Qixi Mi

All-inorganic CsSnI3 is a promising thermoelectric (TE) material featuring “phonon glass-electron crystal” (PGEC) behavior, yet its solution-processed thin films suffer from low electrical conductivity (σ) and poor environmental stability. In this work, we systematically study, by incorporating GeI2 into CsSnI3 thin films, the mechanism of synergistically enhancing the TE performance and stability. Tetragonal CsSn1−xGexI3 (x = 0–4 mol. %, x is the nominal component) films are fabricated via spin-coating and a two-step annealing process. Importantly, Ge incorporation synergistically improves the carrier mobility (μH) and hole concentration by passivating Sn vacancies (reducing scattering) and providing hole compensation via preferential oxidation of Ge. As a result, a maximum power factor (PF) of 112.9 μW m−1 K−2 is achieved at 1 mol. % GeI2 doping, which is 70% higher than that of the undoped sample. Meanwhile, the incorporated Ge ions regulate micro-morphology and act as sacrificial agents via their preferential oxidation, during which a more dense and stable surface forms, protecting the oxidation of Sn2+ and inhabiting H2O invasion. Furthermore, Ge doping increases the tolerance factor (t). These combined effects stabilize the black perovskite phase against its detrimental transition to the yellow non-perovskite phase. This work offers a straightforward and effective route to synergistically boost both the stability and TE PF of all-inorganic Sn-based perovskite films.

The Stoner–Wohlfarth antiferromagnet (AFM), an extension of the classical Stoner–Wohlfarth model originally describing the magnetization reversal in ferromagnetic nanoparticles^1,2, refers to a single-domain AFM whose Néel vector can be coherently switched by the magnetic field. These AFMs not only retain the inherent advantages of antiferromagnetism but also feature controllable Néel vector and a perfect switching ratio, thus emerging as promising building blocks for ultradense magnetic memories and high-throughput computing systems^3,4. However, bulk AFMs are not the Stoner–Wohlfarth AFMs owing to the hard-to-switch Néel vector and inevitable multidomain structure^3,5,6,7. Here we report that CrPS₄, a two-dimensional (2D) van der Waals (vdW) A-type AFM, exhibits ideal characteristics of the Stoner–Wohlfarth AFMs, because of the dominance of antiferromagnetic exchange over the magnetic anisotropy and high quality of vdW interfaces. The antiferromagnetic order undergoes a ferromagnet (FM)-like binary switching with the magnetic field rather than the layer-by-layer flipping observed in other 2D A-type AFMs. Moreover, we deduce the characteristic exchange length of several vdW A-type AFMs and propose a criterion for judging the Stoner–Wohlfarth AFMs. Our work therefore establishes a universal framework for understanding the magnetization reversal in layered AFMs and promotes the effective use of 2D AFMs in advanced spintronic devices.

Van der Waals (vdW) magnets provide a rich landscape for innovative spintronic applications at atomic thickness. Among them, chromium sulfide bromide (CrSBr) stands out as a semiconducting antiferromagnet with the potential for magnetoelectric manipulation. However, the detection and electrical control of 2D magnetism in CrSBr are constrained by its centrosymmetric structure and in-plane antiferromagnetism. To address this challenge, we construct heterostructure devices composed of trilayer CrSBr and monolayer graphene, where interfacial charge transfer breaks the inversion symmetry of both magnetic order and crystallographic structure. The inversion symmetry breaking by charge transfer thus allows a full discrimination of the otherwise degenerate magnetic states using optical second harmonic generation, including the charge transfer induced intermediate magnetic states that consist of antiferromagnetic and ferromagnetic vdW interfaces. Furthermore, gate voltage enables the tuning of charge transfer, effectively modulating the interlayer magnetic coupling and magnetic transitions. Our findings deepen the understanding of optospintronic interaction and magnetoelectric manipulation in vdW magnets, paving the way for electrically tunable 2D spintronic devices.

Tin perovskite solar cells (TPSCs) are considered as a sustainable alternative to their lead-containing counterparts, offering an ideal bandgap, a more stable crystal structure, and better semiconducting properties. However, the fabrication of efficient and able TPSCs has been a challenging task. Among the main components of TPSCs, herein, we investigated the transport layers and their interface with the perovskite layer. Several microscopy techniques revealed inhomogeneity in the common hole transport layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and the electron transport layer (ETL), indene-C₆₀ bisadduct (ICBA). A hydrogen-bond donor molecule d-sorbitol modified the microstructure of PEDOT:PSS, increasing its conductivity and the crystallization density of the overlying perovskite layer. Blending 1% poly(methyl methacrylate) into ICBA rendered a uniform ETL, which facilitated electron transport across its interface with tin perovskite. The photocurrent density, open-circuit voltage, and fill factor of the TPSCs were all enhanced to achieve a power conversion efficiency of 15.8% and excellent short-term stability. Our findings address an often-neglected aspect of device fabrication and provide a new approach to boosting the performance and reproducibility of TPSCs.

Metal halide perovskites have garnered widespread attention for research and applications, thanks to their high adaptability in elemental composition and optoelectronic properties. The mixed Sn–Pb perovskite FASn _0.5 Pb _0.5 I ₃ (FA ⁺ is formamidinium) features a narrow bandgap of 1.25 eV, appropriate for building tandem solar cells, but faces challenges in fabricating uniform, compact films having protected surfaces and scalable dimensions. Herein, a Lewis‐base molecule trimethylthiourea (3T) is applied as a ligand to the FASn _0.5 Pb _0.5 I ₃ system, and find that it favors binding to Sn ²⁺ over Pb ²⁺ . As a result, the tin and lead components crystallize congruently at the unit cell scale. The 3T ligand helps the FASn _0.5 Pb _0.5 I ₃ crystal grains develop into regular shapes and micron sizes, so as to fill in the film thickness and closely contact the substrate. Also, slow evaporation of 3T during annealing inhibits surface defects and renders centimeter‐wide film smoothness. Solar cells made of such FASn _0.5 Pb _0.5 I ₃ films has achieved a power conversion efficiency of 21.5% and a fill factor of 81%. Eliminating methylammonium and a hole transport layer (HTL) from these solar cells substantially boosts their short‐term and storage stabilities. These results will contribute to making streamlined, durable, and large‐area perovskite tandem solar cells.

Polymorphism, commonly denoting diverse molecular or crystal structures, is crucial in the natural sciences. In van der Waals antiferromagnets, a new type of magnetic polymorphism arises, presenting multiple layer-selective magnetic structures with identical total magnetization. However, resolving and manipulating such magnetic polymorphs remain challenging. Here, phase-resolved magnetic second harmonic generation microscopy is used to elucidate magnetic polymorphism in 2D layered antiferromagnet CrSBr, demonstrating deterministic and layer-selective switching of magnetic polymorphs. Using a nonlinear magneto-optical technique, we unambiguously resolve the polymorphic spin-flip transitions in CrSBr bilayers and tetralayers through both the amplitude and phase of light. Remarkably, the deterministic routing of polymorphic spin-flip transitions originates from a ‘layer-sharing’ effect, where the transitions are governed by laterally extended layers acting as ‘control bits’. We envision that such controllable magnetic polymorphism could be ubiquitous for van der Waals layered antiferromagnets, enabling new designs and constructions of spintronic and opto-spintronic devices for probabilistic computation and neuromorphic engineering.