OLED Displays, How do they work?

if we compare these two television screens it is quite clear that the lg oled tv has vibrant colors and better image reproduction quality than any other the answer to this difference is display technology the lg tv is based on the most advanced display technology oled and other tvs are on ips lcd technology let's learn in detail about oled technology interestingly the fundamental image reproduction mechanism is the same in both technologies before seeing oled in detail let's first understand this fundamental the smallest display unit is an element called pixel it has an average size of 0.3 by 0.3 millimeters you can see three different color filters inside a pixel the most amazing thing is that we can achieve any color just by illuminating these filters at different intensities a few examples are shown here now you might doubt that the filters are different pieces how can these three different colors get mixed up and produce a new color let's study this phenomenon with a simple example in a 1 by 1 inch pixel we can see that the colors are distinctive let's reduce the pixel size slowly have you noticed some differences after a certain pixel size the individual colors are not distinguishable we will see the combined color of all this is due to the limited visual resolution of the human eye it can't differentiate between subpixels now let's convert these pixels into digital so each pixel has its own position and color data this data is stored in digital form for future reproduction of the image now let's see how the image reproduction is done practically take a uniform white backlight source keep a color filter containing multiple small red blue and green colors in front of it again place a glass screen in front of it as soon as we turn on the backlight all the filters will glow with equal intensity and what we get at the output is just white color to get the other colors we just need to get different brightness levels for the sub pixels to do this we will use an lcd sheet and a small circuit the polarization of the lcd crystal can be adjusted and we will easily get different brightness levels in the sub pixels now it's time to convert the digital signal we stored to electrical signals these electrical signals are fed into the circuit when the signal is received the crystal in the lcd rotates and polarizes the light in this way we successfully produced our original image there are several disadvantages of this display technology the color reproduction is not that accurate for example when we try to produce a perfect black color using this technology this is what we get this is due to the continuous backlight being on in the background the energy consumption in those display types is quite high because of the common light source for all the pixels what if we provide each pixel with its light source and control it this is a great idea instead of using a common light source use minute and many light sources for every pixel with this method the lcd sheet can also be removed however the issue is that fabrication of such minute leds in the range of micrometers is not practical due to the issue of surface irregularities and their solid nature at room temperature they cannot be miniaturized into micrometer ranges this is why organic led comes into the picture they can be fabricated as small as 6.3 micrometers now let's see how the oled works any led technology works based on electron hole pair recombinations in semiconductor materials please note that only those materials with a suitable band gap in their atoms can emit light in the visible range in organic semiconductors the energy levels of molecules are considered rather than atoms the electrons in a stable state are located in the homo level and those in an excitation state are located in the lumo level let's connect this organic semiconductor to an external power supply using anode and cathode due to this electrons move from the homo to the lumo levels via a power supply and create holes as soon as these electrons enter the lumo layer they recombine with the holes and emit light due to the natural tendency however this process is not simple let's look at the anode side first when we connect the battery's positive terminal to the anode it tries to extract electrons from the organic layer however there is an energy difference between the homo level of the organic layer and the anode which will act as a barrier for electrons the same is the case with the cathode side so the cathode won't be able to inject electrons easily and consumes more energy this problem is solved by adding two different layers between the electrodes and the organic semiconductor due to the addition of those intermediate energy layers the barrier will be reduced and electrons can be easily injected or extracted from the organic layers however here charges have very low mobility due to hopping between the molecules for this reason we add more intermediate layers to further reduce the energy barrier and reduce power consumption let's place such three organic leds behind a filter to control each subpixel independently just by varying the external power supply we can control the electron flow or recombination rate and reproduce any image it is quite obvious that black color reproduction can be perfectly achieved using this technology the current oleds produce only white light a cool and promising feature of oled technology is that we can even avoid the usage of color filters with its help what if we directly obtain rgb color light emission from the oled source itself this is certainly a possibility currently various oled manufacturing companies are working on developing rgb color emitting oled devices by adding various doping materials in emission layers due to the addition of doping material the band gap of an emissive layer is changed accordingly changing the color of light emission thank you for watching the video see you next time

Channel: Lesics

Views: 1,079,947

Keywords:

Id: xAMhX3Drq14

Length: 7min 30sec (450 seconds)

Published: Sun Jan 30 2022