Mario Caironi, Istituto Italiano di Tecnologia, Milano

Jeudi 19 Juin 2014, 14h
Amphi Holweck, Esc C, 1ème etage

Investigation of the structure-property relationship in polymer semiconductors by means of charge modulation micro-spectroscopy

Mario Caironi

Center for Nano Science and Technology @PoliMi
Istituto Italiano di Tecnologia, Via Pascoli, 70/3, 20133 Milano

Polymer semiconductors with steadily improved electronic properties are being synthesized, achieving charge mobility in excess of 1 and 10 cm2/Vs for electrons and holes, respectively. This enables the fabrication of high-performance all-printed, all-polymer transistors, which are among the best candidates for future portable and lightweight electronic applications. After a brief review of recent progresses in our group on all-printed electronics, I will focus on the study of structure-property relationships in high-mobility polymers, i.e. the nexus between film microstructure and electronic properties. This is of paramount importance to develop quantitative models describing charge transport in molecular solids where molecules are bound by weak van der Waals interactions. While pure microstructural investigations, such as those based on X-rays, electron microscopy, or polarized optical probes, provide necessary information for the rationalization of transport in macromolecular solids, a general model predicting how charge accommodates within structural maps is not yet available. Therefore, techniques capable of directly monitoring how charge is distributed when injected into a polymer film and how it correlates to structural domains can help fill this gap. I will show that polarized charge modulation microscopy (p-CMM) can unambiguously and selectively map the orientational order of the only conjugated segments that are probed by mobile charge in the few nanometer thick accumulation layer of a high-mobility polymer-based field-effect transistor. Depending on the specific solvent-induced microstructure within the accumulation layer, p-CMM can image charge-probed domains that extend from submicrometer to tens of micrometers size, with markedly different degrees of alignment. Wider and more ordered p-CMM domains are associated with improved carrier mobility, as extracted from device characteristics. This observation evidences the unprecedented opportunity to correlate, directly in a working device, electronic properties with structural information on those conjugated segments involved in charge transport at the buried semiconductor-dielectric interface of a field-effect device.

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