"Time- and Temperature-Independent Local Carrier Mobility and Effects of Regioregularity in Polymer-Fullerene Organic Semiconductors"

Meng-Ju Sher: Jonathan A. Bartelt, Timothy M. Burke, Alberto Salleo, Michael D. McGehee, Aaron M. Lindenberg; Advanced Electronic Materials, 02/04/16.

Additional Authors: Jonathan A. Bartelt, Timothy M. Burke, Alberto Salleo, Michael D. McGehee, Aaron M. Lindenberg

Abstract:

Organic semiconducting polymers exhibit complex microstructure and disorder over a wide range of length scales, which impact the electronic transport properties relevant for the development of photovoltaic devices. Typical transport measurements blur together intermolecular and intramolecular conduction processes, making it difficult to develop an understanding of how disorder on different length scales impacts device performance. This work uses time-resolved terahertz (THz) spectroscopy to selectively study intramolecular carrier transport in poly(3-hexylthiophene) (P3HT). At 2 THz, P3HT polymers with different side chain regularity have fast THz carrier mobility ranging from 0.1 to 0.4 cm2 V−1 s−1, and the mobility dependence on the side chain regularity is much smaller than studied by other macroscopic mobility measurements. The fast local carrier mobility allows us to understand how the efficiency of charge-transfer state splitting is high in these polymers and shows that local disorder does not strongly impact intramolecular transport processes. Moreover, the local mobility does not exhibit changes with temperature or time within the 1 ns duration probed, indicating that local carrier transport is always fast. To fully understand the differences in time and temperature dependence on carrier transport at different length scales, a transport model that separates local transport from intermolecular carrier hopping is required.