A new member of the IV–V compounds, germanium–phosphorus (Ge–P) compounds, has been shown in experiment and theory to have a tunable bandgap (Eg), excellent chemical stability, strong in‐plane anisotropy, and wide‐range optical absorption, all indicating a promising future in electronic and optoelectronic applications. In this work, the application potential of Ge–P compounds as nonlinear optical (NLO) materials in ultrafast photonics is studied for the first time. The strong light–matter interaction, broad and tunable Ep, and broadband and strong optical response make GeP a likely NLO material for photonics, especially in infrared photonic devices. In addition, 2D GeP nanosheets are mixed with poly(vinylidene fluoride) (PVDF) to obtain a GeP@PVDF composite film, which further improves the stability of the GeP and, for the development of organic photonic devices, helps to slow its degradation. From Z‐scan data and fitting results, it is found that GeP has an excellent broadband NLO response. Moreover, using the GeP@PVDF composite film as a saturable absorber, a high‐stability femtosecond laser with a 722 fs pulse width is obtained in the telecommunications band. Preliminarily, Ge–P compounds display excellent optical properties suggesting that they may be used as NLO materials in advanced photonic devices.

Spinel oxides have attracted widespread interest for electrocatalytic applications owing to their unique crystal structure and properties. The surface structure of spinel oxides significantly influences the electrocatalytic performance of spinel oxides. Herein, we report a Li reduction strategy that can quickly tune the surface structure of CoFe 2 O 4 (CFO) nanoparticles and optimize its electrocatalytic oxygen evolution reaction (OER) performance. Results show that a large number of defective domains have been successfully introduced at the surface of CFO nanopowders after Li reduction treatment. The defective CFO nanoparticles demonstrate significantly improved electrocatalytic OER activity. The OER potential observed a negative shift from 1.605 to 1.513 V at 10 mA cm −2 , whereas the Tafel slope is greatly decreased to 42.1 mV dec −1 after 4 wt % Li reduction treatment. This efficient Li reduction strategy can also be applied to engineer the surface defect structure of other material systems and broaden their applications.

Lead trihalide perovskites have been integrated with atomically thin WS2 and served as absorption layers to improve photoresponsivity in photodetectors. The combination of perovskites and two-dimensional (2D) transition-metal dichalcogenide (TMDC) materials provides the platform to study light–matter interactions and charge transfer mechanisms in optoelectronic devices. Herein, conductive and photoconductive atomic force microscopy were used to image the dark current and photocurrent generated in WS2/CH3NH3PbI3 (MAPbI3) heterostructures. Dark current measurement in the applied voltage range displays characteristic diode behavior, which can be well described by thermionic emission theory. Under laser illumination at 532 nm, the spatially resolved photocurrent images exhibit location-dependent photoresponse, where the photocurrent increases remarkably for the WS2/MAPbI3 heterostructures compared with the bare MAPbI3 regions. Furthermore, comparative surface roughness and 2D Fourier analysis of the topographic and current maps reveal that the interfacial conditions of the WS2/MAPbI3 heterojunctions play an important role in the charge separation process. In addition, WS2/MAPbI3-based photodetectors have been fabricated. Our study provides direct evidence that atomically thin TMDC monolayers can effectively assist the charge separation process and improve the light-to-electric energy conversion, which aids in the design principles and understanding of 2D heterostructured optoelectronic devices.

Tungsten disulfide monolayers have attracted extensive attention in nanoelectronics and optoelectronics applications due to their remarkable electronic and optical properties. High-quality WS2 monolayers with a scalable size and uniform thickness can be synthesized by a chemical vapor deposition method (CVD). However, they commonly contain intrinsic structural defects and different populations of charge carriers, which are responsible for different contributions of excitons, trions, and biexcitons to their photoluminescence (PL) emission. Here, we adopt sodium sulphide (Na2S) solution to chemically treat CVD-grown WS2 monolayers by a simple immersing method. The results show that WS2 monolayers have a significantly enhanced PL emission by a factor of 25-fold and an obvious red-shift of the PL wavelength, resulting from the different excitonic states induced by effective n-type doping after Na2S treatment. This work provides a simple but promising chemical doping route to significantly improve the optical properties of WS2 monolayers and paves the way for the realization of practical WS2 monolayer based optoelectronic applications.

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