Low-Cost Fabrication of Organic Photovoltaics and Polymer LEDs - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 235

Fig. 11 The schematic diagram of blade-slot coating showing the ink supply and coating flows;

and a 8 00

based roll-to-roll coating system

fairly accurately to optimize the device performance. When designing the various
device structures by the solution coating processes, special consideration should be
given to whether each layer thickness can be realized by the practical coating
method such as the blade/roll-to-roll coating equipment.

2.2 Conventional Device Structure in the PLEDs

We now discuss the roll-to-roll fabrication of PLEDs. A typical PLEDs is indium
tin oxide (ITO)/Hole transporting layer/Emissive layer/electron transporting layer/
metal cathode, poly(3,4-ethylenedioxythiophene)poly-(styrenesulfonate) (PEDOT:
PSS) conductive polymer is a commonly used hole transporting layer. Phenyl
substituted poly(para-phenylene vinylene)—known as ''Super Yellow,'' (will
simply be referred as S-Y, Merck, PDY-132) will be used as yellow light-emitting
layer. Zinc oxide (ZnO) nanoparticle (NP) is used as electron transporting layer,
and Al as cathode, poly(ethylene oxide) (PEO), and tetra-n-butylammonium tet-
rafluoborate (TBABF 4 ) in acetonitrile (ionic solution) is used to induce a dipole
layer to adjust the work function of the cathode, as shown in Fig. 12 [ 10 ].

2.3 Flexible and Transparent Electrode for Large-Scale
PLEDs

2.3.1 Optical and Electrical Property of the Roll-to-Roll Coated
Polymer Electrode

Since indium tin oxide (ITO) has good optical and electrical properties, it has been
commonly used as a transparent electrode in displays and solar cells. However, the
cost of the ITO is expensive and mechanical bending strength is poor due to its