Power consumption - Page 12

As OLED is an emissive display technology, an OLED pixel only draws power when it is used - and the brighter it is, the more power it consumers. This of course means that adopting a dark UI is better for your device's power life.

During Google's recent Android Dev Summit, the company detailed the power consumption of the OLED display used in its 2016 Pixel smartphone (an SDC FHD 5" AMOLED). As you can see in the image above, the power consumption is different for each color (with red being the most efficient color and blue the least efficient). Surprisingly the display draws quite a bit of power even when completely black.

The Washington Post's Geoffrey A. Fowler posted an interesting article in which he details how new smartphones are under-performing older ones in terms of battery life. Geoffrey puts 12 smartphones to the same test, and checks which ones dies first.

It is interesting that the new 2018 smartphones under performs similar smartphones released in 2017. Geoffrey's conclusion is that new display technology - high resolution OLEDs, are the culprit. The main reasoning behind that is that the iPhone XR (with its LCD display) performs better than the iPhone XS, even though the XR has a smaller display.

Researchers from Korea's KAIST research institute developed a high-efficiency OLED architecture that uses external scattering medium to achieve an EQE greater than 50%.

Such high EQE was only demonstrated before using complex internal nanostructures or by employing a micro-lens array, but these solutions are complicated to produce and can hinder the OLEDs flexibility and planar structure. The researchers say that their scattering approach maintains the planar geometry , results in flexible OLEDs and can be easily scaled to enable low cost production.

Kyulux announced that it has developed a new blue Hyperfluoresence/TADF OLED emitter. Kyulux managed to extend the lifetime of the material and reached 100 hours at LT95 (@ 750 cd/m²) while maintaining a high EQE of 26% - 22% at 1,000 cd/m². The emission wavelength is 470 nm.

Kyulux says that its blue Hyperfluorescence emitter is the world’s top performing material at the moment. Kyulux now aims to work together with OLED panel makers to improve the systems further by optimizing the device structure and the rest of the OLED stack in pilot production lines.

Researchers from Japan's Kyushu University developed a new technology called singlet fission that enables near-infrared OLED materials to surpass the 100% limit for exciton production - or achieve an internal quantum efficiency (IQE) of over 100%. Singlet fission was already used in OPVs, but this is the first time that it was demonstrated with OLEDs.

Achieving over 100% is possible because at 100% IQE all charges form excitons that emit light. The new technique splits the energy from a high-energy excitons into two low level ones. The new OLED emitter materials use molecules in which singlets can transfer half of their energy to neighboring molecules while keeping half of the energy for themselves - each singlet creates two triplets. The emitters emit near-infrared light.

Researchers from the Universitat Autònoma de Barcelona and TU-Dresden have demonstrated that ultra-stable film formation can be used to to improve the performance of OLED devices.

The researchers grew (using evaporation) the organic materials as ultrastable glasses - a growth condition that allows for thermodynamically most stable amorphous solids. Testing four different phosphorescent emitters, the researchers show significant (over 15%) increases of efficiency and operational stability. The researchers also say that these growing conditions are expected to even be more useful for TADF materials.

Researchers from the University of Michigan developed a new method to cost-effectively extra more light out of OLED displays. To achieve that, the researchers used a Sub-Electrode Micro-Lens Array (SEMLA) placed between the bottom transparent ITO electrode and the glass substrate. Testing on green and white PHOLEDs, the researchers say the SEMLA enhanced light output by a factor of 2.8 (green) and 3.1 (white) compared to a similar device without the lens array.

The researcher say that such an array can be fully transparent and has no impact on the sharpness of the display. The hexagonal array of 10 um lenses can be fabricated using conventional photolithography methods which are quite cost effective. Such a micro-lens array does not change the actual OLED production process.

US-based high-index material maker Pixelligent Technologies announced it raised $7.6 million in a new funding round that will help the company to further drive its product commercialization and accelerate global customer adoption.

This round was led by the Abell Foundation, and included other Baltimore-based investors. This found also included strategic investments from Kateeva and Japan-based advanced material producer Tokyo Ohka Kogyo.

Researchers from Taiwan's National Tsing Hua University (NTHU) developed a new TADF OLED emitter material that maintains its high efficiency at high luminance. The researchers say that this new material is the world's most efficient TADF emitter at high brightness.

The new material is made from two diboron-based molecules, CzDBA and tBuCzDBA. These donoracceptordonor (DAD) type and rod-like compounds concurrently generate TADF with a photoluminescence quantum yield of ~100% and an 84% horizontal dipole ratio in the thin film. The researchers synthesized a green TADF emitter that achieved a a high external quantum efficiency of about 37.8% with an efficiency roll-off of only 0.3% at 1,000 cd/m².

Researchers from the Max Planck Institute for Polymer Research developed a way to improve the current injection from the positive electrode in OLED panels. To enhance the hole injection the researchers covered the positive electrode with an ultrathin layer of an organic semiconductor as a spacer layer between the electrode and the light-emitting organic semiconductor.

Current flowing from an electrode (left) to the organic material (right) via a thin molecular layer (center)

The researchers say that they did not actually expect that adding an extra layer and eliminating the physical contact between the electrode and the emitting layer actually improves the electrical contact.