Electrochemical investigation of an high electron mobility copolymer

Electrochemical methods are a powerful strategy to investigate the structure-property relationship of new advanced organic semiconductors. Here we report a complete electrochemical investigation of the co-polymer P(NDI2OD-T2), which exhibits one of the highest field-effect electron mobility (0.85 cm2/Vs) in a top-gate bottom-contact architecture [1,2]. Studies on P(NDI2OD-T2) highlighted the unconventional face-on microstructure, featuring T2 units flat to the surface while NDI2OD units are tilted with an angle of ~ 40°[3-5]. However, several questions correlating the microstructure to the charge transport properties remain open. In this context by means of electrochemical techniques we were able to gain insight into the charge transport mechanisms of this material. The film has been studied in the neutral, n-doped and p-doped state with different working electrodes (glassy carbon and gold). In particular cyclic voltammetry (CV) provides information about the oxidation and reduction processes and the HOMO-LUMO levels; whereas electrochemical impedance spectroscopy (EIS) allows to investigate mass and charge transfer mechanisms inside the film and the polymer conductivity as well. Moreover film stability and doping and undoping processes were investigated with electrochemical quartz microbalance (EQCM). Interestingly the two reduction processes have been found much more chemically and electrochemically reversible and stable with respect to the oxidation one. On the other hand the oxidative cycle life improves depositing the film on gold electrode. Furthermore the effect was studied of solventinduced long-range order [6] on different P(NDI2OD-T2) films, which significantly affects the electrochemical behaviour. Finally, in order to elucidate the nature of the charged species, spectroelectrochemistry techniques have been applied for the first time to this co-polymer, namely in situ ATR (attenuated total reflection spectroscopy) and in situ EPR/UV-vis. References [1] Z. Chen et al, Nature 2009, 457,679. [2] Z. Chen et al., JACS 2009, 131,8. [3] J. Rivnay et al. , Adv. Mater, 2010, 22, 4359. [4] T. Schuettfort et al., Macromolecules 2011, 44, 1530–1539. [5] E. Giussani. et al., Macromolecules, 2013, 46, 2658. [6] A. Luzio et al., Scientific Report, Article number: 3425, doi:10.1038/srep03425.