Fig. 2: Ultrafast spectroscopy of the OPV blend.

A Schematic representation of states contributing to the TA spectra. Open shapes represent organic semiconductors in the ground state. Coloured shapes are organic semiconductors either in the electronically excited state (green: emissive O-IDTBR exciton; blue: WF3 polaron pair), or in a state created by a charge transfer event (gold: interfacial charge transfer state or charge-separated state), or in the electronic ground state but exposed to field lines of a charge pair, exhibiting a Stark shift of the fundamental electronic transition (light blue for WF3, light green for O-IDTBR). B Contributions to the TA spectra of these states. Identical bands occurring in several states are connected by dashed vertical lines. C TA spectra (dots) and fit functions (solid lines): the spectra were recorded 20 ps after excitation with 10 fs broadband pulses at parallel polarization with the probe pulses for films of pristine WF3 (blue) and annealed O-IDTBR (green). Dotted lines correspond to the normalised linear absorption and the shaded grey area shows the excitation spectrum. D TA of the WF3:O-IDTBR blend at 50 fs delays following photoexcitation (black dots), along with the fit (black line) and its components, following the same colour code as in panel (B). E Same as (D) for 200 ps after photoexcitation. F Dynamics of the concentration of each species included in the spectral modelling of the WF3:O-IDTBR blends (see Supplementary Information). Black dots correspond to the ratio EA/(CT + CS) that enables tracking the first jump of a charge away from the interface. The black solid line is an exponential fit with a 40.5 ps rise time.