Copper chalcopyrite compound CuGaSe₂ (CGS) is a promising material for its application to photoelectrochemical (PEC) water splitting into H₂. In this article, we firstly review operating principle and measurement methods of PEC water splitting by using semiconductor-based electrodes. Then, studies on PEC H₂ evolution over the CGS-based photocathodes were reviewed. For realizing efficient PEC H₂ evolution, surface modifications with a CdS layer and nanoparticulate Pt catalytis were indispensable. Moreover, insertion of a Cu-deficient layer and its further modification with Rb are found to be effective for improvements of PEC properties. Since present photoelectrodes have poor resistances under an operating bias, further functionalization is required to improve the long-term durability for practical uses.

Effective solar energy utilization is extremely important to realize carbon neutral society. Therefore, a power generation technology that can utilize full spectrum of sunlight is required. A thermophotovoltaics (TPV) based solar energy conversion, called as solar-TPV, potentially enables the use of the full spectrum of sunlight and high-efficiency conversion with single-junction cells. Here, we introduce a technology of controlling thermal radiation spectrum which is important to achieve high-efficiency solar-TPV and an experimental result using designed solar-TPV system. In addition, we show a perspective of advanced solar energy utilization by solar-TPV.

To meet the increasing needs to automate the cell culture handling such as separation, purification and collection, we have examined a scheme to use photo-responsive polymer materials as culture substrates. We developed a polymer, which becomes water-dissoluble in sharp response to light irradiation and demonstrated photo-selective cell detachment and collection from the polymer-coated substrate. Also selective cell killing and cutting of cell monolayer was implemented by using the polymer material, which generates acid/heat upon light irradiation. Some of these technologies were applied to the purification of undifferentiated cells and the sectioning of cell monolayer in the maintenance culture of human iPS cells.

Neurons in complex networks communicate with each other through synaptic connections. Molecular dynamics at synaptic terminals in neurons is essential for synaptic plasticity and subsequent modulation of cellular functions in neuronal networks. For realizing artificial control of living neurons, we propose and demonstrate laser-induced perturbation into molecular dynamics in neuronal cells. The optical trapping of cellular molecules such as synaptic vesicles or neurotransmitter receptors labeled with quantum-dots is evaluated by fluorescence analysis. Moreover, we apply femtosecond laser-induced stimulation to evaluate the spatiotemporal activity patterns in cultured neuronal networks. These methods have the potential to modulate synaptic transmission of a particular neuron in neuronal networks without any drugs and genes.

With significant improvements in computer performance and computational techniques, it has become possible to construct a database by performing systematic and exhaustive first-principles calculations on a large number of materials. This computational materials database is now used not only to reference the results of calculations on individual materials, but also to screen materials and as a data set for machine learning. In this paper, we introduce the usefulness of computational material databases and existing databases, as well as the oxide database we have constructed and its application examples.