A study of the degradation of poly(3-octylthiophene)- based light emitting diodes by Surface Enhanced Raman Scattering

Organic light emitting diodes (OLED) based on poly(3-octylthiophene) (P3OT) were studied by on-line Surface Enhanced Raman Scattering (SERS) experiments. A simultaneous reduction of the emitted power and an increase of the SERS signal was observed above an 8 V bias voltage in the case of ITO/P3OT/Al structures. On-line measurements of the temperature and independent tests with an atomic force microscope, performed on the Al cathode before and after current flow, demonstrated that the observed enhancement of the Raman signal was partly thermal and partly electromagnetic in origin, with clear evidence of cathode roughening induced by current flow. In contrast, analogous tests performed on P3OT based OLEDs containing a composite Al+Ag cathode showed that the breakdown was related to electrode delamination.