All-solution blade-slit coated polymer light-emitting diodes

This paper reports that large-scale, all-solution processed, polymer, light-emitting diodes can be fabricated by a new blade-slit coating method under ambient conditions. It is practical to use an ionic solution and a ZnO nanoparticle solution as electron injection and electron transport materials, respectively, through a blade-slit coating system, and reduce the deviation of the layer thickness to less than one-third compared to the result of a conventional blade-only coating system. The standard deviations of the layer thickness coated by the blade-slit process were only 0.68 nm in the hole injection layer (PEDOT:PSS), and 2.3 nm in the polymer light-emitting layer (Super Yellow). In the case of blade-only coating, the standard deviations were 5.7 nm and 5.7 nm, respectively. The film non-uniformities of PEDOT:PSS and the Super Yellow layers fabricated by the blade-slit method were only 2.1% and 2.2%. In the case of blade-only coating, those were 7.9% and 9.1%, respectively. The application area was 80 mm x 70 mm. Moreover, because the devices do not contain any alkali or alkaline earth metals in the electron injection layer, they can be fabricated by an all-solution process in a normal air conditioned environment. The maximum luminous efficiency of all-solution blade-slit coated devices was as high as 5.26 cd/A without alkali metals, and the maximum luminance reached was 14120 cd/m(2) at 7.8 V. These results are comparable to the performance of spin-coated devices. (C) 2012 Elsevier B.V. All rights reserved.