Probing phase transitions and stability of organic semiconductor single crystals by dielectric investigation

The characterization of organic crystalline semiconductors in terms of possible phase transitions with temperature may be very important for the general knowledge of the material but also in view of application in devices: such properties may indeed cause variations in the macroscopic behavior of the material, especially relevant at the operation temperatures of few tens of degrees. Here, phase transitions in alpha-quaterthiophene single crystals are detected and studied by means of dielectric investigation, a powerful tool to go deeper in this matter. After describing the relative dielectric constant and the ac conductivity of the different solid phases, found to display either an insulating or a semiconducting character, quantitative information is provided on the relative stability of the different phases the active material may transform into, by giving an estimate of their entropy content. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3531574]