Development of flat panel displays has been rapidly accelerated by introducing new materials, such as liquid crystal, organic (or plastic) light emitting diodes, and semiconductor light-emitting diodes (LEDs). Among these materials, compound semiconductor LEDs have recently started to be utilized as light emission pixel in commercial displays of ‘The Wall’ by Samsung since 2019, because of excellent physical properties of high quantum efficiency, long term stability, and ease of miniaturization. This tutorial begins with providing a general overview of the materials, fabrication process, and required performances of LEDs for display applications. Then, we mainly focus to the epitaxial growth of GaN-based LEDs, especially, metal–organic vapor phase epitaxy (MOVPE), which is one of the most productive technique for fabricating high performance LEDs. The fundamentals to the MOVPE technique are dealt with explaining the brief development history of GaN-based InGaN LEDs. Doping, heterostructures (i.e. quantum wells), selective growth and epitaxial lateral overgrowth, and nanorod growth are lectured in depth. The recent issues for the miniaturization of LEDs for the micro-LED display applications are discussed. Finally, the strengths of thin film and nanorod LEDs grown by the MOVPE are compared with respect to the performance, fabrication process, and pixelization for future high definition display applications.

This tutorial introduced the various energy storage systems such as lithium-ion battery, redox flow battery and metal-air battery, focusing on their materials and devices. Also, the challenges and prospects of each systems will be discussed in terms of nanomaterials.

This tutorial will cover a wide range of topics, mainly based on crystalline silicon (c-Si) solar cells, from basic principles of solar cells to the state of art solar cell technologies and applications including hydrogen generation. Solar cells are the energy conversion device that converts light energy into electrical energy. To understand the energy conversion process, we should understand 3 important components of solar cells: 1) light source (Sun), 2) active materials, and 3) device structure. And then, we will be ready to figure out 4 important steps of the energy conversion process: light absorption-carrier generation-carrier separation-carrier collection. Also, we will discuss the current status and new challenge of solar cell technologies based on various active materials such as c-Si, organic polymer, and perovskite. At the end of this tutorial, I will also briefly introduce the hydrogen generation process by using solar cells, which is called a photovoltaic-electrochemical (PV-EC) system.

Current cooling technologies mostly rely on vapor compression and fluid-cooled systems. However, they consume ~10% of the global energy and accelerate the depletion of fossil fuels. Moreover, CO2 emissions from space cooling have more than tripled between 1990 and 2018 to reach 1130 million tons, and other environmental issues such as ozone depletion and air pollution are worsening. Radiative cooling, which is how the Earth cools itself, is a passive thermal management strategy. Using the spectral overlap between the peak in Planck’s blackbody radiation at ~300 K and the atmospheric transmission window between 8 and 13 um, unwanted heat can be emitted to outer space without energy consumption or pollutant emission. Recently, reported passive radiative coolers have demonstrated subambient cooling during the daytime. Those coolers are attached on exterior materials, roof, or human skin to draw heat from the periphery through conduction and convection. In this tutorial, we introduce design, fabrication, and characterization of passive radiative cooling structures. Some of recent applications and remaining issues are also discussed.