Environmental Engineering Reference
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Fig. 21 The schematic diagrams of the two device structures, a bottom illuminated conventional
structure and b bottom illuminated inverted structure
operation, about 2-6 V. In addition, the leakage current of the polymer anode
PLEDs was lower than that of ITO anode PLEDs. That is because the polymer
anode of PLEDs had improved surface roughness. The luminous power efficiency
was 4.13 lm/W for PLED with polymer anode and 3.21 lm/W for that on ITO as
shown in Fig.
20
b. Consequently, the PLED made with polymer anode marked
28 % enhanced performance. This is because the polymer anode represents a
higher transparency than the ITO around the wavelength of 560 nm, which is the
emission peak in the EL-spectra of the SY. Furthermore, greatly suppressed
roughness was important to enhance the device efficiency because it reduces
leakage current between the anode and cathode.
2.5 Large-Scale Polymer Solar Cells
Two typical device structures of the polymer solar cells are shown in Fig.
21
. The
left one shows bottom illumination through transparent anode and is referred as
normal type device. Such a device structure is not suitable for roll-to-roll pro-
cessing as both LiF and Al layer will need vacuum deposition due to their high
sensitivity to air and moisture, and LiF layer is extremely thin, of order 1 nm. The
right one is refereed as inverted structure, and is suitable for low-cost fabrication.
The whole functional layers can be fabricated by printing technologies such as
roll-to-roll coating and screen printing.
2.5.1 Uniformity of the Functional Layers in OPVs by Blade Coating
The coating of PEDOT:PSS and ZnO NP layers as a hole extraction layer and
electron transport layer in OPVs is the same as the PLEDs described in the pre-
vious section. The film uniformity by the blade-slit coating show better quality for
the commonly used P3HT:PC
61
BM (20 mg P3HT and 16 mg PC
61
BM in 1.2 g
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