Electronic structure of P3HT film oxidized by ultraviolet–ozone treatment

Recently, solution-processable polymeric semiconductors have been applied in various optoelectronic devices. To improve the surface properties of polymeric films, ultraviolet–ozone (UV–O 3 ) treatment is commonly used. However, the electronic structures of polymeric films altered by UV–O 3 treatment are not sufficiently understood. In this study, we investigated the electronic structures of poly(3-hexylthiophene-2,5-diyl) (P3HT) films with various UV–O 3 treatment times. During UV–O 3 treatment, significant oxidation occurred on both C and S atoms, bleaching the films. The degree of oxidation was higher than that observed in the UV-treated P3HT films without O 3 discussed in the literature. As a result, more C-based compounds were generated. Interestingly, the degree of oxidation with an increase in UV–O 3 treatment time was approximately the same between annealed and unannealed P3HT films. This result can be attributed to inherent film crystallinity based on the high regioregularity of P3HT.