High-mobility and nonhalogenated-solvent-processable n-type organic semiconductors enabled by alkyl-side-chain engineering

Abstract

Organic semiconductors possessing both green-solvent processability and superior efficiency are highly desirable for green electronics. A simple but effective strategy to improve the solubility of high-performance organic semiconductors in nonhalogenated solvents by tuning the branch length of the alkyl side chain is presented herein. We synthesize two new thiophene-diketopyrrolopyrrole-based quinoidal molecules (TDPPQs) bearing alkyl chains with varied side branch length but the same branching position at the third carbon, which are soluble in nonhalogenated solvents such as 2-methyltetrahydrofuran (2-MTHF) and acetone (AT). Based on the TDPPQ compounds, we have carried out systematic studies on the relationship between film microstructure and charge transport in their organic field-effect transistors (OFETs). It is found that the branch length of alkyl chains, the processing solvents, and the processing methods have obvious effects on the thin-film microstructure and lead to remarkable changes in OFET performance. Notably, TDPPQ-B exhibits an exciting electron mobility of up to 2.17 cm² V⁻¹ s⁻¹ in OFETs processed from 2-MTHF solution by edge-casting, which is the first report on nonhalogenated-solvent-processed OFETs with electron mobility above 1 cm² V⁻¹ s⁻¹. This work sheds light on the design of high-performance n-type organic semiconductors processable with environmentally benign solvents.