Lead-based halide perovskites have emerged as excellent semiconductors for a broad range of optoelectronic applications, such as photovoltaics, lighting, lasing and photon detection. However, toxicity of lead and poor stability still represent significant challenges. Fortunately, halide double perovskite materials with formula of A₂M(I)M(III)X₆ or A₂M(IV)X₆ could be potentially regarded as stable and green alternatives for optoelectronic applications, where two divalent lead ions are substituted by combining one monovalent and one trivalent ions, or one tetravalent ion. Here, the article provides an up-to-date review on the developments of halide double perovskite materials and their related optoelectronic applications including photodetectors, X-ray detectors, photocatalyst, light-emitting diodes and solar cells. The synthesized halide double perovskite materials exhibit exceptional stability, and a few possess superior optoelectronic properties. However, the number of synthesized halide double perovskites is limited, and more limited materials have been developed for optoelectronic applications to date. In addition, the band structures and carrier transport properties of the materials are still not desired, and the films still manifest low quality for photovoltaic applications. Therefore, we propose that continuing efforts are needed to develop more halide double perovskites, modulate the properties and grow high-quality films, with the aim of opening the wild practical applications.

Neuromorphic computing simulates the operation of biological brain function for information processing and can potentially solve the bottleneck of the von Neumann architecture. This computing is realized based on memristive hardware neural networks in which synaptic devices that mimic biological synapses of the brain are the primary units. Mimicking synaptic functions with these devices is critical in neuromorphic systems. In the last decade, electrical and optical signals have been incorporated into the synaptic devices and promoted the simulation of various synaptic functions. In this review, these devices are discussed by categorizing them into electrically stimulated, optically stimulated, and photoelectric synergetic synaptic devices based on stimulation of electrical and optical signals. The working mechanisms of the devices are analyzed in detail. This is followed by a discussion of the progress in mimicking synaptic functions. In addition, existing application scenarios of various synaptic devices are outlined. Furthermore, the performances and future development of the synaptic devices that could be significant for building efficient neuromorphic systems are prospected.

Anatase TiO₂ nanoparticles with exposed {001} facets were synthesized from Ti powder via a sequential hydrothermal reaction process. At the first-step hydrothermal reaction, H-titanate nanowires were obtained in NaOH solution with Ti powder and at second-step hydrothermal reaction, anatase TiO₂ nanoparticles with exposed {001} facets were formed in NH₄F solution. If the second-step hydrothermal reaction was carried out in pure water, the H-titanate nanowires were decomposed into random shape anatase-TiO₂ nanostructures, as well as few impurity of H₂Ti₈O₁₇ phase and rutile TiO₂ phase. Then, the as-prepared TiO₂ nanostructures synthesized in NH₄F solution and pure water were applied to the photoanodes of dye-sensitized solar cells (DSSCs), which exhibited power conversion efficiency (PCE) of 7.06% (V_OC of 0.756 V, J_SC of 14.80 mA/cm², FF of 0.631) and 3.47% (V_OC of 0.764 V, J_SC of 6.86 mA/cm², FF of 0.662), respectively. The outstanding performance of DSSCs based on anatase TiO₂ nanoparticles with exposed {001} facets was attributed to the high activity and large special surface area for excellent capacity of dye adsorption.

In this study, an efficient poly(vinylpyrrolidone) (PVP)-assisted hydrothermal method for the in situ growth of WS₂ nanosheets with layer-controllability on reduced graphene oxide (rGO) is reported. The number of layers (from a monolayer to ∼25 layers) of the exfoliated WS₂ can be accurately controlled by adjusting the amount of PVP. The layer structure and the morphology of the as-prepared hybrids are confirmed by field emission scanning electron microscopy and high-resolution transmission microscopy. The X-ray diffraction, Raman, and X-ray photoemission spectroscopy of the obtained WS₂–rGO hybrid nanosheets indicate highly crystallized structures, a clear Raman shift and a stoichiometry, which is dependent on the number of layers. Furthermore, these highly active and durable catalysts exhibit an electrocatalytic current density of 10 mA cm⁻² at a small hydrogen evolution reaction (HER) overpotential (−170 mV) and a Tafel slope of 52 mV dec⁻¹ with an excellent electrocatalytic stability (after 6 months storage).

A dense array of CdS–ZnS core–shell nanorods film (1D vertically aligned) was synthesized through a simple two-step aerosol assisted chemical vapor deposition (AACVD) method. In this configuration, a ZnS nanocrystal (protective shell) was grown in situ on a CdS core, forming nanorod heterostructures to restrain the photo-corrosion and enhance the charge separation and transportation efficiencies of CdS cores. The as-prepared CdS–ZnS films showed elevated photoelectrochemical (PEC) performance (over four times than that of uncoated CdS arrays) with a significant photocurrent density of 7.8 mA cm⁻² (0 V, vs. SCE) and incident photon to electron conversion efficiency (IPCE) values above 35% under AM 1.5G irradiation. Moreover, the stability of the photoelectrode was tested for over 16 min. These results suggest that the dense array of CdS–ZnS core–shell heterostructures provides a unique spatial distribution of the photo-excited charge carriers, as well as stable anti-photo-corrosion ability, and therefore is promising to be a photoelectrode in PEC hydrogen generation from water.

The nanohybrids (NiPS ₃ @DG) exhibit impressively low overpotentials at all pH values, which can even surpass those of Pt/C.