Conjugated Polymer Mesocrystals with Structural and Optoelectronic Coherence and Anisotropy in Three Dimensions

Semiconducting mesocrystalline bulk polymer specimens that exhibit near-intrinsic properties using channel-die pressing are demonstrated. A predominant edge-on orientation is obtained for poly(3-hexylthiophene-2,5-diyl) (P3HT) throughout 2 mm-thick/wide samples. This persistent mesocrystalline arrangement at macroscopic scales allows reliable evaluation of the electronic charge-transport anisotropy along all three crystallographic axes, with high mobilities found along the pi-stacking. Indeed, charge-carrier mobilities of up to 2.3 cm(2) V-1 s(-1) are measured along the pi-stack, which are some of the highest mobilities reported for polymers at low charge-carrier densities (drop-cast films display mobilities of maximum approximate to 10(-3) cm(2) V-1 s(-1)). The structural coherence also leads to an unusually well-defined photoluminescence line-shape characteristic of an H-aggregate (measured from the surface perpendicular to the materials flow), rather than the typical HJ-aggregate feature usually found for P3HT. The approach is widely applicable: to electrical conductors and materials used in n-type devices, such as poly{[N,N '-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5 '-(2,2 '-bithiophene)} (N2200) where the mesocrystalline structure leads to high electron transport along the polymer backbones (approximate to 1.3 cm(2) V-1 s(-1)). This versatility and the broad applicability of channel-die pressing signifies its promise as a straightforward, readily scalable method to fabricate bulk semiconducting polymer structures at macroscopic scales with properties typically accessible only by the tedious growth of single crystals.