In this article we review the progress of multi-layer polymer light-emitting diode (PLED) with emphasis on our own past works. PLED is a promising new technology for large-area, ultra-thin, light weight, and potentially flexible lighting and display. The major obstacle for real application is the difficulty in solution-deposition of multilayer polymer structure, which is required for high efficiency and stability. Electron and hole currents can be balanced only by the introduction of carrier blocking layers in addition to the emissive layer. The separation of the emission zone from the electrode by the blocking layers is also known to be necessary for long lifetime. The following methods for multi-layer deposition of semiconducting polymers are discussed: 1. Weak solvent to reduce the dissolution problem of existing layer; 2. Cross-linking of polymer to make it insoluble; 3. Rinsing of the polymer by pure solvent after a hardening baking; 4. Buffer liquid with high viscosity to cover the first layer as the second layer is deposited; 5. Blade coating with high speed. Methods 1-4 all have their drawbacks whereas blade coating appears to be a universal way to deposit multi-layer of polymers in large area with efficient material usage. In the final part we discuss the remaining challenges and propose a tentative road map for the commercialization of PLED.
|Title of host publication||Handbook of Light Emitting and Schottky Diode Research|
|Publisher||Nova Science Publishers, Inc.|
|Number of pages||26|
|State||Published - 1 Dec 2009|