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20 p3ht - poly(3-hexylthiophene)Figure 2.3.: Assembling of P3HT molecules. In the h-mechanism theassembling of single P3HT chains is driven by the π − πinteractions, resulting in the formation of h-foil (left). Inthe s-mechanism the assembling brings to the formationof s-foils (right).Figure 2.4.: Static interaction between two P3HT chains at differentπ − π distances.a (interdigitation) is sizably smaller (as small as ∼ 0.1 eV/thiophene),showing a weak interaction between hexyl groupsof neighboring chains [3]. Notably, the two minima of Figure2.7 can be linked to the corresponding minima of theedge-to-edge (Figure 2.5) and face-to-face curves (Figure 2.4).The A ′ absolute minimum at distances lower than 14 Å,in Figure 2.7 corresponds to a ideal situation where thepolymer chains (in vacuo and at low T) are fully interdigitated.This is unlike to occur in real systems at finite temperaturewhere the thermal fluctuations of hexyl chainsand other sources of disorder (such as solvents and chemicalcontaminants) hinder the perfect interdigitation. This