OLED display Technology and what OLED mean

OLED display Technology and what OLED mean

 

This is a new display technology that uses organic LED.  In full form it is organic electroluminescent diode. The technology was produced to further increase the efficiency of the displays but reducing the power requirement. Now let us take a look at OLED  display technology and what it means.

What OLED means

As the word suggest, organic matter in the OLED plays a critical role on how the OLED operates. Unlike the LED where the color and the light are produced by two different elements, the OLED technology allows both light and color to be produced by the same diode. In this latest display technology, it is from each pixel that the light and color are produce. This means that each pixel is self-sufficient.

The greatest advantage that OLED displays have over the LED is that   pixels receive luminance and power at individual level.  When the pixel is off, it does not receive any light meaning it is completely black and this gives it a very high contrast ration compare to LCD and LED.

There are not many manufacturers of OLED but many TV manufacturers uses the technology in their display. Such manufacturer include Sony, HiSense, Panasonic, Philips Bang and Olufsen among many others.

Samsung is also producing OLED screens for phones but its best known for its high performance Samsung QLED displays. However, the company announced they are starting to produce OLED panels for their TV as well. The next item on OLED display Technology and what OLED mean topic the difference between QLED and OLED.

Full form: organic light emitting diodes

Difference between QLED and OLED

QLED display technology is not that different from the LED display. However, QLED are LED displays that uses quantum dots to enhance brightness and color of the screen. The first QLED was  developed by Sony in the year 2013. However, the backlight requires different system than that which produces color. In layman terms, QLED are advanced LED. OLED remains the champions of having the luminance and color being produced by a single pixel or diode.

Difference between LED and OLED

Now the next thing on the OLED display Technology and what OLED mean is digging the difference between the OLED and LED.  The major differences are in the light source, lifespan and the size. Let us look at them in details.

Light source

The major difference between the LED and OLED is that while the LED requires a different light source from that producing color, OLED has each pixel receiving power to produce color. This makes them more power efficient and also to have higher color contrast than that given by the LED. The substrate for the OLED can be placed on the plastic materials unlike the case with the LED.

Size

OLED are much thinner compared to LED since there is no need for external light source for the pixel. The fact that they require no backlighting makes them lighter and flexible. This is what rises the probability of them being used in fabrics or cloths.

For now, OLED are much expensive to produce than it is for both LED and LCD. This makes them more expensive to buy than they competitive LCD and LED television sets.

Life span

The OLED has shorter lifespan compared the LED. This is so since there are two elements that are ever present in any environment-moisture and oxygen.  When the moisture and oxygen get inside the substrate, there are black dots that are developed and with time they make the screen useless. OLED has the blue luminance degrading at a faster rate than the red and green luminance. Over time, people will notice the color imbalance after sometime.

The ever-increasing technological improvement promises to solve such issues mentioned above so that OLED could be mass produced at lower costs with improvements that will make them last longer than they current do. LED display method was a major technology rip that soar the necessary reduction of power consumption in the display. CRT technology is long outdated  and can only be used in the schools for teaching and demonstration.

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Types OLED

The OLED technology employs several operation techniques which are used to classify them.  The following are the OLED types classified depending on many factors.

Foldable OLED

the substrates are made majorly on plastic materials and sometimes metallic foils. They are light weight and have found their use in PDA and mobile phones. They are resistant to breaking and shuttering because plastic materials are not as brittle as the glass is.

Passive matrix OLED

Passive matrix OLED are also know as the PMOLED.  this type of OLED has organic layers sandwiched between strips of cathode and anode. The light is emitted in the region between the cathode and anode (this is what makes the pixel).  A very sophisticated circuit determines which cathode and anode pairs receives power and which do not. The higher the current that a pixel receives, the brighter it becomes.  This type of OLED is known to use more power than other OLED displays.  They are good for cell phone, PDA and audio media players.

Active matrix OLED

Active matrix OLED are also known as AMOLED. They are like the PMOLED but now the anode is overlayed with a film of TFT array that forms a matrix. It is the TFT that determines which pixel turns on or off. They consume less power compared to PMOLED since no sophisticated circuitry is needed. AMOLED has their use in large displays such TVs and computer monitors because of their high refresh rates. They are very good for watching videos.

White OLED

White OLED   are able to product white light which has better characteristics than that emitted by the fluorescent lights. The light is more uniform.  Because they are able to give light with true incandescent qualities, they may soon be used at home for light. Their low energy consumption would help reduce the cost of lighting.

Transparent OLED

The transparent OLED  has the substrate, cathode and anode  made of transparent materials. When they are off, they are transparent since light can pass through them in both directions.  They may have the PMOLED or AMOLED circuits.

OLED display Technology and what OLED mean

Top emitting

The top emitting type of OLED is suited for the AMOLED design. The substrate used to make them has either reflective of opaque properties.  This display tech may soon find its used in the smart cards.

How it works

In our previous article on how OLED display screens works, we discussed how every component is wire to produce an image.  Here, I will give a detailed explanation on how OLEDs themselves work. Unlike the LED, the light is emitted by organic material when electrons pass through it. The structure of the OLED screen light emitting layer that is placed between an anode and a cathode.

Many layers

Of course, it is more complicated than that. Between the cathode and anode, there are several layers of materials that perform various functions. Those layers include electron transport layer, blocking layer, emissive layer, hole transport layer, hole injection layer (they are in order from the cathode side). After the anode, there is the substrate (it is not sandwiched like the rest of the layers).  Since this type of display technology is sensitive to moisture and water, there is the need to place an encapsulation layer around the rest of the layers.

Anode

The anode serves to receive electrons when the device is switched on. The electrons are emitted by the cathode.

Organic layers contain molecules that which serve to emit light when current pass through

Emissive layer

Emissive layer is made up organic molecules from plastic materials such as polyfluorene.  They transport electrons that are emitted by the cathode.

Conducting on the hand, unlike the emissive layer, transport the positive charge ( or the holes) from the anode the cathode.

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Cathode

Finally, the cathode is the source of electrons which travel through the layers to the anode. Orgic Light Emitting Diode technology is classified as a real green energy technology.

OLEDs are capable of emitting light brighter light while consuming less power compared to the LED (Light emitting diodes) or the LCDs (liquid crystal display). OLED is as thick as 500nm and could be made up of 2 or three layers of the organic materials.

How OLED are made

There are several methods that used to make OLED. However, though vacuum evaporation is the most common of them all, its inefficient and present challenges when one to scale them up.

Other method of making OLED include inkjet printing and organic vapor phase deposition.  The former has the organic molecules sprayed into the substrate in a similar manner as paint is prayed on wall. This method is not costly and, unlike vacuum evaporation, can be scaled up to screens as large as electronic billboards.

Organic vapor phase deposition has the organic molecules evaporate from a low-pressure reactor chamber and settle on a cool substrate in to a thin film. A carrier gas is needed. This is more efficient and less costly.

Life span

According to the US department of power, the OLED has 40, 000 hours of operation when set at 25% brightness and 10, 000 hours when the brightness is at 100%. The lifespan of the OLED is limited that of the organic material used to make them. According to the experts, LG has managed to make one that has a lifespan of slightly greater than 50,000 hours.  This simply means if one is to watch for 12 hours a day, the OLED would work for 11 year or 6 years if one prefers to watch for 24 hours a day.  This is a little better than most common TV set people use.  However, in the next 10 or so years, it is probable technology will have changed completely.

The blue luminance

A well cited technical report indicated that that blue luminance degraded by 12% after 1, 000 hours of use, the red and green degraded by 7% and 8% respectively after equal hours of use. in the history of OLED, blue luminance has a limited life span of 14, 000 hours.  On the other LED, LCD and PDP displays has their blue luminance limited to between 25, 000 to 40, 000 hours depending on the quality of the manufacturer and model.

When the oxygen and moisture find their way inside the substrate, there are dark sport since two elements results in the degradation of the organic matter with time (degradation takes place even when the display is powered off).  The US department reported that the rate of degradation is proportional to the display brightness where the brighter the screen, the faster it degrades. LG on the other hand reported an improvement in the year 2016 from the 36, 000 of operation to 100, 000 hours.

There are 4 stages involved during the OLED degradation process.

First Stage 1:Charge carriers are recombined when the UV light is absorbed.

Second Stage : homolytic dissociation follows after charge carriers are recombined.

Third stage: formation of radicals after subsequent addition reaction that adds radical

Fourth stage : hydrogen -atom reaction that occurs after stage 3 takes place.

Moisture causes the degradation to take place faster than when the display is exposed to oxygen.

Pros and cons of OLED

Before we are done with OLED display Technology and what OLED mean topic,  let us take a look at the advantages and disadvantages of OLED technology.

Pros
Cost

In the future, the cost of manufacturing the OLED has been projected to be lower than it is today. In theory it is expected they will be far cheaper than it is to produce LCD and plasma displays. However, today, OLED are more expensive to produce than the LCD. Though the vapor deposition method makes it easy to mass produce them, it becomes a problem when more than two layers are involved since accuracy is a requirement for them to work proficiently.  Lining up of such layers could pose a problem. The use of PET (polyethylene terephthalate) can make production of light OLED display very affordable.

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Flexible

The substrate can be placed on a material that is both light and flexible.  It is such reason that makes it possible for them to possibly find applications in the Roll-up displays which can be embedded on cloths or other fabrics.

 

OLED display Technology and what OLED mean
FlexibleOLED screen

Some methods of OLED make it possible for them to be produced on plastic substrate and hence making the durable since plastic is more shutter resistant compared to glass. They do not require backlighting material making them light and hence flexible.

Low power consumption

The LED and LCD technology has the light emitted from the background where only a small fraction of the light is allowed through. This is why it is not possible to have a true black using LED or LCD.  For OLED displays, since the light is emitted by the organic matter, the inactive region gives not light on the black region. This makes them consume less power compared to LED and LCD.

Higher quality pictures

The study shows that they, OLED, has better viewing angle; better than both LED and LCD. Also, greater contrast ratio exists for OLED compared to LED and LCD. The contrast ratio is greater since the light is emitted directly by the OLED pixels where they appear unshifted and accurate even when the viewing is changed.

Response time

Many display technologies today uses a refresh rate of 60 Hz. However, the OLED is such that it has faster response time where refresh rates as high as 240 Hz can be achieved. This new technology has refresh rates that are more than 1, 000 times faster than the LCD since while the LCD has response rate of 1ms (0.001), OLED has 0.01 s (0.000001 s). This quality makes them suitable for applications where strobing is required and therefore can be used to produce effects that are characteristically similar to that produced by CRT. This fast refresh rates could help solve the motion blur seen on the LCD (LCD uses sample and hold technique which causes the blur).

Are thin

Being thin is what makes OLED both flexible and rollable. This makes them safer when transporting them from one place to another. They do not require large space when mounting. They can even be stuck on a wall without the need of a stand or wall mount.

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Cons

Cost: Though they are more environmentally friendly, OLED are more expensive to produce compared the LED and LCD. However, due to their simplicity in design, the cost of producing them is likely to go down in the near future.

Limited lifespan: The life cycle of an OLED screen is limited since it fragile. This is even so when they are subjected to Ultra violate radiation (or direct sunlight). However, research and development carried out today by mobile phone companies promises better performance in the future.

Color imbalance: in the section above, it was discussed that the blue luminance degrades first than the red and green type. It means that with the blue light will appear dimmer compare to the green and the red type. This color imbalance is easy to notice especially when the degradation of the luminance occurs at different rates.  This is what is attributed to the color imbalance after they are used for some time.  If the user has knowledge of color balance, with use of advance circuitry, this problem can be avoided.

Now we are done with OLED display Technology and what OLED mean topic. You can read further on how LED tv displays work.

 

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