OLED displays have advanced significantly since the technology was first developed at the end of the 20th century. OLED technology delivers many benefits over LCD screens including a greater efficiency, no requirement for backlighting and the ability to create flexible, non-linear screen shapes.
AZoOptics spoke to Kirk Lim, of Pacer International, on the science behind OLED screens, an in depth discussion of their advantages and the different types of OLED technology that Pacer International Supply.
What is an OLED? How do they differ from the liquid crystals found in LCD (liquid crystal display) screens?
OLED display panels are made from organic light emitting diodes - solid state devices composed of thin films of organic molecules that create light with the application of electricity. As they emit light, they have the advantage of not requiring any backlighting. This is unlike LCD screens which do require a backlight to be visible.
The thin layer of organic compounds in an OLED is situated between two electrodes, an anode and a cathode, and when the appropriate voltage is applied, the organic molecules emit radiation with a frequency in the visible region, i.e. they create their own light.
In contrast, the liquid crystal cells in LCD screens consist of a thin layer of a liquid crystal sandwiched between two glass sheets with transparent electrodes deposited on their inside faces. The electrodes control the position of the crystals which, in turn, determines how much light can be transmitted through them. An LCD display does not emit any light of its own but instead depends on externally provided illumination such as a backlight.
OLED devices can either be passive matrix (PMOLED) or active matrix (AMOLED).
An AMOLED display consists of an active matrix of organic OLED pixels which have been deposited or integrated onto a thin-film transistor (TFT) array. The TFT array acts as an array of switches, controlling the current flowing to each individual OLED pixel.
Thus AMOLED technology relies on TFT backplane technology – essential in OLEDs above about 1.8” to keep the current stable and the display uniform. AMOLED does not tend to be viable for low volume applications.
PMOLEDs use a simpler control scheme in which each row in the display is controlled sequentially.
An extreme close up of an OLED screen displaying 'white'. Each pixel corresponds to a group of organic molecules that emit either red, blue or green visible radiation. Shutterstock | Carlos Antonio
What advantages can OLEDs deliver that LCDs cannot?
Two common types of LCD are monochrome LCDs and TFT LCDs. For this comparison we assume the LCD is backlit TFT LCD; an LCD really needs backlighting to offer acceptable performance for most applications.
OLED technology allows the displays to be smaller, thinner and lighter than TFT LCD as a backlight is not required. This results in easier integration – the displays are easier to fit into tight spaces, and connections to the display can be shorter so there are fewer EMC problems. Power consumption is also significantly lower.
OLEDs deliver better contrast, sharper images and more vibrant colors than all other technologies, even without a backlight! The ultra-sharp images are due to high contrast of greater than 1000:1. OLEDs have and excellent color definition and a “blacker black”, meaning they have a deeper black than other technologies.
OLEDs have a very fast response time (microseconds rather than milliseconds) meaning no motion blur occurs. They also offer a wide viewing angle of > 170° and a wide operating temperature range of -40°C to +70°C. Lifetimes have improved greatly as high volume OLED opportunities have forced manufacturers to push the technology to new levels to increase efficiency.
Users have demanded high brightness OLED and that has delivered improved longevity. TFT displays still have the edge when it comes to lifetime (the backlight may need replacing but the TFT LCD will still be going strong!) but the latest ultra-reliable yellow OLED range has very long lifetimes rivaling that of TFT.
OLEDs are easier to drive than TFT LCD displays, as you can use a serial bus such as I2C or SPI rather than a more complex RGB interface or microcontroller interface and so need far fewer control lines.
Greener organic OLED technology is better for the environment and easier to manufacture with no backlight.
It should be noted that for color displays, OLEDs are significantly more expensive than other display technologies – this must be taken into account unless the application only requires one colour in the display.
What innovations do you expect the development of differently shaped OLEDs to deliver?
The advent of different shapes paves the way for new applications for which standard shape OLEDs have not been a great fit. Aesthetically, a round display is preferred for applications like wearables, watches, motorbike or bike instrument displays where OLEDs could replace mono LCD.
Letterbox shape OLEDs suit rack based units eg 1U, AV equipment and laptops which are all continuously getting thinner and lighter.
Flexible and curved OLEDs are technically possible, but really require a high volume application to make them cost effective.
Round OLED screens are a desirable component for smartwatches. Shutterstock | Cls Graphics
What environments can OLED screens be used in? Can they be used in environments that LCD screens cannot?
OLEDs perform exceptionally well at extremely low temperatures with little degradation of response time, whereas TFT LCD displays will not function at lower temperatures. This means OLEDs are now a viable alternative to LCDs in many industrial applications.
The combination of brightness, light weight and low power consumption lends itself well to use in extreme environments or for use in underwater applications, although waterproof housing would be required!
OLEDs are better for intrinsically safe environments due to their low power consumption, which keeps currents below maximum acceptable levels, and are much more suitable for wearable applications.
As OLEDs are less vulnerable to fluctuations in temperature and have a low power consumption they are a strong candidate for industrial applications. Shutterstock | Zapp2Photo
What does all of this mean for display manufacturers?
Manufacturing techniques developed for the production of OLEDs, such as layer deposition and ink jet printing techniques, have subsequently benefited the manufacture of other products – an example is PCAP touchscreens.
The advent of mobile electronics with its demand for low power consumption has changed the way materials are used in technology. Battery technology has had to improve, and power supply and efficiency has had to get a lot better. Suppliers have been pushed to improve display efficiencies and reliabilities to meet user demands, with the result that some OLED lifetimes are now rivaling those of TFT displays.
Greener organic OLED technology is better for the environment and easier to manufacture with no backlight, making the technology favorable for environmentally conscientious manufacturers.
In what industries do you see OLED screens delivering the most benefits?
OLEDs represent a new generation in display technology - ideal for handheld instrumentation, automotive displays, portable media players, audio visual display systems and mobile phones.
OLED technology is expected to gradually become an alternative choice to Monochrome LCDs in applications such as instrumentation, measurement equipment, current analysers, bench top equipment, industrial handheld monitors, ticketing machines and vending machines. The Internet of Things opens up yet more opportunities.
The ultra-thin lightweight nature of OLED displays and their extremely low power consumption make them popular for handheld products such as data loggers and monitors, pistol grip thermometers, laser range finders, handheld instruments and handheld meters. New round shapes have opened up applications like wearables, watches, motorbike or bike instrument displays.
Many medical applications such as defibrillators require bright displays with low power consumption. OLEDs are also ideal for the emerging trend of wearable technology, such as mp3 players; recent additions to our OLED range include several modules with diagonal size less than an inch. These bright emissive displays perform well in diving watches, performance swimming monitors and other underwater applications - in the right waterproof housing.
They are ideal for handheld or wearable technology being adopted by the emergency services.
All of these applications are adopting more displays as the supporting electronics and communications continually improve and the functional scope of products increases.
OLED screens are expected to be used extensively in the medical industry. Shutterstock | sfam_photo
Please could you tell our readers more about the OLEDs that Pacer International supply?
We supply a wide range of mono and colour OLEDs, from 0.5” to 5.5”, including white, yellow, blue and RGB.
We offer special sizes such as round and letterbox, very small displays from 0.5”, and high brightness ultra-reliable OLEDs. A variety of packages and interface options are available.
Where can our readers find out more about OLEDs and Pacer International
Full details and accompanying datasheets of our OLED products can be found on our website.
If you would prefer to talk about what screen may be best for your application please contact us directly and we'll be more than happy to help.
About Kirk Lim
Kirk Lim is originally from Malaysia. He studied engineering in the North of England, and embarked upon a career encompassing applications engineering, project engineering, project management and product management – all involving display products and the electronics that drive them.
He joined Pacer in 2006 and brought in the first OLED displays line to set up the displays division. When not extolling the virtues of the latest display technologies, Kirk enjoys badminton, running, skiing and the occasional Tough Mudder challenge! He also travels frequently to the Far East for both business and leisure.
Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.