Mechanical study of the enhanced electron injection via using a Bphen interlayer at Alq3/Cs2CO3 interface

Cs2CO3 is shown as a good electron injection material in organic electronic devices for its strong electron injection ability and being insensitive to the choice of metal cathode. Although it is hypothesized that the organic layer adjacent to the Cs2CO3 is crucial to realize efficient electron injection, little work is carried out to study the electron injection capability of cathode when Cs2CO3 contacts with different organic materials. Here a phenanthroline (Bphen) thin layer has been inserted at Alq(3)/Cs2CO3 interface to improve electron injection, and the responding mechanism is also studied. When locating a 5 nm Bphen layer at Alq(3)/Cs2CO3 interface, OLEDs performed much larger current. A photovoltaic experimental was conducted to study the build-in electrical field in OLEDs, which would give a hint for the work function change of cathode when Bphen interlayer was used; and the ultraviolet-visible absorption spectroscopy was also used to study the electronic structure change of Bphen when it contacts with Cs2CO3. Our study suggest that the cathode work function does not change obviously when Bphen interlayer is used, but much stronger charger transfer takes place between Bphen and Cs2CO3 than that between Alq(3) and Cs2CO3, so that a stronger dipole and a lower electron injection barrier can be expected playing a role at Bphen/Cs2CO3 interface.