LNNano - Brazilian Nanotechnology National Laboratory

A new approach for organic-based devices: electrode architecture leads to extrinsic conduction phenomena

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Leandro Merces1,2, Rafael F. de Oliveira1, Henrique Leonel Gomes3,4, Carlos C. Bof Bufon1,2,*

  1. Brazilian Nanotechnology National Laboratory (LNNano), Campinas, SP, Brazil
  2. University of Campinas (UNICAMP), Campinas, SP, Brazil
  3. University of Algarve, Portugal and
  4. Institute for Telecommunication, Portugal

E-mail: cesar.bof@lnnano.cnpem.br

 

The use of organic materials for electronic applications has several advantages over the conventional silicon-based technology, including the compatibility with flexible substrates and the broad chemical tunability. In addition to the bulk properties of the involved materials, interfaces – especially the electrode/organic semiconductor (OSC) one – are fundamentally relevant to determine the performance of electronic devices. Here, a systematic analysis about the influence of the electrode architecture on the electrical properties of OSC thin films was performed. A set of two-terminal, flat devices have been fabricated and characterized in terms of the electrode configuration either as top or bottom contacts. The device current responses were evaluated as a function of electric field, temperature and film thickness. The top-contact architectures exhibited linear current vs. electric field characteristics. The bottom-contact ones, on the other hand, demonstrated transitions from ohmic transport to space-charge-limited conduction as the electric field increased. Finite-element simulations and first-principle calculations were employed to visualize the current distribution along the OSC film, which showed to depends on the contact geometry. The main study outcome consists of an elegant approach: the well-known space-charge phenomenon is demonstrated to be not an intrinsic property of the OSC film but an extrinsic effect caused by the presence of shallow traps at the vicinity of the substrate interface. This finding contributes to integrate the conventional contact resistance approach, commonly applied in the characterization of contact effects in organic thin-film transistors. The presented results have impact on both the understanding of the charge transport mechanisms in organic thin films and the future design of organic-based devices.

This work was conducted in the Brazilian Nanotechnology National Laboratory (LNNano). The paper entitled “The role of the electrode configuration on the electrical properties of small-molecule semiconductor thin-films” is published in the journal Organic Electronics (doi: 10.1016/j.orgel.2017.06.041).

Acknowledgments:
LNNano/CNPEM (Functional Devices and Systems group, Laboratory of Microfabrication), CAPES, FAPESP (2014/ 25979-2), UNICAMP.