3 Epitaxy: An Interesting Insight into Structural
and Morphological Aspects of P3HT
3.1 Structure Determination of Form I P3HT
The polymorphism of poly(3-alkylthiophene)s (P3ATs) was recognized early on by
Prosa and others [52–57]. For the family of P3AT with n ¼ 3 to 15 for the length of
alkyl side chains, two characteristic layer periods have been observed. This indicates that P3ATs exist in two different crystal structures, called form I and form II,
which differ mainly by the side chain packing. Structural models for both forms I
and II have been proposed by several groups [52–61]. In general, the difficulty in
Fig. 6 (a) Underfocused TEM-BF image of a thin area of an oriented thin film of P3HT with
M w ¼ 7.3 kDa grown by DEC. The flat-on lamellae have been delimitated by dotted lines. (b)
Low-dose HR-TEM image. The flat-on lamellae have been identified by dotted lines. The average
in-plane chain orientation is indicated by a white arrow. The inset corresponds to the fast Fourier
transform. (c) Schematic projections of the chain packing of P3HT seen along the b- and c-axes.(d)
Scheme showing the chain orientation in flat-on and edge-on lamellae seen in the HR-TEM image
and giving the corresponding epitaxial conditions. (Reproduced with permission from [45]
© 2009, American Chemical Society)
Understanding the Structure and Crystallization of Regioregular. . .
93
and Morphological Aspects of P3HT
3.1 Structure Determination of Form I P3HT
The polymorphism of poly(3-alkylthiophene)s (P3ATs) was recognized early on by
Prosa and others [52–57]. For the family of P3AT with n ¼ 3 to 15 for the length of
alkyl side chains, two characteristic layer periods have been observed. This indicates that P3ATs exist in two different crystal structures, called form I and form II,
which differ mainly by the side chain packing. Structural models for both forms I
and II have been proposed by several groups [52–61]. In general, the difficulty in
Fig. 6 (a) Underfocused TEM-BF image of a thin area of an oriented thin film of P3HT with
M w ¼ 7.3 kDa grown by DEC. The flat-on lamellae have been delimitated by dotted lines. (b)
Low-dose HR-TEM image. The flat-on lamellae have been identified by dotted lines. The average
in-plane chain orientation is indicated by a white arrow. The inset corresponds to the fast Fourier
transform. (c) Schematic projections of the chain packing of P3HT seen along the b- and c-axes.(d)
Scheme showing the chain orientation in flat-on and edge-on lamellae seen in the HR-TEM image
and giving the corresponding epitaxial conditions. (Reproduced with permission from [45]
© 2009, American Chemical Society)
Understanding the Structure and Crystallization of Regioregular. . .
93