Charge transport properties of a metal-free phthalocyanine discotic liquid crystal

Abstract

Discotic liquid crystals can self-align to form one-dimensional semiconducting wires, many tens of microns long. In this letter, we describe the preparation of semiconducting films where the stacking direction of the disc-like molecules is perpendicular to the substrate surface. We present measurements of the charge carrier mobility, applying temperature-dependent time-of-flight transient photoconductivity, space-charge limited current measurements, and field-effect mobility measurements. We provide experimental verification of the highly anisotropic nature of semiconducting films of discotic liquid crystals, with charge carrier mobilities of up to 2.8 × 10 −3 cm 2 /Vs. These properties make discotics an interesting choice for applications such as organic photovoltaics.

Non‐Peripheral Tetrahexyl‐Substituted Vanadyl Phthalocyanines with Intermolecular Cofacial π–π Stacking for Solution‐Processed Organic Field‐Effect Transistors

“…[ 18 ] The solubility of Pcs in common organic solvents can be greatly improved by placing substituents on the Pc ring at the peripheral and non-peripheral benzo-sites. [ 12 ] As shown in Figure 1 , the peripheral sites are labeled as 2, 3,9,10,16,17,23, and 24, and the non-peripheral sites are numbered as 1, 4, 8, 11, 15, 18, 22, and 25. Some peripheral tetra-substituted Pcs have been used for the preparation of OFETs by common solution processes (such as spin-casting).…”

“…However, the mobilities of the tetraalkoxy-substituted Pcs were very low (10 − 4 -10 − 3 cm 2 V − 1 s − 1 ). [ 22,23 ] A peripheral tetraalkyl-substituted OVPc exhibited a moderate mobility of 0.017 cm 2 V − 1 s − 1 , [ 11 ] which is still two orders of magnitude lower than that of unsubstituted OVPcs. [ 17 ] Several factors may cause the low mobility of the devices based on these soluble Pcs: 1) the introduction of substituents may alter the packing motif of Pc molecules, leading to a larger intermolecular distance and a smaller π -electron orbital overlap; [24][25][26][27] 2) the edge-on alignment of disc-like Pc molecules for the formation of charge transport channels along the source-drain electrodes direction is often diffi cult; [ 6 ] and 3) tetra-substituted Pcs are a mixture of four structural isomers, [ 12 ] which might remarkably reduce the order of the molecules in the fi lms.…”

Organic Semiconductors: Impact of Disorder at Different Timescales

“…Partially ordered organic semiconductors form an important class of systems where neither the static nor dynamic disorder limit is strictly valid with discotic liquid crystals [94][95][96] and some conjugated polymers [97][98][99][100] being representative examples. [101] The charge transport behaviour observed in these systems is complicated by the presence of nuclear modes with a very broad range of timescales.…”

Charge Transport in Organic Semiconductors: A Multiscale Modeling

“…Recently, PR-TRMC (pulse-radiolysis time-resolved microwave conductivity) measurements probing charge transport at a very local scale have pointed to hole mobility values around 0.2 cm 2 V À1 s À1 [115]. On the other hand, time-of-flight measurements yield charge mobility values on the order of only 10 À3 cm 2 V À1 s À1 [116], thus suggesting that the presence of structural defects strongly affects the charge transport properties. This apparent discrepancy is rationalized here by combining molecular dynamics simulations to characterize structural properties and kinetic Monte Carlo approaches to access the charge transport properties (see Ref.…”