A team of researchers from Hong Kong University and the Korea Electrotechnology Research Institute (KERI) have used 3D printing to create nanoscale display pixels made of perovskite.
3D printing of perovskite nanopixels using a nanopipette. Different chemical compositions enable the fabrication of red (R), green (G), and blue (B) triple pixels. Image via KERI
Last year, the same group of scientists used liquid inks and direct ink writing to fabricate display pixels capable of emitting light. Now, turning their attention to perovskites, the researchers believe they can achieve even greater brightness levels and higher resolution displays using a similar deposition-based 3D printing technique.
Dr. Jaeyeon Pyo, a Senior Researcher at KERI and co-author of the study, believes the 3D printing of light-emitting perovskites can also be used in previously impossible applications in the field of security. For example, the study refers to a multilevel encryption system for the anticounterfeiting of currency notes, whereby nanoscale patterning on dollar bills would enable us to determine if a particular note is genuine or not.
Perovskites are a promising choice of material for several optoelectronic applications due to their exceptional structure and extensive tunability. The compounds offer a number of excellent properties such as large optical absorption, long carrier diffusion length, and high carrier mobility, and they emit light in the presence of a voltage. Unfortunately, their use-cases have been limited to 2D systems until now, owing to a lack of 3D production methods.
From prior research, Pyo's team has already demonstrated that emission intensity (brightness) increases in line with the height of a 3D printed nanopixel. Building on this, the most recent study shows that this intensity can be saturated even further by the depth of field of the optical system used to measure the pixels. Interestingly, the saturation can be leveraged to enable more advanced applications using 3D printed perovskites.
Pyo explains, 'Previously, precise control of the height was required for flattening the brightness of the individual 3D printed pixels. Instead, printing the pixels to the height over the saturation point can provide a uniform brightness without delicate individual height control.'
What this means is that information can be stored securely at different heights in a perovskite pixel. Since the difference in heights over the saturation point is visually indistinguishable using ordinary measurement instruments, the data stored at the different heights would only be accessible using a very specific 3D measuring method ' one that only the developers of the pixels would have access to.
In terms of applicability, one of the most immediate uses is high-resolution optical displays, where the 3D printed nanoscale perovskites can be used to filter color in a backlit display device.
Pyo and the rest of the researchers can also see potential applications in identification, authentication, and currency anticounterfeiting. The 3D printed nano pixels could provide multi level encryption with fluorescent patterns that are only visible with UV light, a microscope, and a specialized, one-of-a-kind 3D measurement system. As such, authorities like central banks could verify whether a specific bank note is authentic or not by checking for the nanoscale perovskite patterning.
The research team is now transitioning from passive illumination to electrically-driven lighting with the 3D printed perovskite pixels. Pyo explains, 'Going beyond the passive lighting from photoluminescence, electrically driven lighting shall open up the possibility of actively controllable lighting devices.'
