A strategy for boosting photovoltaic performance based on a two-dimensional ZrSSe/HfSSe van der Waals heterostructure.

Identifying high-efficiency solar photovoltaic systems with two-dimensional (2D) materials is still an urgent challenge to meet modern energy requirements. Very recently, a 2D heterostructure with type-II band alignment has been confirmed to be more favorable for application in photoelectric conversion. However, the staggered band offset of 2D type-II heterostructures cannot always be guaranteed, nor the intrinsic hindrance mechanism of carrier recombination being clear. In this study, taking the emerging ZrSSe/HfSSe van der Waals heterostructure (vdWH) as a generic example, a boosting strategy for improving the photoelectric performances of 2D vdWHs is proposed. Through a series of in-depth systematic research studies based on first-principles, we demonstrate that via applying a vertical strain, an anticipated band alignment transition from type-I to favorable type-II of this ZrSSe/HfSSe vdWH can be induced due to the interfacial charge redistribution, during which a corresponding enlarged photocurrent can be detected from the latter based device compared to the former. Essentially, such enhanced photocurrent at the incident photon energy (Eph) around the band gap is attributed to the suppressed recombination rate of photoexcited carriers. Moreover, when Eph is increased into the visible light region, the photoelectric conversion performances can be further controlled by vertical strain. These generalized findings not only provide an effective manipulation strategy for enhancing the performances of 2D solar photovoltaic systems, but the intrinsic physical mechanism can also be extended to the next practical design and regulation of other 2D photovoltaic devices.

Turning Ultra-Low Coercivity and Ultra-High Temperature Stability Within 897 K via Continuous Crystal Ordering Fluctuations.

High-performance soft magnetic materials are important for energy conservation and emission reduction. One challenge is achieving a combination of reliable temperature stability, high resistivity, high Curie temperature, and high saturation magnetization in a single material, which often comes at the expense of intrinsic coercivity-a typical trade-off in the family of soft magnetic materials with homogeneous microstructures. Herein, a nanostructured FeCoNiSiAl complex concentrated alloy is developed through a hierarchical structure strategy. This alloy exhibits superior soft magnetic properties up to 897 K, maintaining an ultra-low intrinsic coercivity (13.6 A m-1 at 297 K) over a wide temperature range, a high resistivity (138.08 µΩ cm-1 at 297 K) and the saturation magnetization with only a 16.7% attenuation at 897 K. These unusual property combinations are attributed to the dual-magnetic-state nature with exchange softening due to continuous crystal ordering fluctuations at the atomic scale. By deliberately controlling the microstructure, the comprehensive performance of the alloy can be tuned and controlled. The research provides valuable guidance for the development of soft magnetic materials for high-temperature applications and expands the potential applications of related functional materials in the field of sustainable energy.