  Recently the quantum nature in the energy transport in solar cell and
light-harvesting complexes have attracted much attention, as being triggered by
the experimental observations. We model the light-harvesting complex (i.e.,
PEB50 dimer) as a quantum heat engine (QHE) and study the effect of the
undamped intra-molecule vibrational modes on the coherent energy transfer
process and quantum transport. We find that the exciton-vibration interaction
has non-trivial contribution to the promotion of quantum yield as well as
transport properties of the quantum heat engine at steady state, by enhancing
the quantum coherence quantified by entanglement entropy. The perfect quantum
yield over 90% has been obtained, with theexciton-vibration coupling. We
attribute these improvements to the renormalization of the electronic couplings
effectively induced by exciton-vibration interaction and the subsequent
delocalization of excitons. Finally we demonstrate that the thermal relaxation
and dephasing can help the excitation energy transfer in PEB50 dimer.
