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All about OLED displays – OLED technology guide by Unisystem

 

The abbreviation OLED may be associated with TVs showcased in the electronics shops. We colloquially call them just “OLEDs.” This term derives from “organic light-emitting diode,” which is essential to provide OLED TVs (or broadly speaking – to OLED displays). This article presents OLED technology, one of the youngest display technologies available on the market.

 

Pixel is the smallest controllable element of a picture represented on the screen. The resolution defines the number of horizontal and vertical pixels, which make up each OLED display. The joint number of pixels can be assessed by multiplying the number of horizontal and vertical pixels. For example: in 0.96-inch WEA012864D of 128x64 resolution, there are 128 horizontal pixels and 64 vertical pixels, jointly 8 192 pixels. 

In OLED displays, pixels consist of at least one diode. They can be divided into two groups depending on the number of diodes (and as a result – the number of generated colors): 

monochromatic OLED displays – in these solutions, pixels consist of only one color diode, e.g., white, yellow, red, green, or blue. There are also double-color displays in which colors are spreading in the zones, like in WEO012864MXPP3N00001

- color OLED displays – in these solutions, pixels consist of three subpixels, each made up of three diodes – red, green, and blue (R, G, B, so RGB color mode). The various color tones are generated by mixing these three colors. These color OLED displays are called RGB OLEDs.

How OLED displays work?

OLED displays consist of a few layers, which we present on the scheme below (on the example of RGB OLED):

The voltage applied to the electrodes causes the flowing of the electrons and holes; the electrons flow to the anode, and holes flow to the cathode. If they approach each other, they recombine. It is accompanied by the emission of electromagnetic radiation, which frequency is in the visible region (in other words – emission of light in various colors).

The OLED displays' background

One could say that the history of OLED technology can be date back to the 20th century's fifties when the phenomenon of electroluminescence has been observed for the first time by André Bernanose's team. They applied the voltage to acridine orange, an organic compound, which began to emit the light. In the consecutive years, the phenomenon of electroluminescence has also been recorded in other organic compounds, e.g., in the polymer film set between two metal electrodes, which Roger Partridge has lit up. At the turn of the eighties and nineties of the 20th century, the first more or less functional prototypes of OLED displays are developing. There is worth noticing contribution in the development of OLED technology of two Eastman Kodak‘s employees - Ching Wan Tang and Steven Van Slyke, also the creators of an OLED display prototype.

In 1989, Jeremy Burroughes studied polyphenylene vinylene (PPV). He applied the voltage to PPV, which began to emit green light. It was a go-ahead for further development of OLED technology. However, it took a few subsequent years to devise OLEDs that would be effective enough (so they can be used in OLED displays).

There is also one more worth mentioning date – 2000 when the first plants producing OLED displays begin to operate.

The types of OLED displays

On the market, there are a few types of OLED matrix. Among them, e.g., AMOLED (Active-matrix OLED) and PMOLED (Passive-matrix OLED), refer to controlling the matrix. It can be active (AMOLED, in which each pixel is controlled) or passive (PMOLED, in which a sequence of pixels is controlled). These types of matrix affect the refreshing content frequency and, consequently, the matrix response time.

Another worth attention type of OLED display is a variation of RGB OLED, which is RGBW OLED (also called WOLED, so White OLED). In these matrices, each pixel consists of four subpixels – beyond the standard colors as red, green, and blue; there is also an additional color - white. This modification noticeably improves the quality of color reproduction (and that is why WOLEDs are successfully used in OLED TVs).

The other interesting solution is, e.g., TOLED, that is Transparent OLED. Their transparency is obtained by using transparent contacts on both sides of the device to create displays that can emit light both the top and bottom of the display. This type of OLED displays is ranked as HUDs (Head-Up Displays), a group of transparent solutions that presents data without requiring users to look away from their usual viewpoints. They are widely used in, e.g., transportation (e.g., planes).

The advantages and disadvantages of OLED displays

The pictures present on the OLED displays are perfectly readable due to excellent brightness and contrast, as well as a full viewing angle. There is no need to use backlight in OLED technology, which impacts the decreasing dimensions and weight of OLED modules. However, the lack of backlight does not make them fully energy-efficient solutions. One can notice the diverse power consumption depending on the color scheme of the presented content – it goes down when the images are dark and goes up when the images are bright. Moreover, OLED displays stand out by the swift response time – even less than 10 µs at 25°C (the animation in 100 FPS plays smoothly).

 

 

You can frequently hear that a crucial drawback of OLED displays is the limited lifetime of organic compounds used in OLEDs. (Interestingly, the OLED lifetime depends on… its color.) Imagine that you create a device with at least a 5.0-inch display that is expected to multiannual functioning. In such a case, you can successfully use an OLED display emitting only one color, e.g., green (like WEG010016AGPP5N00000 by Winstar, which lifetime has been estimated up to 100 000 hours). Incessantly, the producers try to extend OLED displays' lifetime, which seems to be a key factor in popularizing OLED technology in, e.g., TVs. Some producers currently declare that their TVs' lifetime reaches at least 100 000 hours (about 11,5 years while operating in continuous mode (24/7)).

Unfortunately, the organic compounds used in OLED displays are prone to environmental factors, most of all, moisture. Even if there is only slight damage on the matrix, the moisture may permeate it, causing the OLED displays' nonreversible failure. Then, how to preserve OLED displays? You can add tempered glass panels on the OLED displays' surfaces – it is an additional service that can be outsourced to Unisystem (just contact us to get a quotation).

What OLED displays for…? The use of OLED displays

On Unisystem’s offer, there is a lot of monochromatic graphic and character OLED displays in a wide range of sizes – from about 0.5- up to 5.85-inches. Their leading supplier is Winstar. They are available in three module types – COG (Chip-on-Glass, with a controller on the glass), COB (Chip-on-Board, with a controller on PCB), and COF (Chip-on-Film, with a controller on a film). 

Possibly, you use OLED displays every day – more and more often, they are used in various wearables, e.g., smartwatches. (Moreover, they can also be applied in medical wearables intended to measure the patient’s vital functions.) Besides, in battery-powered wearables, energy-efficient solutions are desirable, such as OLED displays without a backlight. (The energy-efficiency depends on the interface, of course - as we mentioned, the amount of consumed power goes down when the images are dark and goes up when the images are bright). In these kinds of applications, you preferably will use one of the graphic OLED displays, e.g., 0.66-inch WEO006448A, 0.96-inch WEO012864D, or 1.28-inch WEO012864L. You also should not miss the circular OLED display like 1.18-inch WEO128128B

OLED displays will go well with industry applications, e.g., as screens in portable measuring devices. In this case, the key parameter is the operating temperature – it should be wide enough to provide the OLED module's proper functioning both in low and high temperatures (what enable using them in indoor and outdoor applications). In this case, the aesthetics are not the crucial issue, so character OLED displays should suffice, e.g., 2.88-inch WEH002004B, 2.89-inch WEO002004C, or 3.67-inch WEH001602H.

More and more often, OLED displays are used in devices that we employ in houses or offices, such as audio and video players, amplifiers or equalizers, microwaves, coffee makers, weather stations, as well as other electronic accessories, e.g., computer ones, such as printers or scanners. You may need wide-screen OLED displays in these solutions, e.g., graphic 0.84-inch WEO009616A, 2.59-inch WEG010016F, and 4.90-inch WEG020016A or character 1.23-inch WEO001602B, 2.29-inch WEH001602D, and 3.67-inch WEH004002A. If you need a standard OLED display, you can use, e.g., 0.96-inch WEA012864D.

We can list other potential uses of OLED displays. A few examples of OLED display applications can be indicated in retail, especially in shopping centers. They can be mounted as an additional screen in various kiosks used to pay, e.g., self-service checkouts, ticket machines, or parking meters.

There are almost 200 OLED displays in our shop. However, if there is no model you are looking for, please contact us - we will do our best to find a solution that will go well with your device.

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