High-definition organic LED microdisplays with reduced electrical crosstalk could enhance VR and AR experiences

The rapid advancement of the electronics industry is opening new possibilities for the development of increasingly advanced device components, including displays. Many of the most widely used and highly performing displays developed to date are based on organic light-emitting diodes (OLED), devices based on organic materials that emit light when an electric current is applied to them.

Compared to conventional displays based on liquid crystals, OLED-based displays do not require a backlight and can thus consume significantly less power. Despite their energy-efficiency, the performance of OLEDs, in terms of image quality and color rendition, has been found to decline as the density of pixels increases, due to undesired interactions between adjacent pixels referred to as electrical crosstalk.

Electronics engineers have devised various strategies to overcome this limitation, most of which entail increasing the thickness of an OLED component known as the hole transport layer (HTL), which facilitates the movement of holes in the devices. Yet these strategies can compromise a display’s energy-efficiency, due to increases in the devices’ driving voltages.

Researchers at Hanyang University, Yonsei University and Sogang University in South Korea recently introduced an alternative approach to reduce electrical crosstalk between pixels, which could in turn boost the performance and efficiency of OLED displays.

Their proposed solution, presented in a paper published in Nature Electronics, involves the use of a silicon-integrated small-molecule hole transport layer (SI-HTL) patterned using microlithography, a well-established technique to precisely structure materials on a microscopic scale.

“High-density displays are required for the development of virtual and augmented reality devices,” Hyukmin Kweon, Seonkwon Kim and their colleagues wrote in their paper. “However, increasing the pixel resolution can lead to higher electrical pixel crosstalk, primarily due to a shared hole transport layer. We show that a silicone-integrated small-molecule hole transport layer can be patterned at the wafer scale with microlithography to mitigate electrical pixel crosstalk.”

Using microlithography, the researchers created the SI-HTL layer and integrated it in OLEDs. They then created micro-patterned OLED arrays and tested their performance in a series of tests.

Notably, they found that the hole transport layer they created exhibited an improved performance. The prototype display they created was found to enable remarkable pixel resolutions, while also retaining a good energy efficiency.

“With this approach, we create high-fidelity micro-pattern arrays with a resolution of up to 10,062 pixels per inch on a six-inch wafer,” wrote Kweon, Kim and their colleagues. “The silicone-integrated small-molecule hole transport layer can effectively modulate charge balance within the emission layers, improving the luminance characteristics of organic light-emitting diodes.

“We also show that organic light-emitting diodes integrated with micro-patterned silicone-integrated small-molecule hole transport layers have a reduced electrical pixel crosstalk compared with organic light-emitting diodes with a typical hole transport layer.”

This recent study by Kweon, Kim and their colleagues opens new possibilities for the development of high-definition OLED displays that also exhibit excellent energy-efficiencies. These displays could be integrated into a wide range of electronic devices, including virtual reality (VR) or augmented reality (AR) headsets, smart glasses, wearable technologies, smart phones, and many other electronics.

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