PC 15


Yi-kang Lan, Ching-I Huang*

Institute of Polymer Science and Engineering, National Taiwan University,

No.1, Sec. 4, Roosevelt Rd. Taipei, Taiwan, 10617. ( chingih@ntu.edu.tw)

The performance of a region-regular poly (3-alkylthiophene) system for organic thin-film transistors (OTFTs) is critically dependent on its ability to self-organize. The packing structure of poly (3-alkylthiophene) system, which results from the side chain - side chain packing and thiophene ring - ring stacking, gives insight to estimate the charge mobility and the electron transfer mechanism. Molecular modeling and simulation are carried out to estimate the characteristic packing structure of poly (3-alkylthiophene) systems including P3HT, P3DDT and PQT12.

During the modeling procedures of reducing the system density, we find that due to the well-ordered side chain packing structures both in P3HT and P3DDT systems, there exist energy barriers for the systems. The first energy barrier is about 25-30 kcal/mol and comes from the van der Waals repulsion of the entwining side chain pairs. This barrier blocks the next side chain to attach into the ordered structure. However if the system overcomes the barrier and the ordered side chains are packed in the first local minimum, it deeply stabilizes the packing structure not only the side chain, but also the ring-ring stacking order.

In addition, the corresponding scattering patterns for the simulated structures after 2 million molecular dynamics steps (2 ns) are analyzed in a comparison with the experimental data. In general, these simulated patterns are consistent with the experimental data. The characteristic distances like ring-ring distance are between 3.6 to 3.8 angstrom and the chain - chain distances are about 18 angstrom for the P3HT system. The simulated structures will then be used for further studies of the charge mobility and electron transfer mechanism.