Wavelength dependence of nanoscale photodegradation in poly(3-octylthiophene) thin films

The use of conducting polymers in optoelectronic devices is subject to the understanding of the electro-optical processes that take place at the nanoscale. One of the photo-induced processes that limit their application is the photodegradation, which reduces the device working life. In this work the photodegradation of poly(3-octylthiophene) thin films was studied by combining Kelvin probe microscopy and optical microscopy. In this way, a direct correlation between morphological and contact potential changes with optical density changes as a function of the irradiation wavelength and intensity can be made. These results, complemented with Raman spectra help to clarify the degradation processes that are taking place. We find that the photodegradation strongly depends on the irradiation wavelength blue light being much more aggressive than UV. In addition, the optical properties change abruptly before any substantial change in the morphology is observed.