Abstract: Three novel low-bandgap copolymers containing alkylated 4,7-dithien-2-yl-2,1,3-benzothiadiazole (HBT) and different electron-rich functional groups (dialkylfluorene (PFV-HBT), dialkyloxyphenylene (PPV-HBT) and dialkylthiophene (PTV-HBT)) were prepared by Horner polycondensation reactions and characterized by H-1 NMR, gel permeation chromatography, and elemental analysis. The alkyl side chain brings these polymeric materials good solubility in common organic solvents, which is critical for the manufacture of solar cells in a cost-effective manner. The copolymers exhibit low optical bandgap from 1.48 to 1.83 eV. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers were measured by cyclic voltammetry. Theoretical calculations revealed that the variation laws of HOMO and the LUMO energy levels are well consistent with cyclic voltammetry measurement. The bulk heterojunction photovoltaic devices with the structure of ITO/PEDOT-PSS/polymer: PCBM/LiF/Al were fabricated by using the three copolymers as the donor and (6,6)-phenyl-C-61-butyric acid methyl ester (PCBM) as the acceptor in the active layer. The device based on PTV-HBT: PCBM (1: 4 w/w) achieved a power conversion efficiency of 1.05% under the illumination of AM 1.5, 100 mW/cm(2). (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2715-2724, 2011
Abstract: A new low band gap copolymer containing dialkylfluorene and 4,7-dithienyl-2,1,3-benzothiadiazole (TBT), poly(fluorenevinylene-alt-4,7-dithienyl-2,1,3-benzothiadiazole) (PF-TBT) was synthesized by Heck cross-coupling polymerization. The copolymer is soluble in common organic solvents such as chloroform, tetrahydrofuran and chlorobenzene. The TGA result indicated that the copolymer possesses good thermal stability. The absorption, electrochemical and photovoltaic properties of PF-TBT were investigated and compared with those of poly(fluorenevinylene-alt-4,7-diphenyl-2,1,3-benzothiadiazole) (PF-DBT) whose structure is similar to PF-TBT. The copolymer exhibited a broad absorption band with an absorption edge close to 700 nm and an optical band gap of 1.82 eV. Cyclic voltammetry studies indicated that the relatively low HOMO energy level assured a higher open circuit voltage (V-oc) when PF-TBT is used as the donor material in a photovoltaic cell. The bulk heterojunction (BHJ) solar cell using PF-TBT as the donor and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as the acceptor with the structure of ITO/PEDOT : PSS/copolymer : PCBM/LiF/Al, exhibited a V-oc of 0.86 V, short-circuit current density (J(sc)) of 3.97 mA cm(-2), fill factor (FF) of 0.35, and a power conversion efficiency (PCE) of 1.18% under one sun of AM 1.5 solar simulator illumination (100 mW cm(-2)).
Abstract: We report on semitransparent organic solar cells using a single-layer blend based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the top electrode. The PEDOT:PSS blend was prepared by mixing a high-conductivity formulation of PEDOT:PSS (H.C. Starck CLEVIOS PH-1000) and another formulation of PEDOT:PSS (H. C. Starck CLEVIOS CPP 105D). The PEDOT:PSS blend yields good wetting properties on the hydrophobic surface of a blend of poly(3-hexylthiophene) (P3HT) with phenyl-C-61-butyric acid methyl ester (PC60BM), and shows a conductivity over 400 S cm(-1). Semitransparent organic solar cells using the PEDOT:PSS blend as the top electrode with a structure of glass/ITO/ZnO/P3HT:PC60BM/PEDOT:PSS-blend exhibited an average power conversion efficiency of 2.4% estimated for 100 mW cm(-2) AM 1.5G illumination. (C) 2011 Elsevier B.V. All rights reserved.
Abstract: Semi-transparent inverted polymer solar cells (PSCs) were fabricated by all-spin-coating vacuum-free process. An interfacial layer of poly(allylamine hydrochloride) and dextran (PAH-D) was introduced to modify the surface wettability of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) film for depositing aqueous-solution-processed poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) (CLEVIOS(TM) PH500) (PH500) anode as well as enhancing the adhesion and bonding strength between the active layer (P3HT: PCBM) and conducting polymer electrode (PH500). The photovoltaic performance of the semi-transparent PSCs under top and bottom illumination was investigated and the highest PCE of about 1.86% was achieved under simulated AM 1.5 illumination (100 mW/cm(2)) from the bottom side with a reflective white paper back side. The semi-transparent Cell A have the potential for use as energy-generating color window glasses as well as the subcell of tandem solar cells. The all-spin-coating vacuum-free processing provides a possibility of high-throughput all-solution-processed fabrication of PSCs by roll-to-roll processing. (C) 2010 Elsevier B.V. All rights reserved.
Abstract: Electrochemistry provides a simple and promising method for preparing organic solar cells (OSCs). In this paper, we present a two-step solution-based method to prepare bilayer heterojunction OSCs by electrodepositing polythiophene (PTh) and then spin-coating chloroform solution of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) onto the PTh layer. The influence of film thickness on performance of bilayer solar cells was investigated, and the best performance was achieved when the thickness of PTh and PCBM was 15 nm and 30 nm, respectively. The optimized solar cell showed power conversion efficiency of 0.1% under the illumination of AM 1.5 (100 mW cm(-2)) simulated solar light. This solution-based method offers a new way for processing bilayer OSCs.
Abstract: We report on the properties of inverted polymer solar cells using an ultrathin Al2O3 buffer layer on indium tin oxide (ITO). The ultrathin Al2O3 layer, deposited by the atomic layer deposition method, was found to reduce the work function of ITO and turns ITO into an electron-collecting electrode. The current density-voltage characteristics of unexposed devices showed an s-shape kink. The kink was eliminated upon exposure to ultraviolet (UV) illumination. Inverted solar cells based on P3HT:PC60BM yielded a fill factor of 0.64 and a power conversion efficiency of about 2.8% estimated for 100 mW cm(-2) simulated AM 1.5 illumination.
Abstract: We report on indium tin oxide (ITO)-free and metal-free semitransparent organic solar cells with a high-conductivity poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (PH1000) as both the bottom and the top electrodes. The PH1000 film showed a conductivity of 680 +/- 50 S/cm. A ZnO layer was used as an interlayer to produce an electron-selective electrode. The semitransparent devices with a structure of glass/PH1000/ZnO/poly(3-hexylthiophene):phenyl-C-61-butyric acid methyl ester/PEDOT:PSS (CPP 105 D)/PH1000 exhibited an average power conversion efficiency of 1.8% estimated for 100 mW/cm(2) air mass 1.5 global illumination. This geometry alleviates the need of vacuum deposition of a top electrode. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3499299]
Abstract: We report on the photovoltaic properties of inverted polymer solar cells where the transparent electron-collecting electrode is formed by a ZnO-modified indium tin oxide (ITO) electrode. The ZnO layers were deposited by atomic layer deposition (ALD) with varying thicknesses from 0.1 to 100 nm. The work function, surface roughness, and morphology of ITO/ZnO were found to be independent of the ZnO thickness. However, the device performance was found to be strongly dependent on a critical ZnO thickness, around 10 nm. Below the critical thickness the device performance was degraded because of the appearance of a “kink†in the current voltage characteristics. The kink features became less pronounced after ultraviolet (UV) exposure. This was attributed to oxygen desorption, leading to an increased conductivity of the ZnO layer. At and above this critical thickness, the device performance significantly improved and no longer depended strongly on the thickness of the ZnO layer, in agreement with optical simulations. Instead, these optical simulations showed that the thickness of the active layer plays a more important role than the thickness of the ZnO layer in optimizing the photovoltaic properties of inverted solar cells. Inverted polymer solar cells with an increased thickness of the active layer showed a power conversion efficiency (PCE) of 3.06% estimated for AM1.5G, a 100 mW cm(-2) illumination.
Abstract: We report on the fabrication and performance of polymer-based inverted solar cells utilizing amorphous indium zinc oxide (a-IZO) as the electron-collecting electrode. Amorphous IZO films of 200 nm thickness were deposited by room temperature sputtering in a high-purity argon atmosphere. The films possessed a high optical transmittance in the visible region (>= 80%), a low resistivity (3.3 x 10 (4) Omega cm), a low surface roughness (root mean square = 0.68 nm), and a low work function (4.46 +/- 0.02 eV). Inverted solar cells with the structure a-IZO/P3HT: PCBM/PEDOT:PSS/Ag exhibited a power conversion efficiency of 3% estimated for AM 1.5G, 100 mW/cm(2) illumination. (C) 2010 Optical Society of America
Abstract: Inverted transparent polymer solar cells were fabricated by sequentially depositing several organic layers from fluids, on ITO/glass substrates. ITO was used as a cathode to collect electrons. The photovoltage of these diodes can be increased by up to 400 mV by inserting a buffer layer of polyethylene oxide between ITO and the active layers, which results in 4-fold enhancement of power conversion efficiency under the illumination of 100 mW/cm(2) simulated AM1.5 solar light. The enhancement of V., is consistent with the work function change between ITO and ITO/PEO measured by photoelectron spectroscopy. Solar cell production without vacuum processing may lower production costs. (C) 2008 Elsevier B.V. All rights reserved.
Abstract: A novel poly(p-phenylenevinylene) PPV-based copolymer (3C-OXD-PPV) with electron-deficient oxadiazole segments as the side chain has been successfully synthesized through the Gilch polymerization. The obtained copolymer is soluble in common organic solvents such as chloroform, tetrahydronfuran, and 1,1,2,2-tetrachloroethane. The copolymer was characterized by H-1 NMR, elemental analysis and GPC. TGA measurement of the copolymer shows it has good thermal stability with decomposition temperature higher than 350 degrees C. The absorption, electrochemical properties of the 3C-OXD-PPV were investigated and also compared with the properties of MEH-PPV. The HOMO and LUMO levels of 3C-OXD-PPV were estimated from the electrochemical cyclic voltammograms. Bulk-heterojunction PVCs were fabricated by using 3C-OXD-PPV blended PCBM as an active layer. The PCE of the PVC is 1.60% under 100 mW cm(-2) AM 1.5 illumination, which indicates that 3C-OXD-PPV is a potential candidate for the application of polymer PVC. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1003-1012, 2009
Abstract: We fabricated polymer-based bulk heterojunction (BHJ) solar cells using a donor-acceptor (D-A) molecule N-propyl-3,6-bis[2-(3-dicyanomethylene-5,5-dimethylcyclohex-1-enyl)vin yl]carbazole (PDHC) as the acceptor. The strong photoluminescence (PL) quenching of poly[2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) when mixed with PDHC means that efficient charge transfer has happened between MEH-PPV and PDHC. We used MEH-PPV and poly (3-hexylthiophene) (P3HT) as the donors and PDHC as the acceptor to fabricate BHJ solar cells. The cells with the structure of ITO/PEDOT/polymer:PDHC/LiF/Al exhibited a power conversion efficiency (PCE) about 0.2% under 100 mW/cm(2) white light illumination. The open-circuit voltages (V(oc)s) of 1.14 V of the cells based on MEH-PPV:PDHC and about 0.76 V of the cells based on P3HT:PDHC were achieved, which are higher than the V(oc)s of the corresponding solar cells with phenyl-C-butyric acid methyl ester (PCBM) as the acceptor. In comparison with the cells based on PCBM, the relatively lower PCE of solar cells based on PDHC is due to its low electron mobility of 1.15 x 10(-5) cm(2) V-1 S-1 estimated by the space charge limited current method.
Abstract: New symmetrical pi-conjugated donor-acceptor-donor functionalized molecules consisting of different electron-donating moieties but same alpha-cinnamoyl cyclic ketene dithioacetals (CCKDA) acceptor have been synthesized. The photophysical properties of these compounds indicate that the absorption and emission result from the intramolecular charge-transfer between the donor and the acceptor. Cyclic voltammetry data show that the band gaps of the compounds vary by introducing different donor moieties. Density functional theory calculations provide an insight into the electronic structure of the molecules. The double-layer electroluminescent devices are fabricated by using these molecular materials as light emitting layer. The electroluminescent performance of the device suggests that these donor-acceptor-donor molecules can be good candidates for the application in organic light-emitting diodes. (C) 2008 Elsevier B.V. All rights reserved
Abstract: The influence of two components blend ratio, solution concentration and thermal annealing on the morphology of poly(2-methoxy-5-(2’-ethyl-hexyloxy)-p-phenylenevinylene) (MEH-PPV): N,N’-bis(1-ethylpropyl)-3,4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) blend films spin-cast from chloroform solutions has been studied using atomic force microscopy (AFM). The AFM images show that the dimension of the phase separation increases with the EP-PTC content and total solution concentration. When the annealing temperature increases from 90 to 150 degrees C, the EP-PTC crystal-like clusters grow rapidly. Solar cells based on MEH-PPV: EP-PTC blend films with different weight ratios were fabricated. The device with 1:3 weight ratio has a higher power conversion efficiency (PCE) of 0.072% compared with the devices with 1:1, 1:2 and 1:4 ratio, which increases by about 14 times over that of the device with 1:1 ratio that has a PCE of 0.005%. It is indicated that the optimum Performance of the photovoltaic device is strongly related to the finer phase separation between MEH-PPV and EP-PTC on a submicron scale which enables an efficient dissociation of photogenerated excitons, and the pure EP-PTC phase can build up a percolating network with pathways large enough to enhance electron transport. (C) 2008 Elsevier B.V. All rights reserved.
Abstract: Three conjugated dendrimers containing electron-accepting sulfonyldibenzene (SDB) cores and electron-donating triphenylamine dendrons have been synthesized through a convergent synthetic strategy without any protection/deprotection chemistry. The dendrimers were highly soluble in common organic solvents, and could form good quality optical films by spin coating. Their thermal, optical and electrical properties are manipulated by attaching different peripheral dendrons. Using these dendrimers as donors and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as acceptor, the bulk heterojunction solar cells with a structure of ITO-PEDOT-dendrimers: PCBM-LiF-Al were fabricated. The cell based on dendrimer G0 shows a relatively high power-conversion efficiency (PCE) of 0.34% under AM 1.5 illumination of 100 mW cm(-)2.
Abstract: Two conjugated Compounds P and T which contained 4,7-dithienbenzothiadiazole as central unit and terminal phenyl or thiophene rings, respectively, connected via a cyano vinylene bond, were synthesized. The stable intramolecular charge-transfer status makes possible the compounds to increase the optical absorption band. These compounds exhibited excellent film-forming properties which allowed the preparation of homogenous thin films by the spin-coating technique. The compounds were stable up to about 300 degrees C and showed glass transition temperatures of 64 and 50 degrees C. The absorption spectra were broad and extended from about 300 to 700 nm. They emitted yellow-orange light in solution with photoluminescence (PL) maximum at 574, 578 nm and reddish light in solid state with PL maximum at 663, 702 nm. Organic solar cells based on T (or P) as donor and C60 derivative as acceptor exhibit power conversion efficiencies (PCEs) of 0.11 % (or 0.09%) under one sun of AM1.5 illumination. (C) 2009 Elsevier B.V. All rights reserved.
Abstract: Three novel conjugated copolymers containing alkoxylated 4,7-diphenyl-2,1,3-benzothiadiazole and dialkylfluorene or dialkyloxyphenylene or dialkylthiophene units were prepared by Horner polycondensation reactions. They are all soluble in common organic solvents such as chloroform, tetrahydrofuran, and chlorobenzene. The novel copolymers were characterized by NMR, GPC, and elemental analysis. Thermogravimetric analysis of the copolymers showed they have good thermal stability with the decomposition temperature higher than 350 degrees C. Cyclic voltammetric study shows that the HOMO energy levels of the three copolymers are deep-lying which implies that these copolymers have good stability in the air and the relatively low HOMO energy level assures a higher open circuit potential when they are used in photovoltaic cells. Bulk-heterojunction photovoltaic cells were fabricated with the copolymers as the donors and PCBM as the acceptor. The cells based on the three copolymers exhibited power conversion efficiencies of 0.65, 1.25, 1.62% with high open circuit potential of 0.76, 0.96, and 1.04 V under one sun of AM 1.5 solar simulator illumination (100 mW/cm(2)).
Abstract: The films of two x-shape oligo(thiophene)s, 3, 4-dibithienyl-2, 5-dithienylthiophene (7T) and 2, 5-dibithienyl-3, 4-ditrithienylthiophene (11T), which are prepared by vacuum evaporation, have been investigated as novel electron donor layers in two-layer photovoltaic cells. UV-Vis absorptions show red-shifted and broadened absorptions of the vacuum-evaporated films as compared with those of the corresponding solutions and spin-coating films, which is beneficial for photovoltaic properties. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements show that the vacuum-evaporated films are almost amorphous. Two-layer photovoltaic cells have been realized by the thermal evaporation of 7T and I IT as donors and N, N’-bis(1-ethylpropyl)-3, 4:9,10-perylene bis(tetracarboxyl diimide) (EP-PTC) as an acceptor. An energy conversion efficiency (ECE) of 0.18% of the cell based on 7T with an irradiation of white light at 100 mw/cm(2) has been demonstrated by the measurements of current (I)- voltage (V) curves of the cells to be higher than the ECE of the reference system based on donor dihexylterthienyl (H3T) that is linear and without alpha, beta linkage.
Abstract: Bilayer polymer anode composed of poly(3,4-ethylene-dioxythiophene): polystyrenesulfonate (PEDOT:PSS) (PH500) and PEDOT:PSS (Baytron P VP Al 4083) was used to construct flexible polymer solar cells on plastic substrates polyethylene terephthalate (PET) with a device structure of PET/polymer anode/APFO-3:PCBM/LiF/Al. The power conversion efficiency (PCE) of the indium tin oxide (ITO)-free solar cells achieved 2.2% under illumination of AM1.5 (100 mW cm(-2)), which is 80% of the PCE of the reference cells with ITO on glass. The simplicity of preparing bilayer polymer anode and the comparable performance achieved in the flexible solar cells made the bilayer polymer anode an alternative to ITO for flexible solar cells produced by printing technology. (C) 2008 American Institute of Physics.
Abstract: A cruciform-shaped oligo(phenylenevinylene) (OPV) with a phosphorescent rhenium(I) chromophore incorporated at the centre and grafted triphenylamines around the periphery was designed as a new organic photovoltaic material, in which the chelation of rhenium(I) to the cruciform successfully constructs a three-dimensional intramolecular charge transfer system and extends the exciton lifetime; as a result, the rhenium-OPV complex shows a power conversion efficiency almost two times that of the metal ion-free parent compound.
Abstract: Arrays of reflective multijunction polymer solar cell were demonstrated by folding four separated cells fabricated on a single plastic substrate using conducting polymer poly(3, 4-ethylene-dioxythiophene):polystyrenesulfonate as an anode. The combination of flexible substrate and polymer solar cells (PSCs) makes the construction of multifolded PSCs on one substrate possible. The power conversion efficiency (PCE) of the multifolded reflective PSCs was enhanced by 62% +/- 12% with the folded opening angle of 30 degrees compared to the planar cells. In series connection of four solar cells, an open-circuit voltage (V-oc) of 3.65 V was obtained. (C) 2008 American Institute of Physics.
Abstract: The effects of different solvents on the morphology of poly(2-methoxy-5-(2-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) : N, N ‘-bis(1-ethylpropyl)-3,4,9, 10-perylene bis(tetracarboxyl diimide) (EP-PTC) blend film and the performance of solar cells based on MEH-PPV: EP-PTC blend film were studied. The results show that the phase separation in the blend film using non-aromatic solvents is of micron (0.5-5 mu m) size, which leads to low charge separation efficiency and consequently the low power conversion efficiency of the assembled solar cell; whereas the phase separation in the blend film using aromatic solvents is of nano-size, which increases the interface area of the two phases obviously and consequently increases the ratio of charge separation significantly. The power conversion efficiency of solar cells based on MEH-PPV: EP-PTC blend film using aromatic solvents is improved 30 times of magnitude compared with that of solar cell based on the blend film using non-aromatic solvents.
Abstract: The energy transfer and the luminescent properties of PVK and four novel donor-pi-acceptor( D-pi-A) molecules(CKD, TKD, PKD, NKD) doped systems were investigated with the analysis of UV-Vis absorption spectra, photoluminescent excitation( PLE) spectra and photoluminescent ( PL) spectra. The electroluminescence(EL) properties of the blend system were studied via the characterization of the devices ITO/PE-DOT/PVK: D-pi-A omega-/Alq(3)/Al. The results demonstrate that by changing the donor moieties of D-pi-A molecule, the band gap of D-pi-A molecules can be adjusted. Meanwhile the fluorescence quantum efficiency varies significantly with the stereostructure of donor moieties of D-pi-A molecules. Both the PL and EL spectra show that the energy transfer between PVK and D-pi-A molecules occurs effectively. The emission performance of the blend system could be improved with changing the dopant ratio of PVK and D-v-A molecules. The power efficiency of the device is up to 1.75 cd/A at 729.1 cd/m(2), when the dopant mass fraction between PVK and TKD is 6.0%.
Abstract: Films of MEH-PPV and PPDI blends with weight ratio 1:2 have been prepared by spin-coating and annealing between 0 and 60 min at 95 degrees C. The films were characterized by absorption spectroscopy and atomic force microscopy (AFM). The main emphasis has been on the photon conversion efficiency in the photovoltaic cells as a function of excitation wavelength and applied voltage/electric field. Site selective excitation at wavelengths at which either non-aggregated bulk PPDI or dimers/aggregates of PPDI absorb prove that (i) the rate-limiting process for power conversion is the field-assisted escape of optically generated geminate electron-hole pairs from their mutual coulombic potential and (ii) the photogeneration yield depends on the donor-acceptor topology. A significant difference of the yield has been noted when alkoxy-pendent groups in MEH-PPV are replaced by phenyl-alkoxy groups. (c) 2007 Elsevier B.V. All rights reserved.
Abstract: This paper reports that the blend films of poly (2-methoxy-5-(2’-ethyl-hexyloxy)-p-phenylene vinylene) (MEHPPV) and N, N’-bis(1-ethylpropyl)-3,4: 9,10-perylene bis (tetracarboxyl diimide) (EP-PDI) with the weight ratio of 1: 2.5 have been prepared by spin-coating from chloroform (CF) and chlorobenzene (CB) solutions respectively. The absorption spectra and the morphology of the blend films show that large crystal-like EP-PDI aggregates are formed in film prepared from CB solution, which corresponds to a new absorption shoulder near 590 nm, while there is no shoulder around 590 nm in the UV-Vis absorption spectra of the blend film from CF solution. The electric-field dependence spectra of the photocurrent generation quantum yield of the film from CB solution shows that at weak electric field the EP-PDI aggregates act as more efficient sensitizers, but at strong electric field the quantum yields become almost invariable over the entire spectral range no matter what the state of EP-PDI, monomer or aggregate. At strong electric field, the photocurrent generation yields of both films from CF and CB solution saturate and their yield spectra become spectrally similar, mentioning that at strong electric field the photoexcitons dissociate efficiently and the free charges are collected by the electrodes almost completely.
Abstract: Three novel donor-acceptor molecules (BCPD, BPPD and PDHC) have been investigated as donors for the bulk heterojunction solar cells. BCPD and BPPD have the same acceptor group of TPO while BCPD and PDHC have the similar donor group of-carbazole. The absorption data indicates that the introduction of either strong electron-donating group or strong electron-withdrawing group will induce the red shift of ICT transition absorption. Electrochemistry measurement shows that the three compounds present reversible or partly reversible oxidation and reduction processes. When the donor moiety was changed from carbazole to phenothiazine, the oxidation potentials shifted from 1.10 V to 0.72 V. While the acceptor moiety was changed from TPO to CEM, the reduction potentials shifted from - 1.42 V to -0.92 V. The bulk heterojunction solar cells using the three compounds as donors and PCBM as acceptor were fabricated. The cell based on PDHC containing strong electron-accepting group shows a relatively high energy conversion efficiency of 0.51% under the illumination of white light at 100 MW cm(-2), which is almost two times of the magnitude of the cells based on BCPD and BPPD. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: Two new conjugated dendrimers bearing a triphenylamine moiety as dendrons and 1,3,5-triphenylbenzene as a core have been synthesized through a convergent synthetic strategy. These conjugated dendrimers have high fluorescence quantum yields and exhibit similar absorption and emission behaviors in solutions and in solid films, which demonstrate that these dendrimers form good amorphous states. (c) 2007 Elsevier Ltd. All rights reserved.
Abstract: Four X-shaped oligothiophenes with different conjugation length were investigated as novel electron donors in single-layer bulk-heterojunction solar cells. The UV-vis absorption spectra of blends of compounds 1-4 with 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C-61 show a remarkably red shift and broadening with increasing thiophene number at each of the four branches. The performance of the photovoltaic cells varied significantly with molecular structures of the four oligothiophenes. Conversion efficiencies increased from 0.008% to 0.8% with changing the electron donors from 1 to 4. The maximum incident photon-to-current conversion efficiency of the device based on 4 reaches 31.6%, much higher than those of three other compounds 1-3. Remarkable improvement of the device performance was achieved with increasing the substituted thiophene number. The results show that the photovoltaic effect is dependent on the structural characteristics and the film forming abilities of the X-shaped thiophenes.
Abstract: We prepared ordered, two-dimensional arrays of patterns with silver nanoparticles immobilized on patterned self-assembled monolayers (SAMs) of alkanethiolates on gold, which were used as substrates for surface enhanced Raman scattering (SERS). Using contact-mode atomic force microscopy, we have characterized the formation and structure of such silver pattern assemblies on a microcontact-printed SAM patterned surface. SERS spectra and surface enhanced Raman mapping (SERM) of 4-pyridinethiol SAMs on this novel SERS-active substrate were also investigated. Different SERS activities were observed on the surface of the hierarchical micro/nanostructure. The enhancement factor was studied in detail and the electromagnetic enhancement mechanism was used to explain the SERS effect. Copyright (C) 2006 John Wiley & Sons, Ltd.
Abstract: The energy transfer and the luminescence properties of polyvinyl-carbazole (PVK) and oligomeric phenylenevinylene derivative (2,5-dodecyloxy-1,4-(biphenyl-enevinyl)phenyl)(DBVP) blend system were studied. The energy transfer between PVK and DBVP was investigated by the UV-vis absorption spectra, photoluminescent excitation (PLE) spectra and photoluminescent (PL) spectra of PVK/DBVP blend system. The electroluminescence (EL) properties of the blend system were investigated by characterization with the device ITO/PEDOT/PVK:DBVP (w/w) /LiF/Al. The PL and EL spectra of PVK in the PVK/DBVP system were effectively quenched, which means the effective energy transfer between PVK and DBVP. Because PVK matrix acted as solid solvent, the emission performance of the blend system could be adjusted and improved by changing the ratio of PVK and DBVP. The luminescence efficiency is up to 1.06cd/A at 52cd/m(2), when the weight ratio of PVK:DBVP was 1:2 and the bright blue and green light emission were obtained when the ratio of PVK:DBVP was changed from 20:2 to 1:2.
Abstract: Thiophene-based monodispersed linear pi-conjugated oligomers with a well-defined chemical structure are the subject of considerable current interest related to their potential applications as active material in organic electronics and photonic devices,in molecular electronics. In this paper, we have investigated series of DOT. oligomers, in which EDOT moieties have been inserted either as a median bis-EDOT core or and external end groups by quantum chemical calculations. Their absorption spectral peaks, the frontier molecular orbitals HOMO and LUMO were calculated by using the semi-experiential method AM1 and PM3. It is indicated that the. changing tendency of the calculated results is in good agreement with the experimental observations.
