A flexible organic light-emitting diode (FOLED) is a type of

organic light-emitting diode An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...

(OLED) incorporating a flexible plastic substrate on which the

electroluminescent Electroluminescence (EL) is an optical and electrical phenomenon, in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emission resulting from h ...

organic semiconductor Organic semiconductors are solids whose building blocks are pi-bonded molecules or polymers made up by carbon and hydrogen atoms and – at times – heteroatoms such as nitrogen, sulfur and oxygen. They exist in the form of molecular crystals or ...

is deposited. This enables the device to be bent or rolled while still operating. Currently the focus of research in industrial and academic groups, flexible OLEDs form one method of fabricating a

rollable display A flexible display or rollable display is an electronic visual display which is flexible in nature, as opposed to the traditional flat screen displays used in most electronic devices. In recent years there has been a growing interest from nume ...

Technical details and applications

An OLED emits light due to the

electroluminescence Electroluminescence (EL) is an optical phenomenon, optical and electrical phenomenon, in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emissi ...

of thin films of

s approximately 100 nm thick. Regular OLEDs are usually fabricated on a glass substrate, but by replacing glass with a flexible plastic such as

polyethylene terephthalate Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods ...

(PET) among others, OLEDs can be made both bendable and lightweight. Such materials may not be suitable for comparable devices based on

inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

s due to the need for lattice matching and the high temperature fabrication procedure involved. In contrast, flexible OLED devices can be fabricated by deposition of the organic layer onto the substrate using a method derived from

inkjet Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper and plastic substrates. Inkjet printers were the most commonly used type of printer in 2008, and range from small inexpensi ...

printing, allowing the inexpensive and roll-to-roll fabrication of

printed electronics Printed electronics is a set of printing methods used to create electrical devices on various substrates. Printing typically uses common printing equipment suitable for defining patterns on material, such as screen printing, flexography, gravur ...

. Flexible OLEDs may be used in the production of

electronic paper Electronic paper, also sometimes electronic ink, e-ink or electrophoretic display, are display devices that mimic the appearance of ordinary ink on paper. Unlike conventional flat panel displays that emit light, an electronic paper display ref ...

, or bendable displays which can be integrated into clothing, wallpaper or other curved surfaces. Prototype displays have been exhibited by companies such as

Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...

, which are capable of being rolled around the width of a pencil.

Disadvantages

Both flexible substrate itself as well as the process of bending the device introduce

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

into the materials. There may be residual stress from the deposition of layers onto a flexible substrate, thermal stresses due to the different coefficient of

thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic ...

of materials in the device, in addition to the external stress from the bending of the device. Stress introduced into the organic layers may lower the efficiency or brightness of the device as it is deformed, or cause complete breakdown of the device altogether.

Indium tin oxide Indium tin oxide (ITO) is a ternary composition of indium, tin and oxygen in varying proportions. Depending on the oxygen content, it can be described as either a ceramic or an alloy. Indium tin oxide is typically encountered as an oxygen-saturated ...

(ITO), the material most commonly used as the transparent

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

, is brittle. Fracture of the anode can occur which can increase the

sheet resistance Sheet resistance, is a measure of resistance of thin films that are uniform in thickness. It is commonly used to characterize materials made by semiconductor doping, metal deposition, resistive paste printing, and glass coating. Examples of thes ...

of the ITO or disrupt the layered structure of the OLED. Although ITO is the most common and best understood anode material used in OLEDs, research has been undertaken into alternative materials that are better suited for flexible applications including

carbon nanotube A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...

s. Encapsulation is another challenge for flexible OLED devices. The materials in an OLED are sensitive to air and moisture which lead to

degradation Degradation may refer to: Science * Degradation (geology), lowering of a fluvial surface by erosion * Degradation (telecommunications), of an electronic signal * Biodegradation of organic substances by living organisms * Environmental degradatio ...

of the materials themselves as well as

quenching In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as pha ...

of excited states within the molecule. The common method of encapsulation for regular OLEDs is to seal the organic layer between glass. Flexible encapsulation methods are generally not as effective a barrier to air and moisture as glass, and current research aims to improve the encapsulation of flexible organic light emitting diodes.

References

External links

Are Foldable Laptops the Future?
{{Display technology Conductive polymers Display technology Electronic engineering Flexible electronics Molecular electronics Optical diodes Organic electronics

Technical details and applications

Disadvantages

See also

References

External links