Organic semiconductor defects

Polydiacetylenes (2) come closest to the model one-dimensional organic semiconductor and can be readily obtained in form of large, nearly defect-free single crystals so that a large number of experiments and measurements have been carried out on these materials. Their structure is shown in Figure 3 where also some typical side-groups R are indicated. On table I we summarize some measured va-... 

From a materials perspective, the requirements vary by application, but in general, there is a trend towards low voltage operation and high carrier mobUity. These two typically require the use of very well-ordered organic semiconductors with low defect density. Use of binders within the semiconductor ink is also typically not possible due to the degrading impact of these on carrier transport properties. 

Quite often the mobilities determined for a given molecule, e.g. rabrene or pentacene, differ for different devices in different laboratories, reflecting the problems related to the extraction of the mobility data from the electrical characteristics. Typically, these characteristics are not only defined by the mobilities but also by the contact resistance and of course the presence of domain boundaries defects and impirrities in the organic semiconductor. The determination of the true intrinsic mobility of an organic semiconductor is still a challenge, which has only been overcome in a very few cases. 

An alternative model to account for low mobilities in organic semiconductors is the multitrapping and release model. Traps are locahzed levels as lattice defects or impurities in which charge carriers are immobilized. The ones localized near the center of the bandgap are called deep traps, while the ones close to the conduction or valence band... 

T. P. Nguyen. Defect analysis in organic semiconductors. Mater. Sci. Semicond. Process., 9(1-3) 198-203, February-June 2006. 

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