Probing the electrode-polymer interface in conjugated polymer devices with surface-enhanced Raman scattering

A crucial consideration in organic devices is the role of the interface between a metal electrode and the active polymer material. Here, we use the conjugated polymer poly[2-methoxy-5-(2-ethylhexyl-oxy)-1,4-phenylene-vinylene] (MEH-PPV) with model gold and silver electrodes to perform surface-enhanced Raman scattering (SERS) on the metal-MEH-PPV interface. We observe significant differences between the SERS spectra on the two metals, which we assign to conformational changes of the phenyl rings within the polymer. The difference between gold and silver interfaces can be removed upon thermal annealing, suggesting structural relaxation. Resonance Raman spectra of the two interfaces are identical, implying that the overall conformation of the polymer backbone which supports the pi-electron transition remains unaffected by the different metals. SERS is uniquely sensitive to the interfacial metal/organic layer and provides an important in situ tool to optimizing organic device structures. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3701278]