Thiophene-Diketopyrrolopyrrole-Based Quinoidal Small Molecules as Solution-Processable and Air-Stable Organic Semiconductors: Tuning of the Length and Branching Position of the Alkyl Side Chain toward a High-Performance n-Channel Organic Field-Effect Transistor

Abstract

A series of thiophene-diketopyrrolopyrrole-based quinoidal small molecules (TDPPQ-2-TDPPQ-5) bearing branched alkyl chains with different side-chain lengths and varied branching positions are synthesized. Field-effect transistor (FET) measurement combined with thin-film characterization is utilized to systematically probe the influence of the side-chain length and branching position on the film microstructure, molecular packing, and, hence, charge-transport property. All of these TDPPQ derivatives show air-stable n-channel transporting behavior in spin-coated FET devices, which exhibit no significant decrease in mobility even after being stored in air for 2 months. Most notably, TDPPQ-3 exhibits an outstanding n-channel semiconducting property with electron mobilities up to 0.72 cm(2) V(-1) s(-1), which is an unprecedented value for spin-coated DPP-based n-type semiconducting small molecules. A balance of high crystallinity, satisfactory thickness uniformity and continuity, and strong intermolecular interaction accounts for the superior charge-transport characteristics of TDPPQ-3 films. Our study demonstrates that tuning the length and branching position of alkyl side chains of semiconducting molecules is a powerful strategy for achieving high FET performance.

Trends in molecular design strategies for ambient stable n-channel organic field effect transistors

“…In a separate study, the branching position of the alkyl group was varied in a series of cyanovinyl substituted DPP derivatives and their electrical properties were determined. 200 The highest mobility in a bottom- with a very high current on/off ratio of 10…”

Bismuth Interfacial Doping of Organic Small Molecules for High Performance n‐type Thermoelectric Materials

“…TDPPQ is considered to be ap romising TE material because of its high electron mobility and ability to facilitate superior electrical conductivity, [9] as well as its high electric field-modulated Seebeck coefficient over 600 mVK À1 at an electrical conductivity of > 0.1 Scm À1 (Supporting Information, Figure S1). [8] However, its TE applications are limited by the efficiency of chemical doping.Although Bi is an excellent dopant for many inorganic TE materials, [10] aB i-involved organic TE material has not been reported.…”

“…Herein, Bi is explored as adopant for TDPPQ. [9] Thec hemical doping of TDPPQ was firstly studied by UV/Vis absorption spectroscopy and ultraviolet photoemission spectroscopy (UPS). Thes emiconductor was synthesized according to aprevious report.…”

Synthesis and characterization of solution-processable diketopyrrolopyrrole (DPP) and tetrathienothiophene (TTA)-based small molecules for organic thin film transistors and organic photovoltaic cells

“…For compound 1, a hole mobility as high as 1.0 Â 10 À1 cm 2 V À1 s À1 was obtained on PETS-modified devices measured under N 2 conditions after optimization. The mobility of 1-based OTFTs is about more than 10 times larger than that of 2-based OTFTs, even though the HOMO/LUMO energy levels are almost the same, which also indicates that a considerable difference in hole mobility is predictably observed due to an increase in the contact resistance of the longer insulating branch side chain and less densely packed p-backbone [53,54]. Among all OTFTs examined in this work, those based on compound 4 show the largest degradation, and this is due to the morphological transition.…”