Simultaneous enhancement of charge transport and exciton diffusion in poly($p$-phenylene vinylene) derivatives

Time-resolved luminescence spectroscopy has been used to investigate exciton diffusion in thin films of poly($p$-phenylene vinylene) (PPV)–based derivatives. Due to chemical modifications the PPV derivatives differ by three orders of magnitude in charge carrier mobility as a result of a reduced energetic disorder. From the photoluminescence decay curves of PPV/fullerene heterostructures, the exciton diffusion coefficient was found to increase by one order of magnitude with decreasing disorder. This increase in the diffusion coefficient is compensated by a decrease of the exciton lifetime, leading to an exciton diffusion length of $5–6\mathrm{nm}$ for the various PPV derivatives.

Figure 1

Temperature dependence $\ln \left[{\mu }_p\left(0\right)\right]\sim 1∕T^2$, obtained from Eq. (1) for the studied polymers.

Figure 2

Deconvoluted and normalized luminescence decay curves for NRS-PPV (●), MEH-PPV (∎), and BEH-PPV (▴) for different thicknesses of a polymer film in contact with a poly(F2D) layer. Simulation of these data by Eq. (2) with variable exciton diffusion constant and neat polymer film luminescence decay curves taken as references for each simulation (solid lines).

Figure 3

The relative luminescence quenching in MEH-PPV (∎), BEH-PPV (▴), and NRS-PPV (●) for different thicknesses of the polymer film in contact with the poly(F2D) layer. Fitting of these data to Eq. (4) assuming exciton diffusion length ranging from $6.3\mathrm{nm}$ for MEH-PPV to $5\mathrm{nm}$ for NRS-PPV is shown by solid lines.