Partially conjugated copolymers: a novel tool to tune organic material thermoelectric properties

Possibilities to use conjugated polymers as thermoelectric materials have been widely explored in the last few years, giving rewarding results1,2. Such materials are particularly appealing for room temperature application and flexible devices. Since the main drawback in conjugated polymer thermoelectric application is their low efficiency, several different paths have been explored in order to optimize performances3,4. Among them, the development of copolymers is still a mostly unexplored field, due to the increase of the system complexity that they involve. Although the challenge that they represent under a solid-state physics point of view, copolymers are also a novel chance to gain new information about thermoelectric related features in conjugated polymers. Copolymers mainly used for this purpose are copolymers within two different categories. On one side there are donor-acceptor copolymers5, on the other conjugated-not conjugated copolymers6, or partially conjugated copolymers. An overview of the state of art will be given, in order to collect the results currently achieved in this field considering both categories, with a particular attention to synthetic strategies and performance enhancing procedures adopted. Specifically, the thermoelectric behaviour of a novel poly(3,4-ethylenedioxythiophene) (PEDOT) based copolymer (Figure 1) and its blends with PEDOT:tosylate will be presented and discussed. Such derivative belongs to the second category and the study of thermoelectric properties of its blends with the pristine PEDOT has shown that charge transport is percolative (Figure 2). Percolation (Figure 3) can be a key to tune the organic material thermoelectric properties in order to achieve better performances. The results obtained will be discussed in the light of such purpose and possible future developments will be presented. [1] Q. Wei, M. Mukaida, K. Kirihara, Y. Naitoh and T. Ishida, Materials (Basel)., 2015, 8, 732-750. [2] B. Russ, A. Glaudell, J. J. Urban, M. L. Chabinyc and R. A. Segalman, Nat. Rev. Mater., 2016, 1, 16050. [3]O. Bubnova, Z. U. Khan, A. Malti, S. Braun, M. Fahlman, M. Berggren and X. Crispin, Nat. Mater., 2011, 10, 429-33. [4] S. K. Yee, N. E. Coates, A. Majumdar, J. J. Urban and R. A. Segalman, Phys. Chem. Chem. Phys., 2013, 15, 4024. [5] Y. Hiroshige, M. Ookawa and N. Toshima, Synth. Met., 2006, 156, 1341-1347. [6] P. S. Taylor, L. Korugic-Karasz, E. Wilusz, P. M. Lahti and F. E. Karasz, Synth. Met., 2013