film and therefore usually under nonequilibrium conditions. The microcrystalline
morphology is strongly dependent on the film processing conditions, including the
coating technique itself, but also on the choice of solvent and the nature of the
substrate [5, 67–72]. In addition to the precise deposition conditions, the molecular
parameters of the polymer (molecular weight and regioregularity) have a strong
impact on the morphology [17, 18, 73–75].
In the following section, we review the influence of these different parameters on
the thin film morphology, and also their impact on the functional properties in
devices. The impact of thin film morphology on both the optical and electrical
properties is discussed. The section is structured as follows: First, visual inspection
of P3HT thin films is described, with absorption spectroscopy being an excellent
tool for understanding intra- and interchain order in thin films. Then, the influence
of molecular parameters and processing conditions on the mesoscopic and microcrystalline morphology is discussed. Some findings on the influence of morphology
on charge transport are also included.
4.1 Preparation and Characterization of P3HT Films
4.1.1 Optical Properties of Thin Films
When P3HT films are deposited from solutions prepared using good solvents,
significant color changes can be detected that range from orange to purple
depending on the regioregularity and the molecular weight of the batch. Thin film
Fig. 8 A network of P3HT nanofibrils was grown from a solvent mixture of anisole and
chloroform (4:1 vol%, 0.05 wt%) by slowly cooling the solution from 70
C to 20
C (25
C/h)
[63]. The fibrils were deposited on transistor substrates by spin-coating. (a) AFM height image;
scale bar: 1 μm. (b) Output characteristics of a nanofibril-based bottom gate, bottom contact
transistor with V G ranging from +5 V to À30 V (À5 V/step). (Reprinted with permission from
Samitsu et al. [63]. Copyright (2010) American Chemical Society.)
54
K. Tremel and S. Ludwigs
morphology is strongly dependent on the film processing conditions, including the
coating technique itself, but also on the choice of solvent and the nature of the
substrate [5, 67–72]. In addition to the precise deposition conditions, the molecular
parameters of the polymer (molecular weight and regioregularity) have a strong
impact on the morphology [17, 18, 73–75].
In the following section, we review the influence of these different parameters on
the thin film morphology, and also their impact on the functional properties in
devices. The impact of thin film morphology on both the optical and electrical
properties is discussed. The section is structured as follows: First, visual inspection
of P3HT thin films is described, with absorption spectroscopy being an excellent
tool for understanding intra- and interchain order in thin films. Then, the influence
of molecular parameters and processing conditions on the mesoscopic and microcrystalline morphology is discussed. Some findings on the influence of morphology
on charge transport are also included.
4.1 Preparation and Characterization of P3HT Films
4.1.1 Optical Properties of Thin Films
When P3HT films are deposited from solutions prepared using good solvents,
significant color changes can be detected that range from orange to purple
depending on the regioregularity and the molecular weight of the batch. Thin film
Fig. 8 A network of P3HT nanofibrils was grown from a solvent mixture of anisole and
chloroform (4:1 vol%, 0.05 wt%) by slowly cooling the solution from 70
C to 20
C (25
C/h)
[63]. The fibrils were deposited on transistor substrates by spin-coating. (a) AFM height image;
scale bar: 1 μm. (b) Output characteristics of a nanofibril-based bottom gate, bottom contact
transistor with V G ranging from +5 V to À30 V (À5 V/step). (Reprinted with permission from
Samitsu et al. [63]. Copyright (2010) American Chemical Society.)
54
K. Tremel and S. Ludwigs