We report three types of dicyanodistyrylbenzene (DCS)-based copolymers (PBDT-DCS, PT-DCS, and PNDI-DCS), which present highly balanced ambipolar charge transport characteristics in organic field-effect transistors (OFETs). The introduction of the DCS moiety in a polymer backbone not only lowers the lowest unoccupied molecular orbital (LUMO) level but also increases the crystalline ordering via interchain dipole-dipole interactions. As a result, the LUMO levels for PBDT-DCS, PT-DCS, and PNDI-DCS were decreased to -3.76, -4.00, and -3.99 eV, respectively, which is beneficial for efficient electron injection from Au electrode for improving ambipolar charge transport. The determined hole/electron mobilities of the OFETs were 0.064/0.014, 0.492/0.181, and 0.420/0.447 cm2/(V s) for PBDT-DCS, PT-DCS, and PNDI-DCS, respectively, after thermal annealing at 250 °C. By incorporating the electron-deficient naphthalene diimide (NDI) unit in the copolymers, the n-channel transport was enhanced, with decreasing frontier molecular orbitals with enhanced electron injection and impeded hole injection from the Au electrode. Therefore, PNDI-DCS provided completely symmetric output curves in the positive and negative drain voltage regions with almost equivalent hole and electron mobilities. Benefiting from the balanced ambipolar feature of the PNDI-DCS OFETs, a complementary inverter was successfully fabricated.
Bibliographical noteFunding Information:
H. S. Ryu and M. J. Kim contributed equally to this work. This work was supported by the National Research Foundation (NRF) of Korea (2016M1A2A2940911, 2015M1A2A2057506, and 2015R1D1A1A09056905) and the Center for Advanced Soft Electronics (CASE) under the Global Frontier Research Program (NRF-2013M3A6A5073177), Korea.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry