Formation dynamics of excitons and charge carriers in polythiophene–fullerene blend films were studied by near-IR femtosecond transient absorption spectroscopy and highly sensitive microsecond transient absorption spectroscopy at room temperature. Singlet excitons generated in a regiorandom poly(3-hexylthiophene) (RRa-P3HT) pristine film were converted into triplet excitons with a time constant of > 100 ps through intersystem crossing under low excitation condition. At a high excitation, the singlet decay was much faster because of singlet–singlet annihilation but the triplet formation yield remained relatively high. This finding suggests that triplet excitons are formed via charge recombination of polaron pairs generated from hot excitons. On the other hand, singlet excitons generated in RRa-P3HT/[6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) blend films rapidly decayed with a fast time constants (< 100 fs) and a slow one (~ ps). The fast component is ascribed to the prompt charge formation at the interface between P3HT and PCBM. The slow component is ascribed to singlet exciton migration in large domains to the charge separation interface. The efficient triplet formation was still observed for the blend films even though singlet excitons were strongly quenched. The formation of triplet excitons was slower than the charge formation but much faster than that through intersystem crossing from singlet excitons observed for the RRa-P3HT pristine film, suggesting the triplet formation via charge recombination of ion pairs.