Effects of the Polarity and Bulkiness of End-Functionalized Side Chains on the Charge Transport of Dicyanovinyl-End-Capped Diketopyrrolopyrrole-Based n-Type Small Molecules

So-Huei Kang; Doyoung Lee; Hyunwook Kim; Wonbin Choi; Jiyeon Oh; Joon Hak Oh; Changduk Yang

doi:10.1021/acsami.1c14945

Effects of the Polarity and Bulkiness of End-Functionalized Side Chains on the Charge Transport of Dicyanovinyl-End-Capped Diketopyrrolopyrrole-Based n-Type Small Molecules

ACS Appl Mater Interfaces. 2021 Nov 10;13(44):52840-52849. doi: 10.1021/acsami.1c14945. Epub 2021 Oct 27.

Authors

So-Huei Kang¹, Doyoung Lee², Hyunwook Kim², Wonbin Choi², Jiyeon Oh¹, Joon Hak Oh², Changduk Yang¹

Affiliations

¹ Department of Energy Engineering, School of Energy and Chemical Engineering, Perovtronics Research Center, Low Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulju-gun, Ulsan 44919, Republic of Korea.
² School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826 Republic of Korea.

PMID: 34704746
DOI: 10.1021/acsami.1c14945

Abstract

When designing organic semiconductors, side-chain engineering is as important as modifying the conjugated backbone, which has a significant impact on molecular ordering, morphology, and thus electronic device performance. We have developed three dicyanovinyl-end-capped donor-acceptor diketopyrrolopyrrole-based n-type small molecules (C2C9CN, SiC4CN, and EH4PCN) bearing an identical length of alkyl spacer yet different end-functionalized side chains (i.e., alkyl-, siloxane-, and phosphonate-end pendants). The effects of the end-functionalized side chains on the intrinsic molecular properties, microstructure, and charge transport of the small-molecule series were investigated. In comparison with the alkyl-end side chains, incorporating siloxane-end side chains into the backbone facilitates 2D edge-on oriented high intergrain connectivity/crystallinity and compatibility with the substrate surface, whereas the phosphonate-end analogues have an adverse effect on the film-forming quality due to high polarity. Thereby, an organic field-effect transistor fabricated by SiC4CN shows the best electron mobility up to 1.59 × 10^-1 cm² V^-1 s^-1 along with a high current on/off ratio >10⁵. This study contributes to our understanding of the role of the end-functionalized side chains (e.g., the effects of polarity and bulkiness of the end groups) for the development of high-performance semiconductors.

Keywords: conjugated small molecules; diketopyrrolopyrrole; n-type semiconducting materials; organic field-effect transistors; side-chain effects.