As a hole injection layer for organic devices, a tungsten oxide (WO x ) thin film was vapor-deposited on an indium tin oxide (ITO) substrate, on which a self-assembled monolayer (SAM) of either 3-aminopropyltrimethoxysilane (APS), phenyltrimethoxysilane (PTMS), or octadecyltrimethoxysilane (ODS) was prepared to modify the surface characteristics. The deposition of WOx substantially increased the ionization potential (Ip) of the substrate surface, which was effective in enhancing hole injection. The formation of SAM on WOx reduced Ip, but enabled the control of the surface free energy so as to modify the growth morphology of an organic film deposited on its surface. A hole-only device was prepared using a hole transport material of N,N0-diphenyl-N,N0-bis(3- methylphenyl)-(1,10-biphenyl)-4,40-diamine (TPD). In the space-charge-limited region, a high current was drawn by using an anode that has a high Ip. At low driving voltages, however, the current flow was considerably influenced by the surface free energy. It was found that the PTMS-SAM on WOx gives a satisfactory accommodation of both the work function and the surface energy.
ASJC Scopus subject areas
- Physics and Astronomy(all)