies, namely photovoltaics, batteries, supercapacitors, and thermoelectrics. Although the applications differ from field to field, a common fundamental challenge is to improve the generation and transport of electrons and ions. We highlight the role of high surface area to maximize the surface activity and discuss the importance of optimum dimension and architecture, controlled pore channels, and alignment of the nanocrystalline phase to optimize the transport of electrons and ions. Finally, we discuss the challenges in attaining integrated architectures to achieve the desired performance. Brief background information is provided for the relevant technologies, but the emphasis is focused mainly on the nanoscale effects of mostly inorganic-based materials and devices.

Fullerene-encapsulated porphyrin hexagonal nanorods. An anisotropic donor–acceptor composite for efficient photoinduced electron transfer and light energy conversion

We have successfully constructed fullerene-encapsulated porphyrin hexagonal nanorods in DMF-acetonitrile solution mixed with CTAB surfactant, which demonstrate efficient and characteristic photoinduced electron transfer and light energy conversion properties.

Porphyrin-Based Molecular Architectures for Light Energy Conversion

We have constructed a series of supramolecular photovoltaic cells composed of multi-porphyrin arrays such as porphyrin-alkanethiolate monolayer protected-gold nanoparticles [H2PCnMPC: n is the number of methylene groups in the spacer], porphyrin dendrimers [D n P n ], and porphyrin-peptide oligomers [P(H2P) n ] and fullerene (C60) on nanostructured SnO2 electrodes (OTE/SnO2). These multi-porphyrin arrays form complexes with fullerene molecules and they form clusters in acetonitrile/toluene mixed solvent. The highly colored composite clusters are assembled as three-dimensional arrays onto nanostructured SnO2 films [denoted as OTE/SnO2/(multi-porphyrin array+C60) m ] using an electrophoretic deposition method. These highly organized molecular assembly films attain drastic enhancement of light energy conversion properties as compared to the non-organized reference system. The maximum power conversion efficiency (η) of OTE/SnO2/(H2PC15MPC+C60) m reaches 1.5%, which is 45 times higher than that of the reference system (0.035%).