Conference Program - LOPE-C 2011

SCIENTIFIC CONF. | WEDNESDAY-JUNE 29, 2011
Track 5
Organic and Carbon-based Materials (04:30 pm - 06:00 pm) | LOCATION HARMONIE E / LEVEL C2
05:40 pm Polythiophene: polyethylene blend semiconducting thin-films and transistors by wire-bar coating
Dr Craig Murphy,
National Physical Laboratory, United Kingdom
Organic semiconductors provide the potential for low cost integrated electronic circuits on flexible plastic substrates. In order to enhance the capability for formability and
flexibility of plastic transistors, blended material systems incorporating mechanically tough polymers, such as polyethylene, have recently been created. These mixed
materials possess a higher degree of complexity than single polymer semiconductors and require proper investigation of their physical and chemical structure, plus
electrical properties. Here, we develop the first examples of wire-bar coated thin-films and transistor devices incorporating polythiophene : polyethylene blend organic
semiconductor systems, examining the physical nanostructure, surface chemical composition and electrical characteristics, as a function of polythiophene : polyethylene
component ratio. Wire-bar coating is a simple deposition method for preparing large areas of thin organic films at low cost and processes developed on such equipment are
amenable to scale-up via techniques such as slot die coating, including in roll-to-roll fabrication systems.
The morphology of the semiconductor layers produced has been examined by atomic force microscopy, transmission electron microscopy and X-ray photoelectron
spectroscopy methods to reveal a strong structural dependence on initial composition, with clear evidence of phase separation, including vertical segregation. The 50 : 50
blend (by weight) exhibits a particular striking morphology, whereby micellar regions of semi-crystalline polythiophene (100s nm diameter) are enclosed by a matrix of
lamellar polyethylene material (25-50nm lamella width). In terms of thin-film uniformity all the samples examined were homogeneous over large areas and the morphologies
were reproducible between substrates processed in different coating runs. Bottom gate-bottom contact transistor devices were fabricated using such blends as the
semiconductor layer and the field-effect charge carrier mobility was characterized as a function of blend composition. The combination of polymer blend semiconductors
and large area deposition methods, such as wire-bar coating, provides a route to low cost, high performance, flexible plastic electronic circuits and systems.
page 76