Two-dimensional deformation potential model of mobility in small molecule organic semiconductors: DNTT-C10 and BTBT-C12

The high mobility measured in alkylated DNTT and BTBT molecules [1,2] raises the possibility that band transport may be achievable in solution processed organic semiconductors. Therefore, an acoustic deformation potential model appropriate for transport in two dimensions was employed to estimate upper limits on the hole mobility of DNTT-C10 [1] and BTBT-C12 [2]. Comparison is made to results for a thin-film pentacene structure. Density functional calculations are employed to determine the values of effective masses, deformation potentials and elastic constants required to calculate the mobility along crystallographic axes.[3] According to the model, scattering by acoustic phonons places an upper limit on room temperature mobility within single crystal regions of these materials in the range 50-90 cm2/Vs. The effective masses calculated for the holes in DNTT-C10 and BTBT-C12 are significantly less than those obtained for thin-film pentacene, and this difference is the origin of the superior mobility. The width (in the direction perpendicular to the plane of transport) of the -bonded molecular core is identified as an important parameter governing mobility in 2D systems such as these. The affect of alkyl chains on the mobility will be discussed. [1]K. Nakayama et al, Adv. Mater. 23, 1626 (2011). [2]H. Minemawari et al, Nature 475, 364 (2011). [3]J. E. Northrup, Appl. Phys. Lett. 99, 062111 (2011).