Photophysical properties of organic-inorganic metal halide perovskites as ionic crystals are reviewed, focusing on the defect tolerant nature in electronic structures and high open-circuit voltage (V_oc) performance of photovoltaic cells in relation to suppression of trap-assisted charge recombination at interfaces of perovskite polycrystals. V_oc is enhanced by passivating interfacial defects with ultrathin layers of inorganic and organic compounds. Inorganic nanosheets of Mxene work as passivators, simultaneously functioning as an electron transport layer for planar photovoltaic devices. Thermally stable all-inorganic perovskite devices that enable high V_oc over 1.4 V have been developed with CsPbI₂Br having a junction with an amorphous SnO₂ layer as a passivator. The high V_oc function enables the devices to operate in low illuminance indoor light for IoT applications. The device outputs more than 1.1 V even under 200 lx of LED illumination with the high conversion efficiency of 34 %.

Organic-inorganic hybrid perovskite (OIHP)-type compounds have recently attracted great interest in the field of solar cells and related semiconductor research due to their excellent photoelectric conversion characteristics. OIHP-type compounds consist of organic and inorganic components and have both properties. Recently, we focused on this feature and succeeded in developing chirality-designable semiconductors with strong spin-orbit interaction and noncentrosymmetric ferromagnets by inserting chiral molecules into layered inorganic frameworks consisting of heavy or magnetic atoms. Interestingly, in these materials, we have found that the noncentrosymmetry, which is introduced via chiral molecules, affects the electronic states of inorganic frameworks. In this review, we show a circular photogalvanic effect and nonreciprocal directional dichroism as examples of noncentrosymmetry-induced phenomena realized in the chiral molecule-introduced layered OIHPs.

Power devices are utilized to convert the voltage and frequency of electric power in various fields, including solar power generation, energy storage, wind power generation and electric vehicles. Silicon carbide (SiC) crystals have superior material properties such as a high breakdown field, while SiC power devices exhibit low-loss performance, especially in high-voltage applications. Although the practical use of SiC power devices has been started in various applications, improving the quality, reducing the production cost and enlarging the diameter of SiC wafers are expected to massively expand the production scale and applications of SiC power devices. In this paper, we introduce recent advances in the SiC crystal growth technologies, toward realizing high-power devices and expanding their applicable scopes.

When a crystal becomes thin at the atomic level, peculiar phenomena discretely depending on its layer-numbers (n) start to appear. Multilayer WTe2 is one such example, exhibiting unique ferroelectricity and non-linear transport properties related to the antiphase stacking and Berry-curvature dipole. Here we investigate the electronic band dispersions of multilayer WTe2 (2-5 layers), by performing laser-based micro-focused angle-resolved photoelectron spectroscopy on exfoliated-flakes strictly sorted by n. We observed the insulator-semimetal transition occurring between 2 and 3-layers, as well as the 30-70 meV spin-splitting of valence bands manifesting in even n as a signature of stronger structural asymmetry. Our results fully demonstrate the possibility of a large energy-scale band and spin manipulation through the finite n stacking procedure.

Triboelectric energy harvesters are expected as a power source for self-powered wearable devices since they can generate electricity from the low-frequency motion of the human body. For wearable device applications, high stretchability is required to follow the dynamic three-dimensional surface of the human body. We have realized a stretchable sheet-shaped triboelectric energy harvester with a high output and elasticity. The high output has been achieved by a fluorine plasma treatment for the surface of the dielectric layer. We demonstrate a self-powered signal transmitter and LED-embedded gloves, exploiting the characteristics of the harvester. Furthermore, we propose a highly efficient intermittent operation circuit to drive electronic devices, using a small amount of power generated by the harvester. Our study can contribute to solve the problem of power source limitations in wearable electronics.

DC distribution systems that combine renewable energy sources and storage batteries have attracted attention with the expanding introduction of renewable energy sources and advances in semiconductor and energy storage technology. It is economically and environmentally effective as the next generation power supply system. We also expect to utilize measures for power resilience and Business Continuity Planning (BCP) using DC technology.

This paper introduces recent trends in DC technology and details of the DC distribution demonstration system.