Anisotropic charge transport in large single crystals of π-conjugated organic molecules

Abstract

The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of π-π stacking (along the long axis of the single crystal) with a mobility value in the order of 10(-3) cm(2) V(-1) s(-1), and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm(2) V(-1) s(-1). The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the π-π stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility.

High‐Quality Nano/Micro Hairy Single Crystals Developed from Poly(3‐hexylthiophene)‐Based Conductive–Dielectric Block Copolymers Having Flat‐on and Edge‐on Orientations

“…Their procedure allowed control over the number of density, size, and internal structure of these crystals . In addition, they showed that charge transport through the single crystal was anisotropic . The P3HT single crystals absorbed light at higher wavelengths compared to spin‐cast films and thus a remarkable red shift occurred .…”

Functional molecules and materials by π‐Interaction based quantum theoretical design

“…Hourani et al designed an organic field-effect transistor (OFET) composed of regioregular octamer of 3-hexyl-thiophene (3HT) 8 showing anisotropic charge transport properties. [97] In the p-p stacking direction of this polymeric semiconductor (along the long axis of the single crystal with mobility of 10 23 cm 2 V 21 s 21 ) the charge transport is smaller than that along the molecular axis (in the direction of the thickness of the single crystal with mobility of 0.5 cm 2 V 21 s 21 ). Therefore, the pp stacking interaction controls charge carrier mobility in these polymeric semiconductors.…”

Fine fibrillar and rectangular/hexagonal ordered grains of poly(3-hexyl thiophene) and poly(ethylene glycol) developed by seeding technique

“…In the realm of semiconductive polymers, large single rectangular crystals of 3-hexyl thiophene (3HT) 8 [35,36], nanowires of conjugated poly(p-phenylene ethynylene) derivatives [37], poly(3-hexyl thiophene) (P3HT) nanowhiskers [38], one-dimensional (1D) microwire P3HT single crystals [39], and self-organized two-dimensional (2D) P3HT supramolecules [40,41] were reported. Nascent lateral habits of solution-grown single crystals [42], surface-patterned single crystals [43][44][45][46][47], and conductive-dielectric-conductive single crystals [48][49][50] have also been reported.…”