vapor pressure. Control of the solvent vapor pressure during solidification of the
polymer enabled adjustment of the length of the resulting nanofibrils.
In 1996, Bao and coworkers compared the charge transport properties of P3HT
layers deposited by spin-coating and drop-casting from different solvents [5]. Dropcast films generally showed better charge transport, which was attributed to a higher
degree of order achieved by the slow growth process of the film. However, the use
of different solvents resulted in a significant scattering, and no clear evolution of the
hole mobility as a function of the film drying time was found, which was related to
differences in film quality. In order to achieve a better understanding of this
behavior, a detailed structural investigation of drop-cast and spin-coated layers
Fig. 14 AFM phase images of thin P3HT films of different molecular weight achieved by three
different casting techniques [75]. (Reprinted from Verilhac et al. [75], Copyright (2006), with
permission from Elsevier)
Morphology of P3HT in Thin Films
61