Solar cells are devices for the direct conversion of solar energy into electricity that is the sustainable and ultimate energy source. Currently, the market share by Si-solar cells is as high as 90% and thin-film type cells (e.g., a-Si, CdTe, and CIGS cells) have been expanding its production capacity, replacing Si-cells. However, a high manufacturing cost and still long payback period of them are major hurdles as a ubiquitous energy sources.

Since the organometal trihalide with pervskite crystalline structure was firstly reported in 2009, extensive efforts have been made to enhance its power conversion efficiency and stability. It was unprecedented improvement in solar cells history that the power conversion efficiency reached ~22% in less than 10 years. It is the power conversion efficiency that is comparable to Si solar cells. Our research on perovskite solar cells aims at designing and synthesizing a novel molecular ligands, constituting a robust perovskite structure, which will allow a high efficiency and stability in field conditions.

Li-ion battery (LIB) has been successfully implemented in industry as an energy storage system for electric vehicles and portable electronic devices. Our goal is to ahieve LIB with higher capacity and rate-capability without any safety concern. For this purpose, we develop a novel synthesis route and design microstructure of active materials for cathode and anode based on a deep understanding of crystallography and solid-state chemistry, combined with electrochemical techniques. Our research scope currently covers LiFePO4 and Ni-rich layered cathode materials that are commercially being used, including Li-and Mn-rich cathode materials for next-generaition LIBs.

Semiconductor nanoparticles are often called as "quantum dots" (QDs) because a strong quantum confinement of electron-hole pair occurs when semiconductors are fabricated into nanometer scale. The intrinsic properties such as band gap energy and carriers' lifetime can be tuned simply by varying theirs sizes. Thanks to such unique properties in nanoscale, QDs are widely used in a variety of research fileds. For example, a bright fluoresence even in high concentration with great luminescence stability enables in-situ bioimaging, which means in-situ visualizaiton of a tiny cancer cells is possible during surgical operation. For an energy harvesting, QDs gives us amzaing tools to improve power conversion efficiency that cannot be achieved in thin-film solar cells, that are carrier multiplication and hot-carrier injection. In electronics industry, QDs are emploed as a fluorescent materials for TV, which has been becoming a real commercial sucess. Our research on QDs covers from fundametals (fast carrier dynamics, surface properties and others) to application studies as a display. One of our current interests is on InP/Zn(S,Se) (group III-V) QDs with a high PL quantum yield, by compositional engineering across the single QD.