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Photocurrent
Terms modified by Photocurrent Selected AbstractsUltraviolet Sensors: An Efficient Way to Assemble ZnS Nanobelts as Ultraviolet-Light Sensors with Enhanced Photocurrent and Stability (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Mater. On page 500, Xiaosheng Fang and co-workers demonstrate the successful development of high-performance "visible-blind" microscale ZnS nanobelt-based ultraviolet (UV) light sensors through a newly developed non-lithographic method. Such sensors may prove extremely useful for the detection of harmful near-visible-wavelength UV radiation, of particular interest in locations where the shielding effect of the Earth's atmosphere is deteriorating. [source] An Efficient Way to Assemble ZnS Nanobelts as Ultraviolet-Light Sensors with Enhanced Photocurrent and StabilityADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Xiaosheng Fang Abstract Although there has been significant progress in the fabrication and performance optimization of one-dimensional nanostructure-based photodetectors, it is still a challenge to develop an effective and low-cost device with high performance characteristics, such as a high photocurrent/dark-current ratio, photocurrent stability, and fast time response. Herein an efficient and low-cost method to achieve high-performance ,visible-blind' microscale ZnS nanobelt-based ultraviolet (UV)-light sensors without using a lithography technique, by increasing the nanobelt surface areas exposed to light, is reported. The devices exhibit about 750 times enhancement of a photocurrent compared with individual nanobelt-based sensors and an ultrafast time response. The photocurrent stability and time response to UV-light do not change significantly when a channel distance is altered from 2 to 100,µm or the sensor environment changes from air to vacuum and different measurement temperatures (60 and 150,°C). The photoelectrical behaviors can be recovered well after returning the measurement conditions to air and room temperature again. The low cost and high performance of the resultant ZnS nanobelt photodetectors guarantee their highest potential for visible-blind UV-light sensors working in the UV-A band. [source] Origin of the Reduced Fill Factor and Photocurrent in MDMO-PPV:PCNEPV All-Polymer Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 13 2007M. Mandoc Abstract The photogeneration mechanism in blends of poly[2-methoxy-5-(3,,7,-dimethyloctyloxy)-1,4 - phenylene vinylene] (MDMO-PPV) and poly[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3,,7,-dimethyloctyloxy)-1,4-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV) is investigated. The photocurrent in the MDMO-PPV:PCNEPV blends is strongly dependent on the applied voltage as a result of a low dissociation efficiency of the bound electron,hole pairs. The dissociation efficiency is limited by low carrier mobilities, low dielectric constant, and the strong intermixing of the polymers, leading to a low fill factor and a reduced photocurrent at operating conditions. Additionally, electrons trapped in the PCNEPV phase recombine with the mobile holes in the MDMO-PPV phase at the interface between the two polymers, thereby affecting the open-circuit voltage and increasing the recombination losses. At an intensity of one,sun, Langevin recombination of mobile carriers dominates over trap-assisted recombination. [source] Polymer Solar Cells Based on a Low-Bandgap Fluorene Copolymer and a Fullerene Derivative with Photocurrent Extended to 850,nm,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2005F. Zhang Abstract Polymer solar cells have been fabricated from a recently synthesized low band-gap alternating polyfluorene copolymer, APFO-Green2, combined with [6,6]-phenyl-C61 -butyric acid methyl ester (PCBM) from organic solutions. External quantum efficiencies (EQEs) of the solar cells show an onset at 850,nm and a peak of >,10,% located at 650,nm, which corresponds to the extended absorption spectrum of the polymer. Photocurrent of 3.0,mA,cm,2, photovoltage of 0.78,V, and power conversion efficiency of 0.9,% have been achieved in solar cells based on this new low-bandgap polymer under the illumination of air mass,1.5 (AM,1.5) (1000,W,m,2) from a solar simulator. [source] Correlation of Heterojunction Luminescence Quenching and Photocurrent in Polymer-Blend Photovoltaic DiodesADVANCED MATERIALS, Issue 38-39 2009Astrid Gonzalez-Rabade Charge generation in organic solar cells proceeds via photogeneration of excitons in the bulk that form geminate electron,hole pairs at the heterojunction formed between electron donor and acceptors. It is shown that an externally applied electric field increases the number of free charges formed from the geminate pair, and quenches the luminescence from the relaxed exciplex with one-to-one correspondence. [source] Linear-mode operation of the quantum-dot avalanche photodiode (QDAP)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010David A. Ramirez Abstract We report new results on the design, fabrication and characterization of a novel midinfrared sensor called quantum dot avalanche photodiode (QDAP). The QDAP consists of a quantum dots-in-a-well (DWELL) detector coupled with an avalanche photodiode (APD) through a tunnel barrier. In the QDAP, the photons are absorbed in the DWELL active region while the APD section provides gain. Photocurrent and noise measurements at 77 K were taken to characterize the response of the device. The nonlinear increase in the photocurrent as the APD voltage increases support theoretical predictions about the QDAP capability to work in applications with low photon flux levels. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoelectrical properties of crystalline titanium dioxide thin films after thermo-annealingCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007R. Sathyamoorthy Abstract This paper reports the photoelectrical properties of sol gel derived titanium dioxide (TiO2) thin films annealed at different temperatures (425-900°C). The structure of the as-grown film was found to be amorphous and it transforms to crystalline upon annealing. The trap levels are studied by thermally stimulated current (TSC) measurements. A single trap level with activation energy of 1.5 eV was identified. The steady state and transient photocurrent was measured and the results are discussed on the basis of structural transformation. The photocurrent was found to be maximum for the films annealed at 425°C and further it decreases with annealing at higher temperatures. The photoconduction parameters such as carrier lifetime, lifetime decay constant and photosensitivity were calculated and the results are discussed as a function of annealing temperature. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural, electrical and optical properties of Ge implanted GaSe single crystals grown by Bridgman techniqueCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2006H. Karaa Abstract Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X-Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1 × 109 to 6.5 × 105 ,-cm. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as-grown, 36 and 472 meV for as-implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500°C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (IPC) and illumination intensity (,) was studied and it was observed that the relation obeys the power law, IPC ,,n with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as-grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge-implanted sample was observed with increasing annealing temperatures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Triplet Exciton and Polaron Dynamics in Phosphorescent Dye Blended Polymer Photovoltaic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Chang-Lyoul Lee Abstract The triplet exciton and polaron dynamics in phosphorescent dye (PtOEP) blended polymer (MEH-PPV) photovoltaic devices are investigated by quasi-steady-state photo-induced absorption (PIA) spectroscopy. According to the low-temperature PIA and photoluminescence (PL) results, the increase in strength of the triplet-triplet (T1 - Tn) absorption of MEH-PPV in the blend system originates from the triplet-triplet energy transfer from PtOEP to MEH-PPV. The PtOEP blended MEH-PPV/C60 bilayer photovoltaic device shows a roughly 30%,40% enhancement in photocurrent and power-conversion efficiency compared to the device without PtOEP. However, in contrast to the bilayer device results, the bulk heterojunction photovoltaic devices do not show a noticeable change in photocurrent and power-conversion efficiency in the presence of PtOEP. The PIA intensity, originating from the polaron state, is only slightly higher (within the experimental error), indicating that carrier generation in the bulk heterojunction is not enhanced in the presence of PtOEP. The rate and probability of the exciton dissociation between PtOEP and PCBM is much faster and higher than that of the triplet-triplet energy transfer between PtOEP and MEH-PPV. [source] Bio-inspired Photoelectric Conversion Based on Smart-Gating NanochannelsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Liping Wen Abstract Inspired by the light-driven, cross-membrane proton pump of biological systems, a photoelectric conversion system based on a smart-gating, proton-driven nanochannel is constructed. In this system, solar energy is the only source of cross-membrane proton motive force that induces a diffusion potential and photocurrent flowing through the external circuit. Although the obtained photoelectric conversion performance is lower than that of conventional solid photovoltaic devices, it is believed that higher efficiencies can be generated by enhancing the protonation capacity of the photo-acid molecules, optimizing the membrane, and synthesizing high-performance photosensitive molecules. This type of facile and environmentally friendly photoelectric conversion has potential applications for future energy demands such as the production of power for in vivo medical devices. [source] Influence of Molecular Weight on the Performance of Organic Solar Cells Based on a Fluorene DerivativeADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Christian Müller Abstract The performance of organic photovoltaic (OPV) bulk-heterojunction blends comprising a liquid-crystalline fluorene derivative and a small-molecular fullerene is found to increase asymptotically with the degree of polymerization of the former. Similar to various thermodynamic transition temperatures as well as the light absorbance of the fluorene moiety, the photocurrent extracted from OPV devices is found to strongly vary with increasing oligomer size up to a number average molecular weight, Mn,,,10,kg,mol,1, but is rendered less chain-length dependent for higher Mn as the fluorene derivative gradually adopts polymeric behavior. [source] An Efficient Way to Assemble ZnS Nanobelts as Ultraviolet-Light Sensors with Enhanced Photocurrent and StabilityADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Xiaosheng Fang Abstract Although there has been significant progress in the fabrication and performance optimization of one-dimensional nanostructure-based photodetectors, it is still a challenge to develop an effective and low-cost device with high performance characteristics, such as a high photocurrent/dark-current ratio, photocurrent stability, and fast time response. Herein an efficient and low-cost method to achieve high-performance ,visible-blind' microscale ZnS nanobelt-based ultraviolet (UV)-light sensors without using a lithography technique, by increasing the nanobelt surface areas exposed to light, is reported. The devices exhibit about 750 times enhancement of a photocurrent compared with individual nanobelt-based sensors and an ultrafast time response. The photocurrent stability and time response to UV-light do not change significantly when a channel distance is altered from 2 to 100,µm or the sensor environment changes from air to vacuum and different measurement temperatures (60 and 150,°C). The photoelectrical behaviors can be recovered well after returning the measurement conditions to air and room temperature again. The low cost and high performance of the resultant ZnS nanobelt photodetectors guarantee their highest potential for visible-blind UV-light sensors working in the UV-A band. [source] Observation of a Charge Transfer State in Low-Bandgap Polymer/Fullerene Blend Systems by Photoluminescence and Electroluminescence StudiesADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Yi Zhou Abstract The presence of charge transfer states generated by the interaction between the fullerene acceptor PCBM and two alternating copolymers of fluorene with donor,acceptor,donor comonomers are reported; the generation leads to modifications in the polymer bandgap and electronic structure. In one of polymer/fullerene blends, the driving force for photocurrent generation, i.e., the gap between the lowest unoccupied molecular orbitals of the donor and acceptor, is only 0.1,eV, but photocurrent is generated. It is shown that the presence of a charge transfer state is more important than the driving force. The charge transfer states are visible through new emission peaks in the photoluminescence spectra and through electroluminescence at a forward bias. The photoluminescence can be quenched under reverse bias, and can be directly correlated to the mechanism of photocurrent generation. The excited charge transfer state is easily dissociated into free charge carriers, and is an important intermediate state through which free charge carriers are generated. [source] Photophysics and Photocurrent Generation in Polythiophene/Polyfluorene Copolymer BlendsADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Christopher R. McNeill Abstract Here, studies on the evolution of photophysics and device performance with annealing of blends of poly(3-hexylthiophene) with the two polyfluorene copolymers poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2,,2,,-diyl) (F8TBT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) are reported. In blends with F8TBT, P3HT is found to reorganize at low annealing temperatures (100,°C or below), evidenced by a redshift of both absorption and photoluminescence (PL), and by a decrease in PL lifetime. Annealing to 140,°C, however, is found to optimize device performance, accompanied by an increase in PL efficiency and lifetime. Grazing-incidence small-angle X-ray scattering is also performed to study the evolution in film nanomorphology with annealing, with the 140,°C-annealed film showing enhanced phase separation. It is concluded that reorganization of P3HT alone is not sufficient to optimize device performance but must also be accompanied by a coarsening of the morphology to promote charge separation. The shape of the photocurrent action spectra of P3HT:F8TBT devices is also studied, aided by optical modeling of the absorption spectrum of the blend in a device structure. Changes in the shape of the photocurrent action spectra with annealing are observed, and these are attributed to changes in the relative contribution of each polymer to photocurrent as morphology and polymer conformation evolve. In particular, in as-spun films from xylene, photocurrent is preferentially generated from ordered P3HT segments attributed to the increased charge separation efficiency in ordered P3HT compared to disordered P3HT. For optimized devices, photocurrent is efficiently generated from both P3HT and F8TBT. In contrast to blends with F8TBT, P3HT is only found to reorganize in blends with F8BT at annealing temperatures of over 200,°C. The low efficiency of the P3HT:F8BT system can then be attributed to poor charge generation and separation efficiencies that result from the failure of P3HT to reorganize. [source] Photoelectrochemical Study of Nanostructured ZnO Thin Films for Hydrogen Generation from Water SplittingADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Abraham Wolcott Abstract Photoelectrochemical cells based on traditional and nanostructured ZnO thin films are investigated for hydrogen generation from water splitting. The ZnO thin films are fabricated using three different deposition geometries: normal pulsed laser deposition, pulsed laser oblique-angle deposition, and electron-beam glancing-angle deposition. The nanostructured films are characterized by scanning electron microscopy, X-ray diffraction, UV-vis spectroscopy and photoelectrochemical techniques. Normal pulsed laser deposition produces dense thin films with ca. 200,nm grain sizes, while oblique-angle deposition produces nanoplatelets with a fishscale morphology and individual features measuring ca. 900 by 450,nm on average. In contrast, glancing-angle deposition generates a highly porous, interconnected network of spherical nanoparticles of 15,40,nm diameter. Mott-Schottky plots show the flat band potential of pulsed laser deposition, oblique-angle deposition, and glancing-angle deposition samples to be ,0.29, ,0.28 and +0.20,V, respectively. Generation of photocurrent is observed at anodic potentials and no limiting photocurrents were observed with applied potentials up to 1.3,V for all photoelectrochemical cells. The effective photon-to-hydrogen efficiency is found to be 0.1%, 0.2% and 0.6% for pulsed laser deposition, oblique-angle deposition and glancing-angle deposition samples, respectively. The photoelectrochemical properties of the three types of films are understood to be a function of porosity, crystal defect concentration, charge transport properties and space charge layer characteristics. [source] Organic Photovoltaic Cells Based On Solvent-Annealed, Textured Titanyl Phthalocyanine/C60 HeterojunctionsADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Diogenes Placencia Abstract Organic photovoltaic cells (OPV) with good near-IR photoactivity are created from highly textured titanyl phthalocyanine (TiOPc)/C60 heterojunctions. Vacuum deposited TiOPc thin films are converted to the near-IR absorbing "Phase II" polymorph using post-deposition solvent annealing. The Phase I,,,Phase II transition broadens the absorbance spectrum of the Pc film producing absorptivities (,,,,105,cm,1) from 600,900,nm, along with substantial texturing of the Pc layer. Atomic force microscopy and field-emission scanning electron microscopy of the solvent annealed films show that the surface roughness of the Pc layers is increased by a factor of greater than 2× as a result of the phase transformation. Current,voltage (J,V) responses for white light illumination of ITO (100,nm)/TiOPc (20,nm)/C60 (40,nm)/BCP (10,nm)/Al (100,nm) OPVs show a near doubling of the short-circuit photocurrent (JSC), with only a small decrease in open-circuit photopotential (VOC), and a concomitant increase in power conversion efficiency. Incident photon current efficiency (IPCE) plots confirmed the enhanced near-IR OPV activity, with maximum IPCE values of ca. 30% for devices using Phase II-only TiOPc films. UV-photoelectron spectroscopy (UPS) of TiOPc/C60 heterojunctions, for both Phase I and Phase II TiOPc films, suggest that the Phase II polymorph has nearly the same HOMO energy as seen in the Phase I polymorph, and similar frontier orbital energy offsets, EHOMOPc,ELUMOC60, leading to comparable open-circuit photovoltages. These studies suggest new strategies for the formation of higher efficiency OPVs using processing conditions which lead to enhance near-IR absorptivities, and extensive texturing of crystalline donor or acceptor films. [source] Microstructured Arrays of TiO2 Nanotubes for Improved Photo-Electrocatalysis and Mechanical StabilityADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Daoai Wang Abstract The preparation of micropatterned TiO2 nanotubes (NTs) with tunable morphologies by combining laser micromachining technology and an anodization method is reported. The micropatterned structure can be easily designed and fabricated by laser micromachining a titanium substrate, further anodization of which gives nanotube arrays perpendicularly oriented to the titanium surface. The patterned TiO2 NTs show dramatically improved photocurrent and photocatalytic performances because of their enhanced surface area and light-harvesting capability. The photocurrent density and incident-photon-to-current efficiency at the peak absorption increases by 48 and 39%, respectively, compared to a TiO2 NT array without a patterned structure. It was also found that micropatterning dramatically improves the mechanical stability of the TiO2 NTs on the substrate, which otherwise were liable to peel off from the substrate surface. The strategy will reasonably expand the application of TiO2 NTs in a variety of fields that require enhanced photo-electrocatalysis and mechanical stability. [source] Charge Generation and Photovoltaic Operation of Solid-State Dye-Sensitized Solar Cells Incorporating a High Extinction Coefficient Indolene-Based SensitizerADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Henry J. Snaith Abstract An investigation of the function of an indolene-based organic dye, termed D149, incorporated in to solid-state dye-sensitized solar cells using 2,2,,7,7,-tetrakis(N,N -di- p -methoxypheny-amine)-9,9,-spirobifluorene (spiro-OMeTAD) as the hole transport material is reported. Solar cell performance characteristics are unprecedented under low light levels, with the solar cells delivering up to 70% incident photon-to-current efficiency (IPCE) and over 6% power conversion efficiency, as measured under simulated air mass (AM) 1.5 sun light at 1 and 10,mW cm,2. However, a considerable nonlinearity in the photocurrent as intensities approach "full sun" conditions is observed and the devices deliver up to 4.2% power conversion efficiency under simulated sun light of 100,mW cm,2. The influence of dye-loading upon solar cell operation is investigated and the thin films are probed via photoinduced absorption (PIA) spectroscopy, time-correlated single-photon counting (TCSPC), and photoluminescence quantum efficiency (PLQE) measurements in order to deduce the cause for the non ideal solar cell performance. The data suggest that electron transfer from the photoexcited sensitizer into the TiO2 is only between 10 to 50% efficient and that ionization of the photo excited dye via hole transfer directly to spiro-OMeTAD dominates the charge generation process. A persistent dye bleaching signal is also observed, and assigned to a remarkably high density of electrons "trapped" within the dye phase, equivalent to 1.8,×,1017,cm,3 under full sun illumination. it is believed that this localized space charge build-up upon the sensitizer is responsible for the non-linearity of photocurrent with intensity and nonoptimum solar cell performance under full sun conditions. [source] Recombination-Limited Photocurrents in Low Bandgap Polymer/Fullerene Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Martijn Lenes Abstract The charge transport and photogeneration in solar cells based on the low bandgap-conjugated polymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H -cyclopenta[2,1-b; 3,4-b,]dithiophene)- alt -4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and fullerenes is studied. The efficiency of the solar cells is limited by a relatively low fill factor, which contradicts the observed good and balanced charge transport in these blends. Intensity dependent measurements display a recombination limited photocurrent, characterized by a square root dependence on effective applied voltage, a linear dependence on light intensity and a constant saturation voltage. Numerical simulations show that the origin of the recombination limited photocurrent stems from the short lifetime of the bound electron-hole pairs at the donor/acceptor interface. [source] Design of Multilayered Nanostructures and Donor,Acceptor Interfaces in Solution-Processed Thin-Film Organic Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2008Hiroaki Benten Abstract Multilayered polymer thin-film solar cells have been fabricated by wet processes such as spin-coating and layer-by-layer deposition. Hole- and electron-transporting layers were prepared by spin-coating with poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (PEDOT:PSS) and fullerene (C60), respectively. The light-harvesting layer of poly-(p -phenylenevinylene) (PPV) was fabricated by layer-by-layer deposition of the PPV precursor cation and poly(sodium 4-styrenesulfonate) (PSS). The layer-by-layer technique enables us to control the layer thickness with nanometer precision and select the interfacial material at the donor,acceptor heterojunction. Optimizing the layered nanostructures, we obtained the best-performance device with a triple-layered structure of PEDOT:PSS|PPV|C60, where the thickness of the PPV layer was 11,nm, comparable to the diffusion length of the PPV singlet exciton. The external quantum efficiency spectrum was maximum (ca. 20%) around the absorption peak of PPV and the internal quantum efficiency was estimated to be as high as ca. 50% from a saturated photocurrent at a reverse bias of ,3,V. The power conversion efficiency of the triple-layer solar cell was 0.26% under AM1.5G simulated solar illumination with 100,mW,cm,2 in air. [source] Origin of the Reduced Fill Factor and Photocurrent in MDMO-PPV:PCNEPV All-Polymer Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 13 2007M. Mandoc Abstract The photogeneration mechanism in blends of poly[2-methoxy-5-(3,,7,-dimethyloctyloxy)-1,4 - phenylene vinylene] (MDMO-PPV) and poly[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3,,7,-dimethyloctyloxy)-1,4-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV) is investigated. The photocurrent in the MDMO-PPV:PCNEPV blends is strongly dependent on the applied voltage as a result of a low dissociation efficiency of the bound electron,hole pairs. The dissociation efficiency is limited by low carrier mobilities, low dielectric constant, and the strong intermixing of the polymers, leading to a low fill factor and a reduced photocurrent at operating conditions. Additionally, electrons trapped in the PCNEPV phase recombine with the mobile holes in the MDMO-PPV phase at the interface between the two polymers, thereby affecting the open-circuit voltage and increasing the recombination losses. At an intensity of one,sun, Langevin recombination of mobile carriers dominates over trap-assisted recombination. [source] Photoresponse Properties of CdSe Single-Nanoribbon Photodetectors,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2007Y. Jiang Abstract Photodetectors are fabricated from individual single-crystal CdSe nanoribbons, and the photoresponse properties of the devices are studied systematically. The photodetector shows a high sensitivity towards excitation wavelength with a sharp cut-off at 710,nm, corresponding to the bandgap of CdSe. The device exhibits a high photo-to-dark current ratio of five orders of magnitude at 650,nm, and can function with excellent stability, reproducibility, and high response speed (<,1,ms) in a wide range of switching frequency (up to 300,Hz). The photocurrent of the device shows a power-law dependence on light intensity. This finding together with the analysis of the light intensity-dependent response speed reveals the existence of various traps at different energy levels (shallow and deep) in the bandgap. Coating with a thin SiO2 isolating layer increases the photocurrent but decreases the response speed of the CdSe nanoribbon, which is attributed to reduction of recombination centers on ribbon surface. [source] The Effect of Polymer Optoelectronic Properties on the Performance of Multilayer Hybrid Polymer/TiO2 Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 4 2005P. Ravirajan Abstract We report a study of the effects of polymer optoelectronic properties on the performance of photovoltaic devices consisting of nanocrystalline TiO2 and a conjugated polymer. Three different poly(2-methoxy-5-(2,-ethylhexoxy)-1,4-phenylenevinylene) (MEH-PPV)-based polymers and a fluorene,bithiophene copolymer are compared. We use photoluminescence quenching, time-of-flight mobility measurements, and optical spectroscopy to characterize the exciton-transport, charge-transport, and light-harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic-device performance. We find that photocurrent is primarily limited by the photogeneration rate and by the quality of the interfaces, rather than by hole transport in the polymer. We have also studied the photovoltaic performance of these TiO2/polymer devices as a function of the fabrication route and device design. Including a dip-coating step before spin-coating the polymer leads to excellent polymer penetration into highly structured TiO2 networks, as was confirmed through transient optical measurements of the photoinduced charge-transfer yield and recombination kinetics. Device performance is further improved for all material combinations studied, by introducing a layer of poly(ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonic acid) (PSS) under the top contact. Optimized devices incorporating the additional dip-coated and PEDOT:PSS layers produced a short-circuit current density of about 1,mA,cm,2, a fill factor of 0.50, and an open-circuit voltage of 0.86,V under simulated AM,1.5 illumination (100,mW,cm,2, 1,sun). The corresponding power conversion efficiency under 1,sun was ,,0.4,%. [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] Fullerene Sensitized Silicon for Near- to Mid-Infrared Light DetectionADVANCED MATERIALS, Issue 5 2010Gebhard J. Matt A novel light-sensing scheme based on a silicon/fullerene-derivative heterojunction allows optoelectronic detection in the near- to mid-infrared (IR), which is fully compatible with complementary metal oxide semiconductor (CMOS) technology. Although silicon and the fullerene derivative do not absorb in the IR, a heterojunction of these materials absorbs and generates a photocurrent (PC) in the near- to mid-IR, presumably caused by an interfacial absorption mechanism. [source] Formation of Highly Efficient Dye-Sensitized Solar Cells by Hierarchical Pore Generation with Nanoporous TiO2 SpheresADVANCED MATERIALS, Issue 36 2009Yong Joo Kim Nanoporous TiO2 structures were successfully applied for the fabrication of DSC electrodes, providing high surface areas and large pore sizes at the same time. High photocurrent was induced in these DSCs by great adsorption of dye molecules and efficient electrolyte diffusion, caused by the generated hierarchical pore structures in the TiO2 layer. [source] Nonuniform Nanowire Doping Profiles Revealed by Quantitative Scanning Photocurrent MicroscopyADVANCED MATERIALS, Issue 30 2009Jonathan E. Allen Scanning photocurrent microscopy (SPCM) is used in semiconductor nanowire devices to establish quantitative potential profiles correlated with nonuniformities in electrical resistivity. Surface doping leads to a nonuniform axial photocurrent (a). Surface etching improves the uniformity of the local photocurrent (b) and reduces the radial and axial carrier concentration gradients (c, blue curve after etching). [source] Metallic Nanoparticle Network for Photocurrent Generation and PhotodetectionADVANCED MATERIALS, Issue 29 2009Xian Ning Xie The generation and conduction of photoelectrons in ligated metallic Au NPs are demonstrated, and their key factors include tunneling of photoexcited electrons, the close packing of the NP network, and increased photoelectron-to-intrinsic electron ratio associated with ligand passivation. In view of their inherent characteristics, metallic NPs may provide a promising alternative to semiconductors in photocurrent and photodetection applications. [source] Magnetic-Field Effects in Organic Semiconducting Materials and DevicesADVANCED MATERIALS, Issue 14-15 2009Bin Hu Abstract It 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. [source] Studies of the micellar effect on photogalvanics: Solar energy conversion and storage,EDTA,safranine O,DSS systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2010Prerna Gangotri Abstract The studies of the micellar effect on photogalvanics was done for solar energy conversion and storage in photogalvanic cell containing dioctyl sodium sulphosuccinate as anionic micellar species, EDTA as reductant and safranine O as photosensitizer. The photopotential and photocurrent generated were 800.0,mV and 65.0,µA respectively. The observed conversion efficiency was 0.2532 per cent, the fill factor was 0.38 and the maximum power of the cell was 52.0,µW whereas the power at power point of the photogalvanic cell was 26.34,µW. The rate of initial generation of current was 37.5,µA,min,1. The photogalvanic cell can be used for 80.0,minutes in the dark. The effects of different parameters on the electrical output of the photogalvanic cell were observed and a mechanism has also been proposed for the generation of photocurrent in the photogalvanic cell. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||