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OLED displays without secrets – A guide to OLED technology

The abbreviation “OLED” may be associated with televisions displayed in electronics stores, which are commonly referred to as “OLEDs.” This term comes from the term “organic light-emitting diode” (OLED), without which no OLED TV (or, more generally, display) would exist. In this article, we take a closer look at “OLEDs,” one of the newest technologies available on the market for visualizing information.

A pixel is the smallest element of an image that can be controlled on a display. The resolution defines the number of horizontal and vertical pixels that make up a given OLED display model. The total number of pixels can be determined by multiplying these values. Example: in the 0.96-inch WEA012864D, with a resolution of 128×64 px, there are 128 pixels horizontally and 64 pixels vertically, or a total of 8,192 pixels.

In OLEDs, pixels consist of at least one diode. OLED displays can be divided into two groups in terms of the number of LEDs (and thus the number of colors that can be achieved):

monochrome OLED displays – in these solutions the pixel is formed by only one LED in color, such as white, yellow, red, green or blue. Solutions combining these colors are also available, such as stripes in specific colors as in the WEO012864MXPP3N00001 model.

color OLED displays – in these solutions, the pixels consist of three subpixels, or LEDs in three colors – red, green and blue (R, G and B, or RGB model). As a result of their “mixing” different shades of color are created. This type of matrix is referred to as RGB OLED.

How does OLED work?

OLED displays consist of several layers, which are presented in the diagram below (using the RGB OLED matrix as an example):

rgb oled matrix layers diagram how it works

Applying a voltage to the electrodes causes electrons and holes to move – they are “fed” through the cathode (electrons) and anode (holes). They meet at the emission layer, where their recombination occurs, accompanied by the emission of electromagnetic radiation in the visible spectrum (in other words, glowing in different colors).

History of OLEDs

It can be said that the history of OLEDs dates back to the 1950s, when André Bernanose’s team first observed the phenomenon of electroluminescence in the organic compound under study, i.e. acridine orange, which began to glow when a voltage was applied. In the following years, the phenomenon of electroluminescence was noted in more organic compounds – this was dealt with, among others, by Roger Partridge, who illuminated a polymer film placed between two metallic electrodes. The turn of the 1980s and 1990s saw the development of the first more or less functional OLED display prototypes. Significant contributions to the development of OLED technology were made by Ching Wan Tang and Steven Van Slyke, employees of Eastman Kodak, also creators of the prototype OLED display.

“Green light” for further development of OLED technology turned out to be studied in 1989. by Jeremy Burroughes polyphenylvinylene, which emitted a green light when voltage was applied. However, several more years were needed to develop OLEDs that would guarantee sufficient luminescence efficiency (and could be successfully used in OLED displays).

One more date worth mentioning is 2000, the establishment of the first factories producing OLED displays.

Types of OLED displays

Several types of OLED arrays are available on the market. You can encounter, for example, the terms AMOLED (Active-matrix OLED) and PMOLED (Passive-matrix OLED), which refer to the way the matrix is manipulated – it can be active (AMOLED, control of individual pixels) or passive (PMOLED, control of sequences of pixels), which translates into the refresh rate and, consequently, the matrix response time.

Also worth noting are RGBW OLEDs (you may also encounter the name WOLED, or White OLED), which are a variation of the aforementioned RGB OLED. In these matrices, each pixel is formed by four subpixels – in addition to the standard colors, i.e. red, green and blue, there is an additional one, i.e. white. This modification noticeably improves the quality of color reproduction, which is why WOLEDs are often used in TVs.

Other interesting solutions include. TOLED, or Transparent OLED – transparent OLED displays. Their transparency is achieved by using transparent electrodes that allow light to be emitted on both sides of the display – from the front as well as the back. Such OLED displays fall into the category of HUDs (Head-Up Displays), or head-up displays, which are used in applications that require access to information without having to take your eyes off the view, such as transportation (including airplanes).

Advantages and disadvantages of OLED technology

The images presented on OLED displays are perfectly legible due to the exorbitance of such parameters as brightness and contrast or viewing angles. This technology does not use backlighting, which significantly affects the size and weight of OLED modules. However, it cannot be said that the lack of backlighting makes them fully energy-efficient solutions – it is noticeable that the power consumption varies depending on the color of the displayed content, decreasing with dark images, but increasing with bright ones. In addition, OLED displays also stand out for their lightning-fast response time – less than 10 µs at 25°C, allowing for smooth animation playback of more than a hundred frames per second.

An oft-emphasized shortcoming of OLED displays is the limited lifespan of the organic materials from which the diodes are made. (Interestingly, their lifespan depends on… color.) In devices that are expected to last for many years, and where displays not exceeding 5.0 inches are required, OLED displays glowing in only one color, such as green, can be successfully used (an example is model WEG010016AGPP5N00000 from Winstar, which has an estimated lifetime of 100,000 hours). Work continues unabated on extending the life of OLED displays, which seems to be a key factor in the spread of the technology, such as in televisions. Currently, some manufacturers declare that the lifespan for the TVs they supply is at least 100,000 hours (which translates into about 11.5 years – when used continuously, 24/7).

Unfortunately, the organic materials that make up OLED displays are susceptible to environmental factors, including, most notably, moisture – even minor damage (and moisture penetrating them) can lead to irreparable damage to the matrix. Therefore, it is recommended to protect the surface of OLED displays by applying tempered glass to them – this is an additional service that can be performed at Unisystem (contact us for a quote).

Which OLED to…? Application of OLED displays

Unisystem offers a range of monochrome graphic and character OLED displays with a wide range of diagonal sizes – from approx. 0.5- to 5.85-inch, whose main supplier is Winstar. They are available in three structural variants – COG (Chip-On-Glass, with controller on glass), COB (Chip-On-Board, with controller on PCB) and COF (Chip-On-Film, with controller on tape).

It is possible that you come into contact with OLED displays on a daily basis – they are increasingly used in various types of wearable devices, such as smartwatches. (What’s more, nothing prevents them from also being used in medical wearables used to measure patients’ vital signs.) An additional advantage of OLEDs for battery-powered wearables also becomes the lack of backlighting, which reduces the power consumption of the matrix (this, however, is conditioned by the appearance of the interface – as we mentioned, the amount of power consumption decreases with dark, but increases with bright images). Graphic solutions such as the 0.66-inch WEO006448A, 0.96-inch WEO012864D and 1.28-inch WEO012864L are the most likely to be used in this type of application; round OLEDs, i.e., WEO012864L, are also worth considering. 1.18-inch WEO128128B.
OLED displays are also ideal for industrial applications, such as screens in portable measuring devices. In this case, the key parameter will be the operating temperature, which in the case of products from Winstar ranges from -40° to 80°C. It is a guarantee that OLEDs will function smoothly in both low and high temperatures (allowing them to be widely used in indoor and outdoor applications). Here, aesthetic qualities are not crucial, so sign solutions such as the 2.88-inch WEH002004B, 2.89-inch WEO002004C or 3.67-inch WEH001602H may be sufficient.

Increasingly, OLED displays are also being used in devices we use in our home and office spaces, such as in consumer electronics (including audio/video players, amplifiers and equalizers) and home appliances (including microwaves, coffee makers and weather stations), as well as other electronic accessories such as computers (such as printers and scanners). Widescreen solutions, such as the 0.84-inch graphic WEO009616A, 2.59-inch WEG010016F or 4.90-inch WEG020016A, or the 1.23-inch character WEO001602B, 2.29-inch WEH001602D or 3.67-inch WEH004002A, can work well for these solutions. If you need a model with standard proportions, consider using, for example, the 0.96-inch WEA012864D.
One can enumerate more areas where OLED technology is successfully used – at least a few examples of OLEDs’ application can be pointed out, such as in retail, especially in shopping malls – they are installed, among others. As additional screens at kiosks where we pay fees, such as self-service cash registers, ticket machines and parking meters.

Almost 200 variants of OLED displays are available in our store. Contact us if the model you’re looking for isn’t among them – together we’re sure to find a solution that works perfectly for the device you’re designing.

2020-11-18

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