Low-Cost Fabrication of Organic Photovoltaics and Polymer LEDs - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 243

Fig. 18 The image of
uniform luminance of the
large-area device (the
substrate size was
50 mm 9 100 mm)
fabricated by the blade-slit
coating. Reproduced from
[ 16 ] with permission from
Elsevier 2012

and the maximum luminance voltage of the two devices were almost the same, as
shown in Fig. 19 a, indicating the blade-slit coating method can realize the same
coating quality as that of spin coating but easily covers larger areas. In addition,
Fig. 19 b compares the performance (in terms of luminescence intensity) between
the spin-coated devices and blade-slit coated devices. Though the blade-slit coated
device was made in the air environment, the luminous efficiency of the blade-slit
coated PLED reached 5.26 cd/A. The luminous efficiency of the spin-coated
device fabricated in the Nitrogen-filled glove-box was 6.30 cd/A. These compa-
rable results support the advantage of the blade-slit coating method, which is easier
and less wasteful for materials for large-sized devices (100 mm 9 50 mm) as
shown in Fig. 18 . Furthermore, the luminous efficiency of the PLEDs using the
ZnO and ionic surfactant (6.30 cd/A) are over two-fold higher than that using Ca
transporting layer (3.01 cd/A) as shown in Fig. 19 b. The turn-on voltages of the
two devices are almost the same as 2.2 V as shown in Fig. 19 a. Since the peak
emission wavelength of the S-Y is 560 nm as shown in the EL-spectra in Fig. 19 c,
the optical band gap of the S-Y is calculated at 2.2 eV, the same as turn-on
voltage. This means that the devices have good electrical contact with Al cathode.
In addition, it reveals that the ammonium ions can be effectively incorporated into
the electron injection layer which lowers the electron injection barrier.

2.4.1 Roll-to-Roll Processed PLEDs

In this section, we show that the polymer anode (see Sect. 2.3 ) is superior to the
ITO-PET in making flexible PLEDs and resulting in higher PLEDs performance.
To evaluate the performance between the two devices, the two type devices were
fabricated using the same process, and with similar film thicknesses. As a result,
the turn-on-voltages and voltages at the maximum luminance of the two types of
devices were very similar (Fig. 20 a). It implies that the thickness of each layer in
the two devices is about the same. The maximum luminance of ITO anode PLEDs
was greater than that of polymer anode PLEDs. However, the maximum