HIGHLIGHTS• Lead-based halide perovskite materials have revealed excellent properties in optoelectronic applications. However, the material stability and the toxicity of lead still hinder their large-scale commercial applications.• Lead-free halide double perovskite materials possess the characteristics of environmental friendliness, exceptional stability and tunable optoelectronic properties.• A limited number of halide double perovskites have been synthesized, and extremely few have been developed for optoelectronic applications. Continuing effort is needed to explore more halide double perovskites and modulate the properties for their further applications.ABSTRACT 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 A 2 M(I)M(III)X 6 or A 2 M(IV)X 6 could be potentially regarded as 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.

Nonradiative recombination, the main energy loss channel for open circuit voltage (V oc), is one of the crucial problems for achieving high power conversion efficiency (PCE) in inverted perovskite solar cells (PSCs). Usually, grain boundary passivation is considered as an effective way to reduce nonradiative recombination because the defects (uncoordinated ions) on grain boundaries are passivated. We added the hydroxyl and carbonyl functional groups containing carbon quantum dots (CQDs) into a perovskite precursor solution to passivate the uncoordinated lead ions on grain boundaries. Higher photoluminescence intensity and longer carrier lifetime were demonstrated in the perovskite film with the CQD additive. This confirmed that the addition of CQDs can reduce nonradiative recombination by grain boundary passivation. Additionally, the introduction of CQDs could increase the thickness of the perovskite film. Consequently, we achieved a champion device with a PCE of 18.24%. The device with CQDs retained 73.4% of its initial PCE after being aged for 48 h under 80% humidity in the dark at room temperature. Our findings reveal the mechanisms of how CQDs passivate the grain boundaries of perovskite, which can improve the efficiency and stability of PSCs.

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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.

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 À2 (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.