Photocarrier transport of regiorandom poly(3-hexylthiophene) P3HT in ITO/P3HT/Al sandwich cell configuration has been investigated by means of Time-of-Flight technique. Characteristics of Schottky diode and the magnitude of hole mobility have been found to be affected by impurities involved during the synthesis. The hole mobility in regiorandom P3HT at room temperature has been estimated to be 2.4 10-5 and 2.6 10-4 cm2/V. s before and after the removal of ferric ions, respectively, at a field of 5.0105 V/cm. Field dependencies of mobility before and after purification show unique feature and have been discussed in terms of the disorder model.

Electrical properties of contacts between head-tail coupled poly(3-hexylthiophene), PHT and Al (and Au) in planer type and sandwich type diodes of Al/PHT/Au have been studied. The contact resistances are directly evaluated by probing the potential profile of PHT between the metal electrodes using micromanipulators installed in scanning electron microscope. In the potential profile of planer type diode, a large potential cliff is observed at Al/PHT interface and some appreciable potential step is also found at PHT/Au interface. The contact resistance at the Al/PHT interface deduced from the potential profile shows the bias and its polarity dependence, indicating the existing of the Schottky like junction. At forward bias, it is found that the residual resistance at Al/PHT interface limits the diode performance. The residual resistance is supposed to be insulating layer of Al oxide. At larger reversed bias, the contact resistance at Al/PHT decreased abruptly due to the Zener breakdown. The potential profile of sandwich type diode is similar to that of planer type diode. It is found that even the PHT/Au contact shows the ohmic behavior, the contact resistance is significant as to limit the maximum current of the cells.

Carrier mobilities in poly(3-alkylthiphene) cast films have been studied by means of fabricating a field effect transistor (FET) at the field range of (0.4-1.6)104 V/cm. It is found that the regioregurality is markedly effective to the mobilities than the side chain length. The FET mobilility of the regioregular poly(3-hexylthiophene), PHT is approximately 310-3 cm2/Vs which is larger than that of regiorandom PHT by 3 orders of magnitude. The mobility of regioregular poly(3-dodecylthiophene), PDDT is 810-4 cm2/Vs and is also 3 orders of magnitude larger than that of regiorandom PDDT. The mobilities of regioregular ones decrease, however, those of regiorandom ones increase at higher fields. The FET mobilities are nearly same to the mobilities estimated by the time of flight method. These results have been discussed taking the regularity of the main chain and the length of side chain into consideration.