Organic semiconductor carrier liquids

Yoshimoto, N., Hanna, J.I. Preparation of a novel organic semiconductor composite consisting of a liquid crystalline semiconductor and crosslinked polymer and characterization of its charge carrier transport properties. J. Mater. Chem. 13(5), 1004—1010 (2003)... 

The history of our knowledge of the electrical conductivity of organic solids has been discussed by several authors who were involved in the work on the electrical conductivity of polycyclic aromatic hydrocarbons in the years after 1950 in a special volume of Molecular Crystals, liquid Crystals [6] edited by H. Inokuchi. At the beginning of this newer period of research, there were at least five milestones Stimulated by the measurements of Eley on phthalocyanine, Akamatu and Inokuchi in the year 1950 discovered a thermally-activated specific conductivity with an activation energy of E= 0.39 eV in violanthrone, and obtained similar values for related aromatic soUds [7]. The interpretation given at the time for this value in terms of the model of an intrinsic semiconductor with a band gap AEg = 2E is, to be sure, obsolete today (see below), but the results clearly showed that no conductivity exists at T = 0 and thus no intrinsic charge carriers are present in the crystal. 

Based on recent other works [8, 9], we think that for developing even higher mobility materials it is essential to improve the structural order of the material. This may open new application fields, e.g. the use of active organic materials in semiconductor devices. One promising way is the use of highly ordered liquid crystals. With these materials, however, charge carrier mobilities up to 0.1 cm Ws or even more are realistic, which would make them comparable to single crystalline systems [65]. 

Therefore, accumulation of experimental data on mobilities in various classes of liquid crystals are needed before any structural relationship with charge carrier transport properties is established, leading to a rational design of self-organizing molecular semiconductors. 

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