Noboru Taguchi

Wide-bandgap chalcogenide photovoltaics offer strong potential for tandem solar cells and solar-driven hydrogen generation via water splitting, yet their performance remains limited by persistent interfacial and bulk defects. Here, we demonstrate enhanced efficiency in 1.7–electron volt CuGaSe ₂ thin-film solar cells through aluminum (Al) alloying and rubidium (Rb) incorporation. The Al- and Rb-modified CuGaSe ₂ absorber exhibits fundamentally distinct interfacial chemistry, structural properties, and metastable defect behavior compared with conventional narrow-bandgap Cu (In,Ga)Se ₂ solar cells. Moreover, we demonstrate that introducing a steep Al concentration gradient to engineer a back-surface electric field is a highly effective means of boosting device performance, even at an Al content of approximately 1 atomic % or less. By integrating these strategies, we achieve a higher open-circuit voltage without compromising photovoltaic efficiency, establishing a performance benchmark for wide-bandgap (1.65 to 1.75 electron volts) chalcogenides. These findings highlight the unique characteristics of wide-bandgap chalcopyrites and suggest a promising pathway toward next-generation, high-efficiency photovoltaic technologies.

All-solid-state (ASS) lithium-sulfur batteries are promising power sources with the potential for high capacity and safety. Lithium metal polysulfide cathodes can address issues arising from the low electronic conductivity of Li2S and S. This study synthesized lithium vanadium polysulfides (Lix VSy ) by the mechanochemical treatment of Li2S and V2S3. The Lix VSy system contains nanocomposites of Li2S and LiVS2 in an amorphous matrix; lithiation and delithiation occur in both Li2S and LiVS2 during charging and discharging. LiVS2 enhances the electronic conductivity of Lix VSy (~10-1-10-2 S cm-1) and the reversibility of charge-discharge reactions because of its high electronic conductivity and layered structure. Therefore, ASS batteries with Lix VSy show high capacity (~650 mAh g-1), even without conductive additives. Here, ASS full cells with high loading assembled using a composite cathode comprising Li8VS5.5 and a solid electrolyte in a 80:20 (wt.%) ratio (33 mg cm-2) and a composite Si anode (10.4 mg cm-2) exhibited a high areal capacity of 15 mAh cm-2, resulting in calculation of high energy densities of 853 Wh L-1 and 515 Wh kg-1 when assuming the cells were enlarged and stacked. This study is expected to expedite research on the development of high-performance ASS batteries.

The lithiation mechanism of electrode materials is important for understanding the basic reactions in Li-ion batteries. In particular, zero-strain materials have garnered interest owing to their stable charge–discharge performances. In this study, we investigated the atomistic phase transition mechanism of spinel Li4Ti5O12, a well-known zero-strain material, using high-resolution transmission electron microscopy. A single-crystalline Li4Ti5O12 (100) specimen was prepared and observed in situ at a lattice resolution under electron-beam-assisted lithiation. The lattice fringes originating from the Li plane of the spinel crystal were anisotropically altered during phase transition, suggesting the asymmetrical site shifting of Li atoms during lithiation. This spontaneous symmetry-breaking mechanism for the phase transition is considered essential for the lithiation of spinel lattice.

The lithiation mechanism of electrode materials is important for understanding the basic reactions in Li-ion batteries. In particular, zero-strain materials have garnered interest owing to their stable charge–discharge performances. In this study, we investigated the atomistic phase transition mechanism of spinel Li4Ti5O12, a well-known zero-strain material, using high-resolution transmission electron microscopy. A single-crystalline Li4Ti5O12 (100) specimen was prepared and observed in situ at a lattice resolution under electron beam-assisted lithiation. The lattice fringes originating from the Li plane of the spinel crystal were anisotropically altered during phase transition, suggesting the asymmetrical site shifting of Li atoms during lithiation. This spontaneous symmetry-breaking mechanism for the phase transition is considered essential for the lithiation of the spinel lattice.

We successfully prepared an Fe- and Li-containing polysulfide positive electrode material (Li₈FeS₅–Li₂FeS₂ composite) that shows a high specific capacity (>500 mA h g⁻¹) with improved rate capability in all-solid-state cells.

We report the magnetic and spin frustration properties of Ag-based honeycomb layered tellurates with magnetic honeycomb slabs separated by Ag bilayers.

High-entropy alloys (HEAs) have attracted considerable attention to improve performance of various electrocatalyst materials. A comprehensive understanding of the relationship between surface atomic-level structures and catalytic properties is essential to boost the development of novel catalysts. In this study, we propose an experimental study platform that enables the vacuum synthesis of atomic-level-controlled single-crystal high-entropy alloy surfaces and evaluates their catalytic properties. The platform provides essential information that is crucial for the microstructural fundamentals of electrocatalysis, i.e., the detailed relationship between multi-component alloy surface microstructures and their catalytic properties. Nanometre-thick epitaxially stacking layers of Pt and equi-atomic-ratio Cr-Mn-Fe-Co-Ni, the so-called Cantor alloy, were synthesised on low-index single-crystal Pt substrates (Pt/Cr-Mn-Fe-Co-Ni/Pt(hkl)) as a Pt-based single-crystal alloy surface model for oxygen reduction reaction (ORR) electrocatalysis. The usefulness of the platform was demonstrated by showing the outperforming oxygen reduction reaction properties of high-entropy alloy surfaces when compared to Pt-Co binary surfaces.

Invited for this month's cover picture is the work of Dr. Kataoka, Dr. Taguchi, Dr. Tada and Dr. Takeichi at AIST and Dr. Machida at QST. The cover picture shows that the charge‐discharge cycle characteristics have been improved by reducing the particles size of the layered compound Na_2/3Mn_2/3Ni_1/3O₂ to the several nm level. Read the full text of the Research Article at 10.1002/batt.202200462.