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1. A Broadband Light‐Trapping Nanostructure for InGaP/GaAs Dual‐Junction Solar Cells Using Nanosphere Lithography‐Assisted Chemical Etching

   https://doi.org/10.1002/solr.202400531  

   Wu, Shang‐Hsuan; Cossio, Gabriel; Derkacs, Daniel; Yu, Edward T (November 2024, Solar RRL)

   III–V‐based multijunction solar cells have become the leading power generation technology for space applications due to their high power conversion efficiency and reliable performance in extraterrestrial environments. Thinning down the absorber layers of multijunction solar cells can considerably reduce the production cost and improve their radiation hardness. Recent advances in ultrathin GaAs single‐junction solar cells suggest the development of light‐trapping nanostructures to increase light absorption in optically thin layers within III–V‐based multijunction solar cells. Herein, a novel and highly scalable nanosphere lithography‐assisted chemical etching method to fabricate light‐trapping nanostructures in InGaP/GaAs dual‐junction solar cells is studied. Numerical models show that integrating the nanostructured Al₂O₃/Ag rear mirror significantly enhances the broadband absorption within the GaAs bottom cell. Results demonstrate that the light‐trapping nanostructures effectively increase the short‐circuit current density in GaAs bottom cells from 14.04 to 15.06 mA cm⁻². The simulated nanostructured InGaP/GaAs dual‐junction structure shows improved current matching between the GaAs bottom cell and the InGaP top cell, resulting in 1.12x higher power conversion efficiency. These findings highlight the potential of light‐trapping nanostructures to improve the performance of III‐V‐based multijunction photovoltaic systems, particularly for high‐efficiency applications in space. 

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2. Iridium Oxide Shell Structure on Rutile Titanium Oxide for Efficient Supported Catalyst for the Oxygen Evolution Reaction

   https://doi.org/10.1002/advs.202508036  

   Cazzulani, Elena; Roiron, Camille; Zhang, Lindsay; Ferro, Giovanni; Fairhurst, Alasdair; Cristiani, Pierangela; Chiarello, Gian Luca; Atanassov, Plamen (July 2025, Advanced Science)

   Abstract Proton exchange membrane water electrolysis is a promising technology for the production of hydrogen via water electrolysis. Lower amounts of iridium oxide are needed at the anode to reduce the cost and precious metal dependence of this technology for large‐scale development. The use of iridium oxide catalysts supported on non‐precious supports can help reduce the required iridium loading. This work presents a novel core–shell structure in which a thin layer of IrO₂ is grown on rutile TiO₂ spheres. The structural compatibility between rutile IrO₂ and rutile TiO₂ enables the formation of a continuous IrO₂ shell, unlike on anatase‐rich TiO₂ supports, where only a decorated structure is observed. The core–shell architecture and homogenous IrO₂ distribution on the rutile support is confirmed by imaging, diffraction, and spectroscopy. Electrochemical evaluation demonstrates superior mass activity and pseudo‐capacitance for the core‐shell material (on rutile) than for the decorated structure (on anatase). The core‐shell supported material as electrochemical performance similar to a commercial unsupported IrO₂ catalyst. These results highlight the potential of the rutile IrO₂‐rutile TiO₂interaction for improving catalyst utilization. Such core‐shell materials are promising candidates for an integration in low‐loading systems where unsupported materials suffer in‐plane conductivity losses. 

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3. Influence of Al‐doped SrTiO ₃ cores on hydrogen evolution from SrTiO ₃ /TiO ₂ core‒shell catalysts

   https://doi.org/10.1111/jace.20542  

   Song, Wenjia; Salvador, Paul A; Rohrer, Gregory S (August 2025, Journal of the American Ceramic Society)

   Abstract The hydrogen produced by Al‐doped SrTiO₃/TiO₂core‒shell catalysts with a range of Al‐doped SrTiO₃cores and the same TiO₂shell are compared. The study included SrTiO₃cores doped with different amounts of Al (0, 1, 2, or 3 mol%) added at different points in the synthesis (prior to or during the molten salt treatment) and at different temperatures (900°C, 1000°C, and 1100°C). It was found that core‒shell catalysts with different cores had hydrogen generation rates that varied by a factor of more than 40 and varied with the processing parameters in the same way as the hydrogen generation rates of the cores alone. The best catalysts had 2 or 3 mol% added Al, added during treatment in a SrCl₂molten salt at 1000°C or 1100°C. Because the core absorbs most of the light, its ability to separate and transport photogenerated charge carriers dominates the properties of the core‒shell catalyst. This indicates that, to optimize the properties of core‒shell catalysts, it is essential to optimize the properties of the core. While the shell can be important to protect the core from degradation, it is not as important to the overall reactivity as the core. 

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4. High performance AlGaN/GaN MISHEMTs using N ₂ O treated TiO ₂ as the gate dielectric

   https://doi.org/10.1088/1361-6641/ad96dc  

   Zhama, Tuofu; Cui, Peng; Chen, Zijun; Zhang, Jie; Zhao, Haochen; Wei, Lincheng; Sharma, Ashwani; Bakaul, Saidur; Zeng, Yuping (December 2024, Semiconductor Science and Technology)

   Abstract In this work, TiO₂thin films deposited by the atomic layer deposition (ALD) method were treated with a special N₂O plasma surface treatment and used as the gate dielectric for AlGaN/GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs). The N₂O plasma surface treatment effectively reduces defects in the oxide during low-temperature ALD growth. In addition, it allows oxygen atoms to diffuse into the device cap layer to increase the barrier height and thus reduce the gate leakage current. These TiO₂films exhibit a dielectric constant of 54.8 and a two-terminal current of 1.96 × 10⁻¹⁰A mm⁻¹in 2μm distance. When applied as the gate dielectric, the AlGaN/GaN MISHEMT with a 2μm-gate-length shows a high on/off ratio of 2.59 × 10⁸and a low subthreshold slope (SS) of 84 mV dec⁻¹among all GaN MISHEMTs using TiO₂as the gate dielectric. This work provides a feasible way to significantly improve the TiO₂film electrical property for gate dielectrics, and it suggests that the developed TiO₂dielectric is a promising high-κgate oxide and a potential passivation layer for GaN-based MISHEMTs, which can be further extended to other transistors. 

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5. Temperature‐Dependent Properties of Atomic Layer Deposition‐Grown TiO ₂ Thin Films

   https://doi.org/10.1002/admi.202400855  

   Chowdhary, Nimarta Kaur; Gougousi, Theodosia (July 2025, Advanced Materials Interfaces)

   Abstract This study investigates the presence of titanium oxynitride bonds in titanium dioxide (TiO₂) thin films grown by atomic layer deposition (ALD) using tetrakis dimethyl amino titanium (TDMAT) and water at temperatures between 150 and 350 °C and its effect on the films’ optical and electrical properties. Compositional analysis using X‐ray photoelectron spectroscopy (XPS) reveals increased incorporation of oxynitride bonds as the process temperature increases. Furthermore, depth profile data demonstrates an increase in the abundance of this type of bonding from the surface to the bulk of the films. Ultraviolet‐visible spectroscopy (UV‐vis) measurements correlate increased visible light absorption for the films with elevated oxynitride incorporation. The optical constants (n, k) of the films show a pronounced dependence on the process temperature that is mirrored in the film conductivity. The detection of oxynitride bonding suggests a secondary reaction pathway in this well‐established ALD process chemistry, that may impact film properties. These findings indicate that the choice of process chemistry and conditions can be used to optimize film properties for optoelectronic applications. 

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