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Eco-friendly CuInSnSe (CISnSe) QDs with broadband absorption were engineered via effective ZnSe shell passivation to fabricate highly efficient near-infrared photodetectors.

Narrow-band-gap III-V semiconductor nanowires (NWs) with a suitable band structure and strong light-trapping ability are ideal for high-efficiency low-cost solar water-splitting systems. However, due to their nanoscale dimension, they suffer more severe corrosion by the electrolyte solution than the thin-film counterparts. Thus, short-term durability is the major obstacle for using these NWs for practical water-splitting applications. Here, we demonstrated for the first time that a thin layer (∼7 nm thick) of compact TiO2 deposited by atomic layer deposition can provide robust protection to III-V NWs. The protected GaAs NWs maintain 91.4% of its photoluminescence intensity after 14 months of storage in ambient atmosphere, which suggests the TiO2 layer is pinhole-free. Working as a photocathode for water splitting, they exhibited a 45% larger photocurrent density compared with unprotected counterparts and a high Faraday efficiency of 91% and can also maintain a record-long highly stable performance among narrow-band-gap III-V NW photoelectrodes; after 67 h photoelectrochemical stability test reaction in a strong acid electrolyte solution (pH = 1), they show no apparent indication of corrosion, which is in stark contrast to the unprotected NWs that fully failed after 35 h. These findings provide an effective way to enhance both stability and performance of III-V NW-based photoelectrodes, which are highly important for practical applications in solar-energy-based water-splitting systems.

Colloidal core/shell heterostructured quantum dots (QDs) possessing quasi-type II band structure have demonstrated effective surface passivation and prolonged exciton lifetime, leading to enhanced ...

To develop highly efficient electrochemical catalysts for N2 fixation is important to sustainable ambient NH3 production through the N2 reduction reaction (NRR). Herein, we demonstrate the development of vanadium phosphide nanoparticle on V foil as a high-efficiency and stable catalyst for ambient NH3 production with excellent selectivity. The high Faradaic efficiency of 22% with a large NH3 yield of 8.35 × 10−11 mol·s−1·cm−2 was obtained at 0 V vs. the reversible hydrogen electrode in acid solution, superior to all previously studied V-based NRR catalysts. Density functional theory calculations are also utilized to have an insight into the catalytic mechanism.

Hydrogen is the most promising renewable energy source to replace traditional fossil fuels for its ultrahigh energy density, abundance and environmental friendliness. Generating hydrogen by water splitting with highly efficient electrocatalysts is a feasible route to meet current and future energy demand. Herein, the effects of Ru doping and phosphorization treatment on Co3O4 nanoarrays for water splitting are systemically investigated. The results show that a small amount of phosphorus can accelerate hydrogen evolution reaction (HER) and the trace of Ru dopant can significantly enhance the catalytic activities for HER and oxygen evolution reaction (OER). Ru-doped cobalt phosphorous oxide/nickel foam (CoRuPO/NF) nanoarrays exhibit highly efficient catalytic performance with an overpotential of 26 mV at 10 mA cm−2 for HER and 342 mV at 50 mA cm−2 for OER in 1 M KOH solution, indicating superior water splitting performance. Furthermore, the CoRuPO/NF also exhibits eminent and durable activities for alkaline seawater electrolysis. This work significantly advances the development of seawater splitting for hydrogen generation.

"Green" colloidal quantum dots (QDs)-based photoelectrochemical (PEC) cells are promising solar energy conversion systems possessing environmental friendliness, cost-effectiveness, and highly efficient solar-to-hydrogen conversion. In this work, eco-friendly AgInSe (AISe)/ZnSe core/shell QDs with wurtzite (WZ) phase were synthesized for solar hydrogen production. It was demonstrated that appropriately engineering the ZnSe shell thickness resulted in effective surface defects passivation of the AISe core for suppressed charge recombination in the consequent core/shell AISe/ZnSe QDs. The fabricated environmentally friendly core/shell QDs-based PEC device exhibited improved photo-excited electrons extraction efficiency under optimized conditions and delivered a maximum photocurrent density as high as 7.5 mA cm

Colloidal core–shell quantum dots (QDs) are promising nanosystems exhibiting outstanding optical properties including enhanced photoluminescence quantum yield (PLQY), prolonged exciton lifetime, suppressed Auger recombination (AR) and improved photo-/chemical stability as compared to bare QDs. The band structure of core–shell QDs can be properly tailored via choosing appropriate core and shell materials, resulting in different types of band alignments such as type I, type II, and quasi-type II, which can be used for achieving a variety of high-performance optoelectronic devices including QDs-sensitized solar cells, photoelectrochemical (PEC) cells, luminescent solar concentrators (LSCs), light emitting diodes (LEDs), lasers and photodetectors. In this chapter, we introduced the synthesis and optical properties regarding different types of core–shell QDs and highlighted their band structure tuning for various optoelectronic applications. We also discussed the existing challenges and prospective developments of core–shell QDs-based optoelectronics, which are crucial to pave the way for their future practical usages.

“Giant” core/shell quantum dots (g-QDs) are promising candidates for emerging optoelectronic technologies thanks to their facile structure/composition-tunable optoelectronic properties and outstanding photo-physical/chemical stability. Here, we synthesized a new type of CuInTeSe (CITS)/CdS g-QDs and regulated their optoelectronic properties by controlling the shell thickness. Through increasing the shell thickness, as-prepared g-QDs exhibited tunable red-shifted emission (from 900 to 1200 nm) and prolonged photoluminescence (PL) lifetimes (up to ∼14.0 μs), indicating a formed band structure showing efficient charge separation and transfer, which is further testified by theoretical calculations and ultrafast time-resolved transient absorption (TA) spectroscopy. These CITS/CdS g-QDs with various shell thicknesses can be employed to fabricate photoelectrochemical (PEC) cells, exhibiting improved photoresponse and stability as compared to the bare CITS QD-based devices. The results indicate that the rational design and engineering of g-QDs is very promising for future QD-based optoelectronic technologies.

Bi

Two dimensional MoSe2 mono and few layer were prepared by the atmospheric pressure chemical vapor deposition (CVD). It is essential to understand completely the growth and nucleation mechanism to improve the crystalline quality and size of two dimensional transition metal dichalcogenides materials using CVD. Three different types of MoSe2 surface structure were identified for the different growth temperatures. By changing the growth temperatures, the concentration of MoO3-x and Se vapor precursors vary which derive different nucleation mechanism. Low vapor concentration of reactants leads to mono and bi layer MoSe2 due to 2D planar nucleation while higher concentration of reactants facilitates the self-seeding role that leads to few and multilayers MoSe2. The presence of the defects in monolayer was confirmed by photoluminescence spectra analysis. The surface friction of the mono and few layers were studied experimentally using the lateral force microscopy. The surface friction of MoSe2 depends on the number of layers presents in the surface flakes.

Colloidal heterostructured CuGaS2 (CGS)/CdS core/shell quantum dots (QDs) with a wurtzite (WZ) phase were synthesized via a facile two-step technique. As compared to the bare CGS QDs, the optical properties of such heterostructured CGS/CdS core/shell QDs were tailored to show largely enhanced light absorption in the visible range and an emission peak in the near-infrared (NIR) region at a wavelength of ∼816 nm. As proof of concept, these core/shell QDs were used as light absorbers to fabricate a photoelectrochemical (PEC) cell, which exhibited a maximum saturated photocurrent density of ∼6.5 mA cm−2 and outstanding stability under standard one sun illumination (AM 1.5G, 100 mW cm−2). The results indicate that these NIR core/shell QDs are promising candidates for future QD-based optoelectronic technologies such as QD-sensitized solar cells (QDSCs).

Narrow-band-gap III–V semiconductor nanowires (NWs) with a suitable band structure and strong light-trapping ability are ideal for high-efficiency low-cost solar water-splitting systems. However, due to their nanoscale dimension, they suffer more severe corrosion by the electrolyte solution than the thin-film counterparts. Thus, short-term durability is the major obstacle for using these NWs for practical water-splitting applications. Here, we demonstrated for the first time that a thin layer (∼7 nm thick) of compact TiO2 deposited by atomic layer deposition can provide robust protection to III–V NWs. The protected GaAs NWs maintain 91.4% of its photoluminescence intensity after 14 months of storage in ambient atmosphere, which suggests the TiO2 layer is pinhole-free. Working as a photocathode for water splitting, they exhibited a 45% larger photocurrent density compared with unprotected counterparts and a high Faraday efficiency of 91% and can also maintain a record-long highly stable performance among narrow-band-gap III–V NW photoelectrodes; after 67 h photoelectrochemical stability test reaction in a strong acid electrolyte solution (pH = 1), they show no apparent indication of corrosion, which is in stark contrast to the unprotected NWs that fully failed after 35 h. These findings provide an effective way to enhance both stability and performance of III–V NW-based photoelectrodes, which are highly important for practical applications in solar-energy-based water-splitting systems.

Colloidal quantum dots (QDs) are promising building blocks towards the development of cost-effective and high-efficiency photoelectrochemical (PEC) cells. Unfortunately, the frequent use of QDs possessing heavy metals (e.g. Cd and Pb) in state-of-the-art QD-based PEC technologies is a major obstacle regarding their future commercial perspective. In this work, we synthesized heavy metal-free quaternary CuZnInS3 (CZIS) with variable Cu : Zn ratios and fabricated corresponding QDs-PEC devices via a facile chemical bath deposition (CBD) technique. It is revealed that the tuned CZIS (1Zn) QDs (i.e. Cu : Zn ratio of 1 : 1) can result in optimized optical properties including enhanced quantum yield, suppressed nonradiative recombination and extended excitonic lifetime. Accordingly, as-fabricated CZIS (1Zn) QD-based photoanodes demonstrated increased charge transfer rate and decreased electron transport resistance for improved PEC performance. The results indicate that tuning the composition of heavy metal-free multinary QDs is one of the promising pathways to achieve eco-friendly and high-performance PEC systems for solar hydrogen production.

Colloidal semiconductor quantum dots (QDs) are promising building-blocks for the manufacture of cost-effective photoelectrochemical (PEC) cells towards efficient solar-to-hydrogen conversion. Nevertheless, the state-of-the-art QDs-based PEC systems still suffer from the frequent utilization of highly toxic elements in QDs (Cd and Pb), hindering their future practical applications and potential commercialization. Here, we report a PEC device fabricated using eco-friendly, near-infrared (NIR) ZnAgInSe (ZAISe) QDs and hybrid TiO2/graphene oxide (GO) film. Based on the synergistic effect of QD’s broad light absorption and excellent charge extraction/transport properties of TiO2/GO film, as-assembled QDs-photoanode exhibits an outstanding saturated photocurrent density of ~6.7 mA/cm2 with good stability under standard 1 sun illumination. The introduction of functional GO can lead to the reduced charge transfer resistance, suppressed charge recombination, and enhanced electron transport within the QDs-TiO2 photoanodes. The results offer a facile and effective method to enhance the performance of environmentally friendly QDs-based PEC devices and shed light on the development of low-cost, “green” and high-efficiency solar-to-hydrogen conversion system.

Hydrogen is the most promising renewable energy source to replace traditional fossil fuels for its ultrahigh energy density, abundance and environmental friendliness. Generating hydrogen by water splitting with highly efficient electrocatalysts is a feasible route to meet current and future energy demand. Herein, the effects of Ru doping and phosphorization treatment on Co

Colloidal quantum dot (QD)-based photoelectrochemical (PEC) cells are cost-effective devices showing remarkable solar-to-fuel conversion efficiency. However, the extensive use of highly toxic elements (e.g. Pb and Cd) in QDs' synthesis and device fabrication is still a major challenge towards their practical development. Herein, we fabricate a solar-driven PEC cell based on environmentally friendly Mn-alloyed CuInS2 (MnCIS)/ZnS core/shell QDs, showing more favorable band alignment, efficient charge transfer, reduced charge recombination and lower charge transfer resistance with respect to the control device fabricated using unalloyed CuInS2 (CIS)/ZnS core/shell QDs. An unprecedented photocurrent density of ∼5.7 mA cm−2 with excellent stability was obtained for the as-fabricated MnCIS/ZnS core/shell QD-based PEC device when operated under standard one sun irradiation (AM 1.5G, 100 mW cm−2). These results indicate that the transition metal-alloyed environmentally friendly core/shell QDs are promising for next-generation solar technologies.

Colloidal quantum dots (QDs) are promising for a variety of optoelectronic applications due to their size/shape/composition optical properties. Among various QDs, the core/shell QDs have demonstrated improved optical properties and enhanced photo-/chemical stability with respect to the bare QDs. Specifically, the band structure of the core/shell QDs can be tailored by choosing the appropriate core and shell material, changing the chemical composition, or varying the shell thickness. In this chapter, we review the recent advances of the synthetic approaches, optical properties engineering, and charge dynamics of core/shell QDs with type I, type II, and quasi-type II band structure and highlight their application in solar-driven photoelectrochemical (PEC) cells. The device performance of these core/shell QD-based PEC cells is discussed in detail and their prospective developments toward future device optimizations and commercialization are proposed as well.

Photoelectrochemical (PEC) cells fabricated using environment-friendly colloidal quantum dots (QDs) are promising optoelectronic devices for future practical solar-to-hydrogen conversion. However, the majority of current eco-friendly QDs-based PEC cells exhibited low efficiency mainly due to the charge trapping at QDs’ surface states and interfacial recombination processes in devices. Here, eco-friendly AgInS2 (AIS) QDs-based PEC cells passivated with variable ZnS layers were fabricated and the effects of ZnS surface passivation on corresponding device performance were investigated. It is demonstrated that optimizing the thickness of the ZnS passivation layers can largely suppress the charge trapping/recombination and enhance the electron injection efficiency in the PEC devices, leading to a saturated photocurrent density of ~5.7 mA/cm2 under standard AM 1.5 G solar illumination. Increasing the thickness of ZnS passivation layers can further inhibit the photocorrosion and give rise to higher device stability. These results indicate that ZnS surface passivation is a facile and efficient technique to boost the performance of eco-friendly QDs-based PEC cells.

Bi5O7I belongs to the family of bismuth oxyhalides (BiOX, X = Cl, Br, I), having a unique layered structure with an internal electrostatic field that promotes the separation and transfer of photo-generated charge carriers. Interestingly, Bi5O7I exhibits higher thermal stability compared to its other BiOX member compounds and absorption spectrum extended to the visible region. Bi5O7I has demonstrated applications in diverse fields such as photocatalytic degradation of various organic pollutants, marine antifouling, etc. Unfortunately, owing to its wide band gap of ∼2.9 eV, its absorption lies mainly in the ultraviolet region, and a tiny portion of absorption lies in the visible region. Due to limited absorption, the photocatalytic performance of pure Bi5O7I is still facing challenges. In order to reduce the band gap and increase the light absorption capability of Bi5O7I, doping and formation of heterostructure strategies have been employed, which showed promising results in the photocatalytic performance. In addition, the plasmonic heterostructures of Bi5O7I were also developed to further boost the efficiency of Bi5O7I as a photocatalyst. Here, in this review article, we present such recent efforts made for the advanced development of Bi5O7I regarding its synthesis, properties and applications. The strategies for photocatalytic performance enhancement have been discussed in detail. Moreover, in the conclusion section, we have presented the current challenges and discussed possible prospective developments in this field.

Colloidal quantum dots (QDs) with core/shell architecture can offer tailored electronic and optical properties which are promising for various optoelectronic applications. Here, we report the growth of multifunctional AgGaS2 (AGS)/CdSeS core/shell QDs via a simple two-step synthetic method. In comparison to the bare AGS QDs, as-synthesized core/shell QDs revealed enhanced visible light absorption, red-shifted emission and prolonged exciton lifetime, demonstrating the type II band alignment of the AGS core and CdSeS shell structure for improved charge separation/transfer, as further verified by the measured ultrafast carrier dynamics. The heterostructured core/shell QDs were used to fabricate both the photoelectrochemical (PEC) cells and photodetectors for efficient solar energy conversion and light detection, showing a maximum photocurrent density of ~4.8 mA/cm2 under visible light irradiation and a detectivity of 3.3 × 1010 Jones under wavelength of 510 nm, respectively. These findings indicate that the rational design of core/shell architecture is promising to tailor the optoelectronic properties and band structure of QDs for versatile and high-performance optoelectronic applications.

In this paper, high-index Bi2Se3(2045) films are achieved on a Bi-modified Si(211) substrate with corrugated surface morphologies composed of striplike 19.5° tilted (001) facets by molecular beam epitaxy. The chemical bonds between Bi2Se3(001) faces and Bi-absorbed nanoscale faceted (111) terraces on Si(211) surfaces provide solid lattice constraints which favor the coherent epitaxy of Bi2Se3 films on the Bi-modified Si(211) substrate as compared to the H-passivated Si(211) substrate. This makes Bi2Se3(2045) grown on Bi-modified Si(211) more suitable for device applications. Temperature-dependent I-V measurements of the Bi2Se3(2045)/Si(211) heterojunction are performed which yield a Schottky barrier height of ФB = 0.22 eV at the heterointerface.