CrGeTe3 has recently emerged as a new class of two-dimensional (2D) materials due to its intrinsic long-range ferromagnetic order. However, almost all the reported synthesis methods for CrGeTe3 nanosheets are based on the conventional mechanical exfoliation from single-crystalline CrGeTe3, which is prepared by the complicated self-flux technique. Here we report a solution-processed synthesis of CrGeTe3 nanosheets from a non-van der Waals (vdW) Cr2Te3 template. This structure evolution from non-vdW to vdW is originated from the substitution of Ge atoms on the Cr sites surrounded by fewer Te atoms in the Cr2Te3 lattice due to their smaller steric hindrance and lower energy barrier. These CrGeTe3 nanosheets present regular hexagonal structures with a diameter larger than 1 μm and excellent stability. They exhibit soft magnetic behavior with a Curie temperature lower than 67.5 K. This non-vdW to vdW synthesis strategy promotes the development of CrGeTe3 in ferromagnetism while providing an effective route to synthesize other 2D materials.

Wide-bandgap semiconductors exhibiting a bandgap of ∼1.7–1.9 eV have generated great interest recently due to their important applications in tandem solar cells as top cells and emerging indoor photovoltaics. However, concerns about the stability and toxicity especially in indoor application limit the choice of these materials. Here we report a new member of this family, germanium monosulfide (GeS); this material displays a wide bandgap of 1.7 eV, nontoxic and earth-abundant constituents, and high stability. We find that the little success of GeS solar cells to date is primarily attributed to the challenge in fabricating high-quality polycrystalline GeS films, wherein the high thermal expansion coefficient (α = 3.1 × 10–5 K–1) combined with high crystallization temperature (375 °C) of GeS induces large tensile strain in the GeS film that peels off GeS from the substrate. By introducing a high-α buffer layer between GeS and substrate, we achieve a high-quality polycrystalline GeS thin film that compactly adheres to substrate with no voids. Solar cells fabricated by these GeS films show a power conversion efficiency of 1.36% under AM 1.5G illumination (100 mW cm–2). The unencapsulated devices are stable when stored in ambient atmosphere for 1500 h. Their efficiencies further increase to 3.6% under indoor illumination of 1000 lux.

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Solution processes have been widely used to construct chalcogenide-based thin-film optoelectronic and electronic devices that combine high performance with low-cost manufacturing. However, Ge (II)-based chalcogenide thin films possessing great potential...

Magnetic heterostructures offer great promise in spintronic devices due to their unique magnetic properties, such as exchange bias effect, topological superconductivity, and magneto-resistance. Although various magnetic heterostructures including core/shell, multilayer, and van der Waals systems have been fabricated recently, the construction of perfect heterointerfaces usually rely on complicated and high-cost fabrication methods such as molecular-beam epitaxy; surprisingly, few one-dimensional (1D) bimagnetic heterojunctions, which provide multidegrees of freedom to modulate magnetic properties via magnetic anisotropy and interface coupling, have been fabricated to date. Here we report a one-pot solution-based method for the synthesis of ferromagnetic/antiferromagnetic/ferromagnetic heterojunction nanorods with excellent heterointerfaces in the case of Cr2Te3/MnTe/Cr2Te3. The precise control of homogeneous nucleation of MnTe and heterogeneous nucleation of Cr2Te3 is a key factor in synthesizing this heterostructure. The resulting 1D bimagnetic heterojunction nanorods exhibit high coercivity of 5.8 kOe and exchange bias of 892.5 Oe achieved by the magnetic MnTe/Cr2Te3 interface coupling.

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