A-D-A Type Semiconducting Small Molecules with Bis(alkylsulfanyl)methylene Substituents and Control of Charge Polarity for Organic Field-Effect Transistors
Sung‐Joon Cho, Min Je Kim, Ziang Wu, Jae Hoon Son, Sang Young Jeong, Sungjoo Lee, Jeong Ho Cho, Han Young Woo
Abstract
In this study, we synthesize four different kinds of bis(alkylsulfanyl)methylene-substituted 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene (IDT)-based acceptor-donor-acceptor (A-D-A) type small molecules (IDSIC, IDSIC-4F, IDSIC-4Cl, and IDSTIC) by incorporating electron-withdrawing halogen atoms or electron-releasing thiophene spacers. Herein, enhanced structural planarity and crystalline intermolecular packing are induced by the sp2-hybridized C═C double bond side chains and sulfur–sulfur chalcogen interactions. The fine control of intramolecular charge transfer modulates the electrochemical characteristics and the resulting carrier polarity in organic field-effect transistors (OFETs). Well-balanced ambipolar, n-dominant, and p-dominant charge transport properties are successfully demonstrated in OFETs by modulating the electron-donating or withdrawing strength based on the A-D-A structural motif, resulting in hole/electron mobilities of 0.599/0.553, 0.003/0.019, 0.092/0.897, and 0.683/0.103 cm2/V·s for IDSIC, IDSIC-4F, IDSIC-4Cl, and IDSTIC respectively, after thermal annealing at 200 °C. Thermal annealing of the as-cast films improves the intermolecular packing in an edge-on fashion, which is investigated in detail by grazing incidence X-ray scattering. Finally, complementary logic circuits, i.e., NOT, NAND, and NOR, are fabricated by assembling p-dominant IDSTIC and n-dominant IDSIC-4Cl OFETs. Therefore, a simple and efficient molecular design strategy for fine tuning the charge polarity and charge transport properties of OFET devices is presented.