Open Access Nano Review

Synthesis, structure, and opto-electronic properties of organic-based nanoscale heterojunctions

Bohuslav Rezek1*, Jan Čermák1, Alexander Kromka1, Martin Ledinský1, Pavel Hubík1, Jiří J Mareš1, Adam Purkrt12, Vĕra Cimrová2, Antonín Fejfar1 and Jan Kočka1

Author Affiliations

1 Institute of Physics ASCR, v.v.i., Cukrovarnická 10, 16200 Prague 6, Czech Republic

2 Institute of Macromolecular Chemistry ASCR, v.v.i., Heyrovského nám. 2, 16206 Prague 6, Czech Republic

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Nanoscale Research Letters 2011, 6:238  doi:10.1186/1556-276X-6-238

Published: 18 March 2011

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.