The Synergistic Effect Of Solvent And Epitaxial Crystallization On The Structure And Properties Of Conducting Polymer Poly (3-hexylthiophene) (P3HT)

Polarized organic semiconductor blends can confer desirable properties,such as enhanced charge transport properties and polarized light emission or absorption.A technique that is not only adapted to solution processing but also producing anisotropic conducting blend films is realized by epitaxial crystallization of blends on oriented polymer substrate.The epitaxial structure of P3HT and PCBM on oriented polyethylene(PE)substrate is affected by the boiling point of the used solvent.The P3HT cast from o-dichlorobenzene with high boiling point on PE forms the "side-on" and "face-on" crystals with c-axis parallel to c-axis of PE.While the orientation of "side-on" and "face-on" crystals is poor when P3HT is casted from chloroform with low boiling point.The addition of PCBM does not affect the epitaxial crystallization behavior of P3HT.Moreover,anisotropic structure of PCBM is also obtained on PE substrate.PE substrate efficiently increases the amount of "face-on" crystals and the ratio of "face-on" to "side-on" is 7 times as much as that on PSS:PEDOT substrate.Anisotropic structures lead to anisotropic absorption and photoluminescence properties.The anisotropic optical properties are better for sample cast from o-dichlorobenzene with the dichroic ratio of 2.Photoluminescence polarization ratio(IVH/IVV)for P3HT and P3HT/PCBM film are ca.2,which indicates the potential application as the polarized luminophors.The effect of solvent type and thickness on the epitaxial crystalline structure of P3HT on highly oriented PE films was investigated by using grazing incidence X-ray diffraction(GIXRD).Diffraction results of incident X-rays parallel to the c-axis of the PE molecular chains and the incident X-ray beam perpendicular to the c-axis of PE were obtained,thereby the structural orientation information is obtained within the films.The thickness of the P3HT films varies from 18 nm to 95 nm.The results show that the P3HT films on the highly oriented PE substrates using the two different solvents exhibit the face-on and side-on orientations where the c-axis of P3HT is parallel to the stretching direction of oriented PE.The P3HT film casted from chloroform solution has more face-on crystals.In contrast,a large number of side-on crystals are obtained on oriented PE substrate when P3HT film is casted from o-dichlorobenzene.The face-on crystals from the two solvents decrease with decrease in thickness.Whereas the thinner film prepared by using o-dichlorobenzene solvent contains almost all of the side-on crystals,indicating that longer induction of oriented PE for P3HT crystallization and its degree of ordering also greatly increases.In addition,the UV absorption spectra suggested that the P3HT films obtained from the two different solvents have better anisotropy with decreasing thickness,which is more pronounced by using o-DCB.The dichroic ratio increases from 1.975 to 4.2.However,dichroic ratio is almost similar for the films casted from chloroform.