Structural Stability and Optical Studies of Poly(3-hexylthiophene) in an ITO/PEDOT:PSS/P3HT Interface

An interface between poly(3-hexylthiophene) (P3HT) and poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) was prepared in LiClO4--acetonitrile (ACN) over indium-doped tin oxide (ITO), known as the ITO/PEDOT:PSS/P3HT system. This system was compared with ITO/P3HT with the aim of studying the stability of aromatic, quinone, and semiquinone segments in the polymer matrix and also elucidating the influence of the structure on the efficiency of organic photovoltaic cells (OPVs). Initially, Raman spectroscopy was used, varying the laser power to verify the destabilization of radical cation segments to dication segments in the ITO/P3HT system. Electrochemical impedance spectroscopy (EIS) was used to show the behavior of the charged species and the charge-transfer processes of the different P3HT segments as a function of time since preparation of the studied systems. In addition, photoluminescence (PL) and time-resolved PL spectroscopy showed the optical properties of the interfaces formed, based on the different quantities of segments present. It was possible to conclude that the modification introduced into the interface by PEDOT:PSS favors stabilization of the P3HT radical cation segment, which remains stable in this interface for lengthy periods (240h). This should in turn boost hole extraction, increasing OPV efficiency.