Modern OLED display market: what's new

OLED displays in mobile devices are becoming more and more popular. Once used mainly by flagship Samsung models, this technology is now used both in cheaper Galaxy and in smartphones from other manufacturers - for example, Meizu, Xiaomi, Huawei, Lenovo and OnePlus. Numerous rumors indicate that the next top-end iPhone will also receive an OLED panel - for the first time in the history of the brand. Both IPS LCD and AMOLED displays are now used in both low-end and flagship models. What is the reason for the popularity of OLED, which is growing more and more?

For those who don’t yet know the differences OLED And LCD displays, we prepared this article. Both technologies have their advantages and disadvantages, and when choosing smartphone It is worth considering which panel is installed under its protective glass.

The screen is probably main component any modern smartphone. We commit voice calls less and less, but more and more we use our pocket devices to surf the net, take photos and videos, and communicate in instant messengers. That is, we look at the mobile phone screen almost all the time when it is in our hands.

LCD (Liquid Crystal Display, liquid crystal display)

LCD screens were invented many years ago. LCD panels use liquid crystal light, which is also backlit using a separate system of small lamps. LCD screens are installed in computer monitors, TVs, cameras and many other devices.

Smartphones use two types of LCD panels - TFT LCD and IPS LCD. The first are becoming less and less common - they are inferior to LCD in all respects except cost.

IPS LCDs consume little power and perform well under the sun. The first and, perhaps, main difference from OLED, which immediately catches the eye when compared, is noticeably more low level contrast. As a result, the blacks on an LCD screen will be lighter and paler than those on an OLED screen.

LCD wins in terms of more accurate color display, but quite often manufacturers do not calibrate the screens of their devices well. As a result, the display may instead white display a very pale red or very pale blue tint.

It is worth noting that in the future, smartphones with QLED-type LCD screens may appear on the market. These screens are a little thicker due to the additional layer that distinguishes them from LCDs, but they look much more attractive. To use them in small mobile devices, however, engineers will have to solve many more problems.

OLED (Organic Light-Emitting Diode, organic light-emitting diode)

OLED displays use a special type of LED that emits much more light and does not require a separate backlight system. Thanks to this, the dark areas of the screen become much more pronounced and deep, and the light areas appear richer and brighter in comparison.

In addition, the absence of the need for backlights makes OLED displays thinner than LCDs - they do not have an entire layer that is responsible for lighting the pixels.

OLED screens are also divided into two categories - PMOLED and AMOLED. Basically we only hear about the latter, since PMOLED in smartphones, TVs and other expensive mass devices are not used.

Panels produced using PMOLED technology are very cheap because they use passive matrices, but are not suitable for displaying complex images. Now PMOLED screens can be found, for example, in inexpensive fitness trackers. Such panels cannot be larger than three inches diagonally.

AMOLED (Active Matrix OLED)

AMOLED panels are similar to PMOLED, but differ in the use of an active matrix, which makes them excellent at displaying complex images and changing them quickly. There are no size restrictions for AMOLED screens - they are used like in smart watches (for example, in Apple Watch), and in huge TVs with a diagonal of several tens of inches.

The two main disadvantages of AMOLED are increased battery consumption in many cases and not very high brightness in sunlight.

AMOLED panels consume more energy precisely because each microscopic diode illuminates itself. As we have already found out, this leads to many advantages, but it also leads to the fact that bright picture(eg a photograph of a sunlit garden) requires more current than an LCD. Many apps even have special OLED modes that display as much black as possible on the screen to save battery.

In addition, over time, AMOLED displays degrade faster than LCD, and the rate of deterioration will vary between different areas of such a display. Just a few years ago, pixel burnout was a huge problem - after long use, pale but clearly visible elements of the operating system interface remained forever on the device screen. In the most modern smartphones Samsung and other companies use several tricks to solve this problem. For example, in the Galaxy S8, the position of the on-screen Android navigation buttons constantly shifts by several pixels - the user will not notice this, and there will be no traces of them on the screen even after several years.

Conclusion

In most comparisons, AMOLED displays win, and it is useless to argue with this fact. The colors are more saturated, the contrast is much deeper, and the response speed is faster. But LCD also has its trump cards - better readability under direct sunlight (however, the difference with modern AMOLEDs is almost leveled here), as well as more accurate display of shades.

At the same time, it is worth understanding that the final image quality depends not only on the screen production technology, but also on calibration, and simply on the quality of the matrix. As a result the best way out from the situation (if you want to buy a smartphone with the best display on the market or in a specific price category) will be reading specialized reviews that focus specifically on color quality, brightness and contrast. The choice between AMOLED and IPS LCD should be made at the very beginning.

Most likely, in the future, more and more expensive mobile phones will use AMOLED, and IPS LCD will become a budget solution and replace TFT LCD. Perhaps the transition of the iPhone to a new type of screen panels will push the industry even further. It is because of this that several companies (for example, LG) recently began investing many millions of dollars in factories for the production of OLED screens.

When creating new TV models, manufacturers try to use the newest and most modern technologies. Not long ago, the world saw OLED TV models, which differ from IPS and other technologies in high performance and some other characteristics. This is due to the fact that such panels do not require light filters or additional lighting. Also this feature allows such TVs to be thinner and easier to manufacture than models with IPS technology. But let's first understand what, in general, an OLED display is and how it works.

OLED TV is a TV whose matrix mainly consists of carbon-based organic light-emitting diodes. Such screens are often installed in players, phones and other gadgets. It’s not easy for an ordinary person to imagine such a combination, but it works like this: electrical impulses pass through organic light-emitting diodes, causing them to glow. The color that each of these diodes will glow depends on the color of the phosphor with which it is coated. As is customary, this is a red, blue or green phosphor, the combination of which allows you to obtain a huge number of other colors and shades. OLED TV has the shortest response time among all TVs, a wide viewing angle and excellent light transmission. Such screens have a large number advantages, but also have their disadvantages. Let's discuss all this in order.

How does it all work from the technical side?

In order to create organic light-emitting diodes, thin-film structures with a large number of layers made of polymers are used. When current is applied to the positively charged anode, the electrolytes in the device flow from the negatively charged cathode to the anode. In this case, the cathode gives electrodes to the emissive layer, and the anode takes them from the conductive layer. Thus, the conductive layer becomes positively charged and the emissive layer negatively charged.

Under the influence of voltage, negative and positive particles begin to move towards each other and at certain moments recombine. At the same time, negative particles in such technologies move much faster, and the recombination process occurs near the emission layer. During this process, the energy of the electron is reduced and electromagnetic radiation is released in the visible light region. If the anode is negatively charged, the display will not work, since the electrons will move in a different direction and recombination will not occur.

The anode is often made of indium oxide, which is doped with tin. Such an anode has a high work function, which facilitates the injection of so-called holes into the polymer layer. In addition, it is transparent to visible light. The cathode is often made of calcium or aluminum, since these metals low performance exit.

How OLED TVs are made

Oled TV is manufactured in several stages:

• Selecting a substrate;
• Preparation of the substrate before applying organic light-emitting diodes and other materials to it;
• A control board is manufactured for such radiating sources, both the control system itself and the switching circuits.
• Drawing the structure certain elements and organic layer.
• The workpiece is sealed to prevent dust, moisture and air from entering it.

Organic layers, as well as patterns on them, can be applied using several options. Today, all OLED TVs are made using an FMM shadow mask, which stands for Fine Metal Mask. With its help, a template can be applied to organic matter. After this, those areas of the OLED material that are not covered by the template are removed in a vacuum chamber using evaporation. This is the simplest method, but it is not effective enough, especially when making such panels large size.

There are other application methods, such as inkjet printing or laser annealing. Such methods of depositing organic materials are more efficient and thanks to them, creating OLED panels is much easier.

Materials for OLED TVs and their classification

Today, there are several materials for creating OLED panels. They are mainly divided into two types:

• Consisting of large molecules (P-OLED) - such materials are applied using inkjet printing or by centrifugation. R-OLED has enormous technological capabilities and potential.
• Low molecular weight (OLED) - this material helps make OLED displays much better thanks to evaporation technology. Today, scientists are developing other methods of applying organic material.

However, there is another classification, in which the materials used are divided into:

• Phosphorescent materials are associated with the future of lighting panels. Also, with their help it will be possible to create a large OLED display, but so far such materials do not last as long as we would like.
• Fluorescent materials will last longer, but they are not as effective as phosphorescent materials.

OLED Samsung TVs combine these two materials. Thus, OLED TV uses fluorescent light sources of green and blue flowers, and for red ones they use phosphorescent ones.

OLED displays and their types

Monitors of this type are divided into several types, depending on control methods and other features. We can especially highlight the following types of screens:

• PMOLED monitors have controllers for scanning patterns into columns and rows. This means that the pixel that should light up is calculated by row and column. In order for the entire screen to light up, the location of each pixel must be calculated at high speed. OLED displays are mainly used in LG cameras and other small equipment.
• , compared to ips, has the ability to directly control each individual pixel, which speeds up playback. The diagonal of such screens can reach up to 40 inches, but their cost is much higher than that of IPS screens.
• TOLED is a technology that allows you to create transparent screens and achieve the highest level of contrast. In this case, the light can emit up, down or in both directions. The OLED display has only 70% transparency, and this allows it to be used on a store display or in a helmet virtual reality etc. It can also be combined with many opaque materials that serve as a substrate. Using this technology, it is possible to create devices with a large number of layers or hybrid, for example bidirectional, matrices.
• FOLED. One of the main features of this technology is the ability to create flexible displays by applying organic light-emitting diodes to a flexible plate made of plastic or metal. OLED technology has a particularly thin, light display weight, flexibility, strength and durability.
• SOLED allows you to create folded OLED devices. With this technology, red diodes are arranged in series. At the same time, it is possible to control each element, as well as adjust the color of each pixel by changing the voltage.

Benefits of OLED technology

This technology, used to create an OLED display or TV, has a number of advantages:

• Energy efficiency. Such TVs from LG consume a fairly small amount of energy, which is achieved due to the fact that the monitor does not require additional backlighting. This is due to the fact that each LED not only forms specific color, but also emits light.
• Stylish appearance. Due to the fact that there is no need to additionally install a backlight, the thickness of the screen is also reduced, which means that the weight of the equipment will also decrease. In addition, thanks to the ability to place LEDs on a flexible polymer substrate, curved, transparent or flexible OLED displays can be created.
• Brightness and contrast. Such TVs have a brightness that can reach 100,000 cd/m2. For TVs with other technology, for example, IPS, this level is simply unattainable. The contrast in such TVs is also better. With OLED you can reach 10 million to 1 and that's not the limit.
• Huge viewing angle, that is, you have the opportunity to watch TV from any angle without distorting the picture.
• Maximum response speed up to 0.002 ms. No other TV, including those with IPS technology. Thanks to this speed, the picture is more realistic.

OLED display and its disadvantages

Despite the positive aspects, such TVs also have their drawbacks, although there are not many of them.

• Short service life of diodes of some colors. For TV use diodes corresponding RGB colors, which are fundamental. The problem with OLED panels is that the blue diodes die before the others. On average, organic LEDs of a given color last no more than 3 years.
• High price similar screens. This is due to a large number of defects, as well as rather expensive procedures related to quality control. Because of all this, it is difficult to produce monitors with large or medium-sized displays. However, even among small-sized displays there are many defects. Until now, some companies have OLED displays with a large number of shades of green.

OLED TVs and LED. What's the difference between them?

The present and future of OLED TVs

Today, OLED displays are used mainly in various mobile devices. However, this technology is also popular in TV. LG uses it especially actively. Moreover, many of these TVs are already made using modern technologies, that is, organic LEDs are created on the basis of quantum dots, which are better and much cheaper to produce.

Not long ago, LG released Ultra HD, with a 77-inch diagonal and 3D Smart TV function. Moreover, such a TV can receive and play video and other multimedia files from any type of media. In addition, new TVs from LG have an excellent acoustic system and all the above-described advantages of OLED technology. However, it is worth saying that the price of new OLED TVs from LG is quite high, which is the main drawback.

This company also released another OLED TV with curved screen, having the same characteristics. It is distinguished by an updated operating system and new WRGB technology, which is distinguished by the presence of an additional white subpixel, which cannot be found on TVs with IPS technology. This technology promises to provide the most realistic, clear and smooth image. In addition, the LG TV has a large number of different settings and interfaces. This model is only 4.3 mm.

In the future, LG promises to produce OLED displays of even larger sizes, as well as to develop color rendering technology and try to increase the service life of organic light-emitting diodes. Also quite promising areas of development are transparent OLED displays that can be built into car glass and windows, rollable screens, as well as lighting devices based on OLED technology. By the way, it is worth noting that some of this has already begun to be gradually applied.

Operating principle

To create organic light-emitting diodes (OLEDs), thin-film multilayer structures consisting of layers of several polymers are used. When a voltage positive relative to the cathode is applied to the anode, a flow of electrons flows through the device from the cathode to the anode. Thus, the cathode gives electrons to the emissive layer, and the anode takes electrons from the conducting layer, or in other words, the anode gives holes to the conducting layer. The emissive layer receives a negative charge, and the conductive layer receives a positive charge. Under the influence of electrostatic forces, electrons and holes move towards each other and recombine when they meet. This occurs closer to the emissive layer because in organic semiconductors holes have greater mobility than electrons. During recombination, the energy of the electron decreases, which is accompanied by release (emission) electromagnetic radiation in the visible light region. That is why the layer is called emissive. The device does not work when a voltage negative relative to the cathode is applied to the anode. In this case, holes move towards the anode and electrons move in the opposite direction towards the cathode, and no recombination occurs.
The anode material is usually indium oxide doped with tin. It is transparent to visible light and has high performance exit, which promotes the injection of holes into the polymer layer. Metals such as aluminum and calcium are often used to make the cathode because they have a low work function that facilitates the injection of electrons into the polymer layer.

Classification by control method

There are two types of OLED displays - PMOLED and AMOLED. The difference lies in the way the matrix is ​​controlled - it can be either a passive matrix (PM) or an active matrix (AM).

In PMOLED-Displays use controllers for scanning the image into rows and columns. To light a pixel, you need to turn on the corresponding row and column: at the intersection of the row and column, the pixel will emit light. In one clock cycle, you can make only one pixel glow. Therefore, to make the entire display light up, you need to very quickly send signals to all the pixels by cycling through all the rows and columns. How is it done in old CRTs (cathode ray tubes).

PMOLED-based displays are cheap, but due to the need for horizontal scanning of the image, it is not possible to obtain large displays with acceptable image quality. Typically, PMOLED display sizes do not exceed 3" (7.5 cm)

In AMOLED In displays, each pixel is controlled directly, so they can quickly reproduce the image. AMOLED display sizes can vary large sizes and today displays with a size of 40" (100 cm) have already been created. The production of AMOLED displays is expensive due to complex circuit pixel control, unlike PMOLED displays, where a simple controller is enough to control.

Classification by light-emitting material

Currently, two technologies are mainly being developed that have shown the greatest efficiency. They differ in the organic materials used: micromolecules (sm-OLED) and polymers (PLED), the latter are divided into simply polymers, polymer-organic compounds (POLED), and phosphorescent (PHOLED). Let's talk a little more about the latter. PHOLEDs use the principle of electrophosphorescence to convert up to 100% electrical energy into the world For example, traditional fluorescent OLEDs convert approximately 25-30% of electrical energy into light. Because of their extreme high level energy efficiency, even compared to other OLED, PHOLED is being studied for potential use in large displays such as television monitors or screens for lighting needs. Interestingly, OLED technology can significantly improve the quality of LCD panels, since PHOLED (PHosphorescent Organic Light Emitting Diode) technology is a promising backlight technology for them. According to Universal Display Corporation, the use of PHOLED diodes increases the brightness of panels by four times.

Schemes of color OLED displays
OLED displays based on micromolecules were the first to appear, but they turned out to be too expensive because they were produced using vacuum deposition.

The first step towards creating polymer displays was made in 1989, when scientists at the University of Cambridge managed to synthesize a special polymer - polyphenylene vinylene. Displays of this type can be obtained by applying polymer materials to a base using a special inkjet printer. Sometimes such displays are called LEP (Light-Emitting Polymer). The base can be flexible with a bending radius of 1 cm or less.

However, today micromolecule-based devices are ahead of LEP devices in terms of service life and efficiency. Comparative characteristics The durability and emission efficiency for the two OLED display technologies are given below.

There are three schemes for color OLED displays:

* circuit with separate color emitters;
* WOLOD+CF circuit (white emitters + color filters);
* scheme with conversion of short-wave radiation.

The simplest and usual option– a regular three-color model, which in OLED technology is called a model with separate emitters. Three organic materials emit light of basic colors - R, G and B. This option is the most efficient in terms of energy use, however, in practice it turned out to be quite difficult to select materials that will emit light with the desired wavelength, and even with the same brightness.

The second option is much simpler to implement. It uses three identical white emitters that emit through colored filters, but it is significantly inferior in energy efficiency to the first option, since a significant part of the emitted light is lost in the filters.

The third option (CCM - Color Changing Media) uses blue emitters and specially selected luminescent materials to convert short-wavelength blue radiation into longer wavelengths - red and green. The blue emitter naturally emits “directly”. Each option has its own advantages and disadvantages:

Other types of OLED displays

TOLED- transparent light-emitting devices TOLED (Transparent and Top-emitting OLED) - a technology that allows you to create transparent (Transparent) displays, as well as achieve a higher level of contrast.
Transparent TOLED displays: The direction of light emission can be up only, down only, or both directions (transparent). TOLED can significantly improve contrast, which improves display readability in bright sunlight.
Since TOLEDs are 70% transparent when turned off, they can be mounted directly on a car windshield, on store windows or for installation in a virtual reality helmet... Also, the transparency of TOLEDs allows them to be used with metal, foil, silicon chip and other opaque display substrates forward-mapped (can be used in future dynamic credit cards). Screen transparency is achieved by using transparent organic elements and materials for the manufacture of electrodes.
By using a low reflectance absorber for the TOLED display substrate, the contrast ratio can be an order of magnitude superior to LCDs (mobile phones and military fighter aircraft cockpits). Using TOLED technology, it is also possible to produce multilayer devices (for example SOLED) and hybrid matrices (Bidirectional TOLED TOLED makes it possible to double the displayed area with the same screen size - for devices in which the desired amount of displayed information is wider than the existing one).

FOLED (Flexible OLED) - main feature- flexibility of the OLED display (Demonstration of a flexible OLED display from SONY). Uses plastic or flexible metal plate as a substrate on one side, and OLED cells and sealed thin protective film- on the other. The advantages of FOLED: ultra-thin display, ultra-low weight, strength, durability and flexibility, which allows OLED panels to be used in the most unexpected places. (Space for imagination - the area of ​​​​possible application of OLED is very large).
Staked OLED- a fundamentally new solution from UDC – Staked OLED, folded OLED devices. Main feature new technology is the placement of R-cells (G-, B-) in a vertical (series) and not in a horizontal (parallel) plane, as happens in an LCD display or a cathode ray tube. In SOLED, each subpixel element can be controlled independently. The color of a pixel can be adjusted by changing the current passing through the three color elements (non-color displays use pulse width modulation). Brightness is controlled by changing the current. Advantages of SOLED: high density filling the display with organic cells, thereby achieving good resolution, which means a high-quality picture. (SOLED displays have 3 times improved image quality compared to LCD and CRT).

Advantages compared to LCD displays

* smaller dimensions and weight
* no need for backlighting
* absence of such a parameter as viewing angle - the image is visible without loss of quality from any angle
* instant response (an order of magnitude lower than that of LCD) - essentially a complete absence of inertia
* better color rendering (high contrast)
* lower power consumption at the same brightness
* possibility of creating flexible screens

Brightness. OLED displays provide brightness from a few cd/m2 (for night work) to very high brightness - over 100,000 cd/m2, and their brightness can be adjusted over a very wide dynamic range. Since the life of the display is inversely proportional to its brightness, it is recommended for devices to operate at more moderate brightness levels up to 1000 cd/m2. When the LCD display is illuminated with a bright beam of light, glare appears, and the picture on the OLED screen will remain bright and saturated at any light level (even with a direct hit sun rays to the display).

Contrast. Here OLED is also the leader. OLED displays have a contrast ratio of 1,000,000:1 (LCD contrast ratio 1300:1[unspecified 71 days], CRT 2000:1)
Viewing angles. OLED technology allows you to view the display from any side and from any angle, without losing image quality.
Energy consumption. The energy consumption of OLED displays is one and a half times lower than LCD. The power consumption of PHOLED is even lower.
The need for the benefits demonstrated by organic displays is growing every year. This fact allows us to conclude that humanity will soon see the flourishing of this technology.

But technology does not stand still and a new generation of OLED is ahead

LEDs based on quantum dots. Let us immediately note that the strengths of QDLED devices (Quantum Dot LED - quantum dot LED) are high brightness, low production cost, and a wide range of colors. Almost immediately after the invention of a new type of LEDs, they are predicted to have excellent prospects for becoming the basis for displays of mobile devices (“handhelds”, mobile phones etc.), and even large-format television panels.

By quantum dot, scientists mean a special semiconductor structure that limits the movement of electrons in three dimensions at once. In relation to quantum dot LEDs, the following variation was used: cadmium selenide forms the “core”, and zinc sulfide acts as the limiting “shell”. The main "actors" in in this case are electrons, which, when transitioning from a high energy state to a lower one, emit photons, due to which the glow of the point is formed. The mechanism for changing the color of the LED glow is also quite simple - you just need to change the size of the quantum dot, which leads to a change in the wavelength of the light. Thus, by calculating the required dimensions of the semiconductor structure, it is possible to create LEDs in red, orange, yellow, or green colors. Another advantage of the devices is the highest brightness - up to 9000 cd/sq. m. For example, the brightness of modern displays does not exceed 500 cd/sq. m. That is, the development makes it possible to increase the corresponding parameter by an order of magnitude. Moreover, the technology makes it easy to increase the brightness of LEDs - just by forming a few quantum dots.

At the end I am posting a video to compare the properties of TFT and OLED displays.

Recently, OLED displays have become increasingly popular among mobile manufacturers. What are its advantages and disadvantages compared to LCD?

Mobile devices now come with various types displays: LCD, OLED, . Every mobile maker extols the virtues of the screen used, and some even improve screen technology and develop their own options, e.g. Super AMOLED for Samsung or Optic AMOLED for OnePlus.

Before you buy the next “smartphone with the best display,” you need to figure out how you will benefit from it as a user.

What is OLED?

The abbreviation OLED stands for Organic Light Emitting Diode, that is, organic light-emitting diode, or simply organic LED. To create them, thin films consisting of several layers of carbon material are used.

As the name suggests, these diodes emit light when passed through them electric current. This is one of the main differences between such displays and liquid crystal screens - they do not require additional backlighting.

The ability of organic materials to glow when exposed to electric current was discovered back in the 1950s. But the technology began to develop rapidly and be used in various fields only in recent years.

Operating principle

The LED panel consists of six layers. There are layers at the top and bottom protective glass or plastic. Moreover, the top layer is called insulating, and the bottom layer is called the substrate. Since OLEDs are very sensitive to oxygen and moisture, they play an important role.

Between these layers are the cathode (negative electrode) and anode (positive electrode). And between them are already placed two layers of organic molecules, which are called radiating (next to the cathode, a glow is formed in it) and conducting (next to the anode).

To make LEDs emit light, voltage is passed through the anode and cathode.

As electricity flows in, the cathode gains electrons from the power source and the anode loses them, or in other words, gets holes.

As a result, the electrons make the emitting layer negatively charged and the conducting layer becomes positively charged.

Positive holes are much more mobile than negative electrons, so they jump across the boundary of the conducting layer to the emitting layer. When a hole meets an electron, they cancel each other out and a short burst of energy is released in the form of a particle of light - a photon.

This process is called recombination. Since it occurs many times per second, the LED produces continuous light until the current stops flowing. By using multiple red, green and blue diodes, complex, high-resolution color images are obtained.

Types of OLED

There are two types of LEDs. The traditional version uses small organic molecules placed on glass to produce light. Another type uses large polymer molecules. They are called light-emitting polymers (LEPs) or polymer light-emitting diodes (PLEDs) and are thinner and more flexible.

OLED displays can be built in a variety of ways. In some designs the light exits through the top insulating layer, in others through the substrate. Large panels are also distinguished by the fact that the pixels are formed from individual LED elements.

The placement of the red, blue, and green pixels may also vary: they may be next to each other or on top of each other. In the latter case, more pixels fit into each square centimeter, which provides more high resolution, but the display is thicker.

Benefits of OLED

OLED displays are superior to LCD screens in many ways.

• Small thickness (about 0.2-0.3 mm, as a rule, LCD is about 10 times thicker).
• Light weight.
• Flexibility.
• High brightness.
• Less energy consumption (since no backlight is required).
• High refresh rate (OLED responds 200 times faster, which has great value when playing fast-moving images, such as watching sports or games).
• More natural colors and rich blacks (due to the lack of backlighting of black pixels).
• Wide viewing angle.

Disadvantages of OLED

The main disadvantage of OLED displays is their fragility. Early versions Such screens wore out approximately four times faster than LCDs. With development modern technologies Manufacturers have managed to reduce this difference, and now OLED-based displays can withstand several years of active use.

In addition, as practice shows, red and green diodes last longer than their blue counterparts. Over time, this can cause colors to become distorted.

Another problem is sensitivity to water. As noted above, for this reason the insulating layer plays an important role here.

It's also worth noting that OLED displays are still more expensive to produce than LCDs. As a result, the consumer will have to pay more for a device with an LED panel than for its LCD counterpart. If your display is damaged, repairs may also cost more.

Application

The technology is still relatively new, although more manufacturers are looking to use it in their own products. Now OLED displays are used in the screens of TVs, computers, players, smart watch and smartphones.

Organic LED(English) Organic Light-Emitting Diode (OLED) OLED is a semiconductor device made from organic compounds that effectively emit light when an electric current is passed through them. OLED technology finds its main application in the creation of information display devices (displays). It is expected that the production of such displays will be much cheaper than the production of liquid crystal displays.

1.5" OLED display

Operating principle

To create organic light-emitting diodes (OLEDs), thin-film multilayer structures consisting of layers of several polymers are used. When a voltage positive relative to the cathode is applied to the anode, a flow of electrons flows through the device from the cathode to the anode. Thus, the cathode gives electrons to the emissive layer, and the anode takes electrons from the conducting layer, or in other words, the anode gives holes to the conducting layer. The emissive layer receives a negative charge, and the conductive layer receives a positive charge. Under the influence of electrostatic forces, electrons and holes move towards each other and recombine when they meet. This occurs closer to the emissive layer because in organic semiconductors holes have greater mobility than electrons. During recombination, a decrease in the energy of the electron occurs, which is accompanied by the release (emission) of electromagnetic radiation in the region of visible light. That is why the layer is called emissive.

Diagram of a 2-layer OLED panel: 1. Cathode (−), 2. Emissive layer, 3. Emitted radiation, 4. Conductive layer, 5. Anode (+)

The device does not work when a voltage negative relative to the cathode is applied to the anode. In this case, holes move towards the anode and electrons move in the opposite direction towards the cathode, and no recombination occurs.

The anode material is usually tin-doped indium oxide. It is transparent to visible light and has a high work function, which promotes hole injection into the polymer layer. Metals such as aluminum and calcium are often used to make the cathode, as they have a low work function, facilitating the injection of electrons into the polymer layer.

Advantages compared to Plasma displays

• smaller dimensions and weight

Advantages compared to LCD displays

• smaller dimensions and weight
• no need for backlighting
• absence of such a parameter as viewing angle - the image is visible without loss of quality from any angle
• better color rendering (high contrast)
• lower power consumption at the same brightness
• possibility of creating flexible screens

Brightness. OLED displays provide brightness from a few cd/m2 (for night work) to very high brightness - over 100,000 cd/m2, and their brightness can be adjusted over a very wide dynamic range. Since the life of the display is inversely proportional to its brightness, it is recommended for devices to operate at more moderate brightness levels up to 1000 cd/m2. When the LCD display is illuminated with a bright beam of light, glare appears, and the picture on the OLED screen will remain bright and saturated at any level of illumination (even when direct sunlight hits the display).

Contrast. Here OLED is also the leader. OLED displays have a contrast ratio of 1,000,000:1 (LCD contrast ratio 1300:1, CRT 2000:1)

Viewing angles. OLED technology allows you to view the display from any side and from any angle, without losing image quality.

Energy consumption. Quite low power consumption - about 25W (for LCD - 25-40W). The efficiency of an OLED display is close to 100%, while that of an LCD is −90%. The energy consumption of PHOLED is even lower.

The need for the benefits demonstrated by organic displays is growing every year. This fact allows us to conclude that humanity will soon see the flourishing of this technology.

Story

André Bernanose and his collaborators discovered electroluminescence in organic materials in the early 1950s by applying an alternating current high voltage to transparent thin films of acridine orange dye and quinacrine. In 1960, researchers at Dow Chemical developed controlled alternating current electroluminescent cells using doped anthracene.

The low electrical conductivity of such materials limited the development of the technology until more modern organic materials such as polyacetylene and polypyrrole became available. In 2009, in a number of papers, scientists reported that they had observed high conductivity in iodine-doped polypyrrole. They achieved a conductivity of 1 S/cm. Unfortunately, this discovery was “lost.” And only this year the properties of a bistable switch based on melanin with high conductivity in the “on” state were studied. This material emitted a flash of light when turned on.

Sales volume

The OLED display market is growing slowly but surely. Thus, from April to June 2007, sales growth was + 4%, adding 24% over the year, and reached $123.4 million (Sales volume in the year was ~$85 million).

Some analysts estimate that the organic display market will grow to $3.7 billion by 2010. In 2008, OLED production volumes are expected to increase to 18 thousand units per month. In 2009, production volumes will increase to 50 thousand, and by 2010 - to 120 thousand per month.

Development prospects and areas of application

Today, OLED technology is used by many developers with a narrow focus, for example, to create night vision devices. OLED displays are being built into phones, digital cameras and other equipment that does not require a large full-color screen. There are also organic-based monitors, for example Samsung is actively developing in this area (the limit of 40 inches has been reached). And Epson released a 40-inch display back in 2004. The success can be explained by the fact that the production technology of such displays is similar to the printing technology in inkjet printer, and the company has extensive experience in this matter.

Latest achievements

Sony developments

Other companies

The Nokia N85 smartphone, announced in August 2008 and going on sale in October 2008, is the first smartphone from the Finnish company with an AM-OLED display, a not very expensive all-in-one device.

Optimus Maximus keyboard (Lebedev Studio), released in early 2008 using 48x48-pixel OLED displays (10.1x10.1 mm) for the keys.

OLED can be used in high-resolution holography (Volumetric display). Professor Orbit showed 3D video (potential applications of these materials) on May 12, 2007 at EXPO Lisbon.

OLEDs can also be used as light sources. OLED's efficiency and runtime already exceed those of lamps. OLEDs are used as a source of general lighting (EU - OLLA project).

On March 11, 2008, General Electric (GE Global Research) demonstrated the first successful roll-to-roll OLED as a major advance toward cost-effective production of commercial OLED technology. The 4-year research effort cost $13 million (Energy Conversion Devices, Inc and NIST), GE Global Research.

Chi Mei EL Corp of Tainan, demonstrated 25" (inch) low-temperature transparent silicon Active Matrix OLED at the Society of Information Displays (SID) conference in Los Angeles, USA May 20-22, 2008.