Low-Cost Fabrication of Organic Photovoltaics and Polymer LEDs - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 233

Fig. 9 The irregular streak patterns of the emissive layer in PLEDs with respect to the different
concentrations and coating speeds
electron transport layer, and electron extraction layer) in terms of the coating
performances such as coating thickness, uniformity, and electrical properties.
2.1 Roll-to-Roll and Blade-Coating System
as the Noncontact-Coating Methods
Among the various printing processes to make large area polymer PVs and PLEDs,
the roll-to-roll coating system is one of the most favorable candidates. By adding a
facile doctor blade to the roll-to-roll system, a simple, noncontact coating platform
can be constructed, where the blade does not contact the substrate directly but via a
liquid layer. As compared with the slot-die system, it is a valuable tool for fab-
rication of large-sized thin films.
Since the conventional blade-coating system has advantages such as easy
operation, simple structure, and low cost, it has been widely used in not only
laboratory but also industrial scale. Previously, there have been efforts to make
organic electronics using simple blade coating due to these advantages. However,
there is a serious problem in the conventional blade-coating process: because the
ink supplying is not homogeneous, the layer thickness varies: the initial layer
thickness was frequently thicker than the final layer thickness. In addition, the ink
supply in the slot-die coater relies on the use of external pumping, which cannot be