Stretchable OLEDs - Page 3

In Q2 2011 Samsung submitted a patent application that describes devices with flexible displays. This patent is now public, and it shows several concepts: A "pen" type device that has a stretchable screen, a bracelet type device and a book like device that can open up.

According to the patent, all sorts of displays may be used to power such a display: including e-paper, LCd and of course OLEDs. Flexible OLEDs are coming in 2012 from Samsung, but don't expect such bendable displays yet. The 2012 crop will be plastic-based displays that will be shatterproof, light and thin - but not bendable...

Researchers from UCLA demonstrated an intrinsically stretchable transparent PLED device. The device was fabricated using a simple process that uses single-walled carbon nanotube polymer composite electrodes. The interpenetrating networks of nanotubes and the polymer matrix in the surface layer of the composites lead to low sheet resistance, high transparency, high compliance and low surface roughness.

The new P-OLED prototype can be linearly stretched up to 45% (see photo below) and the composite electrodes can be reversibly stretched by up to 50% with little change in sheet resistance. They say that this is the first stretchable OLED. Back in 2009, researchers from Tokyo demonstrated a stretchable "rubber like" OLED panel which made from many small individual panels (it's not clear whether each small panel was stretchable by itself).

Researchers from UCLA developed a new transparent electrode based on silver nanowires (AgNW) that is a replacement for ITO. The new electrode is made from low-cost and non-toxic materials and is easy to fabricate. It also offers high transparency, low sheet resistance and low surface roughness.

The new electrode is produced on a cross-linked, transparent polyacylate substrate, which is cheaper than glass and can be stiff and rigid or flexible and stretchable. The researchers say that the new electrode could be used to create a shape-memory polymer substrate that can be deformed to various stable shapes - and the deformation is reversible, causes minimal damage to the devices so it can be repeated many times.

Researchers led by John Rogers from the University of Illinois have developed a stretchable/bendable sheets of LEDs and light sensors. They are interested in applications that interface with the human body, and so they prefer inorganic LEDs to OLEDs as they are brighter, more reliable and are more easily made waterproof.

The team has printed an interlaced array of LEDs, on a rigid wafer, then dissolved the top layer of the substrate to release a thin network of LEDs that can be transferred to a flexible, waterproof polymer sheet. Each LED is just 100 microns across (about the width of a human hair) and 2.5 microns thick and is connected to its neighbors by serpentine strands that can accommodate the deformation of stretching and twisting. They managed to put the arrays on aluminum foils, leaves ,sheets of paper and around nylon threads.

University of Tokyo researchers developed a new kind of OLED display, that can actually stretch and deform - like rubber.They showed one displays that is shaped like a face, and showing changing expressions, and another screen that is spherical and shows weather data. The OLEDs were produced by spraying a layer of carbon nanotubes with a fluoro-rubber compound to produce a stretchy, conductive material.

The current prototypes are 100 sq centimeters, and have 256 monochrome pixels. They can be folded at least a thousand times, with no decline in quality. They are working towards better resolution and color displays.

"In the future, displays that once had to be flat can be made spherical, or even moving," says Takao Someya, professor of electronic engineering at the University of Tokyo. "A human-shaped display could be used to show medical diagnosis data, and there are various other applications."