In the race to create displays that are ever-brighter and more detailed, researchers have hit a new milestone. A new OLED architecture, based on a technology originally designed for ultra-thin solar panels, can now pack a hefty 10,000 pixels per inch (ppi), achieving a level of resolution that far surpasses that currently found in cutting-edge smartphones and TVs.
The result of a collaboration between researchers at Stanford University and Samsung's Advanced Institute of Technology (SAIT), the technology taps a so-called 'metaphotonic' material that can control light in a new way.
Commercial OLED televisions currently have a pixel density of about 100 to 200ppi, while the resolution of new smartphones is around 400 to 500ppi. But as well as setting new pixel density records, new OLED displays built on top of the metaphotonic material could be brighter and show better colour accuracy, while costing less to produce.
Organic light-emitting diode (OLED) displays rely on tiny organic compounds that emit light when stimulated by an electric current. Pixels on the screen are composed of stacks of emitters, which each produce either red, green, or blue light. By controlling the cluster of emitting diodes, therefore, it's possible to create visible colours for the human eye to see on the display.
In OLED screens for smartphones, each emitter in the display usually produces one of the primary colours, and is then applied against a metal sheet that filters out the correct diodes in order to control the composition of each pixel. Television displays, on the other hand, use white OLEDs, which emit all three primary colours at once. Filters are then placed over the emitters to determine the final colour of the diode, in order to produce the correct pixel.
Both methods have their shortcomings: thick metal sheets applied to coloured diodes limit the scale of the display, while colour filters applied to white emitters are more power-hungry.
With these limitations in mind, SAIT scientist Won-Jae Joo found himself, a few years ago, attending a presentation by Stanford graduate student Majid Esfandyarpour on an apparently unrelated topic: solar panel designs.
Esfandyarpour was exploring the possibility of creating new materials, called 'metamaterials', to manipulate light in the design of ultra-thin solar cells. Joo immediately saw how the idea could be applied to OLED displays, and soon a partnership was established between Samsung and Stanford's research team.
At the heart of the new OLED architecture that the researchers have now unveiled is a base layer called an 'optical metasurface', which is made of reflective metal and scattered with microscopic pillars that together "wrinkle" the surface of the layer.
These pillars, thanks to their different sizes and arrangements, can manipulate the different wavelengths that are specific to red, blue and green lights. When white light falls onto the pillars, they can in turn "allocate" a specific primary colour to the diodes opposite them. In this way, different pillar patterns on the metasurface define different colours. The researchers compared the process to sound resonating off the cavities of a musical instrument.
The researchers have successfully produced miniature proof-of-concept pixels as part of lab tests using the new method, with promising results. Compared to the OLEDs used in televisions, the metaphotonic material allows for higher colour purity and a twofold increase in luminescence efficiency, meaning that the screen is brighter and uses less energy.
VR and AR application
Displays could get a huge quality boost, therefore, if OLED displays based on the new architecture proposed by Stanford's and Samsung's researchers go into commercial production. But TV and smartphone manufacturers won't be the only players to benefit from the extra pixel density.
"For near-eye microdisplays -- for example, in virtual and augmented reality applications -- the required pixel density runs to several thousand pixels per inch and cannot be met by present display technologies," said the researchers. "An ultrahigh density of 10,000 pixels per inch readily meets the requirements for the next-generation microdisplays that can be fabricated on glasses or contact lenses."
For years, VR headset manufacturers have been trying to refine the quality of visuals to deliver on the promise of "immersive experiences". With current displays, however, it can't be said that users consistently get a convincing experience in virtual worlds.
VR headsets sit centimeters away from the wearer's eyes, meaning that high resolutions are key to creating realistic visuals. The researchers are, therefore, confident that metasurfaces will provide unprecedented levels of detail that could change the game for the industry.
With no time to lose, Samsung is now drafting the next steps to integrate the meta-OLED proof-of-concept into a full-size display.