  We theoretically investigate an exciton transfer process in a donor domain of
organic photovoltaic cells focusing on the roles of local and nonlocal
electron-phonon interactions. Our model consists of a three-level system
described by the Holstein-Peierls Hamiltonian coupled to multiple heat baths
for local and nonlocal molecular modes characterized by Brownian spectral
distribution functions. We chose tetracene as a reference donor molecule, where
the spectral distribution functions of the local and nonlocal modes exist. We
then employ the reduced hierarchy equations of motion (HEOM) approach to
simulating the dynamics of the system under the influence of the environment as
a function of the electron-phonon coupling strength and temperature. We
rigorously calculate the reduced density matrix elements to explain the
timescale of dynamics under the influence of the dissipative local and nonlocal
modes. The results indicate that the strong nonlocal electron-phonon
interaction under high temperature conditions favors the exciton transfer
process and enhances the efficiency of organic photovoltaic materials, while
the lifetime of the exciton becomes shorter due to a low frequency local mode.
