It is a great challenge to develop solution-processed, polymeric hole-injection layers (HILs) that perform better than small molecular layers for realizing high-performance small-molecule organic light-emitting diodes (SM-OLEDs). We have greatly improved the injection efficiency and the current efficiency of SM-OLEDs by introducing conducting polymer compositions composed of polyaniline doped with polystyrene sulfonate and perfluorinated ionomer (PFI) as the HIL. During single spin-coating of conducting polymer compositions, the PFI layer was self-organized at the surface and greatly increased the film work function. It enhanced hole-injection efficiency and current efficiency by introducing a nearly ohmic contact and improving electron blocking. Our results demonstrate that solution-processed polyaniline HILs with tunable work functions are good candidates for reducing process costs and improving OLED performance.

Electrochemical and quartz crystal microbalance (EQCM) methods are used to probe the redox behavior of self-assembled monolayers of viologen derivatives with long alkyl chains and disulfide or thiol groups that provide for attachment to gold electrodes. The EQCM measurements revealed that cations exit and enter the viologen monolayer during reduction and oxidation, respectively. In this study, the self-assembly process of viologen was monitored using resonant frequency (ΔF) and resonant resistance (ΔR). The QCM measurements indicated a mass adsorption for viologen assembling on the gold surface with a frequency change of approximately 135 Hz and calculated its surface coverage (Γ) to be 3.5273×10-9 mol/cm2. Also, a reversible redox process was observed and analyzed with an ionic interaction at the viologen/solution interface using ΔF.

The electro-nanopatterning and mechanism of pattern formation in azobenzene-containing layer-by-layer (LbL) ultrathin films is described using surface probe microscopy techniques. First, arrays of nanodots were patterned on these films to investigate applied time at constant voltage bias dependence in electro-nanopatterning. The anisotropic mass transport and polar alignment of the azobenzene-containing films were observed after applying the electric field and heating the sample locally with the cantilever tip. On the basis of this novel phenomenon, small-sized surface relief gratings (SRG)s and their alignment were fabricated and observed by current-sensing atomic force microscopy. The rate of mass transport for the polymer is mainly controlled by the applied time at constant voltage bias between the cantilever and the electrode/substrate.

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