Ultrafast relaxation dynamics of photoexcitations in poly(3-hexylthiophene) for the determination of the defect concentration

► A 9-fs laser and a broadband lock-in detection system were used in this measurement. ► The time constant for the formation of bound polaron pairs (BPPs) was accurately measured to be 90 ± 2 fs and the time constant for BPPs decay was measured to be 710 ± 40 fs. ► Defect trapping process of bound polaron pairs was determined as 2.8 ps. ► The number of defect sites on P3HT thin film was estimated.