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Dyes in Vertically Aligned Carbon Nanotube Arrays for Solar Cell Applications Gerhard Lackner1, Ingolf Endler2, Frank Meissner2, Sebastian Scholz2, Tobias Mayer-Uhma3, Rocco Liebschner4, Viktor Bezugly4, Jan Meiss5, Martin Mkandawire4, Richard Boucher4, Alexander Michaelis2, and Doru C. Lupascu1 1

University of Duisburg-Essen, Institute for Materials Science, Essen, Germany Fraunhofer Inst. for Ceramic Technologies and Systems, Winterbergstr. 28, Dresden, Germany 3 SiC Processing GmbH, Technikum, Neuteichnitzer Str. 54, Bautzen, Germany 4 Dresden University of Technology, Institute for Materials Science, Dresden, Germany 5 Institute for Applied Photophysics, Dresden University of Technology, Dresden, Germany 2

ABSTRACT The infiltration of dissolved dyes into vertically aligned carbon nanotube arrays (va-CNT) is reported. The ultra hydrophobic surface of the CNT forest can be wetted and hence infiltrated for an appropriate choice of solvent. The dye-infiltrated CNT array forms a well ordered bulk-heterojunction structure for organic solar cells in which the CNT can act as a large electrode or, for appropriate energy levels, as an acceptor material. Derivatives of the small molecule copper phthalocyanine or the polymer poly(3-hexylthiophene) were used as dyes. Drop coating was chosen as the infiltration technique resulting in a completely embedded CNT forest. Field emission secondary electron microscopy analysis illustrates the final layer quality. Common electrical characterization under AM1.5 illumination proves photosensitivity and implies photovoltaic behavior of the composite. INTRODUCTION Since their discovery in 1991 by Iijima [1], carbon nanotubes (CNT) and composites containing CNT have been attracting much attention due to their exceptional electrical, chemical, and mechanical properties [2, 3]. Nevertheless, devices of CNT still have not yet succeeded in matching the intrinsic properties of single CNTs [4, 5]. It is a major challenge to generate structures showing single CNT properties (e.g. their large surface-to-volume ratio and electrical conductivity) with different macroscopic shapes and to also establish the corresponding fabrication processes. Vertically aligned carbon nanotube arrays (va-CNT) can be grown on different substrates using chemical vapor deposition (CVD) with a variety of catalysts [6, 7]. The arrays been reported to have super-hydrophobic properties [8]. So far, CNT arrays have been used as a filler or reinforcement in composites. For the mechanical properties of a CNT composite the degree of nanotube alignment is highly relevant [9, 10]. Methods to embed CNT in a polymeric matrix have been developed and improved using sonication to address the problem of CNT agglomeration and the poor adherence of these agglomerates to the matrix causing stress concentration. We investigate the applicability of composites of dyes with va-CNT as an organic photovoltaic device. A uniform composite matrix of va-CNT and dye was formed. Excitons are generated via light absorption in the dye. These exciton