Team Uses Plasmonics to Improve QD LED Efficiency

Researchers have designed metallic nanostructure substrates that can lower production cost while improving the efficiency of quantum dot (QD) LEDs. For its design, the team exploited the phenomenon of so-called surface plasmonic resonances that can occur when nanoscale metallic structures are exposed to light.

This is a spectrum showing different fluorescence with and without a metallic nanostructure. Courtesy of KAIST.

To enhance the fluorescence intensity of the QD LEDs, the team from Korea Advanced Institute of Science and Technology (KAIST) used different metallic nanostructures for each QD LED. Silver nanodisks were used for red QDs and aluminum nanodisks for green QDs. The team used systematic finite-difference time domain simulations of excitation, spontaneous emission and quantum efficiency enhancement to design the nanodisk arrays.

The researchers calculated results of the overall photoluminescence enhancement factor in a substrate 500 by 500 µm² in size. They reported a 2.37-fold improvement for the aluminum-nanodisk green QD structure and a 2.82-fold improvement for the silver-nanodisk red QD structure.

Experimental results showed 2.26-fold and 2.66-fold enhancements for the aluminum nanodisk and silver nanodisk structures, respectively.

The researchers believe that designing adequate shapes and sizes of metallic nanostructures and ensuring that the emission peak of the fluorophore is in resonance with the localized surface plasmonic (LSP) peak are critical in order to achieve enhancement.

QD LEDs possess very small semiconductor light sources and are considered to be a promising technology for high-performance full-color displays. However, it is expensive to manufacture displays with QD LEDs only. Enhancing the fluorescence of colloidal QD LEDs could be significant because of the large loss of QDs and their quantum yields during fabrication processes and could improve cost-effectiveness.

Professor Yong-Hoon Cho said, “Implementing metallic nanostructures into QD LEDs in a proper manner can reduce the quantity of the QDs required for the system, leading to lower unit prices.”

Based on results, the team believes that future studies of plasmonic enhancement of various light-emitting materials could be useful.

The research was published in Small (doi: 10.1002/smll.201701805).