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Photovoltaic Devices (photovoltaic + device)
Kinds of Photovoltaic Devices Selected AbstractsTriplet 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] The Impact of Polymer Regioregularity on Charge Transport and Efficiency of P3HT:PCBM Photovoltaic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Ralf Mauer Abstract The charge transport in pristine poly(3-hexylthiophene) (P3HT) films and in photovoltaic blends of P3HT with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is investigated to study the influence of charge-carrier transport on photovoltaic efficiency. The field- and temperature dependence of the charge-carrier mobility in P3HT of three different regioregularities, namely, regiorandom, regioregular with medium regioregularity, and regioregular with very high regioregularity are investigated by the time-of-flight technique. While medium and very high regioregularity polymers show the typical absorption features of ordered lamellar structures of P3HT in the solid state even without previous annealing, films of regiorandom P3HT are very disordered as indicated by their broad and featureless absorption. This structural difference in the solid state coincides with partially non-dispersive transport and hole mobilities µh of around 10,4 and 10,5,cm2 V,1 s,1 for the high and medium regioregularity P3HT, respectively, and a slow and dispersive charge transport for the regiorandom P3HT. Upon blending the regioregular polymers with PCBM, the hole mobilities are typically reduced by one order of magnitude, but they do not significantly change upon additional post-spincasting annealing. Only in the case of P3HT with high regioregularity are the electron mobilities similar to the hole mobilities and the charge transport is, thus, balanced. Nonetheless, devices prepared from both materials exhibit similar power conversion efficiencies of 2.5%, indicating that very high regioregularity may not substantially improve order and charge-carrier transport in P3HT:PCBM and does not lead to significant improvements in the power-conversion efficiency of photovoltaic devices. [source] Nanotube Arrays: Template-Directed Liquid ALD Growth of TiO2 Nanotube Arrays: Properties and Potential in Photovoltaic Devices (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Mater. X. Hu, A. Sellinger, et al. present on page 1390 an array of TiO2 nanotubes prepared via a new liquid atomic layer deposition process in porous anodic alumina templates. The ability to reproduce the arrays on various types of substrates including Si and transparent conducting oxides opens opportunities in many exciting opto-electronic applications. The potential of such arrays in ordered bulk-heterojunction solar cells is explored. [source] Template-Directed Liquid ALD Growth of TiO2 Nanotube Arrays: Properties and Potential in Photovoltaic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Thelese R. B. Foong Abstract Dense and well-aligned arrays of TiO2 nanotubes extending from various substrates are successfully fabricated via a new liquid-phase atomic layer deposition (LALD) in nanoporous anodic alumina (AAO) templates followed by alumina dissolution. The facile and versatile process circumvents the need for vacuum conditions critical in traditional gas-phase ALD and yet confers ALD-like deposition rates of 1.6,2.2,Å cycle,1, rendering smooth conformal nanotube walls that surpass those achievable by sol,gel and Ti-anodizing techniques. The nanotube dimensions can be tuned, with most robust structures being 150,400,nm tall, 60,70,nm in diameter with 5,20,nm thick walls. The viability of TiO2 nanotube arrays deposited on indium tin oxide (ITO),glass electrodes for application in model hybrid poly(3-hexylthiophene) (P3HT):TiO2 solar cells is studied. The results achieved provide platforms and research directions for further advancements. [source] High-Performance Organic Photovoltaic Devices Using a New Amorphous Molecular Material with High Hole Drift Mobility, Tris[4-(5-phenylthiophen-2-yl)phenyl]amineADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Hiroshi Kageyama Abstract A new amorphous molecular material, tris[4-(5-phenylthiophen-2-yl)phenyl]amine (TPTPA), is synthesized and characterized. TPTPA forms a stable amorphous glass with a glass-transition temperature of 83,°C when the melt sample is cooled. It also forms amorphous thin films by a thermal deposition technique. TPTPA exhibits a hole drift mobility of 1.0,×,10,2,cm2 V,1 s,1 at an electric field of 1.0,×,105,V cm,1 and at 293,K, as determined by the time-of-flight method, which is of the highest level among those of amorphous molecular materials. pn-Heterojunction organic photovoltaic devices (OPVs) using TPTPA as an electron donor and C60 or C70 as an electron acceptor exhibit high performance with fill factors of 0.66,0.71 and power conversion efficiencies of 1.7,2.2% under air-mass (AM) 1.5G illumination at an intensity of 100,mW cm,2, which are of the highest level ever reported for OPVs using amorphous molecular materials. [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] Single ZnO Nanowire/p-type GaN Heterojunctions for Photovoltaic Devices and UV Light-Emitting DiodesADVANCED MATERIALS, Issue 38 2010Ya-Qing Bie We fabricate heterojunctions consisting of a single n-type ZnO nanowire and a p-type GaN film. The photovoltaic effect of heterojunctions exhibits open-circuit voltages ranging from 2 to 2.7 V, and a maximum output power reaching 80 nW. Light-emitting diodes with UV electroluminescence based on the heterojunctions are demonstrated. [source] Electric-Field Enhancement of Photovoltaic Devices: A Third Reason for the Increase in the Efficiency of Photovoltaic Devices by Carbon NanotubesADVANCED MATERIALS, Issue 20 2010Wonjoo Lee Electric-field enhancement of photovoltaic devices by carbon nanotubes (CNTs) is reported as a third alternative for increasing the efficiency of photovoltaic devices. Due to the formation of an efficient electronic energy-cascade structure, the decrease of the interfacial resistance, and the improvement of the electrical field, the power-conversion efficiency of solar cells was increased by 22% in the presence of the SWNTs. [source] Photovoltaic Devices: High-Efficiency Solar Cell with Earth-Abundant Liquid-Processed Absorber (Adv. Mater.ADVANCED MATERIALS, Issue 20 201020/2010) The image shows a thin-film solar cell, deposited from a hybrid solution-nanoparticle ink, with a background scanning electron microscopy (SEM) image of the zinc-compound particle component of the ink. A cross-sectional SEM image of the device shows the large-grained kesterite absorber layer composed of readily available elements: Cu-Zn-Sn-S-Se. The solution-processed devices offer record power conversion efficiency for kesterite absorber layers, as presented by D. B. Mitzi et al. on page E156. [source] Solar-Energy Production and Energy-Efficient Lighting: Photovoltaic Devices and White-Light-Emitting Diodes Using Poly(2,7-fluorene), Poly(2,7-carbazole), and Poly(2,7-dibenzosilole) DerivativesADVANCED MATERIALS, Issue 8 2010Serge Beaupré Abstract World energy needs grow each year. To address global warming and climate changes the search for renewable energy sources with limited greenhouse gas emissions and the development of energy-efficient lighting devices are underway. This Review reports recent progress made in the synthesis and characterization of conjugated polymers based on bridged phenylenes, namely, poly(2,7-fluorene)s, poly(2,7-carbazole)s, and poly(2,7-dibenzosilole)s, for applications in solar cells and white-light-emitting diodes. The main strategies and remaining challenges in the development of reliable and low-cost renewable sources of energy and energy-saving lighting devices are discussed. [source] Electrode Grids for ITO Free Organic Photovoltaic Devices,ADVANCED MATERIALS, Issue 19 2007K. Tvingstedt Silver grids are utilized to exclude the expensive use of indium tin oxide (ITO) in conjugated polymer photovoltaic devices. The grids are generated by electroless deposition from elastomeric microfluidic channels onto transparent substrates. The organic photovoltaic devices demonstrated here, with minimized series resistance, are confirmed to have characteristics comparable to devices exploiting ITO. [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] Layered Graphene/Quantum Dots for Photovoltaic Devices,ANGEWANDTE CHEMIE, Issue 17 2010Xian Guo Ganz einfach lassen sich Filme aus Graphen- und Quantenpunkt(QD)-Schichten aus wässrigen Lösungen auf transparenten leitfähigen Indiumzinnoxid(ITO)-Substraten aufbringen. Graphen eignet sich dank seiner Struktur und günstigen Austrittsarbeit gut für die Sammlung und Übertragung durch Licht erzeugter Ladungen auf die Elektrode; als Resultat erhält man ein hocheffizientes Photovoltaikelement (siehe Bild; IPCE=Photostromeffizienz, SWNT=einwandige Kohlenstoffnanoröhre). [source] Regioregular poly(3-alkanoylthiophene): Synthesis and electrochemical, photophysical, charge transport, and photovoltaic propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2010Chao Wang Abstract Head-to-tail regioregular poly(3-heptanoylthiophene) (PHOT) was synthesized by Ni-catalyzed polycondensation of the 2,2-dimethyl-1,3-propanediol-protected Grignard monomer followed by deprotection. Cyclic voltammetric (CV) study demonstrates that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of PHOT are 0.5 eV lower in energy than those of the head-to-tail poly(3-hexylthiophene) (HT-P3HT). Their optical band gaps are essentially the same. Incomplete photoluminescence (PL) quenching was observed in thin films of the 1:1 blend of PHOT and HT-P3HT. PHOT displayed a glass transition at ,269 °C and decomposed at ,300 °C according to differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Wide-angle X-ray diffraction (WAXD) study showed that PHOT exists in a not highly ordered state in solid films especially in the ,-stacking direction. Only p -channel activity was observed in field-effect transistors (FETs) for PHOT. The hole mobility was on the order of 10,4 cm2 V,1 s,1. Photovoltaic devices with an active layer of 1:1 blend of PHOT and PC71BM had a power conversion efficiency (PCE) of ,0.5%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source] Poly(3-hexylthiophene) Nanorods with Aligned Chain Orientation for Organic PhotovoltaicsADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Jong Soo Kim Abstract A structured polymer solar cell architecture featuring a large interface between donor and acceptor with connecting paths to the respective electrodes is explored. To this end, poly-(3-hexylthiophene) (P3HT) nanorods oriented perpendicularly to indium tin oxide (ITO) glass are fabricated using an anodic aluminum oxide template. It is found that the P3HT chains in bulk films or nanorods are oriented differently; perpendicular or parallel to the ITO substrate, respectively. Such chain alignment of the P3HT nanorods enhanced the electrical conductivity up to tenfold compared with planar P3HT films. Furthermore, the donor/acceptor contact area could be maximised using P3HT nanorods as donor and C60 as acceptor. In a photovoltaic device employing this structure, remarkable photoluminescence quenching (88%) and a seven-fold efficiency increase (relative to a device with a planar bilayer) are achieved. [source] Depletion of PCBM at the Cathode Interface in P3HT/PCBM Thin Films as Quantified via Neutron Reflectivity MeasurementsADVANCED MATERIALS, Issue 22 2010Andrew J. Parnell Using neutron reflectivity, self-stratification in a model P3HT/PCBM blend is observed. The as-spun and solvent-annealed films show a depletion of PCBM near the top surface and enrichment of PCBM at the substrate (see figure). Depletion of PCBM at the cathode interface in a photovoltaic device could act as a barrier to efficient electron extraction. On thermal annealing, the PCBM depleted region is eliminated; an effect that partially explains the improvement of P3HT/PCBM devices on thermal annealing. [source] Enhanced Charge Separation by Sieve-Layer Mediation in High-Efficiency Inorganic-Organic Solar CellsADVANCED MATERIALS, Issue 7 2009Chien-Hung Lin The introduction of a thin electronic sieve layer of a material with a wide bandgap, such as lithium fluoride (LiF) or silicon oxide (SiOx), at the inorganic-organic interface of an organic photovoltaic device enhances the charge separation and improves the efficiency by more than an order to a maximum of 6.04%. [source] Synthesis and properties of phenothiazylene vinylene-based polymers: New organic semiconductors for field-effect transistors and solar cellsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2010Seon-Kyoung Son Abstract A series of new phenothiazylene vinylene-based semiconducting polymers, poly[3,7-(4,-dodecyloxyphenyl)phenothiazylene vinylene] (P1), poly[3,7-(4,-dodecyloxyphenyl)phenothiazylene vinylene- alt -1,4-phenylene vinylene] (P2), and poly[3,7-(4,-dodecyloxyphenyl)phenothiazylene vinylene- alt -2,5-thienylene vinylene] (P3), have been synthesized via a Horner-Emmons reaction. FTIR and 1H NMR spectroscopies confirmed that the configurations of the vinylene groups in the polymers were all - trans (E). The weight-averaged molecular weights (Mw) of P1, P2, and P3 were found to be 27,000, 22,000, and 29,000, with polydispersity indices of 1.91, 2.05, and 2.25, respectively. The thermograms for P1, P2, and P3 each contained only a broad glass transition, at 129, 167, and 155 °C, respectively, without the observation of melting features. UV,visible absorption spectra of the polymers showed two strong absorption bands in the ranges 315,370 nm and 450,500 nm, which arose from absorptions of the phenothiazine segments and the conjugated main chains. Solution-processed field-effect transistors fabricated from these polymers showed p -type organic thin-film transistor characteristics. The field-effect mobilities of P1, P2, and P3 were measured to be 1.0 × 10,4, 3.6 × 10,5, and 1.0 × 10,3 cm2 V,1 s,1, respectively, and the on/off ratios were in the order of 102 for P1 and P2, and 103 for P3. Atomic force microscopy and X-ray diffraction analysis of thin films of the polymers show that they have amorphous structures. A photovoltaic device in which a P3/PC71BM (1/5) blend film was used as the active layer exhibited an open-circuit voltage (VOC) of 0.42 V, a short circuit current (JSC) of 5.17 mA cm,2, a fill factor of 0.35, and a power conversion efficiency of 0.76% under AM 1.5 G (100 mW cm,2) illumination. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 635,646, 2010 [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] Recharging the Battery of Implantable Biomedical Devices by LightARTIFICIAL ORGANS, Issue 10 2009Carlos Algora Abstract This article describes a new powering system for implantable medical devices that could significantly increase their lifetime. The idea is based on the substitution of the usual implantable device battery for an electric accumulator (rechargeable battery), which is fed by the electric power generated by a photovoltaic converter inside the implantable device. Light impinges on the photovoltaic device through an optical fiber going from the photovoltaic device to just beneath the patient's epidermis. Light can enter the optical fiber by passing through the skin. A complete power-by-light system has been developed and tested with a real implantable pulse generator for spinal cord stimulation. The feasibility of the proposed system has been evaluated theoretically. For example, after 13 h/week of laser exposure, the lifetime of the implantable device would increase by 50%. Other combinations resulting in lifetime increases of more than 100% are also possible. So, the proposed system is now ready to take a further step forward: in vivo animal testing. [source] Perylene,Oligothiophene,Perylene Triads for Photovoltaic ApplicationsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2005Jens Cremer Abstract A series of novel acceptor,donor,acceptor triad systems, consisting of head-to-tail-coupled oligo(3-hexylthiophene)s integrated between two terminal perylenemonoimides are described. These hybrid molecules, which differ by the length of the oligothiophene units from a quaterthiophene up to a dodecithiophene were synthesized by an effective palladium-catalyzed Ullmann-type homo-coupling reaction in good yields. The optical and electrochemical properties of these compounds were determined, and on the basis of this series structure-property relationships have been established which provide vital information for the fabrication of the corresponding photovoltaic devices. Because the synthesized perylenyl-oligothiophenes distinguish themselves by a high absorption between 300 and 550 nm and an almost complete fluorescence quenching of the perylene acceptor, they meet the requirements for organic solar cells. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [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] The Effect of Nanoparticle Shape on the Photocarrier Dynamics and Photovoltaic Device Performance of Poly(3-hexylthiophene):CdSe Nanoparticle Bulk Heterojunction Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Smita Dayal Abstract The charge separation and transport dynamics in CdSe nanoparticle:poly(3-hexylthiophene) (P3HT) blends are reported as a function of the shape of the CdSe-nanoparticle electron acceptor (dot, rod, and tetrapod). For optimization of organic photovoltaic device performance it is crucial to understand the role of various nanostructures in the generation and transport of charge carriers. The sample processing conditions are carefully controlled to eliminate any processing-related effects on the carrier generation and on device performance with the aim of keeping the conjugated polymer phase constant and only varying the shape of the inorganic nanoparticle acceptor phase. The electrodeless, flash photolysis time-resolved microwave conductivity (FP-TRMC) technique is used and the results are compared to the efficiency of photovoltaic devices that incorporate the same active layer. It is observed that in nanorods and tetrapods blended with P3HT, the high aspect ratios provide a pathway for the electrons to move away from the dissociation site even in the absence of an applied electric field, resulting in enhanced carrier lifetimes that correlate to increased efficiencies in devices. The processing conditions that yield optimum performance in high aspect ratio CdSe nanoparticles blended with P3HT result in poorly performing quantum dot CdSe:P3HT devices, indicating that the latter devices are inherently limited by the absence of the dimensionality that allows for efficient, prolonged charge separation at the polymer:CdSe interface. [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] Stable Inverted Polymer/Fullerene Solar Cells Using a Cationic Polythiophene Modified PEDOT:PSS Cathodic InterfaceADVANCED FUNCTIONAL MATERIALS, Issue 15 2010David A. Rider Abstract A cationic and water-soluble polythiophene [poly[3-(6-pyridiniumylhexyl)thiophene bromide] (P3PHT+Br,)] is synthesized and used in combination with anionic poly(3,4-ethylenedioxythiophene):poly(p -styrenesulfonate) (PEDOT:PSS), to produce hybrid coatings on indium tin oxide (ITO). Two coating strategies are established: i) electrostatic layer-by-layer assembly with colloidal suspensions of (PEDOT:PSS),, and ii) modification of an electrochemically prepared (PEDOT:PSS), film on ITO. The coatings are found to modify the work function of ITO such that it could act as a cathode in inverted 2,5-diyl-poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61 -butyric acid methyl ester (PCBM) polymer photovoltaic cells. The interfacial modifier created from the layer-by-layer assembly route is used to produce efficient inverted organic photovoltaic devices (power conversion efficiency ,2%) with significant long-term stability in excess of 500,h. [source] The Impact of Polymer Regioregularity on Charge Transport and Efficiency of P3HT:PCBM Photovoltaic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Ralf Mauer Abstract The charge transport in pristine poly(3-hexylthiophene) (P3HT) films and in photovoltaic blends of P3HT with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is investigated to study the influence of charge-carrier transport on photovoltaic efficiency. The field- and temperature dependence of the charge-carrier mobility in P3HT of three different regioregularities, namely, regiorandom, regioregular with medium regioregularity, and regioregular with very high regioregularity are investigated by the time-of-flight technique. While medium and very high regioregularity polymers show the typical absorption features of ordered lamellar structures of P3HT in the solid state even without previous annealing, films of regiorandom P3HT are very disordered as indicated by their broad and featureless absorption. This structural difference in the solid state coincides with partially non-dispersive transport and hole mobilities µh of around 10,4 and 10,5,cm2 V,1 s,1 for the high and medium regioregularity P3HT, respectively, and a slow and dispersive charge transport for the regiorandom P3HT. Upon blending the regioregular polymers with PCBM, the hole mobilities are typically reduced by one order of magnitude, but they do not significantly change upon additional post-spincasting annealing. Only in the case of P3HT with high regioregularity are the electron mobilities similar to the hole mobilities and the charge transport is, thus, balanced. Nonetheless, devices prepared from both materials exhibit similar power conversion efficiencies of 2.5%, indicating that very high regioregularity may not substantially improve order and charge-carrier transport in P3HT:PCBM and does not lead to significant improvements in the power-conversion efficiency of photovoltaic devices. [source] Ultrafast Hole-Transfer Dynamics in Polymer/PCBM Bulk HeterojunctionsADVANCED FUNCTIONAL MATERIALS, Issue 10 2010Artem A. Bakulin Abstract Ultrafast dynamics of the hole-transfer process from methanofullerene to a polymer in a polymer/PCBM bulk heterojunction are directly resolved. Injection of holes into MDMO-PPV is markedly delayed with respect to [60]PCBM excitation. The fastest component of the delayed response is attributed to the PCBM,polymer hole-transfer process (30,±,10,fs), while the slower component (,150,fs) is provisionally assigned to energy transfer and/or relaxation inside PCBM nanoclusters. The charge generation through the hole transfer is therefore as fast and efficient as through the electron-transfer process. Exciton harvesting efficiency after PCBM excitation crucially depends on the concentration of the methanofullerene in the blend, which is related to changes in the blend morphology. Ultrafast charge generation is most efficient when the characteristic scale of phase separation in the blend does not exceed ,20,nm. At larger-scale phase separation, the exciton harvesting dramatically declines. The obtained results on the time scales of the ultrafast charge generation after PCBM excitation and their dependence on blend composition and morphology are instrumental for the future design of fullerene-derivative-based photovoltaic devices. [source] Nanomorphology and Charge Generation in Bulk Heterojunctions Based on Low-Bandgap Dithiophene Polymers with Different Bridging AtomsADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Mauro Morana Abstract Carbon bridged (C-PCPDTBT) and silicon-bridged (Si-PCPDTBT) dithiophene donor,acceptor copolymers belong to a promising class of low bandgap materials. Their higher field-effect mobility, as high as 10,2,cm2 V,1,s,1 in pristine films, and their more balanced charge transport in blends with fullerenes make silicon-bridged materials better candidates for use in photovoltaic devices. Striking morphological changes are observed in polymer:fullerene bulk heterojunctions upon the substitution of the bridging atom. XRD investigation indicates increased ,,, stacking in Si-PCPDTBT compared to the carbon-bridged analogue. The fluorescence of this polymer and that of its counterpart C-PCPDTBT indicates that the higher photogeneration achieved in Si-PCPDTBT:fullerene films (with either [C60]PCBM or [C70]PCBM) can be correlated to the inactivation of a charge-transfer complex and to a favorable length of the donor,acceptor phase separation. TEM studies of Si-PCPDTBT:fullerene blended films suggest the formation of an interpenetrating network whose phase distribution is comparable to the one achieved in C-PCPDTBT:fullerene using 1,8-octanedithiol as an additive. In order to achieve a balanced hole and electron transport, Si-PCPDTBT requires a lower fullerene content (between 50 to 60,wt%) than C-PCPDTBT (more than 70,wt%). The Si-PCPDTBT:[C70]PCBM OBHJ solar cells deliver power conversion efficiencies of over 5%. [source] Measurement of Charge-Density Dependence of Carrier Mobility in an Organic Semiconductor BlendADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Christopher G. Shuttle Abstract Here, a new methodology for analyzing the charge-density dependence of carrier mobility in organic semiconductors, applicable to the low-charge-density regime (1014,1017,cm,3) corresponding to the operation conditions of many organic optoelectronic devices, is reported. For the P3HT/PCBM blend photovoltaic devices studied herein, the hole mobility µ is found to depend on charge density n according to a power law µ(n) , n,, where ,,=,0.35. This dependence is shown to be consistent with an energetic disorder model based upon an exponential tail of localized intra-band states. [source] High-Performance Organic Photovoltaic Devices Using a New Amorphous Molecular Material with High Hole Drift Mobility, Tris[4-(5-phenylthiophen-2-yl)phenyl]amineADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Hiroshi Kageyama Abstract A new amorphous molecular material, tris[4-(5-phenylthiophen-2-yl)phenyl]amine (TPTPA), is synthesized and characterized. TPTPA forms a stable amorphous glass with a glass-transition temperature of 83,°C when the melt sample is cooled. It also forms amorphous thin films by a thermal deposition technique. TPTPA exhibits a hole drift mobility of 1.0,×,10,2,cm2 V,1 s,1 at an electric field of 1.0,×,105,V cm,1 and at 293,K, as determined by the time-of-flight method, which is of the highest level among those of amorphous molecular materials. pn-Heterojunction organic photovoltaic devices (OPVs) using TPTPA as an electron donor and C60 or C70 as an electron acceptor exhibit high performance with fill factors of 0.66,0.71 and power conversion efficiencies of 1.7,2.2% under air-mass (AM) 1.5G illumination at an intensity of 100,mW cm,2, which are of the highest level ever reported for OPVs using amorphous molecular materials. [source] | |||||||||||||||||||||||||||||||