  Organic molecular materials are potential high-performance thermoelectric
materials. Theoretical understanding of thermoelectric conversion in organic
materials is essential for rational molecular design for efficient energy
conversion materials. In organic materials, non-local electron-phonon coupling
plays a vital role in charge transport and leads to complex transport
mechanisms, including hopping, phonon-assist current, band, and transient
localization. In this work, based on time-dependent density matrix
renormalization group (TD-DMRG) method, we look at the role of non-local
electron-phonon coupling on the thermoelectric conversion in organic systems
described by Holstein-Peierls model. We calculate the current-current
correlation and the heat current-current correlation functions. We find that
(i) non-local electron-phonon coupling has very weak influence on Seebeck
coefficient because of the cancellation between heat current-current
correlation function and the current-current correlation function, but it has
strong influence on conductivity through dynamic disorders; (ii) doping
concentration has a strong influence on both conductivity and Seebeck
coefficient significantly, and the optimal doping ratio to reach the highest
power factor is 3%-10% fillings.
