World’s smallest OLED pixel could transform smart glasses

Physicists at Julius-Maximilians-Universität Würzburg (JMU) have now overcome that barrier. Using specially designed optical antennas, the team has built what they describe as the smallest pixel ever created. The research group, led by Professors Jens Pflaum and Bert Hecht, reported the advance in the journal Science Advances.

A Full HD Display on One Square Millimeter

"With the help of a metallic contact that allows current injection into an organic light-emitting diode while simultaneously amplifying and emitting the generated light, we have created a pixel for orange light on an area measuring just 300 by 300 nanometers. This pixel is just as bright as a conventional OLED pixel with normal dimensions of 5 by 5 micrometers," says Bert Hecht, describing the key finding of the study.

For scale, a nanometer is one millionth of a millimeter. At 300 by 300 nanometers, these pixels are extraordinarily small. In fact, a projector or display with a resolution of 1920 x 1080 pixels could fit within an area of just one square millimeter. Such compact dimensions could allow a display to be built directly into the arms of a pair of glasses, with the projected light directed onto the lenses.

OLED technology relies on multiple ultra thin organic layers positioned between two electrodes. When electricity passes through, electrons and holes recombine inside the active layer. This process excites the organic molecules, which then release energy as light quanta. Because each pixel produces its own light, no separate backlight is required. That design enables deep blacks, vibrant colors, and energy efficient performance for augmented and virtual reality (AR and VR) devices.

Why Shrinking OLED Pixels Is So Difficult

Simply scaling down existing OLED designs does not work at the nanoscale. The Würzburg team found that electrical current does not spread evenly when the structure becomes extremely small. "As with a lightning rod, simply reducing the size of the established OLED concept would cause the currents to emit mainly from the corners of the antenna," says Jens Pflaum, explaining the underlying physics. The gold antenna used in the device is shaped like a cuboid measuring 300 by 300 by 50 nanometers.

"The resulting electric fields would generate such strong forces that the gold atoms becoming mobile would gradually grow into the optically active material," Pflaum continues. These thread like growths, known as filaments, would keep extending until they created a short circuit and destroyed the pixel.

Insulation Layer Prevents Short Circuits

To solve this problem, the researchers introduced a precisely engineered insulating layer above the optical antenna. This layer leaves only a circular opening with a diameter of 200 nanometers at the center. By blocking current from flowing in at the edges and corners, the design ensures stable and reliable operation of the nano light-emitting diode. Under these conditions, filament formation is prevented. "Even the first nanopixels were stable for two weeks under ambient conditions," says Bert Hecht, describing the result.

The team's next goal is to boost efficiency beyond the current level of one percent and extend the color range to cover the full RGB spectrum. Achieving those milestones would clear the path for a new generation of miniature displays "made in Würzburg." In the future, displays and projectors based on this technology could become so compact that they are nearly invisible when integrated into wearable devices, from eyeglass frames to contact lenses.