Low-Cost Fabrication of Organic Photovoltaics and Polymer LEDs - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 234

Fig. 10 The control of the irregular streak patterns by adding surfactant (Dynol 604, Air product
inc.) and isopropyl alcohol (IPA)
thin enough, e.g., for the electron injection layer using the low-viscous solutions.
To address the nonuniform film thickness problem, a pre-metering mechanism, or
nozzle system should be added like that used in a slot coating. In order to achieve
better film uniformity for much thinner organic layers such as the electron
injection layer in PLED and to solve the fundamental ink supplying problem, we
attach a simple slide glass to the blade surface to meter the solution. The whole
system was developed with 8 00 -based rollers and it is driven by an AC servo-motor.
As shown in Fig. 11 the solution contained in the slit between the glass plate and
the blade flows and created a meniscus in front of the glass, followed by a
homogeneous laminar flow at the back of the blade. This fine laminar flow is the
key to uniformity and better film quality. The control variables of the film
thickness are the blade gap, the slit gap, the blade speed, the ink concentration, and
the surface energy of the substrate, and the slit.
The blade-slit coating method utilizes only the gravity of the solution for the ink
supply, the flow rate can be minimized effectively. The estimated minimal thickness
of the blade-slit coating is around a few nanometers. The minimal wet film thickness
in the slot-die system is around 1 lm, and the estimated dry film thicknesses are few
tens of nanometers. Because the device performance sensitively depends on the film
thickness in the organic electronics, the thickness of each layer should be controlled