Ultrafast Charge and Triplet State Formation in Diketopyrrolopyrrole Low Band Gap Polymer/Fullerene Blends: Influence of Nanoscale Morphology of Organic Photovoltaic Materials on Charge Recombination to the Triplet State

Figure 3

Displayed are selected fs-TA spectra of thin films at various delay times and at different laser powers: (a, b, c) FINE blends (using cosolvents ODCB/DIO); (d, e, f) COARSE blends obtained from CHCl₃; (g, h, i) pristine PDPP polymer films. Delay times are indicated. Excitation was performed at 530 nm. Note: if we go from (a) to (b) to (c) (or from (d) to (e) to (f) or from (g) to (h) to (i)) the relative amount of ultrafast triplet formation (1100 nm band) by singlet fission is reduced at early times; if we go from (g) to (d) to (a) (or from (h) to (e) to (b) or form (i) to (f) to (c)) the relative amount of ultrafast charge generation is increased (1350 nm band).

(a) FINE blend, 28 μJ/cm²

(b) FINE blend, 13 μJ/cm²

(c) FINE blend, 4 μJ/cm²

(d) COARSE blend, 28 μJ/cm²

(e) COARSE blend, 13 μJ/cm²

(f) COARSE blend, 4 μJ/cm²

(g) Polymer, 28 μJ/cm²

(h) Polymer, 13 μJ/cm²

(i) Polymer, 4 μJ/cm²