Keywords Crystallization Á Epitaxy Á Poly(3-hexylthiophene) Á Thin films Á
Transmission Electron Microscopy
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
2 Epitaxy: Principle and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
2.1 Epitaxy of Semicrystalline Polymers: The Case of Polyolefins . . . . . . . . . . . . . . . . . . . . . 85
2.2 Epitaxy of Semiconducting Polymers on Aromatic Crystal Surfaces . . . . . . . . . . . . . . . 87
2.3 Directional Epitaxial Crystallization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3 Epitaxy: An Interesting Insight into Structural and Morphological Aspects of P3HT . . . 93
3.1 Structure Determination of Form I P3HT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3.2 Folded Chain Versus Extended Chain Crystallization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4 Conclusions and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
1 Introduction
Plastic electronics has undergone increasing development over the last few decades
and now appears as a major and challenging new research field. This is due in part
to the ongoing efforts in the synthesis of new semiconducting polymers (SCPs) that
show improved opto-electronic properties and are processable using low cost
deposition methods (spin-coating, ink-jet printing, etc.) [1–8]. Interest in this field
is also related to the increasing control of device manufacture and understanding
of structure–property relationships [9–11]. Intrinsically, SCPs exhibit strongly
anisotropic optical and electronic properties and, therefore, the control of both the
polymer chain direction and the crystal orientation in thin films is essential
[12, 13]. For instance, in the case of regioregular poly(3-hexylthiophene), preferential contact planes of crystallites on a substrate influence the charge transport
properties and device performance to a large extent [12]. The ‘edge-on’ and ‘faceon’ orientations of the polymer backbones on a substrate [14–19] can favor charge
transport along different directions to the substrate normal or to the orientation
of an applied electric field [20]. From a device manufacture point of view, orientation of SCPs chains can be of high interest to channel charge carriers along one
preferential direction and thus reduce parasitic current paths between adjacent
OFETs in a dense array of transistors [2, 21–23]. Besides orientation,
nanostructuring of conjugated polymers is another essential aspect that influences
for instance photovoltaic activity in organic solar cells (OSC) based on a bulk
heterojunction [24, 25]. This chapter presents the state-of-the-art concerning the
structure and the morphology in highly oriented and/or nanostructured thin films of
regioregular poly(3-alkylthiophene)s prepared by epitaxy. The first part of this
contribution presents various examples of orientations obtained for polyolefins
and P3HT as well as the corresponding structural investigations using TEM and
X-ray diffraction methods. The second half of this chapter shows the interest of
84
M. Brinkmann et al.
Transmission Electron Microscopy
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
2 Epitaxy: Principle and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
2.1 Epitaxy of Semicrystalline Polymers: The Case of Polyolefins . . . . . . . . . . . . . . . . . . . . . 85
2.2 Epitaxy of Semiconducting Polymers on Aromatic Crystal Surfaces . . . . . . . . . . . . . . . 87
2.3 Directional Epitaxial Crystallization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3 Epitaxy: An Interesting Insight into Structural and Morphological Aspects of P3HT . . . 93
3.1 Structure Determination of Form I P3HT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3.2 Folded Chain Versus Extended Chain Crystallization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4 Conclusions and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
1 Introduction
Plastic electronics has undergone increasing development over the last few decades
and now appears as a major and challenging new research field. This is due in part
to the ongoing efforts in the synthesis of new semiconducting polymers (SCPs) that
show improved opto-electronic properties and are processable using low cost
deposition methods (spin-coating, ink-jet printing, etc.) [1–8]. Interest in this field
is also related to the increasing control of device manufacture and understanding
of structure–property relationships [9–11]. Intrinsically, SCPs exhibit strongly
anisotropic optical and electronic properties and, therefore, the control of both the
polymer chain direction and the crystal orientation in thin films is essential
[12, 13]. For instance, in the case of regioregular poly(3-hexylthiophene), preferential contact planes of crystallites on a substrate influence the charge transport
properties and device performance to a large extent [12]. The ‘edge-on’ and ‘faceon’ orientations of the polymer backbones on a substrate [14–19] can favor charge
transport along different directions to the substrate normal or to the orientation
of an applied electric field [20]. From a device manufacture point of view, orientation of SCPs chains can be of high interest to channel charge carriers along one
preferential direction and thus reduce parasitic current paths between adjacent
OFETs in a dense array of transistors [2, 21–23]. Besides orientation,
nanostructuring of conjugated polymers is another essential aspect that influences
for instance photovoltaic activity in organic solar cells (OSC) based on a bulk
heterojunction [24, 25]. This chapter presents the state-of-the-art concerning the
structure and the morphology in highly oriented and/or nanostructured thin films of
regioregular poly(3-alkylthiophene)s prepared by epitaxy. The first part of this
contribution presents various examples of orientations obtained for polyolefins
and P3HT as well as the corresponding structural investigations using TEM and
X-ray diffraction methods. The second half of this chapter shows the interest of
84
M. Brinkmann et al.