On the origin of efficient electron injection at phosphonate-functionalized polyfluorene/aluminum interface in efficient polymer light-emitting diodes

Ultraviolet and x-ray photoelectron spectroscopy are used to explore the underlying mechanism of efficient electron injection at phosphonate-functionalized polyfluorene (PF-EP)/Al interface in polymer light-emitting diodes (PLEDs). It is proposed that both the favorable interfacial dipoles of phosphonate groups and intense coordination interaction between the phosphonate groups and Al at PF-EP/Al interface are responsible for the efficient electron injection. As a result, the PLEDs with PF-EP/Al cathode demonstrate superior performance compared to the PLEDs with Ba or Ca cathode due to efficient electron injection and suppressed exciton-quenching at cathode interface. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3475021]