Thin film charge carrier mobility

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... 

Recently in thin film electronics research, inorganic (particulate) films have received a lot of attention [3, 23]. High charge carrier mobilities (mainly n-type) and good environmental stability make inorganic materials highly favourable for electronics applications. Their generally problematic processability, however, limits current application in printed electronics. 

Comparing the situation for PTCDA with the above discussed cases of pery-lene and pentacene which exhibit a large diffusion already at room temperature (due to their smaller sublimation enthalpy) thus indicates that the film structure of large molecules such as PTCDA prepared at room temperature may not represent the thermodynamic equilibrium structure. Finally, we note that PTCDA reveals only a rather small charge carrier mobility (for thin films values of less than 3 X 10 cmW s were reported [67]), and thus is not well suited for the fabrication of OFETs. 

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. 

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