Production of Nanoparticle & Fabrication of New Materials by Controlling Multifunctional Structure

1.  Long-term stable stacked CsPbBr3 quantum dot films for highly efficient white light generation in LEDs

In recent years, how to express colors more vividly and naturally has been raised as a major issue among researchers in the field of display. Producing colors is decided according to the light emitting spectrum of each light emitting diodes (LEDs) presenting red, green, blue. If the light emitting spectrum has narrow full width at half maximum (FWHM), the purity of light emitting material will be improved which can produce more vivid images close to the nature’s colors when applying to display.

In recent years, semiconducting metal halide perovskite quantum dots (QD) have become attractive for use in many applications due to their outstanding electrical and optical properties.

Particularly, metal halide perovskite materials are suitable for application in white LEDs (WLEDs) and displays due to their wide color tenability (from 400 to 800 nm) with control of the bandgap, narrow full width at half maximum (FWHM) of the emission band (around 20 nm), and high photoluminescence quantum yields (PLQYs), as well as their low temperature synthesis process and low cost compared with inorganic luminescence materials such as phosphor.

The research team proposed an efficient and simple method to improve the stability of CsPbBr₃ perovskite QDs and developed highly efficient white LED. They successfully prepared fully inorganic CsPbBr₃ perovskite QD films as the green-emitting luminescence material for white light generation. High quality

CsPbBr₃ perovskite QD films with a FWHM of 21 nm as well as a high absolute PLQY of 37.2% were obtained. This demonstrates that the prepared film is a potential candidate with highly desirable characteristics for both lamp and display technology. The highly efficient CsPbBr₃ perovskite QD film with Sr₂Si₅N₈ : Eu²⁺ phosphor is applied to an InGaN blue LED chip, which demonstrates the luminous efficacy of 67.93 lm W⁻¹ under a forward-bias current of 20 mA. Finally, the bright CsPbBr₃ perovskite QD film can be a new material in a wide range of applications such as in optoelectronic devices.

This article was published in 2016’s November edition of the world renowned scientific journal, Nanoscale.

2.  Mesoporous Ni–Fe oxide multi-composite hollow nanocages for efficient electrocatalytic water oxidation reactions

In recent years, because of depleting fossil fuels and environmental concerns, eco-friendly renewable energy conversion technologies based on sustainable energy sources have attracted tremendous attention, such as water splitting, CO₂ conversion and fuel cells.

Among them, Hydrogen (H₂) fuel produced via the water splitting process using electrocatalytic and photocatalytic methods has been a widely considered candidate to solve energy and environmental problems due to its carbon neutral, abundant, and sustainable energy sources. As a clean and sustainable technique, electrochemical water splitting could supply a large-scale hydrogen source. The anode reaction, namely the oxygen evolution reaction (OER) is one of the main steps in electrochemical water splitting.

However, the OER limits the whole water splitting reaction due to (1) issue with substituting metal based oxide materials (2) short lifetime. In order to resolve these problems, extensive research activities have focused on multi-composite transition metal (Ni, Fe, Mn, Co, etc.) oxides and hydroxides, perovskites, and carbon-based materials as candidate catalysts for water splitting.

Using a simple two-step hydrothermal method and calcination process, SKKU research team demonstrated the synthesis of mesoporous NiO/NiFe₂O₄ multi-composite hollow NCs via Ni₃[Fe(CN)₆]₂ PBA nanocube precursors. Such mesoporous NiO/NiFe₂O₄ multi-composite hollow NCs after 1h of calcination in air at 500°C demonstrate enhanced OER activity with a remarkably low Tafel slope (58.5 mV dec^-1), a low over potential of 303 mV at a current density of 10 mA cm², and excellent cycling stability in alkaline electrolytes, superior to most reported hierarchical structures of binary transition metal oxides/hydroxides.

Moreover, further such synthetic approaches can be carried out to explore the potential application of mesoporous and hollow binary transition metal oxides for advanced performance energy conversion and storage.

This article was published in the world renowned research paper, Journal of Materials Chemistry A on Feb. 28^th.