| 1. |
- Chen, Youchun, et al.
(författare)
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Insights into the working mechanism of cathode interlayers in polymer solar cells via [(C8H17)(4)N](4)[SiW12O40]
- 2016
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 4:48, s. 19189-19196
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Tidskriftsartikel (refereegranskat)abstract
- A low-cost (amp;lt;$1 per g), high-yield (amp;gt;90%), alcohol soluble surfactant-encapsulated polyoxometalate complex [(C8H17)(4)N](4)[SiW12O40] has been synthesized and utilized as a cathode interlayer (CIL) in polymer solar cells (PSCs). A power conversion efficiency of 10.1% can be obtained for PSCs based on PTB7-Th (poly[[2,6-4,8-di(5-ethylhexylthienyl) benzo[1,2-b;3,3-b]-dithiophene][3-fluoro-2[(2-ethylhexyl) carbonyl] thieno [3,4-b]-thiophenediyl]]):PC71BM ([6,6]-phenyl C71-butyric acidmethyl ester) due to the incorporation of [(C8H17)(4)N](4)[SiW12O40]. Combined measurements of current density-voltage characteristics, transient photocurrent, charge carrier mobility and capacitance-voltage characteristics demonstrate that [(C8H17)(4)N](4)[SiW12O40] can effectively increase the built-in potential, charge carrier density and mobility and accelerate the charge carrier extraction in PSCs. Most importantly, the mechanism of using [(C8H17)(4)N](4)[SiW12O40] as the CIL is further brought to light by X-ray photoemission spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) of the metal/ [(C8H17)(4)N](4)[SiW12O40] interface. The findings suggest that [(C8H17)(4)N](4)[SiW12O40] not only decreased the work function of the metal cathodes but also was n-doped upon contact with the metals, which provide insights into the working mechanism of the CILs simultaneously improving the open circuit voltage, short circuit current and fill factor in the PSCs.
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| 2. |
- Li, Weiwei, et al.
(författare)
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Tailoring side chains of low band gap polymers for high efficiency polymer solar cells
- 2010
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Ingår i: Polymer. - : Elsevier Science B.V., Amsterdam.. - 0032-3861 .- 1873-2291. ; 51:14, s. 3031-3038
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Tidskriftsartikel (refereegranskat)abstract
- High efficiency organic solar cells (OSCs) require conjugated polymers with a low band gap, broad absorption in visible and IR region, high carrier mobility, and relatively high molecular weight as p-type donor materials. Flexible side chains on the rigid polymer backbone are crucial for the solubility of conjugated polymers. In this work, four polymers with the main chain structure of fluorene-thiophene-benzothiadiazole-thiophene and flexible side chains located on fluorene, thiophene, and benzothiadiazole moiety, respectively, have been synthesized by Suzuki-Miyaura-Schluter polycondensation. Photovoltaic device measurements with a device configuration of ITO/polymer:PC71BM blends/LiF/Al show that P1 carrying octyloxy chains on benzothiadiazole rings gives the best performance, with a power conversion efficiency of 3.1%.
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| 3. |
- Li, Weiwei, et al.
(författare)
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Benzothiadiazole-Based Linear and Star Molecules : Design, Synthesis, and Their Application in Bulk Heterojunction Organic Solar Cells
- 2009
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Ingår i: CHEMISTRY OF MATERIALS. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 21:21, s. 5327-5334
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Tidskriftsartikel (refereegranskat)abstract
- Star molecules have many advantages, such as monodispersity, excellent solubility, and vast structures with different functional groups. A set of four-arm star molecules with benzothiadiazole as the core, oligothiophene its the arm, and triphenylamine its the end group and their linear counterparts were designed and synthesized Organic solar cells (OSCs) fabricated with these star molecules and [6,6]-phenyl C-71 butyric acid methyl ester (PC71BM) by spin-coating from solution demonstrate similar short circuit current density (J(sc)) and fill factor (FF) but larger open circuit voltage (V-oc) in comparison With solar cells fabricated with corresponding linear molecules and PC71BM A power conversion efficiency (PCE) of 18%, with J(sc) = 4.9 mA/cm(2), V-oc = 0 92 V, and FF = 0 41 was achieved with one of these star molecules
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| 4. |
- Carlegrim, Elin, et al.
(författare)
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Characterization of the Ni/V(TCNE)x interface for hybrid spintronics applications
- 2010
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Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 11:6, s. 1020-1024
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Tidskriftsartikel (refereegranskat)abstract
- Vanadium tetracyanoethylene, V(TCNE)x, is an organic-based magnet with properties suitable for spintronics applications, e.g. spin valves. In this paper we propose a new hybrid organic spin valve design where V(TCNE)x is used as a spin-transporting and spin-filtering layer sandwiched between two ferromagnetic (FM) metal contacts, i.e. FM/V(TCNE)x/FM. As the spin injection and detection of such a device occurs at the interfaces the quality of those are of crucial importance. Therefore, the Ni/V(TCNE)x interface has been investigated by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption spectroscopy (NEXAFS) as well as compared with XPS results from a model system, Ni/TCNE. Ni chemically interact with both the vinyl and cyano groups but there is no evidence for significant diffusion of Ni into the V(TCNE)x film. As the chemical interaction affects the spin injection and detection negatively by modifying the lowest unoccupied molecular orbital (LUMO) and destroying the magnetic ordering network at the surface, these results indicate that there is need for a buffer layer between V(TCNE)x and Ni, and in extension most likely between V(TCNE)x and any FM contact.
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| 5. |
- Chen, Yulan, et al.
(författare)
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Facile Synthesis of 3,8-Dibromo-Substituted Phenanthridine Derivatives and Their Conjugated Polymers
- 2010
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Ingår i: MACROMOLECULES. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:3, s. 1349-1355
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Tidskriftsartikel (refereegranskat)abstract
- We present an efficient and convenient synthesis of 3,8-dibromophenanthridine derivatives and their conjugated polymers and demonstrate that phenanthridine-containing conjugated polymers can be used as luminescent chemosensor materials. High molecular weight poly(phenanthridine-co-fluorene)s (P1, P2) and poly(phenanthridine-co-p-phenylene) (P3) were synthesized by palladium-catalyzed Suzuki-Miyaura-Schluter polycondensation (SMSPC). These phenanthridine-containing polymers are of high quantum yields in solution and show reversible optical response to protonation and deprotonation of the phenanthridine rings.
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| 6. |
- Harada, K., et al.
(författare)
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Ionized impurity scattering in n -doped C60 thin films
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:9
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Tidskriftsartikel (refereegranskat)abstract
- Carrier transport in organic films is usually dominated by hopping process, leading to different temperature dependence from that of inorganic crystals. The aurhors demonstrate that n -doped C60 films show temperature dependence analogous to inorganic semiconductors. At low temperatures, the conductivity increases with temperature, around room temperature, a maximum is reached and then the conductivity decreases. These observations are confirmed by the dependence of mobility on doping level. In contrast to previous reports for organic thin films, the C60 films show a decrease of mobility with increasing doping levels, i.e., they follow the well-known Matthiessen rule which is generally observed in inorganic semiconductors. © 2007 American Institute of Physics.
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| 7. |
- Li, Fenghong, et al.
(författare)
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Blue organic light-emitting diodes based on Mes2B [p-4, 4' -biphenyl-NPh(1-naphthyl)]
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:3
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Tidskriftsartikel (refereegranskat)abstract
- Here, we report highly efficient blue organic light-emitting diodes (OLEDs) with Mes2 B [p-4, 4' -biphenyl-NPh(1-naphthyl)] (BNPB) as a blue emitter. It is found that both efficiencies and electroluminescent color are very sensitive to the selection of electron transport materials in the devices. For an optimized structure [indium tin oxide/2,3,5,6-tetrafluoro-7,7,8,8- tetracyanoquinodimethane (1 nm) N, N' -di(naphthalen-1-yl)- N, N' -diphenyl-benzidine (45 nm) /BNPB (20 nm) /1,3,5-tris(2- N - phenylbenzimidazolyl) benzene (30 nm) /LiF (1 nm) /Al] with BNPB as an undoped blue emitter, a maximum current efficiency can reach 3.5 cdA. It is found that BNPB emits two distinct peaks, one of around 450 nm and the other of 485 nm, and their respective emission intensities depend on the nature of majority charge carrier in the emission layer. © 2008 American Institute of Physics.
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| 8. |
- Li, Fenghong, et al.
(författare)
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Electronic structure and molecular orientation of pentacene thin films on ferromagnetic La0.7Sr0.3MnO3
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 81:20, s. 205415-1-205415-6
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Tidskriftsartikel (refereegranskat)abstract
- Pentacene thin films deposited on a ferromagnetic electrode, La0.7Sr0.3MnO3 (LSMO), have been studied using near-edge x-ray absorption fine structure (NEXAFS), ultraviolet photoemission spectroscopy (UPS), and atomic force microscopy (AFM). Here we present electronic structure and molecular orientation of pentacene thin film on LSMO. No evidence related to covalent bonding or significant charge transfer between pentacene and LSMO has been found in the NEXAFS or UPS results. UPS measurements suggest that the vertical ionization potential of pentacene on LSMO is 4.9 eV. Our results extracted from NEXAFS indicate that molecular long axis of pentacene stands on the LSMO substrate surface with a tilt angle of about 22 degrees +/- 2 degrees between the main molecular axis and the substrate surface normal. AFM images show the terracelike crystalline grain formed by stacking pentacene crystalline layers and a rough crystal-layer spacing of 14-15 angstrom. Findings deduced from UPS, NEXAFS, and AFM consistently demonstrate that pentacene stands on LSMO with a tilt angle.
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| 9. |
- Li, Fenghong, et al.
(författare)
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Modified Surface Electronic and Magnetic Properties of La(0.6)Sr(0.4)MnO(3) Thin Films for Spintronics Applications
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:34, s. 16947-16953
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Tidskriftsartikel (refereegranskat)abstract
- We present the surface electronic and magnetic properties of half-metal La(0.6)Sr(0.4)MnO(3) (LSMO) thin film modified by a simple cleaning procedure, the so-called SC1 (5 H(2)O, 1 NH(4)OH, I H(2)O(2)), at 85 degrees C for 10-40 min in ambient atmosphere. In this study, photoemission spectroscopy (XPS/UPS), X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD) are used to characterize these properties of the manganites. Thanks to SC1 treatment, the work function of LSMO changes from 4.0-4.1 to 4.8-4.9 eV obtained from UPS measurements, while its surface roughness changes from 0.268 to 0.796 nm in AFM images. Combined 0 1s, Mn 2p, Sr 3d, La 4d, and Mn 3s core-level XPS spectroscopy investigations suggest that Mn and Sr contents decrease at the surface and the Mn value becomes 3.7 due to SC1 treament. Mn L-edge XAS spectra of LSMO thin film demonstrate that SC1 treatment results in a removal of Mn(2+) and an increase of the Mn(4+) concentration. OK-edge XAS spectra further prove an enhancement of hybridization between O 2p orbitals and e(g)down arrow, of Mn 3d induced by more Mn(4+). XMCD results show that SC1 treatment does not induce any drastic changes of magnetic properties of the LSMO thin film surface.
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| 10. |
- Li, Fenghong, et al.
(författare)
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Tuning Work Function of Noble Metals As Promising Cathodes in Organic Electronic Devices
- 2009
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Ingår i: CHEMISTRY OF MATERIALS. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 21:13, s. 2798-2802
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Tidskriftsartikel (refereegranskat)abstract
- Work function (WF) modification of metal electrodes by adsorbing electron-rich or electron-deficient molecules oil metal surfaces has become a field of significant interest. The barrier for charge carrier injection in organic semiconductor devices can be reduced by molecular adsorption, leading to all interfacial dipole. Here, we demonstrate that the WF of noble metals such as ALL call be decreased significantly by adsorbing air stable n-type dopant acridine orange base (AOB) thin film. When a (sub)monolayer AOB is deposited on sputter-cleaned Au, the WF of the substrate changes from 5.2 to 3.5 eV. At complete coverage of the Au Surface, the WF is further reduced to 3.3 eV. When a (sub) monolayer of AOB is inserted between Au and C-60 thin film, the barrier of electron injection is decreased by 0.4 +/- 0.1 eV as compared to an Au-C-60 interface without AOB. Polymer solar cells with AOB/Au as a cathode have a similar open circuit voltage and comparable power conversion efficiency with devices using LiF/Al as a cathode, demonstrating that the AOB-modified gold electrode is an efficient low-work-function contact. Given the low positive pinning energy of 3.3 eV for AOB, we expect that other conventional high-work-function materials (Ag, ITO. La0.7Sr0.3MnO3 and even PEDOT:PSS) can be modified by AOB as effectively as Au.
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