Origin of Charge Carrier Transport Properties in Smectic E Phase

Abstract

We have identified liquid crystalline phase emerged in an alkoxyalkl derivative of phenylbenzothienobenzothiphene (Ph-BTBT), i.e., 2-(propoxybutyl)-7-phenylbenzothienobenzithiophene Ph-BTBT-4O-3, and studied its charge carrier transport properties by Time-of-Flight experiments. Ph-BTBT-4O-3 exhibited smectic E phase (SmE) at a wide temperature range of -130 to 200 °C over 300 K, and its hole mobility was determined as a function of temperature and electric field. At the low temperature range lower than room temperatures, hole mobility exhibited Poole-Frenkel like dependence and carrier transport properties characterized by 81 meV for a Gaussian width of the density of states. On the other hand, hole mobility did not depend on electric field at the range beyond the room temperatures up to 200 °C and exhibited Arrhenius type of activation energy of 0.11 eV, from which we estimated reorganization energy of 0.44 eV. We discuss the present results in comparison with the previous results from 2-(thiopropoxybutyl)-7-phenylbenzothienobenzithiophene (Ph-BTBT-4S-3).