The linewidth of the broad spectrum so obtained was ∼100 nm (FWHM), centered at 13000 cm -1 . The bandwidth of laser pulse has been adjusted so that it covered, both, the polaron peak, P2 of P3HT and the second vibronic feature of the F 4 TCNQ anion. The photon-echo signal is generated by obtaining a phase-matching in the boxcar geometry. The 2D spectra for different population time, T = t 3 -t 2 were acquired by scanning the delay time τ = t 1 -t 2 in the range of [-128 fs, 128 fs] with a step size of 1 fs. At each delay step time τ , 150 spectra were averaged to reduce the noise. The waiting time T = t 3 -t 2 was linearly scanned till 1 ps with steps of 10 fs. The energy of the excitation pulse is tuned to ∼12 nJ with the spot size of ∼80 µm on the sample and 1 kHz repetition rate. To minimize light scattering, the precursor solution sample was filtered using a 0.2 µm filter and then sealed in a 1 mm quartz cell (Starna). To avoid any sample degradation during the measurements, the sealed quartz cell in the 2D setup was placed on a precise 2D translator and moved at a speed of ∼20 cm s -1 in both directions. 2D spectra were retrieved from the measured photon-echo (PE) signals using the "invariant theorem". The details of the data analysis has been described in previous reports from our group.