• Energy Research

Abstract Novel perylene diimide Py-PDI and naphthalene diimide Py-NDI possessing chelating pyridyl groups have been synthesized. The materials are comparatively investigated as electron acceptors in small molecular photovoltaic cells comprising zinc phthalocyanine ZnPc as an electron donor component. It was shown that these compounds form self-assembled coordination complexes with ZnPc in solution and co-evaporated solid blends. Py-PDI and Py-NDI used as electron acceptor materials in photovoltaic cells with donor ZnPc significantly outperform the reference materials, i.e. perylene and naphthalene diimides that possess no chelating pyridyl groups. Superior photovoltaic performance of Py-PDI and Py-NDI is explained by a complex formation between these compounds and ZnPc. Such interactions of donor and acceptor materials strongly improve photoinduced charge carrier generation. This gives great advantages not just for the construction of organic solar cells but also for organic photodetectors. The devices fabricated in this study are also useful as fast and highly sensitive photodetectors with response times of less than 10 microseconds as well as a strong photoconductive behavior under forward bias.

Bulk-heterojunction plastic solar cells (PSC) produced from a conjugated polymer, poly(2-methoxy-5-(3',7'-dimethyloctyl-oxy)-1,4-phenylenevinylene) (MDMO-PPV), and a methanofullerene [6,6]-phenyl C-61-butyric acid methyl ester (PCBM) were investigated using photocurrent imaging techniques to determine characteristic patterns of efficiency and degradation. The solar cells with power efficiencies of up to 2.6% showed significant inhomogeneities and variations depending on the preparation steps (e.g. aluminum deposition), Suggesting there is still room for improvements. A characteristic feature of the well-known photoinduced and dark cell degradation is the formation of islands of higher efficiency. Degradation mechanisms appear to have a morphological component. The imaging technique will open opportunities for combinatorial plastic solar cell research. (C) 2004 Elsevier B.V. All rights reserved.

AbstractThe majority of energy storage devices like batteries, fuel cells or electrolyzers require heterogeneous electrodes. Immobilization of redox‐active organic molecules by a polymeric approach seems to be a promising route towards organic electrodes for electrocatalytic energy storage or in batteries. Although numerous reports on synthesis and application of new poly‐anthraquinones exist, a universal guideline or tool for selection of the best polymer, concerning several energy storage applications, is still underdeveloped. Moving into the direction of developing such a tool, we have selected and synthesized three poly(anthraquinones). NMR, FTIR, UV‐Vis, TGA, contact angle measurement and SEM revealed certain structure‐property trends, which can be correlated with the performance in the electrochemical investigation. The insights gained within this work demonstrate correlations between the FTIR frequencies and the electrochemical reduction potential, as well as between the polymer hydrophobicity and the electrochemical performance.

A model organic semiconductor (MDMO-PPV) was used for testing a modified version of a photoelectrochemical scanning droplet cell microscope (PE-SDCM) adapted for use with nonaqueous electrolytes and containing an optical fiber for localized illumination. The most attractive features of the PE-SDCM are represented by the possibility of addressing small areas on the investigated substrate and the need of small amounts of electrolyte. A very small amount (ng) of the material under study is sufficient for a complete electrochemical and photoelectrochemical characterization due to the scanning capability of the cell. The electrochemical behavior of the polymer was studied in detail using potentiostatic and potentiodynamic investigations as well as electrochemical impedance spectroscopy. Additionally, the photoelectrochemical properties were investigated under illumination conditions, and the photocurrents found were at least 3 orders of magnitude higher than the dark (background) current, revealing the usefulness of this compact microcell for photovoltaic characterizations.

A series of novel soluble nature-inspired flavin derivatives substituted with short butyl and bulky ethyl-adamantyl alkyl groups was prepared via simple and straightforward synthetic approach with moderate to good yields. The comprehensive characterization of the materials, to assess their application potential, has demonstrated that the modification of the conjugated flavin core enables delicate tuning of the absorption and emission properties, optical bandgap, frontier molecular orbital energies, melting points, and thermal stability. Moreover, the thin films prepared thereof exhibit smooth and homogeneous morphology with generally high stability over time.

Abstract A quasi-solid-state dye-sensitized solar cells (DSSCs) employing a commercial glue (“SuperGlue ® ”) as electrolyte matrix was fabricated. The cyano groups of the cyanoacrylate can form a supramolecular complex with tetrapropylammonium cations. This immobilizes the cations and therefore might lead to a favored anionic charge transport necessary for a good performance of the iodide/triiodide electrolytic conductor. Obtaining energy conversion efficiencies of more than 4% under 100 mW/cm 2 of simulated A.M. 1.5 illumination, the cyanoacrylate quasi-solid-state electrolyte is an ordinary and low-cost compound which has fast drying property and offers significant advantages in the fabrication of solar cells and modules as it is in itself is a very good laminating agent. The influences of different porous layer thicknesses of titanium oxide and various kinds of cations on DSSC performance and long-term stability are presented.

AbstractA broad review of homogeneous and heterogeneous catalytic approaches toward CO2 reduction using organic, organometallic, and bioorganic systems is provided. Electrochemical, bioelectrochemical and photoelectrochemical approaches are discussed in terms of their faradaic efficiencies, overpotentials and reaction mechanisms. Organometallic complexes as well as semiconductors and their homogeneous and heterogeneous catalytic activities are compared to enzymes. In both cases, their immobilization on electrodes is discussed and compared to homogeneous catalysts in solution.