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Topological Hall effect (THE) has been used as a powerful tool to unlock spin chirality in novel magnetic materials. Recent focus has been widely paid to THE and possible chiral spin textures in two-dimensional (2D) layered magnetic materials. However, the room-temperature THE has been barely reported in 2D materials, which hinders its practical applications in 2D spintronics. In this paper, we report a possible THE signal featuring antisymmetric peaks in a wide temperature window up to 320 K in Cr1.2Te2, a new quasi-2D ferromagnetic material. The temperature, thickness, and magnetic field dependences of the THE lead to potential spin chirality origin that is associated with the spin canting under external magnetic fields. Our work holds promise for practical applications in future chiral spin-based vdW spintronic devices.

Antimony selenosulfide, Sb2(S,Se)3, is a promising next-generation solar cell material with superior photovoltaic properties and high stability. However, the efficiency of Sb2(S,Se)3 solar cells lags far behind its theoretical value and other well-established thin-film solar cells. Herein, we report a one-step hydrothermal process by employing selenourea as a selenium source for a single-phase and compact Sb2(S,Se)3 light absorber film, which possessed a desirable bandgap of 1.50 eV. When a low-cost and planar dithieno[3,2-b:2′,3′-d]pyrrole-cored small molecule (DTPThMe-ThTPA) is used as the hole transporting material, the interfacial energy level alignment is optimized. We disclose that chemical interaction formed between neighbouring thiophene and Sb atoms is critical for carrier collection and suppression of charge recombination, resulting in a champion efficiency of 9.7% with DTPThMe-ThTPA and increased stability, which is comparable to the device based on conventional Spiro-OMeTAD.

Fullerene derivatives with strong electron-accepting abilities have been extensively used as electron transport layers (ETLs) of inverted (p–i–n) planar heterojunction perovskite solar cells (iPSCs); however the effect of a specific heteroatom site within the fullerene derivative on its electron transport properties has scarcely been studied. Herein, by employing pyridinecarboxaldehydes bearing different nitrogen sites within the pyridine moiety as a reactant, three novel pyridine-functionalized fullerene derivatives with variable nitrogen sites (abbreviated as C60-n-Py, where n is the relative position of pyridine nitrogen with the site of pyridine moieties linked to the pyrrolidine ring of fullerene derivatives, n = 2, 3, 4) were synthesized facilely via a one-step 1,3-dipolar cycloaddition reaction, and their molecular structures as well as molecular packing were unambiguously determined by X-ray single crystal diffraction. Despite that C60-n-Py (n = 2, 3, 4) exhibit negligible difference in the molecular energy level and optical absorption, when using C60-n-Py as a novel ETL in CH3NH3PbI3 (MAPbI3) iPSC devices, their electron transport properties are found to sensitively depend on the nitrogen site within the pyridine moiety, and the C60-3-Py-based device shows the highest power conversion efficiency (PCE) of 17.57%, surpassing those of C60-2-Py- and C60-4-Py-based devices (12.79% and 16.51%, respectively). The discrepancy of the electron transport properties of C60-n-Py is primarily due to the difference in the coordination interaction between the pyridine moiety and the Pb2+ ion of the MAPbI3 perovskite layer, which is determined by the nitrogen site according to X-ray photoelectron spectroscopic (XPS) characterization and theoretical studies. The stronger coordination interaction between the pyridine moiety and the Pb2+ ion for the C60-3-Py-based device leads to reinforced passivation of the trap state within the MAPbI3 perovskite film, affording improved device performance and ambient stability of the C60-3-Py device. Moreover, C60-n-Py (n = 2, 3, 4) were further used as ETLs of Cs0.05FA0.83MA0.12PbI2.55Br0.45 (abbreviated as CsFAMA) iPSC devices, and C60-3-Py shows the best ETL performance as well, confirming the universality of our approach in steering the electron transport properties of C60-n-Py.

Topological Hall effect (THE) has been used as a powerful tool to unlock spin chirality in novel magnetic materials. Recent focus has been widely paid to THE and possible chiral spin textures in two-dimensional (2D) layered magnetic materials. However, the room-temperature THE has been barely reported in 2D materials, which hinders its practical applications in 2D spintronics. In this paper, we report a possible THE signal featuring antisymmetric peaks in a wide temperature window up to 320 K in Cr

An organic ligand-free solution method is developed for preparing homogeneous core-shell quantum-dot (QD)-modified pure Cs4PbBr6 microcrystals on a large scale (∼12 g) at room temperature. The ligand-free Cs4PbBr6 microcrystals show a high green photoluminescence quantum yield of 76% with 360 nm of excitation light, which is attributed to their unique microarchitecture, with several features including quantum confinement of the outer QDs, stability of the inner Cs4PbBr6 microcrystals, improved light trapping, and interfacial recombination. UV-vis-near-IR and photoluminescence analyses provide valued evidence to support the ligand-free Cs4PbBr6 with synergy between the QDs and microcrystals.

In CH3NH3PbI3 based perovskite solar cells (PSCs), the subtle pinholes and grain boundaries are hardly avoided in the formation of perovskite film. The defected film often leads to a reduced efficiency due to a larger amount of electron trap sites which induce carrier recombination leading to electron loss. In this work, ultrafine exfoliated graphitic carbon nitride (E-g-C3N4) nanoparticles are successfully synthesized by H2SO4 intercalation and NH3 stripping. The E-g-C3N4 has a lot of N H or O H groups, which could coil into nanoparticles spontaneous from nanosheets by hydrogen bonds. As an application in PSCs, the E-g-C3N4, as doping materials between MAPbI3 and the hole transport materials (HTMs), could magically self-recognize CH3NH3PbI3 grain boundaries and locate on them. Electron-hole recombination is greatly reduced even after incorporating trace of E-g-C3N4 by decreasing the deep electron trap centers at grain boundaries. As a result, the power conversion efficiency (PCE) of 15.8% is achieved for the MAPbI3 based PSCs, which is 35% higher than the reference cell. Thus, it is a universal and efficient method to weaken the influence of unavoidable defects existing in pinholes and grain boundaries, and develop the low-cost preparation for large-area PSCs in general conditions.

We present the first report of a new suspension method for obtaining cubic MAPbBr3 single crystal with a concave surface. The cubic MAPbBr3 crystal with microconcavity possesses good crystallinity and carrier lifetime. Excellent photoelectric performance was provided by the concavity-based MAPbBr3 photodetectors because of the good light trapping and shortened carrier pathway. As a result, the concavity-based photodetector exhibits superior responsivity of 62.9 and 5.43 A W–1 and EQE of 1.50 × 104% and 1.30 × 103% under low-power and high-power 520 nm irradiation of 3.67 μW cm–2 and 35.4 mW cm–2 at 3 V, respectively, which are more than 500% higher than those of the plane-based photodetector. In particular, the concavity-based photodetector has an ultrahigh detectivity of 6.5 × 1012 Jones at ultralow power of 3.67 μW cm–2, which is 6.5 times higher than that of the planar device.

Fullerene derivatives have been popularly applied as electron transport layers (ETLs) of inverted (p–i–n) planar heterojunction perovskite solar cells (iPSCs) due to their strong electron-accepting abilities, and so far, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) has been the most commonly used ETL, which suffers, however, from high cost due to the complicated synthetic route. Herein, novel pyridine-functionalized fullerene derivatives (abbreviated as C60-Py) were synthesized facilely via a one-step 1,3-dipolar cycloaddition reaction and applied as ETLs superior to PCBM in iPSC devices. Three pyridine-functionalized fullerene derivatives with different alkyl groups, including methyl, n-butyl, and n-hexyl, grafted onto the pyrrolidine moiety (abbreviated as C60-MPy, C60-BPy, and C60-HPy, respectively) were synthesized. According to cyclic voltammogram study, the chain length of the N-alkyl group has negligible influence on the molecular energy level of C60-Py. However, the ETL performance of C60-Py ...

Layers of two-dimensional material are bonded together by van der Waals force, as a result, there is no need to take into consideration of the lattice mismatch in the formation of heterojunction, which is endowed with the characteristics of simple stacking in method, free of limitation to the type of materials and diverse changes. However, although the Van Der Waals heterojunction is relatively easy to stack, it is still difficult to generate inter-layer coupling between the thin crystal layers that form the Van Der Waals heterojunction. In most cases, the stacked heterojunction is simply stacked together without any new effects. Therefore, the realization of heterojunction coupling is a difficult problem to be considered in the process of preparing Van Der Waals heterojunction. In this paper, a method based on solution immersion and hot plate heating is proposed to optimize the mechanical stacking of Van Der Waals heterojunctions. It is found that the heterojunctions prepared by normal mechanical stacking method are usually uncoupled before treatment, but they can be stably coupled after treatment. Our method, simple, fast with low-cost, has been repeatedly verified to have a high success rate of coupling, which is suitable for most experimental groups to use and reproduce.

Summary Inorganic semiconductor Sb2(S,Se)3 possesses a suitable bandgap, environmentally benign elemental composition, and excellent stability, offering ample promise for next-generation low-cost solar cells. Here, we demonstrate that perovskite quantum dots (QDs), including CH3NH3PbBr3 and CsPbBr3, can serve as highly efficient and air-stable hole extraction materials in Sb2(S,Se)3 solar cells. Through a proper pre-treatment of the colloidal QDs, a 25-nm-thick QD film can be obtained with excellent uniformity and charge transport properties. Spectroscopic and photoelectrochemical analysis show that perovskite QDs can effectively extract holes from Sb2(S,Se)3 with suppressed carrier recombination. The perovskite QDs/Sb2(S,Se)3 heterojunction also establishes an increased built-in potential so that open-circuit voltage is pronouncedly enhanced. Finally, the device based on perovskite QDs/Sb2(S,Se)3 heterojunction boosts the efficiency from 4.43% to 7.82%, setting a record value, to the best of our knowledge, in Sb2(S,Se)3 solar cells. Our research manifests another application of perovskite materials and practical strategy toward efficiency improvement of Sb2(S,Se)3 solar cells.

Molybdenum disulfide (MoS2) as a representative transition-metal dichalcogenide (TMD) has been extensively used as a noble-metal-free cocatalyst for photocatalytic hydrogen (H2) production, but suffers from poor photocatalytic activity due to the catalytic inactivity of its basal plane. Herein, by bounding another metal-free cocatalyst, C60, with MoS2, we report the first MoS2-C60 hybrid featuring a van der Waals heterostructure prepared via a facile and eco-friendly solid-state mechanochemical route. C60 bounding onto the edge of MoS2 nanosheets leads to the decreases of both the number of layers and the size of MoS2 nanosheets, as well as a negative shift of the conduction band minimum along with a positive shift of valance band maximum relative to the bulk MoS2 and MoS2 ball-milled without C60 (MoS2-BM). Under the optimized weight ratio of MoS2:C60 (1:1) in the raw mixture subject to ball-milling, MoS2-C60 hybrid containing 2.8 wt% C60 shows an exceptional visible light photocatalytic H2 production rate of 6.89 mmol h−1 g−1 in the presence of a photosensitizer Eosin Y (EY), which is significantly enhanced relative to the bulk MoS2 and pristine C60, both of which show almost no photocatalytic H2 activity. Thus, the synergistic enhancement of photocatalytic activities of both MoS2 and C60 is revealed.

Organometal halide CH3NH3PbI3 (MAPbI3) has been commonly used as the light absorber layer of perovskite solar cells (PSCs), and, especially, another halide element chlorine (Cl) has been often incorporated to assist the crystallization of perovskite film. However, in most cases, a predominant MAPbI3 phase with trace of Cl– is obtained ultimately and the role of Cl involvement remains unclear. Herein, we develop a low-cost and facile method, named hydrochloric acid vapor annealing (HAVA) post-treatment, and realize a rapid conversion of MAPbI3 to phase-pure MAPbCl3, demonstrating a new concept of phase engineering of perovskite materials toward efficiency enhancement of PSCs for the first time. The average grain size of perovskite film after HAVA post-treatment increases remarkably through an Ostwald ripening process, leading to a denser and smoother perovskite film with reduced trap states and enhanced crystallinity. More importantly, the generation of MAPbCl3 secondary phase via phase engineering is bene...

Cu2−xGeS3 is a kind of inorganic semiconducting compound with earth abundant elemental storage, excellent chemical stability and environmentally friendly characteristics. It has been used as a light absorption material in traditional p–n junction thin film solar cells. This research presents that Cu2−xGeS3 can also serve as a highly efficient hole transporting material for perovskite solar cells with enhanced stability. The results show that perovskite solar cells based on the Cu2−xGeS3 film can retain 95% power conversion efficiency when exposed to 50% relative humidity for 30 days in air under room lamp light irradiation, while the device using spiro-OMeTAD as the hole transporting material degrades considerably in 2 days and nearly completely degrades in 10 days. Mechanistic investigation shows that the inherent stability and hydrophobic nature of the Cu2−xGeS3 film contribute to the enhanced moisture stability. This investigation provides a material choice for high-efficiency perovskite solar cells with enhanced moisture stability.

An organic ligand-free solution method is developed for preparing homogeneous core-shell quantum-dot (QD)-modified pure Cs

In two-dimensional layered materials, layer number and stacking order have strong effects on the optical and electronic properties. Tungsten disulfide (WS

We present the first report of a new suspension method for obtaining cubic MAPbBr

Titanium oxide (TiO

In two-dimensional layered materials, layer number and stacking order have strong effects on the optical and electronic properties. Tungsten disulfide (WS2) crystal, as one important member among transition metal dichalcogenides, has been usually prepared in a layered 2H prototype structure with space group P63/mmc ([Formula: see text]) in spite of many other expected ones such as 3R. Here, we report simultaneous growth of 2H and 3R stacked multilayer (ML) WS2 crystals in large scale by chemical vapor deposition and effects of layer number and stacking order on optical and electronic properties. As revealed in Raman and photoluminescence (PL) measurements, with an increase in layer number, 2H and 3R stacked ML WS2 crystals show similar variation of PL and Raman peaks in position and intensity. Compared to 2H stacked ML WS2, however, 3R stacked one always exhibits the larger red (blue) shift of Raman [Formula: see text] (A1g) peak and the appearance of PL A, B and I peaks at lower energies. Thereby, PL and Raman features depend on not only layer number but also stacking order. In addition, circularly polarized luminescence from two prototype WS2 crystals under circularly polarized excitation has also been investigated, showing obvious spin or valley polarization of these CVD-grown multilayer WS2 crystals.

Titanium oxide (TiO2 ) has been commonly used as an electron transport layer (ETL) of regular-structure perovskite solar cells (PSCs), and so far the reported PSC devices with power conversion efficiencies (PCEs) over 21% are mostly based on mesoporous structures containing an indispensable mesoporous TiO2 layer. However, a high temperature annealing (over 450 °C) treatment is mandatory, which is incompatible with low-cost fabrication and flexible devices. Herein, a facile one-step, low-temperature, nonhydrolytic approach to in situ synthesizing amino-functionalized TiO2 nanoparticles (abbreviated as NH2 -TiO2 NPs) is developed by chemical bonding of amino (-NH2 ) groups, via TiN bonds, onto the surface of TiO2 NPs. NH2 -TiO2 NPs are then incorporated as an efficient ETL in n-i-p planar heterojunction (PHJ) PSCs, affording PCE over 21%. Cs0.05 FA0.83 MA0.12 PbI2.55 Br0.45 (abbreviated as CsFAMA) PHJ PSC devices based on NH2 -TiO2 ETL exhibit the best PCE of 21.33%, which is significantly higher than that of the devices based on the pristine TiO2 ETL (19.82%) and is close to the record PCE for devices with similar structures and fabrication procedures. Besides, due to the passivation of the surface trap states of perovskite film, the hysteresis of current-voltage response is significantly suppressed, and the ambient stability of devices is improved upon amino functionalization.