聚合物基片对柔性有机发光器件性能的影响

Influences of Polymer Substrates on Flexible Light-emitting Diodes

以聚合物基片柔性ITO膜为透明电极,制备了ITO/TPD/Alq3/Al结构柔性有机发光器件,并与在相同条件下制备的玻璃基片相同结构器件作了比较。研究了不同基片对有机材料及器件性能的影响,指出选择不易吸湿、耐温高、热胀系数小的聚合物材料,提高柔性ITO膜的附着力和导电性,结合柔性ITO膜的具体特性,优化有机层的蒸镀条件,是提高柔性有机发光器件发光亮度和稳定性的重要途径。

Organic lightemitting diodes (OLEDs) with excellent performances have been reported. However, such devices are typically deposited on glass substrates because of structural or processing constraints. The use of thin flexible substrates in OLEDs allows lightweight, mechanically flexible, unbreakable emissive flatpanel displays, but the flexibility of the substrate adds much difficulty to the fabrication technology. Since the first report of flexible OLEDs, performance improvements of them are slower, and fewer researchers are involved in compared with that of glassbased devices. Advanced developments, especially the complicated effects of substrate material on the devices are required before this technology is available in commercial products. Here vacuumdeposited OLEDs based on indium tin oxide (ITO)coated polymer substrate are demonstrated. Electroluminescent smallmolecule material 8hydroxyquinoline aluminum (Alq3) was used and complemented by the holetransport material tetraphenyldiamine (TPD). ITO films were etched with HCl+Zn solution to stripes ～10mm and supersonic cleaned. TPD, Alq3 and Al films were deposited by heat evaporation in a base vacuum of 2×10-3Pa. By masking each slide before Al deposition, several active areas of ～20mm2 were achieved.The lightemitting and mechanical characteristics of the devices were investigated, the influence of substrate material on ITO properties and Alq3 morphology and thus the device performance were studied, and the failure mechanisms of the devices were analyzed.As a result, the brightness of the flexible OLEDs reached 200cd/m2, which meets the need of practical display. These devices can be bent over a radius of curvature larger than 1cm without any observable changes in their characteristics. The substrate materials, the deposition methods and conditions influence ITO structure, photoelectric properties, and morphology of subsequently deposited organic films. The ITO films could deposit on polymer substrates without latticematching requirements, but the mismatched thermal expanding coefficients of polymer and ITO play a reverse role on the increase of brightness and stability. Also, the Alq3 morphology is sensitive to the evaporating condition, which is difficult to control. It is shown that ITO films, when precoated on polymer substrates with good resistance to gas, moisture and thermal expansion, provide flexible contacts suitable for OLED applications, and that optimal evaporating conditions of organic films for different substrates are necessary in order to optimize the flexible OLEDs' characteristics.