Different contact formations at the interfaces of C60/LiF/Al and C60/LiF/Ag

C60 has been used as an electron accepting and transporting material in various organic electronic devices. In such devices, Al and Ag have been adopted as a common cathode in combination with electron injection layers (EIL), e.g., LiF. We found that the initial interface formations of C60/LiF/Al and C60/LiF/Ag are quite different in terms of interfacial electronic structures. We measured the interfacial electronic structures with photoemission spectroscopy and found that LiF works well as an EIL on Al but performs poorly on Ag. The origin of this difference could be attributed to the larger interface dipole on Al, highlighting the importance of the choice of cathode materials.