Polaronic effects and charge transport in donor-acceptor semiconducting polymers

Molecular polaron theories, when applied to high mobility donor-acceptor semiconducting polymers along the chain, indicate that polaronic effects can be very small. These effects include changes to the electronic bandwidth and effective mass resulting from the strong coupling of phonons with charge carriers.¹ The bandwidth and effective mass remain essentially unchanged with increasing temperature and are adequate for band transport to take place along the chain. However, the small mean free path obtained from the polymer mobility is still an obstacle in understanding band transport in polymers. We invoke the statistical distribution of carrier free paths and consider the carriers with small free paths as effectively localized due to strong scattering. Only carriers with adequately large free paths can participate in band transport.² For such carriers, we are able to apply the Boltzmann Transport Equation with appropriate scattering mechanisms to calculate band mobility and the results are in good agreement with experimental data.

¹ Y.C. Cheng and R.J. Silbey, J. Chem. Phys. 128, (2008).
² X. Wang, L.F. Register, and A. Dodabalapur, Phys. Rev. Appl. 11, 64039 (2019).