Surface modification of TiO2 by a self-assembly monolayer in inverted-type polymer light-emitting devices

A self-assembled monolayer, N-[3-(trimethoxysily)propyl]ethylenediamine (PEDA-TMS), is employed to modify a titanium dioxide (TiO2) surface for tuning its conduction band to match the energy level of high-yellow phenyl-substituted poly(para-phenylenevinylene) copolymer (HY-PPV) for fabricating inverted-type polymer light-emitting diodes (I-PLEDs). Ultraviolet photoemission spectroscopy (UPS) and electron-dominated devices were used to investigate changes of the electron-injection barrier. A PEDA-TMS-modified device achieved much higher brightness (3148 cd/m2) than that of the bare TiO2 device (no luminescence). The air stability of the proposed device is highly improved by the use of stable electrodes and injection layers. These significant improvements make TiO2 application to PPV-based PLEDs.