Lead‐Free,Blue Emitting Bismuth Halide Perovskite Quantum Dots

Lead halide perovskite quantum dots (QDs) are promising candidates for future lighting applications, due to their high quantum yield, narrow full width at half maximum (FWHM), and wide color gamut. However, the toxicity of lead represents a potential obstacle to their utilization. Although tin(II) has been used to replace lead in films and QDs, the high intrinsic defect density and oxidation vulnerability typically leads to unsatisfactory material properties. Bismuth, with much lower toxicity than lead, is promising to constitute lead‐free perovskite materials because Bi³⁺ is isoelectronic to Pb²⁺ and more stable than Sn²⁺. Herein we report, for the first time, the synthesis and optical characterization of MA₃Bi₂Br₉ perovskite QDs with photoluminescence quantum yield (PLQY) up to 12 %, which is much higher than Sn‐based perovskite nanocrystals. Furthermore, the photoluminescence (PL) peaks of MA₃Bi₂X₉ QDs could be easily tuned from 360 to 540 nm through anion exchange.     

Lead‐Free,Blue Emitting Bismuth Halide Perovskite Quantum Dots

Lead halide perovskite quantum dots (QDs) are promising candidates for future lighting applications, due to their high quantum yield, narrow full width at half maximum (FWHM), and wide color gamut. However, the toxicity of lead represents a potential obstacle to their utilization. Although tin(II) has been used to replace lead in films and QDs, the high intrinsic defect density and oxidation vulnerability typically leads to unsatisfactory material properties. Bismuth, with much lower toxicity than lead, is promising to constitute lead‐free perovskite materials because Bi³⁺ is isoelectronic to Pb²⁺ and more stable than Sn²⁺. Herein we report, for the first time, the synthesis and optical characterization of MA₃Bi₂Br₉ perovskite QDs with photoluminescence quantum yield (PLQY) up to 12 %, which is much higher than Sn‐based perovskite nanocrystals. Furthermore, the photoluminescence (PL) peaks of MA₃Bi₂X₉ QDs could be easily tuned from 360 to 540 nm through anion exchange.     

Cucurbiturils brighten Au nanoclusters in water

Gold nanoclusters (AuNCs) with well-defined atomically precise structures present promising emissive prospects for excellent biocompatibility and optical properties. However, the relatively low luminescence efficiency in solutions for most AuNCs is still a perplexing issue to be resolved. In this study, a facile supramolecular strategy was developed to rigidify the surface of FGGC-AuNCs by modifying transition rates in excited states via host–guest self-assembly between cucurbiturils (CBs) and FGGC (Phe–Gly–Gly–Cys peptide). In aqueous solutions, CB/FGGC-AuNCs presented an extremely enhanced red phosphorescence emission with a quantum yield (QY) of 51% for CB[7] and 39% for CB[8], while simple FGGC-AuNCs only showed a weak emission with a QY of 7.5%. Furthermore, CB[7]/FGGC-AuNCs showed excellent results in live cell luminescence imaging for A549 cancer cells. Our study demonstrates that host–guest self-assembly assisted by macrocycles is a facile and effective tool to non-covalently modify and adjust optical properties of nanostructures on ultra-small scales.

A host–guest self-assembly approach was developed to brighten Au₂₂(FGGC)₁₈ nanoclusters between CB[n] (n = 7, 8) and FGGC peptide in aqueous solutions.     

Stable Perovskite Quantum Dots Coated with Superhydrophobic Organosilica Shells for White Light‐Emitting Diodes

Metalammonium lead perovskite (MAPbX₃, MA=CH₃NH₃⁺; X=Cl, Br, I) quantum dots (QDs) have attracted tremendous attention due to their outstanding optical properties. However, they usually suffer from poor stability towards water or moisture, which seriously limits their practical applications. Here, we report a simple and effective approach to improve the stability of MAPbBr₃ QDs by encapsulating them with superhydrophobic fluorinated organosilica (FSiO₂) shells. The water‐resistant stability of the superhydrophobic MAPbBr₃ QDs/FSiO₂ is significantly enhanced and they display strong fluorescence even after immersion in water for 12 hours. This method is readily extended to prepare superhydrophobic MAPbBr_2.4Cl_0.6 QDs/FSiO₂ and MAPbI₃ QDs/FSiO₂ powders. These superhydrophobic MAPbX₃ QDs/FSiO₂ can be further used to fabricate white light‐emitting diodes (LEDs) with comparable color to pure white emission.     

Encapsulating Perovskite Quantum Dots in Iron‐Based Metal–Organic Frameworks (MOFs) for Efficient Photocatalytic CO2 Reduction

Improving the stability of lead halide perovskite quantum dots (QDs) in a system containing water is the key for their practical application in artificial photosynthesis. Herein, we encapsulate low‐cost CH₃NH₃PbI₃ (MAPbI₃) perovskite QDs in the pores of earth‐abundant Fe‐porphyrin based metal organic framework (MOF) PCN‐221(Fe_x) by a sequential deposition route, to construct a series of composite photocatalysts of MAPbI₃@PCN‐221(Fe_x) (x=0–1). Protected by the MOF the composite photocatalysts exhibit much improved stability in reaction systems containing water. The close contact of QDs to the Fe catalytic site in the MOF, allows the photogenerated electrons in the QDs to transfer rapidly the Fe catalytic sites to enhance the photocatalytic activity for CO₂ reduction. Using water as an electron source, MAPbI₃@PCN‐221(Fe_0.2) exhibits a record‐high total yield of 1559 μmol g^?1 for photocatalytic CO₂ reduction to CO (34 %) and CH₄ (66 %), 38 times higher than that of PCN‐221(Fe_0.2) in the absence of perovskite QDs.     

The atomic-level structure of bandgap engineered double perovskite alloys Cs2AgIn1−xFexCl6

Although lead-free halide double perovskites are considered as promising alternatives to lead halide perovskites for optoelectronic applications, state-of-the-art double perovskites are limited by their large bandgap. The doping/alloying strategy, key to bandgap engineering in traditional semiconductors, has also been employed to tune the bandgap of halide double perovskites. However, this strategy has yet to generate new double perovskites with suitable bandgaps for practical applications, partially due to the lack of fundamental understanding of how the doping/alloying affects the atomic-level structure. Here, we take the benchmark double perovskite Cs₂AgInCl₆ as an example to reveal the atomic-level structure of double perovskite alloys (DPAs) Cs₂AgIn_1−xFe_xCl₆ (x = 0–1) by employing solid-state nuclear magnetic resonance (ssNMR). The presence of paramagnetic alloying ions (e.g. Fe³⁺ in this case) in double perovskites makes it possible to investigate the nuclear relaxation times, providing a straightforward approach to understand the distribution of paramagnetic alloying ions. Our results indicate that paramagnetic Fe³⁺ replaces diamagnetic In³⁺ in the Cs₂AgInCl₆ lattice with the formation of [FeCl₆]³⁻·[AgCl₆]⁵⁻ domains, which show different sizes and distribution modes in different alloying ratios. This work provides new insights into the atomic-level structure of bandgap engineered DPAs, which is of critical significance in developing efficient optoelectronic/spintronic devices.

Through Fe³⁺-alloying, the bandgap of benchmark double perovskite Cs₂AgInCl₆ can be tuned from 2.8 eV to 1.6 eV. The atomic-level structure of Cs₂AgIn_1−xFe_xCl₆ was revealed by solid-state nuclear magnetic resonance (ssNMR).     

Controlling the alignment of 1D nanochannel arrays in oriented metal–organic framework films for host–guest materials design

Controlling the direction of molecular-scale pores enables the accommodation of guest molecular-scale species with alignment in the desired direction, allowing for the development of high-performance mechanical, thermal, electronic, photonic and biomedical organic devices (host–guest approach). Regularly ordered 1D nanochannels of metal–organic frameworks (MOFs) have been demonstrated as superior hosts for aligning functional molecules and polymers. However, controlling the orientation of MOF films with 1D nanochannels at commercially relevant scales remains a significant challenge. Here, we report the fabrication of macroscopically oriented films of Cu-based pillar-layered MOFs having regularly ordered 1D nanochannels. The direction of 1D nanochannels is controllable by optimizing the crystal growth process; 1D nanochannels align either perpendicular or parallel to substrates, offering molecular-scale pore arrays for a macroscopic alignment of functional guest molecules in the desired direction. Due to the fundamental interest and widespread technological importance of controlling the alignment of functional molecules and polymers in a particular direction, orientation-controllable MOF films will open up the possibility of realising the potential of MOFs in advanced technologies.

Orientation-controlled Cu₂(Linker)₂DABCO MOF films on macroscopic scales are fabricated for the development of high-performance devices; the direction of 1D nanochannels is controllable either perpendicular or parallel to substrates.     

On-surface isostructural transformation from a hydrogen-bonded network to a coordination network for tuning the pore size and guest recognition

Rational manipulation of supramolecular structures on surfaces is of great importance and challenging. We show that imidazole-based hydrogen-bonded networks on a metal surface can transform into an isostructural coordination network for facile tuning of the pore size and guest recognition behaviours. Deposition of triangular-shaped benzotrisimidazole (H₃btim) molecules on Au(111)/Ag(111) surfaces gives honeycomb networks linked by double N–H⋯N hydrogen bonds. While the H₃btim hydrogen-bonded networks on Au(111) evaporate above 453 K, those on Ag(111) transform into isostructural [Ag₃(btim)] coordination networks based on double N–Ag–N bonds at 423 K, by virtue of the unconventional metal–acid replacement reaction (Ag reduces H⁺). The transformation expands the pore diameter of the honeycomb networks from 3.8 Å to 6.9 Å, giving remarkably different host–guest recognition behaviours for fullerene and ferrocene molecules based on the size compatibility mechanism.

A hydrogen-bonded network on a Ag(111) surface can transform into an isostructural Ag(i) coordination network, giving drastically different host–guest recognition behaviours.     

A window-space-directed assembly strategy for the construction of supertetrahedron-based zeolitic mesoporous metal–organic frameworks with ultramicroporous apertures for selective gas adsorption

Despite their scarcity due to synthetic challenges, supertetrahedron-based metal–organic frameworks (MOFs) possess intriguing architectures, diverse functionalities, and superb properties that make them in-demand materials. Employing a new window-space-directed assembly strategy, a family of mesoporous zeolitic MOFs have been constructed herein from corner-shared supertetrahedra based on homometallic or heterometallic trimers [M₃(OH/O)(COO)₆] (M₃ = Co₃, Ni₃ or Co₂Ti). These MOFs consisted of close-packed truncated octahedral cages possessing a sodalite topology and large β-cavity mesoporous cages (∼22 Å diameter) connected by ultramicroporous apertures (∼5.6 Å diameter). Notably, the supertetrahedron-based sodalite topology MOF combined with the Co₂Ti trimer exhibited high thermal and chemical stability as well as the ability to efficiently separate acetylene (C₂H₂) from carbon dioxide (CO₂).

A series of supertetrahedron (ST)-based sodalite (sod)-topology zeolitic MOFs specimens ST-sod-MOFs featuring ultramicroporous square windows and a mesoporous sodcage have been synthesized via a window-space-directed assembly approach.     

Lanthanide MOFs for inducing molecular chirality of achiral stilbazolium with strong circularly polarized luminescence and efficient energy transfer for color tuning

We present herein an innovative host–guest method to achieve induced molecular chirality from an achiral stilbazolium dye (DSM). The host–guest system is exquisitely designed by encapsulating the dye molecule in the molecule-sized chiral channel of homochiral lanthanide metal–organic frameworks (P-(+)/M-(−)-TbBTC), in which the P- or M-configuration of the dye is unidirectionally generated via a spatial confinement effect of the MOF and solidified by the dangling water molecules in the channel. Induced chirality of DSM is characterized by solid-state circularly polarized luminescence (CPL) and micro-area polarized emission of DSM@TbTBC, both excited with 514 nm light. A luminescence dissymmetry factor of 10⁻³ is obtained and the photoluminescence quantum yield (PLQY) of the encapsulated DSM in DSM@TbTBC is ∼10%, which is close to the PLQY value of DSM in dilute dichloromethane. Color-tuning from green to red is achieved, owing to efficient energy transfer (up to 56%) from Ln³⁺ to the dye. Therefore, this study for the first time exhibits an elegant host–guest system that shows induced strong CPL emission and enables efficient energy transfer from the host chiral Ln-MOF to the achiral guest DSM with the emission color tuned from green to red.

Homochiral Ln-MOFs are synthesized to encapsulate achiral dyes to induce strong circularly polarized luminescence with a luminescence dissymmetry factor of 10⁻³.     

Amino‐Assisted Anchoring of CsPbBr3 Perovskite Quantum Dots on Porous g‐C3N4 for Enhanced Photocatalytic CO2 Reduction

Halide perovskite quantum dots (QDs) have great potential in photocatalytic applications if their low charge transportation efficiency and chemical instability can be overcome. To circumvent these obstacles, we anchored CsPbBr₃ QDs (CPB) on NH_x‐rich porous g‐C₃N₄ nanosheets (PCN) to construct the composite photocatalysts via N?Br chemical bonding. The 20 CPB‐PCN (20 wt % of QDs) photocatalyst exhibits good stability and an outstanding yield of 149 μmol h^?1 g^?1 in acetonitrile/water for photocatalytic reduction of CO₂ to CO under visible light irradiation, which is around 15 times higher than that of CsPbBr₃ QDs. This study opens up new possibilities of using halide perovskite QDs for photocatalytic application.     

A reduced-dimensional polar hybrid perovskite for self-powered broad-spectrum photodetection

Polar hybrid perovskites have been explored for self-powered photodetection benefitting from prominent transport of photo-induced carriers and the bulk photovoltaic effect (BPVE). However, these self-powered photodetection ranges are relatively narrow depending on their intrinsic wide bandgaps (>2.08 eV), and the realization of broad-spectrum self-powered photodetection is still a difficult task. Herein, we successfully obtained a polar multilayered perovskite, (I-BA)₂(MA)₂Pb₃I₁₀ (IMP, MA⁺ = methylammonium and I-BA⁺ = 4-iodobutylammonium), via rational dimension reduction of CH₃NH₃PbI₃. It features the narrowest bandgap of 1.71 eV in a BPV material. As a consequence, the integration of narrow bandgap and BPVE causes the self-powered photodetection to extend to 724 nm for IMP, and a repeatable photovoltaic current reaching 1.0 μA cm⁻² is acquired with a high “on/off” ratio of ∼10³ and photodetectivity (∼10⁹ Jones) at zero bias. This innovative research provides a foothold for adjusting the physical properties of hybrid perovskites and will expand their potential for self-powered broad-spectrum detection.

A polar hybrid perovskite with a wide-spectrum absorption extending to 724 nm was obtained . Benefitting from the narrow bandgap and bulk photovoltaic effects, self-powered broad-spectrum photodetection was achieved in hybrid perovskites.     

Alloying a single and a double perovskite: a Cu+/2+ mixed-valence layered halide perovskite with strong optical absorption

Introducing heterovalent cations at the octahedral sites of halide perovskites can substantially change their optoelectronic properties. Yet, in most cases, only small amounts of such metals can be incorporated as impurities into the three-dimensional lattice. Here, we exploit the greater structural flexibility of the two-dimensional (2D) perovskite framework to place three distinct stoichiometric cations in the octahedral sites. The new layered perovskites A^I₄[Cu^II(Cu^IIn^III)_0.5Cl₈] (1, A = organic cation) may be derived from a Cu^I–In^III double perovskite by replacing half of the octahedral metal sites with Cu²⁺. Electron paramagnetic resonance and X-ray absorption spectroscopy confirm the presence of Cu²⁺ in 1. Crystallographic studies demonstrate that 1 represents an averaging of the Cu^I–In^III double perovskite and Cu^II single perovskite structures. However, whereas the highly insulating Cu^I–In^III and Cu^II perovskites are colorless and yellow, respectively, 1 is black, with substantially higher electronic conductivity than that of either endmember. We trace these emergent properties in 1 to intervalence charge transfer between the mixed-valence Cu centers. We further propose a tiling model to describe how the Cu⁺, Cu²⁺, and In³⁺ coordination spheres can pack most favorably into a 2D perovskite lattice, which explains the unusual 1 : 2 : 1 ratio of these cations found in 1. Magnetic susceptibility data of 1 further corroborate this packing model. The emergence of enhanced visible light absorption and electronic conductivity in 1 demonstrates the importance of devising strategies for increasing the compositional complexity of halide perovskites.

A novel 2D halide perovskite with stoichiometric quantities of Cu⁺, Cu²⁺, and In³⁺ in the inorganic slabs shows emergent properties not seen in Cu^II or Cu^I–In^III perovskites, including enhanced visible-light absorption and electronic conductivity.     

Oxygen accelerated scalable synthesis of highly fluorescent sulfur quantum dots

Here, we report a facile and efficient approach for the large-scale synthesis of highly fluorescent sulfur quantum dots (SQDs) from inexpensive elemental sulfur under a pure oxygen (O₂) atmosphere. The important finding of this work is that the polysulfide (S_x²⁻) ions could be oxidized to zero-valent sulfur (S[0]) by O₂, which is the accelerator of the reaction. The SQDs prepared by this method possess nearly monodisperse size (1.5–4 nm), high fluorescence quantum yield (21.5%), tunable emission, and stable fluorescence against pH change, ionic strength variation and long-term storage. Moreover, the reaction yield of SQDs reached as high as 5.08% based on the content of S element in SQDs, which is much higher than other reported approaches (generally <1%). The prepared SQDs could be easily processed for widespread applications thanks to their low toxicity and superior dispersibility both in water and common organic solvents. These high-quality SQDs may find applications similar to or beyond those of carbon QDs and silicon QDs.

Highly fluorescent sulfur quantum dots could be rapidly and massively synthesized from inexpensive elemental sulfur under a pure O₂ atmosphere.     

Synthesis, structural characterization and selectively catalytic properties of metal-organic frameworks with nano-sized channels: A modular design strategy

Modular design method for designing and synthesizing microporous metal-organic frameworks (MOFs) with selective catalytical activity was described. MOFs with both nano-sized channels and potential catalytic activities could be obtained through self-assembly of a framework unit and a catalyst unit. By selecting hexaaquo metal complexes and the ligand BTC (BTC=1,3,5-benzenetricarboxylate) as framework-building blocks and using the metal complex [M(phen)₂(H₂O)₂]²⁺ (phen=1,10-phenanthroline) as a catalyst unit, a series of supramolecular MOFs 1-7 with three-dimensional nano-sized channels, i.e. [M¹(H₂O)₆]·[M²(phen)₂(H₂O)₂]₂·2(BTC)·xH₂O (M¹, M²Co(II), Ni(II), Cu(II), Zn(II), or Mn(II), phen=1,10-phenanthroline, BTC=1,3,5-benzenetricarboxylate, x=22−24), were synthesized through self-assembly, and their structures were characterized by IR, elemental analysis, and single-crystal X-ray diffraction. These supramolecular microporous MOFs showed significant size and shape selectivity in the catalyzed oxidation of phenols, which is due to catalytic reactions taking place in the channels of the framework. Design strategy, synthesis, and self-assembly mechanism for the construction of these porous MOFs were discussed.     

Solid-state NMR spectroscopy: an advancing tool to analyse the structure and properties of metal–organic frameworks

Metal–organic frameworks (MOFs) gain increasing interest due to their outstanding properties like extremely high porosity, structural variability, and various possibilities for functionalization. Their overall structure is usually determined by diffraction techniques. However, diffraction is often not sensitive for subtle local structural changes and ordering effects as well as dynamics and flexibility effects. Solid-state nuclear magnetic resonance (ssNMR) spectroscopy is sensitive for short range interactions and thus complementary to diffraction techniques. Novel methodical advances make ssNMR experiments increasingly suitable to tackle the above mentioned problems and challenges. NMR spectroscopy also allows study of host–guest interactions between the MOF lattice and adsorbed guest species. Understanding the underlying mechanisms and interactions is particularly important with respect to applications such as gas and liquid separation processes, gas storage, and others. Special in situ NMR experiments allow investigation of properties and functions of MOFs under controlled and application-relevant conditions. The present minireview explains the potential of various solid-state and in situ NMR techniques and illustrates their application to MOFs by highlighting selected examples from recent literature.

Metal–organic frameworks (MOFs) gain increasing interest due to their outstanding properties like extremely high porosity, structural variability, and various possibilities for functionalization.     

High‐Performance CsPb1−xSnxBr3 Perovskite Quantum Dots for Light‐Emitting Diodes

All inorganic CsPbBr₃ perovskite quantum dots (QDs) are potential emitters for electroluminescent displays. We have developed a facile hot‐injection method to partially replace the toxic Pb²⁺ with highly stable Sn⁴⁺. Meanwhile, the absolute photoluminescence quantum yield of CsPb_1−x Sn_x Br₃ increased from 45 % to 83 % with Sn^IV substitution. The transient absorption (TA) exciton dynamics in undoped CsPbBr₃ and CsPb_0.67Sn_0.33Br₃ QDs at various excitation fluences were determined by femtosecond transient absorption, time‐resolved photoluminescence, and single‐dot spectroscopy, providing clear evidence for the suppression of trion generation by Sn doping. These highly luminescent CsPb_0.67Sn_0.33Br₃ QDs emit at 517 nm. A device based on these QDs exhibited a luminance of 12 500 cd m⁻², a current efficiency of 11.63 cd A⁻¹, an external quantum efficiency of 4.13 %, a power efficiency of 6.76 lm w⁻¹, and a low turn‐on voltage of 3.6 V, which are the best values among reported tin‐based perovskite quantum‐dot LEDs.     

Use of a cyclo-P4 building block – a way to networks of host–guest assemblies

Despite the proven ability to form supramolecular assemblies via coordination to copper halides, organometallic building blocks based on four-membered cyclo-P₄ ligands find only very rare application in supramolecular chemistry. To date, only three types of supramolecular aggregates were obtained based on the polyphosphorus end-deck complexes Cp^RTa(CO)₂(η⁴-P₄) (1a: Cp^R = Cp′′; 1b: Cp^R = Cp′′′), with none of them, however, possessing a guest-accessible void. To achieve this target, the use of silver salts of the weakly coordinating anion SbF₆⁻ was investigated as to their self-assembly in the absence and in the presence of the template molecule P₃Se₄. The two-component self-assembly of the building block 1a and the coinage-metal salt AgSbF₆ leads to the formation of 1D or 3D coordination polymers. However, when the template-driven self-assembly was attempted in the presence of an aliphatic dinitrile, the unprecedented barrel-like supramolecular host–guest assembly P₃Se₄@[{(Cp′′Ta(CO)₂(η⁴-P₄))Ag}₈]⁸⁺ of 2.49 nm in size was formed. Moreover, cyclo-P₄-based supramolecules are connected in a 2D coordination network by dinitrile linkers. The obtained compounds were characterised by mass-spectrometry, ¹H and ³¹P NMR spectroscopy and X-ray structure analysis.

A one-pot self-assembly template-controlled reaction is reported to result in a 2D coordination network of first host-guest assemblies P₃Se₄@[{(Cp′′Ta(CO)₂(η⁴-P₄))Ag}₈]⁸⁺ of 2.49 nm in size based on an organometallic complex with a cyclo-P₄ end-deck.     

Free-standing metal–organic framework (MOF) monolayers by self-assembly of polymer-grafted nanoparticles

We report a general method for the synthesis of free-standing, self-assembled MOF monolayers (SAMMs) at an air–water interface using polymer-brush coated MOF nanoparticles. UiO-66, UiO-66-NH₂, and MIL-88B-NH₂ were functionalized with a catechol-bound chain-transfer agent (CTA) to graft poly(methyl methacrylate) (PMMA) from the surface of the MOF using reversible addition-fragmentation chain transfer polymerization (RAFT). The polymer-coated MOFs were self-assembled at the air–water interface into monolayer films ∼250 nm thick and capable of self-supporting at a total area of 40 mm². Mixed-particle films were prepared through the assembly of MOF mixtures, while multilayer films were achieved through sequential transfer of the monolayers to a glass slide substrate. This method offers a modular and generalizable route to fabricate thin-films with inherent porosity and sub-micron thickness composed of a variety of MOF particles and functionalities.

We report a general method for the synthesis of free-standing, self-assembled MOF monolayers (SAMMs) at an air–water interface using polymer-brush coated MOF nanoparticles.     

CsPbBr3–CdS heterostructure: stabilizing perovskite nanocrystals for photocatalysis

The instability of cesium lead bromide (CsPbBr₃) nanocrystals (NCs) in polar solvents has hampered their use in photocatalysis. We have now succeeded in synthesizing CsPbBr₃–CdS heterostructures with improved stability and photocatalytic performance. While the CdS deposition provides solvent stability, the parent CsPbBr₃ in the heterostructure harvests photons to generate charge carriers. This heterostructure exhibits longer emission lifetime (τ_ave = 47 ns) than pristine CsPbBr₃ (τ_ave = 7 ns), indicating passivation of surface defects. We employed ethyl viologen (EV²⁺) as a probe molecule to elucidate excited state interactions and interfacial electron transfer of CsPbBr₃–CdS NCs in toluene/ethanol mixed solvent. The electron transfer rate constant as obtained from transient absorption spectroscopy was 9.5 × 10¹⁰ s⁻¹ and the quantum efficiency of ethyl viologen reduction (Φ_EV⁺˙) was found to be 8.4% under visible light excitation. The Fermi level equilibration between CsPbBr₃–CdS and EV²⁺/EV⁺˙ redox couple has allowed us to estimate the apparent conduction band energy of the heterostructure as −0.365 V vs. NHE. The insights into effective utilization of perovskite nanocrystals built around a quasi-type II heterostructures pave the way towards effective utilization in photocatalytic reduction and oxidation processes.

The insights into effective utilization of perovskite nanocrystals built around a CsPbBr₃–CdS heterostructure pave the way towards their utilization in photocatalytic reduction and oxidation processes.