Minze T. Rispens

Influence of the solvent on the crystal structure of PCBM and the efficiency of MDMO-PPV:PCBM ‘plastic’ solar cells

Two crystal structures of PCBM, obtained from different crystallisation solvents, are presented; a proposed link with solvent dependence of the efficiency of MDMO-PPV:PCBM solar cells is described.

The influence of materials work function on the open circuit voltage of plastic solar cells

c ¨¨ ¨ Abstract Conjugated polymeryfullerene plastic solar cells of the first generation were consisting of two distinct layers, made of the donor polymer and of the acceptor fullerene, respectively, sandwiched between two metal contacts. By mixing the polymer and the fullerene components, thus replacing a single flat junction with an interpenetrating network bulk-heterojunction, the device efficiency was dramatically improved. As a further step to proceed with the development of plastic solar cells, we developed the bulk diffusion bilayer approach, allowing the creation of donor-acceptor diffused interfaces with less restrictions to the phase compatibility of the two components. For a novel series of fullerenes, the bulk diffusion bilayer approach is shown to yield devices with comparable efficiencies as the blend bulk heterojunction approach. Bulk-heterojunction devices show unusually high open circuit voltage (V ) values. These values cannot be explained by the metal-insulator-metal (MIM) model that has been OC often used for organic light emitting diodes. In order to investigate the origin of the V in bulk-heterojunction plastic solar cells, OC we have prepared PPV based devices varying both the metal negative contact and the fullerene acceptor. Fullerene derivatives with varying acceptor strength, (i.e. the first reduction potential ) were used as electron acceptors in bulk-heterojunction plastic solar cells produced with the blend as well as the diffusion bilayer approach. The open circuit voltage of the devices was found to correlate directly with the acceptor strength of the fullerenes, while it was rather insensitive to variations in the workfunction of the negative electrode metal. These results suggest that the quasi-Fermi level of the fullerene pins the Fermi level of the evaporated negative metal contact. 2002 Elsevier Science B.V. All rights reserved.

A supramolecular array of fullerenes by quadruple hydrogen bonding.

General remarks. All reagents and solvents were used as received or purified using standard procedures. [60]Fullerene (99.5%) was purchased from Southern Chemical Group, LLC and used without purification. All reactions were performed under a nitrogen atmosphere unless indicated otherwise. Flash chromatography was performed using Kieselgel Merck Type 9385 (230-400 mesh). Analytical thin layer chromatography (TLC) was performed using aluminum coated Merck Kieselgel 60 F254 plates. Melting points were determined with a Mettler FP1 melting point apparatus equipped with a Mettler FP2 microscope. H-NMR and C-NMR spectroscopy were performed on a Varian Unity Plus (500 MHz) instrument or on a Varian VXR-300 (300 MHz) instrument as indicated, at 298 K. Coupling constants (J) are denoted in Hz. Multiplicities are denoted as follows: s = singlet, d = doublet, t = triplet, q = quartet, p = pentet, dd = double doublet, m = multiplet, br = broad. FT-IR spectra were recorded on a Mattson Galaxy 4020 instrument. UV-Vis spectra were recorded on a Hewlett Packard HP 8452 UV-Vis spectrophotometer. High Resolution Mass Spectroscopy (HRMS) were performed on a JEOL JMS 600 spectrometer (positive ion EI mode). MALDI-TOF-MS measurements were performed on a Micromass TofSpec E apparatus (negative-ion reflector mode) by using elemental sulfur as a matrix (See: Brune, D. C. Rapid Commun. Mass Spectrom. 1999, 13, 384 389). Measurements were performed on aliquots of the analyte (1 mg/mL) and elemental sulfur (10 mg/mL) in CS2 or CHCl3. HPLC analyses were performed on a Hewlett Packard HP LC-Chemstation 3D (HP 1100 Series) using an analytical Cosmosil Buckyprep column (4.6 x 250 mm). Cyclic Voltammetry was performed using an Autolab PGStat 100. Elemental analysis were performed by the Microanalytical Department of this laboratory.

Asymmetric 1,3-dipolar cycloadditions to 5-(R)-menthyloxy-2(5H)-furanone

Various diazo compounds, nitrile oxides, nitrones and azomethine ylides were examined in 1,3-dipolar cycloadditions to enantiomerically pure 5-(R)-menthyloxy-2(5H)-furanone 1a. Pyrazoline 9 was obtained in 100% c.y. as a mixture of 2 diastereoisomers in ratios up to 72 : 28, whereas pyrazoline 16 was obtained in 100 % c.y. as a single enantiomer. Photochemically pyrazolines 9 and 10 have been converted to cyclopropanes 11 and 13. Under thermal conditions pyrazoline 9 is converted to 4-methyl-5-menthyloxy-2(5H)-furanone. Isoxazoles 21a-24a were obtained enantiomerically pure via nitrile oxide addition to 1a in 64-67% yield. Nitrone addition afforded isoxazolidines 27, 28 and 34 with complete anti-facial- and regiochemistry, but with endo-exo selectivities up to 76%. Enantiomerically pure isoxazolidines were obtained in 25-75% yield. Pyrrolidine 36 was obtained diastereomerically pure in 81% c.y. Pyrrolidines 42 and 45, however, were obtained as diastereomeric mixtures in 37% resp. 6% yield.

Catalytic enantioselective allylic oxidation

Several chiral Cu(II)-complexes of cyclic amino acids catalyse the enantioselective allylic oxidation of cyclohexene to cyclohexenyl esters. Cyclohexenyl propionate was obtained in 86% yield with e.e.s up to 61%.

New manganese catalysts for alcohol oxidation

Abstract The in situ prepared manganese complexes based on ligands 1 – 6 have been used in the catalytic oxidation of alcohols to aldehydes or ketones. Highly active and selective catalysts were found with excellent turnover numbers (up to 900) using aqueous hydrogen peroxide as oxidant at ambient temperatures. EPR spectroscopy and electrospray mass spectrometry has indicated that dinuclear species may be involved in the catalytic oxidations. Comparing the rate of oxidation of benzyl-d 7 alcohol with that of benzyl alcohol by the different catalysts yielded isotope effects ( k H / k D ) of 2.2–4.3. Although the exact nature of the oxidising species has not been elucidated, these results indicate that hydroxyl radicals are not involved in these processes.

Injection-limited electron current in a methanofullerene

The dark current of bulk-heterojunction photodiodes consisting of a blend of a methanofullerene (PCBM) as n-type electron acceptor and a dialkoxy-(p-phenylene vinylene) (OC1C10−PPV) as a p-type electron donor sandwiched between electrodes with different work functions has been investigated. With ohmic contacts for hole and electron injection, the dark current appears completely dominated by the electron current in the PCBM, as a result of a much higher electron mobility. This electron current is bulk space-charge limited. With Au as a high work function metal, the electron current becomes injection limited. The injection-limited electron current from the Au electrode into PCBM is explained within a thermally assisted hopping model. In spite of the presence of an injection barrier of about 0.76 eV, the injection-limited electron current from a Au electrode into PCBM still exceeds the bulk-limited hole current in OC1C10−PPV.

1,3-DIPOLAR CYCLOADDITIONS TO 5-METHOXY-2(5H)-FURANONE

Abstract Various nitrile oxides and nitrones, ethyl diazoacetate and an azomethine ylide were examined in 1,3-dipolar cycloadditions to 5-methoxy-2[5H]-furanone, in particular with respect to regio- and diastereoselectivities. Isoxazoles 13–17 and isoxazolidines 21, 22 and 24 were obtained in high yields with anti-facial selectivities and regioselectivities exceeding 95%. In the case of pyrazoline 26 minor amounts of syn-facial adduct are also observed, whereas lactone annulated pyrrolidines 28 are obtained as mixtures of regio-isomers.

A poly(p-phenylene ethynylene vinylene) with pendant fullerenes

In order to obtain a predefined nanoscopic phase segregation of semiconducting polymers and fullerenes for application in photovoltaic devices we have prepared a conjugated polymer with dangling fullerenes. For this purpose an oligo(p-phenylene vinylene) with acetylene end groups has been polymerized with a diiodo-aryl-fullerene derivative via a Pd-catalyzed coupling reaction. Photoinduced absorption (PIA) and photoluminescence spectra give evidence of a photoinduced electron transfer in this novel polymer.

Supramolecular organization of fullerenes by quadruple hydrogen bonding

Quadruple hydrogen bonded fullerene dimer 8 with a very high dimerisation constant (Ka 1.0 × 106 M−1) was synthesised and fully characterised.