Transport band-like

Figure 1 Schematic presentation of the two different mechanisms governing charge transport in organic semiconductors. The so-called hopping transport assumes a thermally activated hopping between charge-traps and is always present, the resulting mobilities are very small. For certain materials a mechanism yielding much higher mobilities has been observed, which is commonly referred to as band-like , thus implying a similarity to band-transport observed in conventional semiconductors.

Comparing with conventional amorphous organic semiconductors [16], it is characteristic that conjugated polymer films consist of crystal-like domains, in which jt-conjugated chains are stacked closely, and an amorphous domain, in which polymer chains are disordered [115]. In crystal-like domains, band-like carrier transport that is similar to that of molecular crystals should be possible. However, hopping transport influenced by structural disorder is the dominant process in the amorphous domains. The total carrier transport process is dominated mainly by that in amorphous domains, resulting in bulk carrier transport characteristics similar to those of amorphous organic semiconductors. 

A generalization of the Marcus theory establishes an important criterion for activationless ( band-like ) or localized transport namely, the former occurs when 2t>X, while the latter dominates when 2t molecular polaron model developed before can be derived from the fact that the reorganization energy is linked to the the molecular polarization time, and the transfer integral to the residence time, so the first inequality can also write and the... 

Electrical conduction and heat transport are closely linked, the connection being described by three thermoelectric coefficients, the Seebeck coefficient (or thermopower), the Peltier coefficient and the Thomson coefficient, all of which have relevance to thermoelectric power generation and refrigeration. In perovskites, the most reported values are for the Seebeck coefficient. The magnitude and sign (+ or -) of the Seebeck coefficient are related to the concentration and type of mobile charge carriers present. For band-like perovskites, the magnitude of the Seebeck coefficient is proportional to the density of states, either in the conduction band, for electron transport, or the valence band for hole transport. 

D. Kafer, A. Basir, X. Dou, G. Witte, K. Mullen, C. Woll, Evidence for band-like transport in graphene-based organic monolayers. Adv. Mater. 22, 384-388 (2010)... 

Kang and coworkers also explored steady-state and pulsed photo-also trons-polyphenylacetylene films doped with inorganic and organic electron acceptors, particularly iodine and 2,3-dichloro-5,6-dicyano-/7-benzoquinone. They concluded that charge transport occurs by a band like mechanism that is... 

Wang S, Chia PJ, Chua LL, Zhao LH, Png RQ, Sivaramakrishnan S, Zhou M, Goh RGS, Friend RH, Wee ATS, Ho PKH (2008) Band-like transport in surface-functionalized highly solution-processable graphene nanosheets. Adv Mater... 

Flowever, the charge carrier motions in many organic semiconductors are between these two limits. It is thus expected that more sophisticated microscopic charge transport theories need to be developed to unify the concepts of the band-like and hopping transport. Indeed, many work along this line have been performed." It is known, however, that most of those rigorous quantum approaehes are limited to tens of sites because of the numerical convergence problem and computer memory limitations. 

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