Abstract
Organic semiconducting donor–acceptor polymers are promising candidates for stretchable electronics owing to their mechanical compliance. However, the effect of the electron-donating thiophene group on the thermomechanical properties of conjugated polymers has not been carefully studied. Here, thin-film mechanical properties are investigated for diketopyrrolopyrrole (DPP)-based conjugated polymers with varying numbers of isolated thiophene moieties and sizes of fused thiophene rings in the polymer backbone. Interestingly, it is found that these thiophene units act as an antiplasticizer, where more isolated thiophene rings or bigger fused rings result in an increased glass transition temperature (T g ) of the polymer backbone, and consequently elastic modulus of the respective DPP polymers. Detailed morphological studies suggests that all samples show similar semicrystalline morphology. This antiplasticization effect also exists in para-azaquinodimethane-based conjugated polymers, indicating that this can be a general trend for various conjugated polymer systems. Using the knowledge gained above, a new DPP-based polymer with increased alkyl side chain density through attaching alky chains to the thiophene unit is engineered. The new DPP polymer demonstrates a record low T g , and 50% lower elastic modulus than a reference polymer without side-chain decorated on the thiophene unit. This work provides a general design rule for making low-T g conjugated polymers for stretchable electronics.
| Original language | English |
|---|---|
| Article number | 1800899 |
| Journal | Advanced Electronic Materials |
| Volume | 5 |
| Issue number | 5 |
| DOIs | |
| State | Published - May 2019 |
| Externally published | Yes |
Funding
S.Z. and M.U.O. contributed equally to this work. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Science under award number of SC0019361. S.R.-G. would like to thank NSERC for financial support through a Discovery Grant (Grant No. RGPIN-2017-06611). L.H. and J.D.A. are grateful for support from the National Science Foundation (Grant No. NSF OIA-1757220). S.L. and D.Z. thank National Science Foundation of China (Grant No. #21790345) for providing funding. The authors thank Naresh Eedugurala, Eric King, and Zhiyuan Qian for helpful discussions during the experiments, Sarah Morgan group for AFM instrument access. The authors thank Changwoo Do (ORNL) for assistance during SANS experiment. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. A portion of this research was conducted at the Center for Nanophase Materials Sciences and Spallation Neutron Source, which is a DOE Office of Science User Facility. Part of the work was performed as a user project at the Molecular Foundry, which was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Keywords
- conjugated polymers
- conjugation linkers
- stretchable electronics
- structure–property relationship
- thermomechanical properties