Charge carrier mobility and diffusion in conjugated polymers
Final Report Abstract
We were able to determine the charge carrier mobility and diffusion in organic semiconductors by a combination of simulations and experiments. For simulation studies of the exciton diffusion in organic semiconductors, often, the master equation approach was used to calculate the diffusion coefficient, which—as we found out—leads to erroneous results. We were able to find a way to compute the diffusion coefficients correctly by using the master equation with a small force which was then extrapolated to zero. These results fit perfectly well together with Monte Carlo simulations, and represent therefore computationally efficient pathway to predict correct exciton diffusion coefficients. We outlined above why these results have implications beyond the scope of the current proposal. We studied the charge transport in detail by extracting charge carrier mobility distribution from timeof-flight photocurrent transient measurements. This approach allows to study charge transport in systems with comparably high energetic disorder adequately. Our results were, we believe, important to understand the role of disorder on charge transport. Finally, we investigated the connection between charge carrier mobility and diffusion. Even though we found a non-analytical scaling of the diffusivity with the applied electric field due to experimental restrictions such as the limited sample thickness, our findings are consistent with theoretical predictions of field stimulated diffusion and the generalized Einstein–Smoluchowski relation. We note that while we found clear experimental evidence for these effects, the latter are often not considered in the evaluation and interpretation of experimental results. This, however, will be important to understand charge transport and recombination in thin organic semiconductor devices for photovoltaics and light emission.
Publications
- Band bending at the P3HT/ITO interface studied by photoelectron spectroscopy. Org. Electron., 15, 1552 (2014)
M. Schneider, A. Wagenpfahl, C. Deibel, V. Dyakonov, A. Schöll, and F. Reinert
(See online at https://doi.org/10.1016/j.orgel.2014.03.012) - Distribution of charge carrier transport properties in organic semiconductors with gaussian disorder. J. Appl. Phys. 115, 183702 (2014)
J. Lorrmann, M. Ruf, D. Vocke, V. Dyakonov, and C. Deibel
(See online at https://doi.org/10.1063/1.4875683) - Prediction of charge and energy transport in organic crystals with quantum chemical protocols employing the hopping model. PhD thesis, Würzburg (2015)
V. Stehr
