Scientists advance affordable, sustainable solution for flat screens and wearable technology

A research team led by Lawrence Berkeley National Laboratory (Berkeley Lab) has developed a “supramolecular ink,” a new technology for use in OLED (organic light-emitting diode) displays or other electronic devices. Made from inexpensive, Earth-abundant elements rather than expensive and scarce metals, supramolecular ink could enable more affordable and environmentally sustainable flat screen displays and electronic devices.

“By replacing precious metals with Earth-abundant materials, our supramolecular ink technology could be a game-changer for the OLED display industry,” said principal investigator Peidong Yang, senior faculty scientist in the Division of Science. of Materials at Berkeley Laboratory and professor of chemistry and materials science. and engineering at UC Berkeley.

“What’s even more exciting is that the technology could also extend its reach to printable organic films for manufacturing wearable devices, as well as luminescent art and sculpture,” he added.

If you have a relatively new smartphone or flat-screen TV, there’s a good chance it has an OLED display. OLEDs are expanding rapidly in the display market because they are lighter, thinner, use less power and have better image quality than other flat panel technologies.

This is because OLEDs contain small organic molecules that emit light directly, eliminating the need for the additional backlight layer found in a liquid crystal display (LCD). However, OLEDs can include rare and expensive metals such as iridium.

But with the new material, which the Berkeley Lab team described in a study published in the magazine Science—Electronic display manufacturers could adopt a cheaper manufacturing process that also requires much less energy than conventional methods.

The new material consists of powders containing hafnium (Hf) and zirconium (Zr) that can be mixed in solution at low temperatures (from room temperature to about 176 degrees Fahrenheit (80 degrees Celsius)) to form a semiconducting “ink.”

Small molecular “building block” structures within the ink self-assemble in solution, a process researchers call supramolecular assembly. “Our approach can be compared to building with LEGO blocks,” said Cheng Zhu, a co-author of the paper and a Ph.D. candidate in materials science and engineering at UC Berkeley.

These supramolecular structures allow the material to achieve stable and high-purity synthesis at low temperatures, Zhu explained. He developed the material while working as a research affiliate in Berkeley Lab’s Materials Sciences Division and a graduate student researcher in the Peidong Yang group at Berkeley Lab and UC Berkeley.

Spectroscopy experiments at UC Berkeley revealed that the supramolecular ink compounds are highly efficient emitters of blue and green light, two indicators of the material’s potential application as an energy-efficient OLED emitter in electronic displays and 3D printing.

Subsequent optical experiments revealed that supramolecular ink compounds that emit blue and green exhibit what scientists call quantum efficiency close to unity. “This demonstrates its exceptional ability to convert almost all of the absorbed light into visible light during the emission process,” Zhu explained.

To demonstrate the color and luminescence tunability of the supramolecular ink in an OLED emitter device, Berkeley Lab researchers fabricated a prototype thin-film display from the composite ink. This “alphabet movie” illustrates the application of supramolecular ink in the creation of quick-change programmable displays. Credit: Peidong Yang and Cheng Zhu/Berkeley Lab. Science.

To demonstrate the material’s color and luminescence tunability as an OLED emitter, the researchers fabricated a prototype thin-film display from the composite ink. With an interesting result, they discovered that the material is suitable for programmable electronic displays.

“The alphabet film serves as a compelling example illustrating the application of supramolecular ink-like emissive thin films in creating fast-switching displays,” Zhu said.

Additional experiments at UC Berkeley demonstrated that the supramolecular ink is also compatible with 3D printing technologies, such as for designing decorative OLED lighting.

Zhu added that manufacturers could also use the supramolecular ink to make wearable devices or high-tech clothing that illuminate for safety in low-light conditions, or wearable devices that display information through light-emitting supramolecular structures.

The supramolecular ink is another demonstration by the Peidong Yang laboratory of new sustainable materials that could enable cost-effective and energy-efficient semiconductor manufacturing. Last year, Yang and his team reported a new “multi-element ink,” the first “high-entropy” semiconductor that can be processed at low temperature or at room temperature.

With their demonstrated stability and lifetime, supramolecular ink compounds could also help in the commercial advancement of ionic halide perovskites, a thin-film solar material that the display industry has been eyeing for decades. With their low-temperature synthesis in solution, ionic halide perovskites could enable cheaper manufacturing processes for display manufacturing. But high-performance halide perovskites contain the element lead, which is of concern for the environment and public health.

In contrast, the new supramolecular ink, which belongs to the ionic halide perovskite family, offers a lead-free formulation without compromising performance.

Now that they have successfully demonstrated the potential of the supramolecular ink in OLED thin films and 3D-printable electronic devices, the researchers are exploring the material’s electroluminescent potential. “This involves focused and specialized research on how well our materials can emit light through electrical excitation,” Zhu said. “This step is essential to understand the full potential of our material to create efficient light-emitting devices.”

Other authors of the study include Jianbo Jin (co-first author), Zhen Wang, Zhenpeng Xu, Maria C. Folgueras, Yuxin Jiang, Can B. Uzundal, Han KD Le, Feng Wang, and Xiaoyu (Rayne) Zheng.