Abstract: The effect of a LiF interlayer on the photovoltaic characteristics of the ITO/PEDOT:PSS/MEH-PPV:C₆₀（0wt%,10wt% and 20wt%）/Al composite device has been investigated.For undoped MEH-PPV devices（0wt%）,the modified devices show an increase in both the V_oc and I_sc.However,for composite devices（10wt% and 20wt%）,the modified devices show an increase in the V_oc,but a decline in the I_sc.These changes of photovoltaic properties are attributed to the dipole layer between composite film and Al cathode due to the introduction of LiF layer.This dipole layer equivalently lowers the work function of cathode,which enhances the build-in potential and thus V_oc.The different effects of LiF on the undoped and composite devices are caused by the different LUMO of C₆₀ and MEH-PPV.