Neil Gregory Pschirer

Polyphenylene-Based Materials for Organic Photovoltaics

Energy will be one of the most important factors to influence human society in the 21st century.1,2 Cost, availability, and sustainability of energy have a significant impact on the quality of our lives, development of global economies, relationships between nations, and the stability of our environment. Scientists are now focusing on the development of renewable energies3 generated from natural resources such as sunlight, wind, rain, tides, and geothermal heat. Among these, the sun has the potential to make the largest energy contribution: only one hour of sunshine (3.8 × 1023 kW) is more than enough to satisfy the highest human demand for energy for an entire year (1.6 × 1010 kW in 2005).4-7 Solar cells, also called photovoltaics,8 are devices based on solar technology which convert sunlight directly into electricity under the photovoltaic effect. Becquerel was the first to recognize this effect in 1839, when he shined light * To whom correspondence should be addressed. E-mail: muellen@ mpip-mainz.mpg.de. † Max Planck Institute for Polymer Research. ‡ BASF SE. Chen Li studied chemistry and completed his Master’s thesis under the supervision of Professor He Tian at the East China University of Science and Technology in 2003. In 2004, he joined the group of Professor Klaus Müllen at the Max Planck Institute for Polymer Research to work on functional rylene dyes for dye-sensitized solar cells. He received his Ph.D. in 2008 from the Johannes Gutenberg University of Mainz. Presently he works in the same group as a project leader, and his research interests are functional dyes and pigments as well as their applications.

An Improved Perylene Sensitizer for Solar Cell Applications

1,6-Dithiophenol-substituted perylene organic sensitizer 1 was synthesized, and its photovoltaic properties in dye-sensitized solar cells were assessed. When anchored onto TiO2 film, the dye exhibits an unprecedented incident monochromatic photon-to-current conversion efficiency of 87 % and yields a power conversion efficiency of 6.8 % under standard AM 1.5 solar conditions.

ALKYNE METATHESIS WITH SIMPLE CATALYST SYSTEMS : HIGH YIELD DIMERIZATION OF PROPYNYLATED AROMATICS; SCOPE AND LIMITATIONS

Abstract High yield dimerization of propynylated benzenes and propynylnaphthalene by a mixture of Mo(CO) 6 and 4-chlorophenol at 140 °C in 1,2-dichlorobenzene is reported to give the corresponding disubstituted alkynes. The scope and limitation of the reaction and the influence of substitution pattern and substitution type are discussed. Oxygen or nitrogen carrying substrates metathesize in moderate to good yields and ortho -alkyl substituted examples form the respective tolanes very efficiently.

Rainbow Perylene Monoimides: Easy Control of Optical Properties

Perylene dyes have been widely used as photoreceptors in organic photovoltaics because of their outstanding photo-, thermal and chemical stability as well as their excellent photophysical properties. Herein we describe a novel generation of perylene dyes based on N-(2,6-diisopropylphenyl)-perylene-3,4-dicarboximide. The optical properties of these novel perylenes can be finely tuned via the substituents in the 1-, 6- and 9-positions of the perylene core. The facile synthesis, tunable orbital and absorption properties, and electrochemical potentials help us to design efficient perylene sensitizers for solar-cell applications.

Perylenes as sensitizers in hybrid solar cells: how molecular size influences performance

Dye-sensitized solar cells (DSCs), one kind of hybrid solar cells, are being intensively developed due to their high efficiency and low cost. One of the main factors to improve the efficiency is the minimization of the recombination of holes and electrons at the TiO2/dye/electrolyte interface. To suppress the charge recombination, dye arrangement on the TiO2 surface plays the pivotal role in DSCs. Herein we report three perylene sensitizers of various molecular sizes, which are derived from the introduction of different groups in the 1,6-positions of the perylene core. The same donor (di-p-tert-octylphenylamino) and acceptor (anhydride) moieties in these perylene sensitizers render them highly similar spectroscopic and electrochemical properties, which can be used to compare the effect of the dye-loading on the TiO2 surface, namely, the photovoltaic performance as a function of the sensitizer size. These results will help in better understanding the complex relationship between the molecular size and the device performance.

Double Donor-Thiophene Dendron-Perylene Monoimide: Efficient Light-Harvesting Metal-Free Chromophore for Solid-State Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) based on a stable largeband nanostructured semiconductor, such as titanium dioxide, are low cost and easily processable alternatives to conventional silicon wafers, and as such have lately drawn much attention. In particular, the solid-state DSCs show great potential owing to their increased stability compared to liquid DSCs. The reason for this stability is the exchange of the liquid electrolyte, which often bears the problem of leakage and electrode corrosion, for a solid hole-conducting material, mainly 2,2’,7,7’-tetrakis(N,N-para-dimethoxyphenylamino)-9,9’-spirobifluorene (spiro-MeOTAD). However, compared to the parent liquid DSCs, solid-state DSCs have shown much lower efficiencies. Whilst ruthenium-based sensitizers, and now a first porphyrin sensitizer, have shown efficiencies up to approximately 11 % in liquid cells, solidstate DSCs only reach values of up to 6 %. Most of the more efficient sensitizers are ruthenium-based, which have drawbacks such as cost, sustainability, and limited ease of band-gap manipulation. One very stable and metal-free alternative are sensitizers based on perylene monoimides, which are known for their excellent chemical, photochemical, and thermal stability as well as high absorptivity and acceptor ability. Another outstanding class of chromophores are thiophenes, in particular oligothiophenes, for their highly variable optical properties according to their architecture, extraordinary charge transport properties, and extinction. Both perylenes and thiophenes have found wide application in optoelectronic devices. Herein, we present a donor–acceptor perylene monoimide with a branched terthiophene spacer group and a triphenylamine donor moiety (1 a, Scheme 1) as well as a naphthalene analogue (1 b, Scheme 1). As reported by Thomas et al. and Fischer et al., the combination of a triphenylamine donor and a branched oligothiophene spacer in combination with a 2-cyanoacrylate acceptor gave good efficiencies of up to 6.15 % and 6.8 % in liquid DSCs and up to 2.6 % in a solid-state DSC. Furthermore, three moieties—triphenylamine, oligothiophene, and perylene monoimide—have recently caused a stir in a p-DSC (NiO), showing a sevenfold increase in energy conversion efficiencies compared to preceding sensitizers. However, we have designed our sensitizers for n-DSCs (TiO2), in which the perylene sensitizer 1 a in particular shows an outstanding efficiency of 3.8 % under 1.5 AM illumination (1 sun). To the best of our knowledge, this is an unprecedented performance for a perylene sensitizer, the best perylene sensitizer for solid-state DSCs so far being ID176 with an efficiency of 3.2 %. Both compounds were prepared by the initial introduction of the terthiophene spacer group by Suzuki coupling with the brominated perylene (or naphthalene) imide, successive Suzuki coupling with the triphenylamine donor, and finally saponification and imidization with glycine to yield the final product (Scheme 1). As described above, both sensitizers consist of an acceptor unit with a carboxylic acid anchor in the imide structure, a branched terthiophene (a a connection and a b connection of the thiophene units) and a triphenylamine donor. In [a] H. Wonneberger, Dr. C. Li, Prof. Dr. K. M llen Max-Planck Institute for Polymer Research Ackermannweg 10, 55128 Mainz (Germany) Fax: (+49) 6131-379-100 E-mail : lichen@mpip-mainz.mpg.de muellen@mpip-mainz.mpg.de [b] Dr. C.-Q. Ma, Prof. Dr. P. B uerle Institute of Organic Chemistry II and Advanced Materials University of Ulm Albert-Einstein-Allee 11, 89081 Ulm (Germany) [c] Dr. N. Pschirer, Dr. I. Bruder, Dr. J. Schçneboom, Dr. P. Erk BASF SE 67056 Ludwigshafen (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000895.

Ring-closing alkyne metathesis with simple catalyst systems: an access to molecular triangles and rhomboids

Treatment of the siloxane monomer 2 with a mixture of molybdenum hexacarbonyl and 4-chlorophenol at 140 °C furnished the corresponding cyclotrimer 3 and the cyclotetramer 4.

Synthesis and characterization of poly[1,5‐(3,7‐di‐tert‐butyl)naphthyleneethynylene] by alkyne metathesis

The synthesis and structural characterization of the novel polynaphthylene-ethynylene system is reported. The polymer, poly[1,5-(3,7-di-tert-butyl)naphthyleneethynylene] was obtained by efficient alkyne metathesis of 1,5-dipropynyl-3,7-di-tert-butylnaphthalene, which itself is available in three steps starting from naphthtalene.

Novel liquid-crystalline PPE-naphthalene copolymers displaying blue solid-state fluorescence

Synthesis of poly(p-phenyleneethynylene)s (PPEs) containing 1,5-diethynyl-3,7-di-tert-butylnaphthalene leads to novel phenylene-naphthylene-ethynylene copolymers which show strong blue luminescence in the solid state.

Synthesis and crystal structure of catena-poly[Rh2(OAc)4(C27H15N3)]⋅2CH2CL2, a novel Rh(II) organic/inorganic coordination polymer

A new coordination polymer, catena-poly[Rh2(OAc)4(C27H15N3)]⋅2CH2Cl21 has been synthesized by self-assembly from Rh2(OAc)4 dimer units and the new ligand, 1,3,5-tris[(2-pyridyl)ethenyl]benzene 2. The compound was characterized by single crystal X-ray diffraction and was found to crystallize in the triclinic space group P-1, with a = 10.8206(9) Å, b = 14.0331(12) Å, c = 15.0901(12) Å, α = 113.965(2)°, β = 100.250(2)°, γ = 90.462(2)°, and Z = 2. The one-dimensional polymer contains two crystallographically different Rh-dimer units, both located about crystallographic inversion centers. Each Rh2(OAc)4 unit connects in a trans fashion with the potentially tridentate ligand giving an overall 1:1 metal dimer-to-ligand ratio. This arrangement leaves a third nitrogen donor site on the ligand uncoordinated.