Figure 2.

(a) Ground state absorption and photoluminescence (PL) spectra of PC₆₀BM (blue) and PC₇₀BM (red) of 1 mg/ml chlorobenzene solutions and spin-coated films. The PL spectra have been corrected for detector response. (b) Time evolution of PL measured at their peaks using time-correlated single photon counting with excitation wavelength of 470 nm. The PL kinetics were not dependent on the probe wavelength, which suggests that the PL spectra shown in panel (a) corresponded to the same optical transition. The solid lines show the fits of a mono-exponential decay model with the displayed time constants.