High-entropy herringbone alloy Eutectic high-entropy alloys have a dual phase structure that could be useful for optimizing a material’s properties. Shi et al . found that directional solidification of an aluminum-iron-cobalt-nickel eutectic high-entropy alloy created a herringbone-patterned microstructure that was extremely resistant to fracture (see the Perspective by An). The structure contained lamellae of hard and soft phases, and the cracks that formed in the hard phase were arrested at the boundary of the soft phase. This, along with stress transfer, allowed a tripling of the maximal elongation while retaining high strength. —BG

Molybdenum trioxide (MoOX, X < 3), with a large work function, can induce upward band bending in crystalline silicon (c‐Si) when constructing a heterojunction, which makes it an attractive candidate for hole‐selective contact in c‐Si solar cells. Herein, the passivation property and hole selectivity of MoOX thin films are investigated on p‐type c‐Si wafers using MoOX/aluminum (Al) as rear contacts. To elevate the performance from the aspect of light management, silver (Ag) and copper (Cu) are further used as back electrodes instead of Al. Solar cells with Ag electrodes deliver the best performance with a power conversion efficiency of 18.74%, followed by Cu (17.61%) and Al (16.36%) electrodes, attributing to the better reflectivity of Ag and Cu. It is also noted that solar cells with MoOX/Ag and MoOX/Cu contacts show significant degradation under room temperature storage. The interfacial evolutions are then carefully studied as a function of elevated temperature that accelerate the thermodynamic process. The degradation mechanism involves redox reaction and metal diffusion at the MoOX/metal interfaces. This work points out the importance of selecting the adjacent layers of MoOX and regulating the interfaces to stabilize the MoOX‐based c‐Si solar cells.

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