Get access
Advertisement

Roll-to-Roll Cohesive, Coated, Flexible, High-Efficiency Polymer Light-Emitting Diodes Utilizing ITO-Free Polymer Anodes

Authors

  • Seongbeom Shin,

    1. Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701, South Korea
    Search for more papers by this author
  • Minyang Yang,

    1. Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701, South Korea
    Search for more papers by this author
  • L. Jay Guo,

    1. Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, Michigan, 48109, USA
    Search for more papers by this author
  • Hongseok Youn

    Corresponding author
    1. Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, Michigan, 48109, USA
    • Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, Michigan, 48109, USA.

    Search for more papers by this author

Abstract

This paper reports solution-processed, high-efficiency polymer light-emitting diodes fabricated by a new type of roll-to-roll coating method under ambient air conditions. A noble roll-to-roll cohesive coating system utilizes only natural gravity and the surface tension of the solution to flow out from the capillary to the surface of the substrate. Because this mechanism uses a minimally cohesive solution, the roll-to-roll cohesive coating can effectively realize an ultra-thin film thickness for the electron injection layer. In addition, the roll-to-roll cohesive coating enables the fabrication of a thicker polymer anode film more than 250 nm at one time by modification of the surface energy and without wasting the solution. It is observed that the standard sheet resistance deviation of the polymer anode is only 2.32 Ω/□ over 50 000 bending cycles. The standard sheet resistance deviation of the polymer anode in the different bending angles (0 to 180°) is 0.313 Ω/□, but the case of the ITO-PET is 104.93 Ω/□. The average surface roughness of the polymer anode measured by atomic force microscopy is only 1.06 nm. Because the surface of the polymer anode has a better quality, the leakage current of the polymer light-emitting diodes (PLEDs) using the polymer anode is much lower than that using the ITO-PET substrate. The luminous power efficiency of the two devices is 4.13 lm/W for the polymer anode and 3.21 lm/W for the ITO-PET. Consequently, the PLEDs made by using the polymer anode exhibited 28% enhanced performance because the polymer anode represents not only a higher transparency than the ITO-PET in the wavelength of 560 nm but also greatly reduced roughness. The optimized the maximum current efficiency and power efficiency of the device show around 6.1 cd/A and 5.1 lm/W, respectively, which is comparable to the case of using the ITO-glass.

Get access to the full text of this article

Ancillary