Relaxation of photogenerated Carrieres in P3HT PCBM Organic Blends

The after pulse time resolved microwave conductivity TRMC decays observed in P3HT PCBM blends display a dependence on time close to t b, 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 t b 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 conten