Organic semiconductors have been intensely investigated because of their unique properties, including mechanical flexibility and solution-processability. Hence, it has been used in various optoelectronic devices, including organic solar cells (OSCs) and organic light-emitting diodes (OLEDs). However, a short lifetime has been regarded as a critical factor that hinders their commercialization. In this regard, a fundamental understanding of degradation of polymers is necessary.
  In this study, we investigated the effect of ultraviolet-ozone (UVO) treatment on the electronic structures of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) films. To analyze the optical properties of the polymeric thin films according to the UVO treatment time, we performed UV-vis and photoluminescence (PL) spectroscopies. Also, the electronic structure of thin films were studied by using X-ray photoelectron spectroscopy (XPS). The significant oxidation and decrease in thickness were observed. This study provides a useful information on the surface modification of polymeric films.