How Long Do OLEDs Last?
Researchers and consumers are both very interested in how long OLEDs last. Issues like black spots, burn-in, and pixel failure still affect OLED devices. However, developments in OLED technology have worked to tackle these issues and improve device lifespan.
What is the Lifespan of an OLED?
In televisions, the projected lifespane (or lifetime) sits at 100,000 hours. This figure considers an avergae usage of 8 hours per day. In comparison, LCDs average between 30,000 – 60,000 hours with similar use. The self-illuminating nature of OLED devices means there is no need for backlighting, which largely accounts for the increase in lifespan.
Research shows that consumers tend to replace products once they begin to show a loss in function, and not necessarily when they have completely broken down. The problem is an acute one in OLEDs. Due to issues like burn-in and black spots inside OLED panels, it is one that becomes a matter of aesthetics too.
This disparity leads to two defintions of device lifespan: the expected lifetime and the actual lifetime. The actual lifetime is the length of time a product is used before being discarded. Whereas, the expected lifetime is the time we expect a product to function flawlessly under normal conditions of use.
Whichever definition we turn to, OLED lifetime in general cannot ultimately be precisely determined. Yet, a technical definition for the lifetime refers to the time taken for the luminance to decrease by 50% of the initial luminance.
OLED Degradation
OLED degradation determines the lifespan of an OLED device. It is affected by operational factors, fabrication or manufacturing conditions, and device usage.
Temperature Effects
Long time use may increase the device temperature during operation, potentially leading to thermal degradation and reduced lifetime. It can cause thermal expansion which damages the device, or even melt the organic materials within the OLED device.
Brightness
The brightness of an OLED device increases as the electrical current increases, but this can lead to OLED degradation. Therefore, OLED lifetime is inversely proportional to brightness. Researchers are currently working to find ways of improving OLED lifetime, through increased brightness at lower voltages.
Dark spots
Dark spots are non-emissive regions of a display. These form at the interface between organic and conducting layers of OLEDs. They can be caused by the presence of moisture, dust particles, pinholes, spikes on the ITO layer and short-circuits.
Luminance
When it comes to luminance, there can be problems caused by both increases and decreases. As the luminance increases, a larger concentration of excitons accumulates leading to an increased probability for degradation processes to occur.
Once the luminance had dropped by half, the OLED device is said to have reached its lifetime. As well as the accumulation of degradation products and charge carriers, luminance efficiency may be reduced by increases in temperature.
Blue OLEDs
The use of blue OLEDs presents problems because these emitters have a shorter operational lifetime.
Today blue OLEDs continue to be the focus of intense research. Improving upon lifespan has involved a search for materials with a wider band gap, such as phosphorescent and thermally activated delayed fluorescence (TADF) emitters.
Increasing OLED Lifespan
Current research is vested toward improvements in the materials and architecture of OLEDs devices. Scientists have come up with ways of reducing or avoiding some of the common problems with OLED technologies.
Encapsulation
The major problem for dark spot formation is that of pinholes. Pinholes in the interlayers can lead to oxidation of the cathode, giving rise to a non-emissive area or dark spot. One solution to the problem is encapsulation. This process prevents oxygen and moisture entering the organic layer of the OLED display.
Improved Components
The sensitivity of various components leaves OLED devices vulnerable to electrical failures and short circuits. Researchers are experimenting with the use of stable metals like Ag in the cathode to improve upon device lifetime.
New Fabrication Methods
OLED production needs to be highly controlled. This is essential to preventing the introduction of impurities during fabrication. It is also required due to the sensitivity of OLED materials to environmental factors including temperature, moisture, and UV light. Researchers have found that OLED devices fabricated in a new vacuum chamber can achieve a lifetime almost twice that of standard OLEDs.
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OLED Burn-In
As the commercial popularity of OLEDs increased, their advantages over the traditional LED-powered displays became clear.
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How Do Transparent OLEDs Work?
TOLEDs only contain transparent layers, unlike standard OLEDs which include some opaque layers. The transparent layers allow light to pass through the device from all angles but also render parts of the window or display panel opaque when in use.
Read more...Additional Reading
Furukawa, T. et al. (2015) Dual enhancement of electroluminescence efficiency and operational stability by rapid up conversion of triplet excitons in OLEDs. Sci Rep 5. doi.10.1038/srep08429.
Kim, S. et al. (2016) Design of fluorescent blue light-emitting materials based on analyses of chemical structures and their effects, Materials Science and Engineering R Reports, 99. doi.10.1016/j.mser.2015.11.001.
Magnier, L. et al. (2022) Replaced too soon? An exploration of Western European consumers’ replacement of electronic products, Resources, Conservation and Recycling, 185. doi.10.1016/j.resconrec.2022.106448.