Compared with the blendsbased on fullerene acceptors, the EL comes from charge transferstate emission, which is red-shifted relative to the donor/acceptor singlet emission, the EL of the blends based on NFAs mainlycomes from the singlet excitons in the donor polymers [167],which means reducing the energy offset of the donor and acceptor can reduce the energy losses from both the radiative recombination and nonradiative recombination.