Buried interfaces: interfacial interactions in materials for polymer-LED applications

Chemical interactions at the interface between a precursor polymer for poly(p-phenylenevinylene), namely poly(p-xylylene-α-tetrahydrothiophene chloride), and an indium–tin–oxide (ITO) transparent electrode, have been studied through polymer films of > 10 nm thick using x-ray photoelectron spectroscopy. The HCl released in the conversion process interacts with the surface of the ITO substrate at the polymer/substrate interface, leading to the formation of indium chloride, which then diffuses into the polymer. It appears that ITO, or possibly the indium chloride generated at the interface, acts as a catalyst for the thermal elimination reaction. The results show unequivocally that interfacial interactions are of major importance in understanding, and ultimately improving, the performance of polymer-based electroluminescent devices, and that interfaces buried under > 10 nm of polymer may be studied.