Enhancement of electron injection into a light-emitting polymer from an aluminum oxide cathode modified by a self-assembled monolayer

A self-assembled monolayer (SAM) of octylphosphonate was deposited on an AlOx electrode using the tethering by aggregation and growth (T-BAG) procedure. Ultraviolet photoemission spectroscopy (UPS) measurements showed a decrease in the substrate work function from 3.8 to 3.3 eV. Poly [9,9' -dioctylfluorene-co-bis-N,N' -(4-butylphenyl)-diphenylamine] (TFB) films spin coated on the bare and the SAM-modified oxide surfaces were investigated by UPS. A shift in molecular levels, corresponding to a reduction in the electron injection barrier, was observed for the SAM-modified electrode. This barrier lowering was confirmed by current-voltage measurements showing a corresponding increase in electron current through the TFB/SAM/AlOx device. (c) 2008 American Institute of Physics.