Time-of-flight analysis of charge mobility in a Cu-phthalocyanine-based discotic liquid crystal semiconductor

Abstract

We used a time-of-flight method to study the charge carrier mobility properties of a molecular-aligned discotic liquid crystal semiconductor based on Cu-phthalocyanine. The heated isotropic-phase semiconductor material was sandwiched between transparent electrodes coated onto glass substrates without conventional alignment layers. This was then cooled, and a discotic liquid crystal semiconductor cell was obtained, which we used to make mobility measurements. The material had a fixed molecular alignment due to the supercooling of the hexagonal columnar mesophase. It was clarified that the carrier mobility for electrons was as high as it was for holes at room temperature. The maximum value of negative charge mobility reached 2.60×10−3cm2∕Vs, although negative carrier mobility is often much lower than positive carrier mobility in other organic semiconductors, including conventional Cu-phthalocyanine vacuum-deposited films.

Effect of Interface on the Orientation of the Liquid Crystalline Nickel Phthalocyanine Films

“…[1][2][3][4] To date, the number of discotic liquid crystals (LC) derived from more than 50 different cores comes to about 3000. Recent advances in basic design principles and synthetic approaches toward the preparation of most frequently encountered discotic liquid crystals, their relevant mesomorphic and physical properties, as well as some aspects of application are described in two recent critical reviews by Kumar 5 and Laschat and coauthors.…”

Conducting polymer discotic hybrids for organic semiconductor applications

“…The crude oil was purified by column chromatography, the column was washed with n-hexane, to remove the excess 1-(6-bromohexyl)-1H-pyrrole and the solvent switched to 32:9 hexane:ether solvent to elute the pure product as a clear oil. (80 mg, Yield: 14%) 1 …”

“…1 This property has already been exploited in other photovoltaic devices 2 , however some of the inherently lower conductivities exhibited by many of the discotic materials with respect to alternative organic conductors, has caused them to lose favour in the organic semiconductor field. However liquid crystals represent a near ideal material for bulk manufacturing, given their selfassembling properties and self-healing abilities.…”

Self‐Organized Discotic Liquid Crystals as Novel Organic Semiconductors

“…Initial charge-carrier [36,37]. By using the TOF technique, Ohta and coworkers found ambipolar charge transport (negative charge mobility of 2.4 × 10 −3 cm 2 V −1 s −1 and a positive mobility of 2.2 × 10 −3 cm 2 V −1 s −1 ) in the Col h of a Cu-phthalocyanine compound 10 [57]. This was surprising at the time, since it was generally believed that the negative carrier mobilities should be much lower than the positive carrier mobilities in electron-rich organic semiconductors, including conventional vacuum-deposited films of Cu-phthalocyanines.…”