Microscopic Morphology of Thin Films of Phthalocyanine/Perylene Blends for Organic Solar Cell Devices
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I9.43.1
Microscopic morphology of thin films of phthalocyanine/perylene blends for organic solar cell devices Alexandru Vlad1, Dana A. Serban1, Pascal Viville2, Vinciane De Cupere3, Gael Zucchi3, Sorin Melinte1, Vincent Bayot1, Roberto Lazzaroni2, and Yves Geerts3 1 DICE, Universite catholique de Louvain, Louvain-la Neuve, Belgium. 2 SCMN, Universite de Mons-Hainaut, Mons, Belgium. 3 LCP, Universite Libre de Bruxelles, Bruxelles, Belgium. ABSTRACT We report on the microstructure of 2(3)-9(10)-16(17)-23(24)-tetra(2-decyltetradecyloxy)phthalocyanine/peryleneoleylamine (PcH2/PTCDI) blends. Thin films, to be used as active layers in organic photovoltaic cells, were prepared by spin coating and spin casting of dilute toluene solutions on indium tin oxide (ITO) substrates. The morphology of the thin films has been studied using Tapping Mode (TM) atomic force microscopy (AFM), whereas Scanning Electron Microscopy (SEM) was used to reveal the various top electrode morphologies, inherent to the different film processing conditions. INTRODUCTION The quest for novel, highly-performant organic solar cells dates back to the 1980s, when Tang [1] presented the first successful attempt to pass beyond the conventional single layer device. During the last two decades, various schemes for cell design and active layer have been suggested and demonstrated. They can be roughly divided into the following categories: (i) small-molecule systems [1-3], (ii) blends of donor- and acceptor-like conjugated polymers [4,5], (iii) dye-sensitized electrochemical devices [6,7], and (iv) hybrid devices consisting of inorganic semiconductor nanostructures filled with organic materials [8,9]. In this work we test the ability of thin films of liquid crystal PcH2/PTCDI blends to form active layers in photovoltaic solar cell devices. The blends under study show absorption over the entire solar spectrum, thus favoring significant light conversion efficiencies. In addition, thanks to their liquid crystalline nature, they exhibit an interesting columnar organization at ambient temperature that can favor the vertical migration of the charges towards the electrodes [10]. Furthermore, their solubility in common organic solvents gives the advantage of low-cost processing. EXPERIMENTAL DETAILS Molecular PcH2/PTCDI blends, in 3:1 and 1:1 molar ratio, were diluted in toluene and deposited onto commercially available ITO substrates from Merck KgaA and PGO (Praezisions Glas und Optik). No significant changes in morphology of the thin films have been observed upon the use of these different types of ITO. The organic layers were obtained by spin casting and spin coating. The difference between these two techniques consists in the fact that, for the spincoated samples, the substrate is accelerated after the deposition of the solution, whereas for spincasted samples the substrate rotates at constant speed during the solution deposition.
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A careful cleaning of the substrates was carried out prior the deposition of thin organic layers. It begins with the strippin
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