Environmental Engineering Reference
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Fig. 15 The light-emitting images of the blade-coated devices, non-uniformly coated by the only
blade coating (left) and uniformly coated layer utilizing the slit nozzle
blade-slit coated onto the emissive layer, with a slit gap of 210 lm. Finally, the ionic
solution was blade-slit coated onto the ZnO NP layer, with the slit gap of 350 lm.
The ZnO NPs dispersed solution, dissolved in 1-butanol at a concentration of
30 mg/mL, was synthesized according to the method described by Beek et al. [ 24 ]
The ZnO NPs appeared rather monodispersed with an average size of approximately
5 nm. The ZnO NPs layer was thin and porous, which allows the ionic solution
containing TBABF 4 and PEO to permeate into the porous ZnO NP layer. The alu-
minium cathode (100 nm) was thermally evaporated under 2 9 10 -6 torr in this
demonstration, but could be replaced by the blade-coated Ag paste. The film uni-
formity of the emissive layer is easily verified by UV-light exposure as shown in
Fig. 16 . However, the other layer should be measured by surface profiler or SEM
image. The amount of the solution for each layer to be coated is only 25 lL in area of
50 mm 9 50 mm. The whole volume of the slit space is 550 lL. In addition, it is
inexpensive and easy to change and clean the nozzle for the different solutions. The
blade-slit coating employs transparent slide glass for the slit capillary, which is quite
useful to observe the fluids flow in the slit nozzle.
2.3.4 Uniformity of the Functional Layers in PLEDs Coated
by Blade-Slit Coating
As stated, the blade-slit coating improved the coating uniformity in the moving
direction. The measured standard deviations of the blade-only coated PEDOT:PSS
(hole injection layer) and Super Yellow (yellow light-emitting polymer, structure
shown in Fig. 17 ) layers were about 5.7 and 5.7 nm, respectively, representing a
nonuniformity of 7.9 and 9.1 %, respectively, of film thickness. These were cal-
culated from thickness data measured at ten given positions (2 columns and 5
rows, each spaced 25 and 12 mm, respectively) in the area of the coated layer
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