Beside bright field and electron diffraction, Low dose HR-TEM was also used to
show structural differences between various M w fractions of P3HT. In HR-TEM
images, a contrast is observed between the π-stacked polythiophene backbones and
the layers of alkyl side chains. Therefore, it is possible to measure the average
length of P3HT stems (chain segments) (L c ) along the chain direction c P3HT and the
number of unit cells along the side chain direction a P3HT in P3HT nanocrystals.
Figure 12 shows representative HR-TEM images of P3HT films grown by slowDEC. Two main points can be noted with increasing M w : (1) the average stem
(chain) length (L c ) in the crystalline domains increases substantially from 6 to
16 nm, and (2) the lateral extension of the domains in the direction of the side
chains (L a ) decreases from 25 to 13 stems. Apparently, in the regime of chain
folding, the use of slow growth rates leads to longer stem lengths in the crystalline
domains, suggesting that in most P3HT samples (spin-coated and drop-cast films),
Fig. 11 Evolution of the lamellar morphology (top row), ED pattern (middle row), and azimuthal
distribution of the (1 0 0) reflection (bottom row) obtained for epitaxied P3HT films grown by
slow-DEC in TCB for three P3HT samples with different molecular weights. The insets in the top
sequence correspond to the fast Fourier transform
100
M. Brinkmann et al.
show structural differences between various M w fractions of P3HT. In HR-TEM
images, a contrast is observed between the π-stacked polythiophene backbones and
the layers of alkyl side chains. Therefore, it is possible to measure the average
length of P3HT stems (chain segments) (L c ) along the chain direction c P3HT and the
number of unit cells along the side chain direction a P3HT in P3HT nanocrystals.
Figure 12 shows representative HR-TEM images of P3HT films grown by slowDEC. Two main points can be noted with increasing M w : (1) the average stem
(chain) length (L c ) in the crystalline domains increases substantially from 6 to
16 nm, and (2) the lateral extension of the domains in the direction of the side
chains (L a ) decreases from 25 to 13 stems. Apparently, in the regime of chain
folding, the use of slow growth rates leads to longer stem lengths in the crystalline
domains, suggesting that in most P3HT samples (spin-coated and drop-cast films),
Fig. 11 Evolution of the lamellar morphology (top row), ED pattern (middle row), and azimuthal
distribution of the (1 0 0) reflection (bottom row) obtained for epitaxied P3HT films grown by
slow-DEC in TCB for three P3HT samples with different molecular weights. The insets in the top
sequence correspond to the fast Fourier transform
100
M. Brinkmann et al.