Organic semiconductors charge carrier mobility

Figure 17.1 Organic semiconductor charge carrier mobility requirements to allow fulfillment of the commercial roadmap for displays driven by organic TFTs...

Klenkler RA, Xu G, Aziz H, Popovic ZD (2006) Charge-carrier mobility in an organic semiconductor thin film measured by photoinduced electroluminescence. Appl Phys Lett 88 242101... 

The channel length is limited by the process technology, while the charge carrier mobility is basically a material property, but also depends on the degree of order in the organic semiconductor. The greatest hole mobilities to date, which amount to several cmWs, were observed in vapour-deposited small organic molecules [1, 4, 14], in polymers they are typically between 10 and 0.1 cmWs (for comparison crystalline silicon can have a hole mobility of up to 500 cm Ws) [15—23]. 

As a result of the above, and of the direct competition between molecule-substrate and intermolecular interactions, the presence of the metal or insulator can induce interface polymorphs which do not exist in the bulk. Examples for this are the specific thin film phases of pentacene on insulators [16, 74, 75] or metals (e.g., Cu(llO) [16]), the a- and 3-phases of tetraeene on Ag(l 11) [69], or the square phases of PTCDA on Ag(l 11) [30] and Au(l 11) [84]. It is evident that the charge carrier mobilities of organic semiconductors will depend on the crystal phase. 

Most probably a higher dielectric constant of the insulating layer causes a broader distribution of the electronic states in the organic semiconductor, resulting in the reduced charge carrier mobility. 

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