Modification of PTCDA/Co Interfacial Electronic Structures Using Alq3 Buffer Layer

The interfacial electronic structures and energy level alignment between 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and Co substrate with a tris-(8-hydroxy-quinoline) aluminum (Alq(3)) buffer layer have been investigated using synchrotron-based photoemission spectroscopy (PES). It was found that the electronic structures at the PTCDA/Co interface can be modified by inserting an Alq(3) buffer layer. As long as equilibrium is established at PTCDA/Alq(3)/Co interfaces, the electron injection barrier (Delta(c)) at the PTCDA/Co interface decreases by 0.3 eV with an Alq(3) buffer layer, which is independent of the thickness of the Alq(3) interlayer. This energy level alignment can be satisfactorily explained by substrate to organic overlayer charge transfer through the buffer layer. Our findings have potential applications in spin-valve devices based on n-type organic materials by reducing the interfacial electron injection barrier.