Structural stability of poly(3-methylthiophene) and polydiphenylamine blend as an interface applied to hole injector

In this study, interfaces between poly(3-methylthiophene) (P3MT) and polydiphenylamine (PDPA) were prepared on an electrode of indium tin oxide (ITO) (ITO/PDPA:P3MT) or Pt (Pt/PDPA:P3MT) in LiClO₄–acetonitrile (ACN) and in diphenyl phosphate (DPHP)–LiClO₄–ACN. These systems were compared with those consisting of homopolymers (ITO/PDPA and ITO/P3MT) with the aim of studying the stability of quinone and semiquinone segments in the matrices of blends capable of enhancing the efficiency of organic photovoltaic cells. Raman spectroscopy and electrochemical impedance spectroscopy (EIS) were used as a function of time after preparation of the systems studied. The behavior of charged species in the blend matrix as a function of the applied potential were verified by taking in situ Raman spectra of the Pt/PDPA:P3MT system, also facilitated by the identification of the charge transfer processes of the different P3MT segments by means of EIS. Electron paramagnetic resonance spectroscopy was used to quantify, as time progressed, the radical cation segments present in the polymer matrices after preparation. Ex situ Raman spectroscopy of the ITO/PDPA:P3MT system synthesized in LiClO₄–ACN was used to compare it with the ITO/P3MT interface, which revealed that as time progressed the radical cation segments lost stability more slowly, subsequently boosting the dication segments. However, for the ITO/PDPA:P3MT system in DPHP–LiClO₄–ACN, this process occurred more rapidly.