Synthesis,structure, and opto-electronic properties of organic-based nanoscale heterojunctions |
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Authors: | Bohuslav Rezek Jan Čermák Alexander Kromka Martin Ledinský Pavel Hubík Jiří J Mareš Adam Purkrt Vĕra Cimrová Antonín Fejfar Jan Kočka |
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Affiliation: | 1.Institute of Physics ASCR, v.v.i,Prague 6,Czech Republic;2.Institute of Macromolecular Chemistry ASCR, v.v.i,Prague 6,Czech Republic |
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Abstract: | Enormous research effort has been put into optimizing organic-based opto-electronic systems for efficient generation of free
charge carriers. This optimization is mainly due to typically high dissociation energy (0.1-1 eV) and short diffusion length
(10 nm) of excitons in organic materials. Inherently, interplay of microscopic structural, chemical, and opto-electronic properties
plays crucial role. We show that employing and combining advanced scanning probe techniques can provide us significant insight
into the correlation of these properties. By adjusting parameters of contact- and tapping-mode atomic force microscopy (AFM),
we perform morphologic and mechanical characterizations (nanoshaving) of organic layers, measure their electrical conductivity
by current-sensing AFM, and deduce work functions and surface photovoltage (SPV) effects by Kelvin force microscopy using
high spatial resolution. These data are further correlated with local material composition detected using micro-Raman spectroscopy
and with other electronic transport data. We demonstrate benefits of this multi-dimensional characterizations on (i) bulk
heterojunction of fully organic composite films, indicating differences in blend quality and component segregation leading
to local shunts of photovoltaic cell, and (ii) thin-film heterojunction of polypyrrole (PPy) electropolymerized on hydrogen-terminated
diamond, indicating covalent bonding and transfer of charge carriers from PPy to diamond. |
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