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  Moehl,T.; Kytin,V.G. ;Bisquert,J, ; Kunst, M. ; Bolink,H.J. ;Garcia-Belmonte, G.: Relaxation of photogenerated Carrieres in P3HT:PCBM Organic Blends. ChemSusChem 2 (2009), p. 314-320

Abstract:
The after-pulse time-resolved microwave conductivity (TRMC) decays observed in P3HT:PCBM blends display a dependence on time close to tb, independent of excitation intensity, in the 10 ns–1 ms range. This is explained in terms of the relaxation of carriers in a Gaussian density of states (DOS). The model is based on a demarcation level that moves with time by thermal release and retrapping of initially trapped carriers. The model shows that when the disorder is large the after-pulse decay of the type tb is obtained, while at low disorder and large temperature the carrier distribution becomes independent of time. In the measurements different b values were observed depending on the solvent used for spin-coating: 0.4–0.6 for chlorobenzene and 0.3–0.4 for toluene. The model was applied to extract the shape of the DOS from the TRMC decays, giving a dispersion parameter of about 120 meV for blends with high P3HT content.