Electrical and Structural Characterization of Poly(3-hexylthiophene)–Polydiphenylamine Blends Synthesized on Various Conductive Substrates

Abstract

With the aim of assessing whether polydiphenylamine (PDPA) can be used as an inductor layer for stabilizing the radical cation in the polymer matrix of poly(3-hexylthiophene) (P3HT), as used in photovoltaic devices, interphases between P3HT and PDPA films were prepared electrochemically on platinum (Pt), tin-doped indium oxide (ITO), and gold (Au) electrodes in lithium perchlorate-acetonitrile (LiClO4-ACN) solution, being denoted as Pt/PDPA:P3HT, ITO/PDPA:P3HT, and Au/PDPA:P3HT, respectively. To characterize the interphases deposited on the different electrodes, Raman spectroscopy was used to monitor the behavior of the segments in the blend matrix compared with homopolymer films deposited on the different conducting electrodes, to study the stability of the quinone and semiquinone segments of PDPA and P3HT. Bode phase diagrams obtained by electrochemical impedance spectroscopy (EIS) were used to verify the prepared systems as a function of time since preparation. It was found that the polaron structure (oxidized thiophene ring radical cation segments) was stable for 97 h when the blend was synthesized under controlled temperature (22°C) conditions at constant potential of 1.70 V applied for 60 s to the surface of the Pt electrode. For the blends synthesized on ITO and Au, these conditions resulted in greater stabilization of the bipolaron structure (dication segments). These findings reveal the effect of PDPA induction over the P3HT layer in stabilizing the semiquinone and quinone forms, compared with interfaces formed solely by homopolymers in contact with the different electrodes.