Gas-Phase Organosilane Self-Assembled Monolayers on Indium Tin Oxide Electrodes: Effects of Terminal Groups and...

Gas-phase thermal deposition was used to form three organosilane self-assembled monolayers on indium tin oxide (ITO) anodes: amine-terminated (NH₂SAM), methyl-terminated (CH₃SAM), and trifluoropropyl-terminated (F₃SAM). Surface characterisation using water contact angle goniometry, ultraviolet photoelectron spectroscopy, and atomic force microscopy was combined with green organic light emitting diode (OLED) fabrication and J-V-L measurements to determine how terminal group chemistry and deposition time affect device performance. F₃SAM increased the ITO work function from 3.72 to 4.47-4.72 eV, resulting in ultrasmooth surfaces (R_a = 0.20 nm) and a maximum luminescence of ~6000 cd m^-2, eleven times higher than bare ITO (540 cd m^-2). CH₃SAM enhanced luminescence through surface passivation at 10 min (3374 cd m^-2), but decreased quickly with extended deposition durations due to multilayer roughening. NH₂SAM reduced the work function to 3.42 eV and gradually decreased hole injection, resulting in a turn-on voltage of 10-11 V after 180 min. These results indicate that terminal group polarity and deposition duration are the two most important parameters in gas-phase SAM engineering of ITO anodes for OLEDs.