In the absorption spectrum of pure P3HT, the original absorption of P3HT centred at 550 nm and 512 nm corresponds to [pi]-[pi]* transition, which is due to the 0-0 and the 0-1 transitions, respectively, where 0-n means a
vibronic transition from the ground vibrational state of the ground singlet electronic state to the nth vibrational state of the first excited singlet electronic state and is in very good agreement with values reported in the literature [38, 39].