The impact of electronic structures on the functionality of transition metal oxide-based intermediate connectors for tandem organic light-emitting devices is investigated by studying the interfaces and the corresponding devices. For a typical transition metal oxide-based intermediate connector, consisting of a heterointerface between MoO₃ and Mg-doped tris(8-quinolinolato)aluminum (Mg:Alq₃), it is identified that MoO₃ is essential to the charge generation and separation process, which occurs at the interface between MoO₃ and the adjacent hole-transporting layer (HTL) viaelectron transfer from the highest occupied molecular orbital of the HTL into the conduction band of MoO₃. In addition, the incorporation of a Mg:Alq₃ layer is indispensable to the functionality of the intermediate connector, which not only facilitates the electron injection from MoO₃ into the electron-transporting layer of the adjacent electroluminescent (EL) unit, but also blocks the leakage of holes across the intermediate connector into the HTL of the other adjacent EL unit.