Melt‐Processing of Conjugated Liquid Crystals: A Simple Route to Fabricate OFETs

Abstract

Melt‐processing of 5,5′‐bis(4‐hexylphenyl)‐2,2′‐bithiophene leads to a favorable morphology of the conjugated liquid crystal in the channel of an OFET (see figure) and a fivefold improvement of the mobility over that found for conventional devices fabricated by evaporation. This process does not require solvents or vacuum‐deposition processes.

Liquid‐Crystalline Rigid‐Core Semiconductor Oligothiophenes: Influence of Molecular Structure on Phase Behaviour and Thin‐Film Properties

“…They persisted to room temperature making this compound a promising material for FET applications. [10] The phase evolution of DTT5 was also monitored by XRD. Figure 2 shows the variation of the XRD profile on increasing the temperature from room temperature to 145 8C and then cooling back to room temperature (scan rate 5 8C min…”

“…Note that the mobility values for smectic liquid crystalline semiconductors can be optimised by improving the molecular alignment on the device surface. In particular, as already reported, [10,26] using silane-treated SiO 2 /Si surfaces may help the homeotropic alignment of the molecules into a single monodomain. Detailed investigations of the FET behaviour of DTT5 films upon annealing at the transition temperatures using silane-treated FET devices are currently under way.…”

“…[10] One way to achieve LC properties in oligothiophenes is to add long aliphatic chains to one or both ends of unsubstituted rod-like oligomers. [11] By this approach the balance between the order induced by the aromatic rigid backbone and the disorder induced by the flexible alkyl ends usually Abstract: The design, synthesis and properties of liquid-crystalline semiconducting oligothiophenes containing dithienothiophene (DTT), benzothiadiazole (BTZ) and carbazole (CBZ) rigid cores are described.…”

Trichlorosilanes as Anchoring Groups for Phenylene‐Thiophene Molecular Monolayer Field Effect Transistors

“…It has been recognized that conjugated mesogens can be self-organized into large area monodomains without defects caused by grain boundaries by processing in the mesophase. [ 18,19 ] Conjugated mesogens based on a phenylene-bithiophene core (PTTP) are promising semiconductors employed in OFETs due to the simple synthesis and favorable liquid crystalline phase behavior. [19][20][21] Further, the introduction of the phenylene units lowers the HOMO level leading to improved device stability in…”

“…The sequence of liquid crystalline phases (I-SmA-G), in a PTTP mesogen, allowed melt processing of homeotropically aligned fi lms and strong intermolecular π-π interaction between adjacent molecules. [ 19 ] Hence, PTTP was chosen as the semiconducting core for the molecular monolayer, n-hexyl (C 6 ) chain as the end-capping group and a fl exible dodecane (C 12 ) spacer linked the semiconducting core to the trichlorosilane anchoring group.…”