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–O3) treatment is commonly used. However, the electronic structures of polymeric films altered by UV–O3 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–O3 treatment times. During UV–O3 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 O3 discussed in the literature. As a result, more C-based compounds were generated. Interestingly, the degree of oxidation with an increase in UV–O3 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.