The field of disordered organic molecular films, and organic semiconductors in general is developing very fast, mainly due to applications as mechanically flexible, inexpensive electronic and opto-electronic devices; however, the physical properties of these materials are still ambiguous.

In this research we studied various electronic properties of organic thin film transistors in high lateral resolution using Kelvin probe force microscopy. This approach enabled us to explore the electronic energy structure of organic thin films (bulk and grain boundaries) as a function of interface treatments, interface charge traps, and exposure to ambient. The measurements were conducted on organic p-type semiconductors such as Pentacene, dinaphto-thieno-thiophene (DNTT) and n-type semiconductors such as hexadecafluorocopperphthalocyanine (F₁₆CuPc) and five core-dichlorinated naphthalene diimides (NDIs). The measurements were analyzed by a model which takes into account the level bending in the organic film, the effective accumulation layer and the change of the organic capacitance as function of the gate bias. We found that the density of state is larger in the organic materials which were grown on hydrophilic surfaces. Moreover, we show that high DOS is induced significant Fermi level pinning deep in the gap. We also observed direct correlation between mobility decreases as function of exposure to air on n-type transistors. The results are discussed in view of their effect on organic thin film transistors performance.