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TU Dresden » Faculty of Mechanical Science and Engineering » Institute for Materials Science » Chair of Materials Science and Nanotechnology

» presentations   » 2014.07.01-05

Improving the Optical Properties and Charge Transport Parameters of Near-Infrared Absorbers

Sebastian Radke, Frank Ortmann, Reinhard Scholz, Karl Leo, Gianaurelio Cuniberti

ICSM 2014

2014.07.01-05; Turku, Finland

Efficient organic infrared absorber materials are required in order to enhance the performance of organic tandem solar cells. A promising class already used successfully in organic solar cells are 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs). We combine electronic structure calculations, molecular dynamics simulations, and charge transfer studies to analyze the intramolecular electronic properties and the intermolecular coupling in the crystal phase as well as their impact on the charge carrier mobility and the optical properties for several potential candidates in a comparative fashion. As a first remarkable result, it turns out that the benzannulation of the molecular core improves both electron and hole transfer by significantly reducing the internal reorganization energy. By attaching additional functional groups, especially electron-donating ones, the shape of the frontier molecular orbitals can be modified, further decreasing the internal reorganization energy and improving the intermolecular coupling. These modifications come along with a reduction of the HOMO-LUMO gap shifting the absorption maximum towards higher wavelengths. Based on our theoretical studies, we formulate design rules for the class of BODIPYs improving both optical and charge transport properties and, thus, the performance of corresponding photovoltaic devices.

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