A Solution Processable Dithioalkyl Dithienothiophene (DSDTT) Based Small Molecule and Its Blends for High Performance Organic Field Effect Transistors

Abstract

The 3,5-dithiooctyl dithienothiophene based small molecular semiconductor DDTT-DSDTT (1), end functionalized with fused dithienothiophene (DTT) units, was synthesized and characterized for organic field effect transistors (OFET). The thermal, optical, electrochemical, and computed electronic structural properties of 1 were investigated and contrasted. The single crystal structure of 1 reveals the presence of intramolecular locks between S­(alkyl)···S­(thiophene), with a very short S–S distance of 3.10 Å, and a planar core. When measured in an OFET device compound 1 exhibits a hole mobility of 3.19 cm2 V–1 s–1, when the semiconductor layer is processed by a solution-shearing deposition method and using environmentally acceptable anisole as the solvent. This is the highest value reported to date for an all-thiophene based molecular semiconductor. In addition, solution-processed small molecule/insulating polymer (1/PαMS) blend films and devices were investigated. Morphological analysis reveals a nanoscopic vertical phase separation with the PαMS layer preferentially contacting the dielectric and 1 located on top of the stack. The OFET based on the blend comprising 50% weight of 1 exhibits a hole mobility of 2.44 cm2 V–1 s–1 and a very smaller threshold voltage shift under gate bias stress.

Heteroalkyl‐Substitution in Molecular Organic Semiconductors: Chalcogen Effect on Crystallography, Conformational Lock, and Charge Transport

“…It is known that the shearing process can efficiently orient organic semiconductor molecules in thin films. [ 30,32,47 ‐– 49 ] First, Figure 8 points that all 1 , 1B , and 1C films exhibit (00 l ) reflections in the out‐of‐plane direction, which results from the periodic stacking of the selenotetradecyl side chains and molecular backbone along the film thickness. Sharp Bragg spots progressing up to (002) are seen for 1 , corresponding to a d lam of 19.2 Å (determined from (001) at q z = 0.33 Å −1 ).…”

“…[ 44–46 ] Among them, fused‐thiophene‐based small molecules have been widely explored due to the highly planar structures, strong intermolecular S…S interactions and extensive π‐conjugation. [ 47–51 ]…”

“…[ 47,52–54 ] Heteroatoms have also been utilized to bridge a thiophene/molecular unit with an alkyl chain as well as introduced at different position of the alkyl substituent. [ 47–50,55 ] The use of a heteroatom (X) and its location in the chain strongly affect energetic states, molecular conformation, solubility, and film wettability. [ 47,55,56 ] For instance, when replacing a CH 2  group in 3,3′‐dialkyl‐2,2′‐dithiophene with an S linker in 3,3′‐dithioalkyl‐2,2′‐dithiophene the latter structure is completely planar and, when integrated into larger molecular motifs, it retains substantial solubility in several organic solvents.…”

Organic Semiconductor–Insulator Blends for Organic Field‐Effect Transistors

“…[ 26,27 ] Generally, high values of off current, SS, and V th in experimental results of continuously applied bias stress indicate poor electrical stability, that is, bias‐stress instability. [ 28–31 ] Incorporating inert insulators in OSCs is commonly used for stability enhancement. [ 19,32 ] For example, Lee et al highlighted that the insulator‐tailored device was less vulnerable to the off‐bias stress that manifested as a smaller V th shift over stress time compared with the neat poly(didodecylquaterthiophene‐ alt ‐didodecylbithiazole) (PQTBTz‐C12) device.…”

Out-of-Plane Alignment of Conjugated Semiconducting Polymers by Horizontal Rotation in a High Magnetic Field

“…Conjugated polymers have attracted great interest for various applications such as thin-film organic field-effect transistors (OFETs), − organic light-emitting diodes (OLEDs), − and organic solar cells (OSCs) − because of their low cost, good mechanical flexibility, and compatibility with large-area fabrication. Nevertheless, most polymer-based thin-film devices exhibit inferior charge carrier mobility due to the fact the active films exhibit a semicrystalline structure with numerous small aggregation domains coexisting with lots disordered and amorphous regions.…”