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Microspectroscopy techniques for mapping the opto-electronic properties of organic thin-film transistors


Solution processable organic field-effect transistors (OFETs) have recently reached a mature stage that preludes their adoption in a variety of commercial applications from light-weight, stretchable, large-area sensors to low-cost, flexible electronic circuits. The optimization of performances required for such applications demands a deep understanding of the device physics: with the aim to investigate the relationship between thin films micro-structure and charge transport properties, we developed a probing technique capable of providing local information regarding field and charge distribution along the channel of a working device. By coupling modulation spectroscopy techniques to a confocal microscope, we are able to image the opto-electronic properties of organic semiconductors with a lateral resolution of about 500 nm.

As we recently reported, exploiting Charge Modulation Microscopy it is possible to image the charge distribution inside the channel of an n-type organic transistor based on the high-mobility polymer poly{[ N , N' -bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (Polyera's ActivInk™ N2200). Our method allows to directly probe buried layers in a transparent device and does not require highly controlled test conditions (e.g. ultrahigh-vacuum). Interestingly, we unveiled a sub-micrometer texture of charge modulation features along the channel of the transistor, which were attributed to the packing motif of the polymer chains in the nanometer-thick accumulation layer of the device. These important evidences provide us with a deeper insight in charge transport properties in a relevant class of semiconducting materials.

Related IIT publications
  • C. Sciascia, N. Martino, T. Schuettfort, B. Watts, G. Grancini, M. R. Antognazza, M. Zavelani-Rossi, C. R. McNeill, M. Caironi, "Sub-Micrometer Charge Modulation Microscopy of a High Mobility Polymeric n-Channel Field-Effect Transistor", Advanced Materials, 23, 5086–5090 (2011) DOI: 10.1002/adma.201102410
  • C. Sciascia, M. Celebrano, M. Binda, D. Natali, G. Lanzani, J. R. Cabanillas-Gonzalez, "Electric field and charge distribution imaging with sub-micron resolution in an organic Thin-Film Transistor", Organic Electronics, 13, 66– 70 (2012) DOI: 10.1016/j.orgel.2011.09.023
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