Space charge effects are dominant in organic electronic devices regarding carrier injection and transport properties. On the other hand, nanoparticle researches have also found various applications based mainly on the ability to accumulate charge. Therefore, to further our understanding of the space charge effects, we have introduced Si nanoparticles (5nm diameter) in various metal-insulator-metal (MIM) structures. Pentacene, one of the most promising organic semiconductors for OFET, was used for this investigation.
Standard I-V measurements revealed significant change of properties with the inclusion of nanoparticles. On the aluminum (Al, 30nm)/pentacene (300nm) /gold (Au, 10nm) structure, with the nanoparticle-embedded pentacene, carrier injection became possible from both sides and both electrodes exhibited Schottky contact, compared with typical blocking contact on the Al electrode and Schottky injection on the Au electrode. Impedance spectroscopic results confirm this finding, and further distinguish the bulk and interface behaviours. Carrier concentration was shown to increase with both positive and negative bias, indicating almost identical injection from both electrodes. This effect can be explained by the space charge introduced by the nanoparticles and gives us powerful tool for design of carrier injection barrier and transport properties.
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