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Circuit Voltage (circuit + voltage)
Kinds of Circuit Voltage Selected AbstractsIntermediate Temperature Anode-Supported Fuel Cell Based on BaCe0.9Y0.1O3 Electrolyte with Novel Pr2NiO4 CathodeFUEL CELLS, Issue 1 2010G. Taillades Abstract A proton conducting ceramic fuel cell (PCFC) operating at intermediate temperature has been developed that incorporates electrolyte and electrode materials prepared by flash combustion (yttrium-doped barium cerate) and auto-ignition (praseodymium nickelate) methods. The fuel cell components were assembled using an anode-support approach, with the anode and proton ceramic layers prepared by co-pressing and co-firing, and subsequent deposition of the cathode by screen-printing onto the proton ceramic surface. When the fuel cell was fed with moist hydrogen and air, a high Open Circuit Voltage (OCV,>,1.1,V) was observed at T,>,550,°C, which was stable for 300,h (end of test), indicating excellent gas-tightness of the proton ceramic layer. The power density of the fuel cell increased with temperature of operation, providing more than 130,mW,cm,2 at 650,°C. Symmetric cells incorporating Ni-BCY10 cermet and BCY10 electrolyte on the one hand, and Pr2NiO4,+,, and BCY10 electrolyte on the other hand, were also characterised and area specific resistances of 0.06,,,cm2 for the anode material and 1,2,,,cm2 for the cathode material were obtained at 600,°C. [source] Plasma Sputtering Deposition of PEMFC Porous Carbon Platinum Electrodes,FUEL CELLS, Issue 2 2008H. Rabat Abstract A novel method is proposed to fabricate the active catalytic layers of proton exchange membrane fuel cells (PEMFC). A plasma sputtering technique is used to deposit a porous columnar carbon film (column diameter of 20,nm) followed by the catalyst (platinum) deposition directly on the proton-conducting membrane. The study of Pt diffusion shows that the optimised catalysed layers correspond to low plasma pressure operation (0.5,Pa) below a platinum loading limit of about 90,,g,cm,2. The initial carbon porosity is then maintained and Pt nanoparticles are present in all parts of the carbon layer. A membrane electrode assembly (MEA) is then achieved by alternate depositions of carbon and platinum onto both sides of the membrane. The results show the importance of the porous carbon structure. A significant increase in the catalyst efficiency is observed compared to a commercial fuel cell when measuring open circuit voltage. [source] Tuning Conversion Efficiency in Metallo Endohedral Fullerene-Based Organic Photovoltaic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Russel B. Ross Abstract Here the influence that 1-(3-hexoxycarbonyl)propyl-1-phenyl-[6,6]-Lu3N@C81, Lu3N@C80,PCBH, a novel acceptor material, has on active layer morphology and the performance of organic photovoltaic (OPV) devices using this material is reported. Polymer/fullerene blend films with poly(3-hexylthiophene), P3HT, donor material and Lu3N@C80,PCBH acceptor material are studied using absorption spectroscopy, grazing incident X-ray diffraction and photocurrent spectra of photovoltaic devices. Due to a smaller molecular orbital offset the OPV devices built with Lu3N@C80,PCBH display increased open circuit voltage over empty cage fullerene acceptors. The photovoltaic performance of these metallo endohedral fullerene blend films is found to be highly impacted by the fullerene loading. The results indicate that the optimized blend ratio in a P3HT matrix differs from a molecular equivalent of an optimized P3HT/[6,6]-phenyl-C61 -butyric methyl ester, C60,PCBM, active layer, and this is related to the physical differences of the C80 fullerene. The influence that active layer annealing has on the OPV performance is further evaluated. Through properly matching the film processing and the donor/acceptor ratio, devices with power conversion efficiency greater than 4% are demonstrated. [source] Surface Design in Solid-State Dye Sensitized Solar Cells: Effects of Zwitterionic Co-adsorbents on Photovoltaic PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Mingkui Wang Abstract In solid-state dye sensitized solar cells (SSDSCs) charge recombination at the dye-hole transporting material interface plays a critical role in the cell efficiency. For the first time we report on the influence of dipolar co-adsorbents on the photovoltaic performance of sensitized hetero-junction solar cells. In the present study, we investigated the effect of two zwitterionic butyric acid derivatives differing only in the polar moiety attached to their common 4 carbon-chain acid, i.e., 4-guanidinobutyric acid (GBA) and 4-aminobutyric acid (ABA). These two molecules were implemented as co-adsorbents in conjunction with Z907Na dye on the SSDSC. It was found that a Z907Na/GBA dye/co-adsorbent combination increases both the open circuit voltage (Voc) and short-circuit current density (Jsc) as compared to using Z907Na dye alone. The Z907Na/ABA dye/co-adsorbent combination increases the Jsc. Impedance and transient photovoltage investigations elucidate the cause of these remarkable observations. [source] Organic Thin-Film Photovoltaic Cells Based on Oligothiophenes with Reduced Bandgap,ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007C. Uhrich Abstract The best polymeric solar cells reported so far are based on a so-called bulk heterojunction of a polythiophene as donor and a soluble fullerene derivative as acceptor. However, these cells still suffer from an unsatisfying photovoltage, typically below 0.7,V. Here, we show that we can achieve higher photovoltages using a new terthiophene end-capped with electron withdrawing dicyanovinyl groups (DCV3T) that increase both the ionization energy and even more strongly the electron affinity of the compound. The new material is tested in cells using a photoactive heterojunction to separate the excitons generated in the oligomer and a p-doped wide-gap transport layer. The solar cells show an open circuit voltage of up to 1.04,V and a broad spectral sensitivity band ranging from 420,nm to 650,nm. Solar cells based on such oligothiophenes are promising candidates for stacked organic solar cells tailored to the sun-spectrum. Moreover, we present first examples of a new concept for organic solar cells: By blending DCV3T with fullerene C60, an enhanced generation of triplet excitons on the oligomer can be achieved via a back and forth transfer of excitons (ping-pong-effect). [source] Role of the Charge Transfer State in Organic Donor,Acceptor Solar CellsADVANCED MATERIALS, Issue 37 2010Carsten Deibel Charge transfer complexes are interfacial charge pairs residing at the donor,acceptor heterointerface in organic solar cell. Experimental evidence shows that it is crucial for the photovoltaic performance, as both photocurrent and open circuit voltage directly depend on it. For charge photogeneration, charge transfer complexes represent the intermediate but essential step between exciton dissotiation and charge extraction. Recombination of free charges to the ground state is via the bound charge transfer state before being lost to the ground state. In terms of the open circuit voltage, its maximum achievable value is determined by the energy of the charge transfer state. An important question is whether or not maximum photocurrent and maximum open circuit voltage can be achieved simultaneously. The impact of increasing the CT energy,in order to raise the open circuit voltage, but lowering the kinetic excess energy of the CT complexes at the same time,on the charge photogeneration will accordingly be discussed. Clearly, the fundamental understanding of the processes involving the charge transfer state is essential for an optimisation of the performance of organic solar cells. [source] On mass transport in an air-breathing DMFC stackINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2005G. Q. Lu Abstract An 8-cell air-breathing direct methanol fuel cell (DMFC) stack with the active area of 5 cm2 of each cell has been developed. Stainless steel plates of 500 µm thickness with flow channels were fabricated using photochemical etching method as the current collectors. Different conditioning methods for membrane electrode assembly (MEA) activation were discussed. With proper control of water crossover to the cathode, cathode flooding was avoided in the DMFC stack. Methanol crossover at open circuit voltage (OCV) in the air-breathing DMFC was measured. Further, it was found that flow maldistribution might occur in the parallel flow field of the stack, making carbon dioxide gas management at the anode necessary. Using humidified hydrogen in the anode with a high flow rate, the oxygen transport limiting current density was characterized and found to be sufficient in the air-breathing cathode. The stack produced a maximum output power of 1.33 W at 2.21 V at room temperature, corresponding to a power density of 33.3 mW cm,2. Copyright © 2005 John Wiley & Sons, Ltd. [source] Synthesis and characterization of cyclopentadithiophene-based low bandgap copolymers containing electron-deficient benzoselenadiazole derivatives for photovoltaic devicesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2010In Hwan Jung Abstract We have synthesized two cyclopentadithiophene (CDT)-based low bandgap copolymers, poly[(4,4-bis(2-ethyl-hexyl)-4H -cyclopenta[2,1- b:3,4- b,]dithiophene-2,6-diyl)- alt -(benzo[c][1,2,5]selenadiazole-4,7-diyl)] (PCBSe) and poly[(4,4-bis(2-ethyl-hexyl)-4H -cyclopenta[2,1- b:3,4- b,]dithiophene-2,6-diyl)- alt -(4,7-dithiophen-2-yl-benzo[c][1,2,5]selenadiazole-5,5,-diyl)] (PCT2BSe), for use in photovoltaic applications. Through the internal charge transfer interaction between the electron-donating CDT unit and the electron-accepting benzoselenadiazole, we realized exceedingly low bandgap polymers with bandgaps of 1.37,1.46 eV. The UV,vis absorption maxima of PCT2BSe were subjected to larger hypsochromic shifts than those of PCBSe, because of the distorted electron donor,acceptor (D,A) structures of the PCT2BSe backbone. These results were supported by the calculations of the D,A complex using the ab initio Hartree-Fock method with a split-valence 6-31G* basis set. However, PCT2BSe exhibited a better molar absorption coefficient in the visible region, which can lead to more efficient absorption of sunlight. As a result, PCT2BSe blended with [6,6]-phenyl-C61 -butyric acid methyl ester (PC61BM) exhibited a better photovoltaic performance than PCBSe because of the larger spectral overlap integral with respect to the solar spectrum. Furthermore, when the polymers were blended with PC71BM, PCT2BSe showed the best performance, with an open circuit voltage of 0.55 V, a short-circuit current of 6.63 mA/cm2, and a power conversion efficiency of 1.34% under air mass 1.5 global illumination conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1423,1432, 2010 [source] Enhancement of photocurrent of polymer-gelled dye-sensitized solar cell by incorporation of exfoliated montmorillonite nanoplateletsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008Chi-Wei Tu Abstract Poly(n -isopropylacrylamide) (PNIPAAm) and its nanocomposite with exfoliated montmorillonite (MMT) were prepared by soap-free emulsion polymerization and individually applied to gel the electrolyte systems for the dye-sensitized solar cells (DSSCs). Each exfoliated MMT nanoplatelet had a thickness of , 1 nm, carried , 1.8 cation/nm2, and acted like a two-dimensional electrolyte. The DSSC with the LiI/I2/tertiary butylpyridine electrolyte system gelled by this polymer nanocomposite had higher short-circuit current density (Jsc) compared to that gelled by the neat PNIPAAm. The former has a Jsc of 12.6 mA/cm2, an open circuit voltage (Voc) of 0.73 V, and a fill factor (FF) of 0.59, which harvested 5.4% electricity conversion efficiency (,) under AM 1.5 irradiation at 100 mW/cm2, whereas the latter has Jsc = 7.28 mA/cm2, Voc = 0.72 V, FF = 0.60, and , = 3.17%. IPCE of the nanocomposite-gelled DSSC were also improved. Electrochemical impedance spectroscopy of the DSSCs revealed that the nanocomposite-gelled electrolytes significantly decreased the impedances in three major electric current paths of DSSCs, that is, the resistance of electrolytes and electric contacts, impedance across the electrolytes/dye-coated TiO2 interface, and Nernstian diffusion within the electrolytes. The results were also consistent with the increased molar conductivity of nanocomposite-gelled electrolytes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 47,53, 2008 [source] Thienopyrazine-Based Low-Bandgap Poly(heteroaryleneethynylene)s for Photovoltaic DevicesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2006Raja Shahid Ashraf Abstract Summary: Low-bandgap ,-conjugated polymers that consist of alkyl thiophene/alkoxy phenylene and 2,3-diphenylthieno[3,4- b]pyrazine units have been prepared in high yields by a Sonogashira polycondensation. The copolymers are characterized by NMR, IR, UV, GPC, and elemental analysis. Thin films of the polymers P1, P2, and P3 exhibit an optical bandgap of ,1.57,1.60 eV. Under simulated AM 1.5 conditions P2/PCBM devices on polyester foil provide a short circuit current of ISC,=,10.72 mA,·,cm,2, an open circuit voltage of Voc,=,0.67 V, and a power conversion efficiency of 2.37%. Schematic of the photovoltaic device made from the polymers synthesized here. [source] Pyroelectric coupling in thin film photovoltaicsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 4 2007Victor G. Karpov Abstract We propose a theory of thin film photovoltaics in which one of the polycrystalline films is made of a pyroelectric material grains such as CdS. That film is shown to generate strong polarization improving the device open circuit voltage. Implications and supporting facts for the major photovoltaic types based on CdTe and CuIn(Ga)Se2 absorber layers are discussed. Band diagram of a pyroelectric (CdS) based PV junction. Arrows represent the charge carrier photo-generation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Solar cell as a heat engine: energy,entropy analysis of photovoltaic conversionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2008Tom MarkvartArticle first published online: 13 NOV 200 Abstract A thermodynamic theory for the voltage or free energy generated by a quantum solar energy converter which has recently been proposed, is developed here in a more direct and simpler way. We consider separately the luminescence and conversion of a single photon of the incident radiation. The energy/entropy balance for the conversion process yields an expression for the voltage in a form familiar from the classical thermodynamics of the work carried out by the heat engine. A similar balance for the absorption and emission of light gives an expression for the irreversible entropy generation which reduces the open circuit voltage generated by the solar cell. Detailed expressions for losses due to individual mechanisms, including non-radiative recombination, are obtained with the use of an approximation where photons in the incident and emitted beams are modelled as an ideal two-dimensional gas. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modeling of spatially inhomogeneous solar cells by a multi-diode approachPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2005P. O. Grabitz Abstract An equivalent circuit model consisting of parallel connected diodes with different electronic quality simulates the electronic properties of solar cells with spatially inhomogeneous material quality. Variations of the local saturation current density result in a degradation of the open circuit voltage, the fill factor and, in consequence, of the overall power conversion efficiency. However, a local series resistance introduced into this network limits this degradation by preventing areas with high saturation current density to dominate the electronic losses of the entire device. Analyzing the integral current/voltage-curves of the networks shows the diode ideality larger than unity to result from resistive limitations to the spatially inhomogeneous current flow. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pt/SiO2 as addition to multilayer SPSU/PTFE composite membrane for fuel cellsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2008L. Wang Abstract A multilayer composite membrane was prepared by reinforcing sulfonated polysulfone (SPSU) with porous polytetrafluoroethylene (PTFE), and adding Pt/SiO2,Nafion® membranes on both sides of the SPSU/PTFE membrane to self-humidify and protect the inside membrane. The ex situ Fenton test and open circuit voltage (OCV) accelerated test show that the composite membrane has better stability than the initial membrane because of the protection of the outside Pt/SiO2,Nafion layers. The composite membrane has similar performance to that of NRE-212 under the fully humidified condition and better performance than NRE-212 without humidifying. The self-humidifying membrane shows great potential for use in low humidifying conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] High efficiency all-GaAs solar cellPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 2 2010Abderrahmane Belghachi Abstract The reduction of surface recombination in GaAs solar cells is known to be a major concern for photovoltaic cells designers. A common technique used to reduce this effect is to cover the GaAs surface with a wide band gap window layer, therefore the creation of a heterojunction. To avoid a heterojunction with its inconveniences; interface surface states, poor photon absorption in addition to the technological exigencies, one can use an all-GaAs solar cell. In this type of structure, a thin highly doped layer is created at the surface known as a front surface field (FSF). The main role of an FSF layer is to reduce the effect of front surface recombination and the enhancement of light-generated free carriers' collection. This is achieved by the drastic reduction of the effective recombination at the emitter upper boundary. In this work, a simple analytical model is used to simulate the influence of the FSF layer on GaAs solar cell parameters; photocurrent, open circuit voltage and energy conversion efficiency. The effects of the FSF layer doping density and its thickness on the cell performance are discussed by using computed results. Copyright © 2010 John Wiley & Sons, Ltd. [source] Voltage dependent photocurrent collection in CdTe/CdS solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2007Steven Hegedus Abstract The voltage dependence of the photocurrent JL(V) of CdTe/CdS solar cells has been characterized by separating the forward current from the photocurrent at several illumination intensities. JL(V) reduces the fill factor (FF) of typical cells by 10,15 points, the open circuit voltage (VOC) by 20,50,mV, and the efficiency by 2,4 points. Eliminating the effect of JL(V) establishes superposition between light and dark J(V) curves for some cells. Two models for voltage dependent collection give reasonable fits to the data: (1) a single carrier Hecht model developed for drift collection in p-i-n solar cells in which fitting yields a parameter consistent with lifetimes of 10,9,s as measured by others; or (2) the standard depletion region and bulk diffusion length model fits almost as well. The simple Hecht-like drift collection model for photocurrent gives very good agreement to J(V) curves measured under AM1·5 light on CdTe/CdS solar cells with FF from 53% to 70%, CdTe thickness from 1·8 to 7·0,µm, in initial and stressed states. Accelerated thermal and bias stressing increases JL(V) losses as does insufficient Cu. This method provides a new metric for tracking device performance, characterizes transport in the high field depletion region, and quantifies a significant FF loss in CdTe solar cells. Copyright © 2007 John Wiley & Sons, Ltd. [source] Highly-efficient Cd-free CuInS2 thin-film solar cells and mini-modules with Zn(S,O) buffer layers prepared by an alternative chemical bath processPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2006A. Ennaoui Abstract Recent progress in fabricating Cd- and Se-free wide-gap chalcopyrite thin-film solar devices with Zn(S,O) buffer layers prepared by an alternative chemical bath process (CBD) using thiourea as complexing agent is discussed. Zn(S,O) has a larger band gap (Eg,=,3·6,3·8,eV) than the conventional buffer material CdS (Eg,=,2·4,eV) currently used in chalcopyrite-based thin films solar cells. Thus, Zn(S,O) is a potential alternative buffer material, which already results in Cd-free solar cell devices with increased spectral response in the blue wavelength region if low-gap chalcopyrites are used. Suitable conditions for reproducible deposition of good-quality Zn(S,O) thin films on wide-gap CuInS2 (,CIS') absorbers have been identified for an alternative, low-temperature chemical route. The thickness of the different Zn(S,O) buffers and the coverage of the CIS absorber by those layers as well as their surface composition were controlled by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray excited Auger electron spectroscopy. The minimum thickness required for a complete coverage of the rough CIS absorber by a Zn(S,O) layer deposited by this CBD process was estimated to ,15,nm. The high transparency of this Zn(S,O) buffer layer in the short-wavelength region leads to an increase of ,1,mA/cm2 in the short-circuit current density of corresponding CIS-based solar cells. Active area efficiencies exceeding 11·0% (total area: 10·4%) have been achieved for the first time, with an open circuit voltage of 700·4,mV, a fill factor of 65·8% and a short-circuit current density of 24·5,mA/cm2 (total area: 22·5,mA/cm2). These results are comparable to the performance of CdS buffered reference cells. First integrated series interconnected mini-modules on 5,×,5,cm2 substrates have been prepared and already reach an efficiency (active area: 17·2,cm2) of above 8%. Copyright © 2006 John Wiley & Sons, Ltd. [source] Characterization of electrochemically active bacteria utilizing a high-throughput voltage-based screening assayBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009Justin Biffinger Abstract Metal reduction assays are traditionally used to select and characterize electrochemically active bacteria (EAB) for use in microbial fuel cells (MFCs). However, correlating the ability of a microbe to generate current from an MFC to the reduction of metal oxides has not been definitively established in the literature. As these metal reduction assays may not be generally reliable, here we describe a four- to nine-well prototype high throughput voltage-based screening assay (VBSA) designed using MFC engineering principles and a universal cathode. Bacterial growth curves for Shewanella oneidensis strains DSP10 and MR-1 were generated directly from changes in open circuit voltage and current with five percent deviation calculated between each well. These growth curves exhibited a strong correlation with literature doubling times for Shewanella indicating that the VBSA can be used to monitor distinct fundamental properties of EAB life cycles. In addition, eight different organic electron donors (acetate, lactate, citrate, fructose, glucose, sucrose, soluble starch, and agar) were tested with S. oneidensis MR-1 in anode chambers exposed to air. Under oxygen exposure, we found that current was generated in direct response to additions of acetate, lactate, and glucose. Biotechnol. Bioeng. 2009;102: 436,444. © 2008 Wiley Periodicals, Inc. [source] The Influence of Charge Transport and Recombination on the Performance of Dye-Sensitized Solar CellsCHEMPHYSCHEM, Issue 1 2009Mingkui Wang Dr. Abstract Electrochemical impedance spectroscopy (EIS) and transient voltage decay measurements are applied to compare the performance of dye sensitized solar cells (DSCs) using organic electrolytes, ionic liquids and organic-hole conductors as hole transport materials (HTM). Nano-crystalline titania films sensitized by the same heteroleptic ruthenium complex NaRu(4-carboxylic acid-4,-carboxylate) (4,4,-dinonyl-2,2,-bipyridyl)(NCS)2,, coded Z-907Na are employed as working electrodes. The influence of the nature of the HTM on the photovoltaic figures of merit, that is, the open circuit voltage, short circuit photocurrent and fill factor is evaluated. In order to derive the electron lifetime, as well as the electron diffusion coefficient and charge collection efficiency, EIS measurements are performed in the dark and under illumination corresponding to realistic photovoltaic operating conditions of these mesoscopic solar cells. A theoretical model is established to interpret the frequency response off the impedance under open circuit conditions, which is conceptually similar to photovoltage transient decay measurements. Important information on factors that govern the dynamics of electron transport within the nanocrystalline TiO2 film and charge recombination across the dye sensitized heterojunction is obtained. [source] Adsorption of 4 -tert- Butylpyridine on TiO2 Surface in Dye-Sensitized Solar CellsCHINESE JOURNAL OF CHEMISTRY, Issue 1 2008Bi-Tao XIONG Abstract 4 -tert- Butylpyridine (4-TBP) has been widely used as additive in dye-sensitized solar cells (DSC), owing to its improvement of the fill factor and the open circuit voltage of DSC. In this paper, the adsorption of 4-TBP on the rutile TiO2(110) surface in DSC was studied by using the density functional theory at DFT/B3LYP level. By comparing the results with those attained from experiments, it was concluded that the 4-TBP could chemiadsorb on the incompletely covered surface Ti atoms in the electrode. The probable mechanism of compressed recombination by coordinated 4-TBP in DSC was proposed. [source] Triplet Formation in Fullerene Multi-Adduct Blends for Organic Solar Cells and Its Influence on Device PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Clare Dyer-Smith Abstract In organic solar cells, high open circuit voltages may be obtained by choosing materials with a high offset between the donor highest occupied molecular orbital (HOMO) and acceptor lowest unoccupied molecular orbital (LUMO). However, increasing this energy offset can also lead to photophysical processes that compete with charge separation. In this paper the formation of triplet states is addressed in blends of polyfluorene polymers with a series of PCBM multi-adducts. Specifically, it is demonstrated that the formation of such triplets occurs when the offset energy between donor ionization potential and acceptor electron affinity is ,1.6 eV or greater. Spectroscopic measurements support a mechanism of resonance energy transfer for triplet formation, influenced by the energy levels of the materials, but also demonstrate that the competition between processes at the donor,acceptor interface is strongly influenced by morphology. [source] Combined effects of conjugation pattern and alkoxy side chains on the photovoltaic properties of thiophene-containing PPE-PPVsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2007Daniel Ayuk Mbi Egbe Abstract This contribution presents the synthesis and properties of four thiophene-containing poly(- p -arylene-ethynylene)/poly(- p -arylene-vinylene)s, PIa-b and PIIa-b, whose repeating units (RU) consist either of 1:2 or 2:2 triple bond/double bond ratio, and which bear linear alkoxy side chains not longer than octyloxy and branched 2-ethylhexyloxy. PIa-b and PIIa-b exhibit similar absorption and emission behaviour in dilute solution (,a = 483,486 nm, ,e = 540 nm) as well as in solid state (,a = 500, 530 nm, ,e = 560 nm), whereby slightly higher fluorescence quantum yields (,f) were obtained for PI than for PII systems, as a result of higher number of thiophene units within the RU of PII. An enhancement of the ,f -value from 0% to 3% is obtained after replacing linear octadecyloxy in PIIc-e by bulky branched 2-ethylhexyloxy in PIIa-b. Nonoptimized solar cells of configuration ITO/PEDOT:PSS/polymer: PCBM (1:3 weight ratio)/LiF/Al show open circuit voltages as high as 900 mV for PIa-b and 800 mV for PIIa-b. Reducing the size of the side chain from R = 2- ethylhexyl in PIa to R = methyl in PIb leads to a significant increase of the short circuit current, ISC, from ca. 2.5 mA to ca. 3.7 mA and consequently to an enhancement of the energy conversion efficiency, ,AM1.5, from ca. 1.2% to ca. 1.7%. This is due to an extended donor-acceptor interfacial area, as evidenced by AFM topology pictures showing smaller nanoscale clusters size in PIb than in PIa active layer. The same change led to minimal effect in PII systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1619,1631, 2007 [source] Effects of water vapor introduction during Cu(In1,xGax)Se2 deposition on thin film properties and solar cell performancePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006S. Ishizuka Abstract The effects of water vapor introduction during the growth of Cu(In1,xGax)Se2, specifically CuInSe2 (CISe), Cu(In,Ga)Se2 (CIGSe), and CuGaSe2 (CGSe) thin films were studied. We have developed thus far a novel technique to improve CIGSe (x , 0.5) cell performance by means of water vapor introduction during CIGSe deposition. In this study, we have examined the effectiveness of water vapor introduction for other x -compositions (CISe and CGSe). Variations in the electrical properties observed in CIGSe (x , 0.5), that is, increasing hole density and conductivity with water vapor introduction, were also observed in CISe and CGSe. Water vapor introduction affected solar cell performance as well; open circuit voltages, short circuit current densities, and efficiencies were improved. The improvements in cell performance are thought to be related to annihilation of donor defects arising from Se-vacancies by incorporation of oxygen from the water vapor. In addition to this, the sodium content in the CIGSe layers was found to depend on the partial pressure of water vapor during deposition. This result suggests that the improvement mechanism is also related with the so-called ,Na-effects'. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Plasmas for texturing, cleaning, and deposition: towards a one pump down process for heterojunction solar cellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010Mario Moreno Abstract Low temperature plasma deposition of a-Si:H thin films has emerged as a promising alternative for high efficiency hetero junction (HJ) solar cells. In this work we study plasma processes for texturing and cleaning c-Si wafers pursuing a low cost dry fabrication process of HJ solar cells. We have studied two independent plasma processes: i) Texturing of c-Si wafers using SF6 - O2 plasmas in a RIE system, in order to reduce the surface reflectance and therefore improve the light trapping. The effects of the RF power and gas ratio on the c-Si surface texture have been studied in detail. Highly textured surfaces, with very low reflectance values (around 6% in the range of 300 , 1000 nm) have been achieved. ii) Etching of the native oxide and passivation of the c-Si surface by plasma, in a standard RF PECVD system. We used SiF4 plasma with optimized conditions for an efficient native oxide removal, and without breaking the vacuum, 40 nm of a-Si:H were deposited in order to passivate the c-Si surface. High effective lifetime values were obtained (,eff , 1.5 ms), providing high implicit open circuit voltages (Voc , 0.713 V) and low surface recombination velocities (Seff < 9 cm s -1). (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis of star-shaped molecules with pyrene-containing ,-conjugated units linked by an organosilicon coreAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2010Joji Ohshita Abstract Star-shaped molecules with pyrene-containing ,-conjugated units linked by an organosilicon core (Py3Si and Py3C) were prepared and their applications to thin-film transistors (TFTs) and photovoltaic cells were studied. Bottom-contact type TFTs with spin-coated films of the star-shaped compounds as the active layers were prepared and the field-effect mobility (µFET) and Ion/Ioff ratios were determined to be approximately 10,5 cm2 V,1 s,1 and 104, respectively. Photovoltaic properties of Py3Si and Py3C were studied in the cells, ITO,PEDOT-PSS,Py3Si or Py3C-PCBM,LiF,Al. Although the power conversion efficiency (PCE) of the cells was only about 0.04%, they showed high open circuit voltages (Voc) of 0.8,0.9 V, indicating the high potential of this type of compound as a host material. 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