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.