III-V colloidal quantum dots (CQDs) with large and well-controlled diameters are of interest in applications from red light emitters to deep short-wave infrared (SWIR) photodetectors, yet nanocluster-seeded syntheses often encounter an empirical "size wall" in the ∼5-8 nm diameter range. Here, we identify monomer release and transfer from nanoclusters to growing seeds as a key kinetic constraint during extended injection and growth. We show that short-chain carboxylic acids (SCCAs) can act as transient ligands that increase nanocluster lability and enhance monomer transfer, enabling continuous growth beyond this plateau. 1H NMR using 13C-labeled acetic acid quantifies a ∼1:1 myristate/acetate ligand ratio on the initial nanoclusters, with diffusion-ordered spectroscopy (DOSY) supporting the transient surface association of acetate; 2H NMR of CQDs grown with deuterated acetic acid (CD3COOH) shows no residual deuterium signal, indicating that acetate promotes growth without persisting on the final CQD surface. Across a C1 (formic) to C4 (butyric) SCCA screen, C2 (acetic) acid provides the best balance of volatility and lability. Incorporating SCCAs at the nanocluster stage yields InAs CQDs with excitonic features extending up to 1800 nm. XPS and indium K-edge XANES/EXAFS analyses indicate diminished oxide-related features in acetic acid-derived samples compared with size-matched controls. We fabricate photodetectors with a 1520 nm exciton, extending InAs CQD photodetection into the deep SWIR.

PbS colloidal quantum dots (CQDs) with tunable near-infrared bandgaps are promising for applications in photovoltaics, light-emitting devices, and photodetectors. Device optimization requires a clear understanding of the electronic structure. Photoelectron spectroscopy probes the occupied states of ligand-functionalized PbS CQDs. However, ultraviolet photoelectron spectroscopy (UPS) probes only the electronic structure at the CQD surface and cannot access core electronic states. To obtain comprehensive surface and core information, we combined UPS and X-ray photoelectron spectroscopy (XPS) to simultaneously determine band structures and employed a gas cluster ion beam (GCIB) sputtering for depth profiling. The CQDs are initially covered by iodine and oxygen; the oxygen acts as an acceptor that partially compensates the heavily n-type iodine ligands, resulting in a weak n-type surface, whereas the sulfur-enriched core exhibits a strong p-type structure. After removal of surface oxygen, the surface of the iodine-passivated quantum dots exhibits n+-type, and the core demonstrates weak p-type. These ensemble-averaged measurements reveal a surface sharp n+-p transition in PbS CQDs, arising from competition between iodide-induced electron donation and oxygen-induced compensation at the surface together with the sulfur-rich core composition.

Colloidal quantum dot (CQD) thin films hold promise for low-cost and high-resolution short-wave infrared imaging, yet their performance is hindered by an inhomogeneous energy landscape arising from the CQD synthetic polydispersity and ligand exchange process. Herein, by adopting a mild solvent in the solid-state ligand exchange process, this process transitions from kinetically favorable to thermodynamically stable, thereby obtaining the PbS CQD film with a homogeneous energy landscape. The optimal CQD film exhibits a sharp bandtail and largely reduced density of trap states, effectively suppressing thermal carrier generation and a trap-associated generation-recombination process. Consequently, the photodetector achieves an ultralow reverse-bias dark current density (Jdark) of 5.8 × 10-9 A cm-2 at -0.3 V. This is among the lowest reported Jdark to date. Furthermore, efficient carrier extraction to the electron acceptor is achieved under zero bias conditions, and the photocurrent exhibits weak dependence on reverse bias, both helpful for attaining linear output in the source-follower scheme.

The deterministic integration of multiple materials is the cornerstone of the semiconductor industry, traditionally accomplished through complex microfabrication techniques, such as lithography, transfer, and wafer bonding. Inspired by biological systems that precisely form intricate intracellular structures, self-assembly offers an efficient, bottom-up pathway for monolithic integration. The challenge, however, lies in controlling the transport of multiple components within the inherently chaotic and confined fluidic environments of microfabrication, which typically induces mixed phases and structural disorder. Herein, we utilize capillary bridges with Marangoni vortex flow to guide the segregation of colloidal quantum dots (CQDs) by size, enabling the efficient self-assembly of multicomponent microstructures. The fluid flow in our system establishes a regulated concentration gradient. This gradient drives the diffusiophoresis of larger CQDs away from the evaporation front, inducing a "small-at-front" segregation. The versatility and robustness of our platform are demonstrated by the various phase-segregated microstructures with customizable morphologies and diverse compositions. To showcase its practical application, we leverage this technique to integrate dual-wavelength lasers within a single photonic circuit, achieving the on-chip propagation of coherent light for optical communications. Our work introduces a novel approach to multicomponent microfabrication.

Colloidal quantum dot light-emitting diodes (QD-LEDs) offer narrowband, color-pure emission, solution processability, and wavelength tunability for next-generation displays. However, commercialization is hindered by positive aging-a storage-driven drift in which device external quantum efficiency (EQE) increases for several days before peaking, reflecting slow interfacial trap passivation in oxide electron-transport layers (ETLs). This drift delays qualification, complicates calibration, and degrades device-to-device uniformity because the as-fabricated performance does not represent the final state. Here, we suppress positive aging by pre-stabilizing ZnMgO ETLs via single-source chloride doping (MgCl2), which mitigates oxygen vacancy (OV)-related defect signatures. Time-dependent X-ray photoelectron spectroscopy, single-carrier device measurements, and steady-state/time-resolved QD photoluminescence show that undoped ZnMgO undergoes gradual defect passivation during storage, whereas Cl-doped ZnMgO remains nearly time-invariant. As a result, devices with Cl-doped ZnMgO reach peak EQE at day 0 and maintain it during storage, while devices with undoped ZnMgO require several days to reach peak efficiency. In addition, as-fabricated QD-LEDs employing Cl-doped ZnMgO exhibit ≈1.8× higher peak EQE and ≈1.3× longer operational lifetime than undoped controls, with negligible positive aging signatures. This intrinsic ETL stabilization enables day-0 calibration, improves uniformity and yield, and removes the need for storage-driven conditioning-identifying single-source chloride doping as a practical route to robust ZnMgO ETLs for display applications.

To broaden the potential applications of colloidal quantum dots, sustainable synthetic protocols must be developed and optimised. In this report, we use a low-temperature water-based synthesis of Cu-In-Zn-S quantum dots (CIZS) and we analyse the effect of different ligands (citrate, ascorbate, glutathione, cysteine and mercapto-acetic acid) on crystal growth and composition. The ligands employed have a strong effect on the metal incorporation within the nanocrystal, leading to wide tunability of the photophysical behaviour of the resulting CIZS quantum dots.

Photoinduced electron transfer (PET) in colloidal quantum dots (QDs) is important for solar-energy applications. However, in these systems, interfacial charge transfer competes with intrinsic recombination losses. We investigated PET kinetics in CdSe-based QDs with different shell architectures (CdSe, CdSe/CdS, and CdSe/CdS/ZnS) using anthraquinone as an electron acceptor to study the effects of surface trap-mediated relaxation and tunneling barriers. Inorganic shells effectively suppress trap-mediated nonradiative decay but simultaneously inhibit PET by introducing tunneling barriers and reducing the thermodynamic driving force. Conversely, bare CdSe QDs exhibit intrinsically fast electron transfer but suffer from dominant surface trap-mediated relaxation, limiting PET efficiency. By resolving the distinct contributions, we demonstrate that the surface modification of bare QDs can tune the nonradiative relaxation rate and PET efficiency without the penalty of a tunneling barrier. Therefore, the surface-engineered control of nonradiative decay in shell-free QDs is a critical design parameter for optimizing energy-conversion systems.

Dependence of Short-Range Energy Transfer Behavior on the Average Distance between Colloidal Quantum Dots in Solutions: Implications for Resonance Energy Transfer

Bolometric detection offers a compelling route to room-temperature mid- and long-wave infrared (MWIR/LWIR) photodetection by measuring temperature-induced conductivity changes in a thermistor element thermally coupled to an absorber. However, conventional thermistor materials such as vanadium oxide (VOx) and amorphous silicon (a-Si) exhibit moderate temperature coefficient of resistance (TCR) values (-2 to -3%/K). Higher TCRs have been achieved using SiGe/Si quantum wells (∼-5%/K), yet these require costly epitaxial growth and further improvements are hindered by lattice mismatch-induced defects. Here, we report a novel thermistor platform based on colloidal quantum dots (CQDs) that circumvents these limitations by exploiting their lattice-mismatch-free nature. By tuning the size and surface chemistry of lead chalcogenide CQDs, we engineer the energetic potential landscape to modulate thermal activation energy, achieving TCR values of up to -9%/K. We further integrate this CQD thermistor with a plasmonic metamaterial absorber (PMA), enabling room-temperature wavelength-selective photodetection across the mid- to long-wave infrared (MWIR/LWIR) spectrum. The bolometer detectors exhibited LWIR response with a time constant of ∼8ms and room-temperature detectivity approaching 106 Jones at 9µm, without using microelectromechanical systems (MEMS) technology.

Colloidal quantum dot light-emitting diodes (QLEDs) typically rely on ZnO-based electron transport layers (ETLs), which often suffer from excessive electron injection and an undesirable positive aging effect. Herein, we demonstrate a new class of ZnxCd1-xS alloy nanocrystals as bandgap- and mobility-tunable ETLs for inverted QLEDs. By varying the Zn/Cd ratio, the optical bandgap of the ZnxCd1-xS nanocrystals can be continuously tuned from 2.52 to 3.85 eV, enabling precise alignment of the conduction band minimum with the quantum dot emissive layer. Furthermore, an in situ ligand exchange with 3-mercaptopropionic acid (MPA) is employed to replace the long-chain insulating oleylamine ligand, significantly enhancing the film conductivity by nearly 2 orders of magnitude. MPA-treated Zn0.1Cd0.9S-based QLED achieves a maximum external quantum efficiency of 16.4% and a peak luminance of 139,937 cd m-2, representing an ∼93% enhancement over the untreated device. This work establishes composition- and ligand-engineered ZnxCd1-xS alloy nanocrystals as versatile and efficient ETL platforms for next-generation QLEDs.

Photocrosslinkers with dual-functional crosslinking mechanisms for direct photolithographic patterning of quantum dots.

Spectral down-shifting colloidal quantum dot solids for enhanced photosynthetic biofuel production

Tunable intraband transitions in colloidal quantum dots (QDs) have emerged as a promising platform for electronic transitions relevant to mid- to long-wavelength infrared optoelectronic devices. However, their broad device applications have been limited by an incomplete understanding of their spectroscopic and electrical properties. In this study, we investigate both the optical and electrical characteristics of N-doped PbS QDs using ultrafast mid-infrared transient absorption spectroscopy and temperature-dependent carrier transit time measurements. Our findings reveal intraband absorption coefficients ranging from 6 × 103 to 13 × 103 cm-1, accompanied by varying carrier recombination pathways associated with different doping levels. Notably, the average carrier relaxation lifetime is 88 ps for 5.4 nm QDs, whereas highly doped 7.7 nm QDs exhibit a significantly shorter carrier lifetime of 20 ps. These results not only elucidate the intraband optical properties of PbS QDs but also provide valuable insights for comparing carrier lifetimes to carrier transit times, thereby offering guidance for the design of future mid-infrared optoelectronic devices.

A critical challenge in nanophotonics is developing scalable and versatile fabrication methods that can precisely control photonic and plasmonic properties across large areas without compromising optical performance. Recently, significant progress has been made in the synthesis of colloidal quantum dots (QDs) and plasmonic nanoparticles. These advances, combined with precise and defect‐free assembly approaches, have overcome longstanding limitations in fabrication. Our approach integrates the benefits of top‐down nanoimprint lithography with bottom‐up self‐assembly techniques, including template‐assisted self‐assembly (TASA), layer‐by‐layer (LbL) assembly, and physical vapor deposition. Through mode‐resolved photoluminescence (PL) analysis, supported by electromagnetic simulations, we identify previously unreported metal‐assisted hybrid guided‐mode resonances (MA‐hGMRs) at near‐normal incidence (approximately 1°). This mode exhibits a quality factor (Q‐factor) of up to 18.6 and yields PL enhancement nearly threefold. The centimeter‐scale metasurfaces also allow us to resolve MA‐GMR and Rayleigh‐anomaly surface‐plasmon‐polariton modes, which arise from specific combinations of the QD and gold nanoparticle (AuNP) layers. Structural characterization analyses verify that the layer thicknesses and grating profiles remain uniform across centimeter‐scale areas, which is crucial for achieving reproducible device performance. These correlations between structure and optical response provide practical guidelines for designing colloidal metasurfaces with tailored emission characteristics.

HgTe colloidal quantum dots (CQDs) hold great promise for the next generation of low-cost and large-format infrared imagers. The implementation of the ZnO/HgTe/ZnTe double heterojunction enables HgTe imagers in photovoltaic mode. However, it remains challenging to further improve the performance and stability of the detector. Here, we propose a hybrid passivation strategy employing methylammonium iodide (MAI) and HgI2 to address this challenge. This approach generates strongly bound X-type HgI3- ligands that effectively passivate the HgTe CQDs surface. The hybrid passivated HgTe CQDs demonstrate enhanced colloidal stability and surface passivation, which translate into improved detector performance and stability. The resulting photodetector achieves a remarkable external quantum efficiency (EQE) of 66.8% at 1620 nm under zero bias, a specific detectivity of 1.45 × 1012 Jones, and a dark current density as low as 185 nA/cm2. The HgTe CQD detectors were successfully integrated with thin-film transistor (TFT) readout circuits. The enhanced stability of the detectors based on hybrid passivated HgTe CQDs was verified at both the single-pixel and array levels.

Colloidal semiconductor quantum dots (QDs) have been synthesized extensively via hot-injection approaches. Using cadmium sulfide (CdS) as a model system, we present compelling evidence for the first time that similar prenucleation clusters (PNCs) appear in both hot-injection and heating-up approaches to CdS QDs. Two reactions were studied. One reaction was in ODE (1-octadecene), with Cd(OA)2 (cadmium oleate) and SODE (sulfur powder dissolved in ODE). The other reaction was in TDO (1-tetradecanol), with Cd(OA)2 and STDO (sulfur powder dissolved in TDO). Furthermore, we reveal that the preformed PNC disappeared faster at a higher temperature and QDs emerged. When PNC-containing samples from the two reactions were dispersed at room temperature, magic-size clusters (MSC-311 displaying optical absorption peaking at ∼311 nm) developed. Accordingly, we conclude that the two-step model proposed by Yu provides more precise explanations to the N/G of QDs and the appearance of MSCs than the LaMer model does.

Charge-carrier transport in semiconductor colloidal quantum dot (CQD) solids has been the subject of extensive debate and investigation for more than a decade. Understanding the underlying transport mechanisms in CQD assemblies is critical for unlocking their full potential in optoelectronic applications. To date, a widely accepted view holds that carrier transport in conventional ligand-capped glassy CQD solids is a non-adiabatic hopping process, supported by both experimental observations and theoretical models. In contrast, recent advances have enabled the self-assembly of CQDs into long-range-ordered superlattices with epitaxial connections between neighboring QDs. These superlattices are expected by many to exhibit band-like transport, potentially overcoming the limitations of hopping conduction in disordered systems. However, definitive experimental evidence and a comprehensive theoretical framework for charge transport in such highly ordered structures remain lacking. While the formation mechanisms of these superlattices have been widely explored, this Perspective aims to provide insight into the current understanding of charge-carrier transport in epitaxially connected CQD superlattices.

Near-infrared (NIR) wavelengths offer a powerful approach for non-invasive physiological monitoring due to the deep tissue penetration and ability to detect various endogenous molecules such as hemoglobin species, water, and lipids. Herein, we demonstrate a high-speed, non-contact photoplethysmography (PPG) system based on indium arsenide (InAs) colloidal quantum dots (CQDs). To this end, a seedless injection-based one-pot method was devised to synthesize monodisperse NIR InAs CQDs. This scalable approach enables precise bandgap tuning from 1.53 to 1.09 eV, aligning with the absorption spectra of hemoglobin and oxyhemoglobin. Furthermore, the proposed CQD-based PPG system is integrated into a real-time acquisition platform. Exercise-induced desaturation tests show that the CQD-based PPG system exhibits consistent oxygen saturation rate (SpO2) trends compared to commercial oximeters, exhibiting a considerable agreement of 99.76% (SpO2 range: 90%-92%). The system also shows reliable operation with a bandwidth up to 2.5 kHz under multi-lock-in detection.

Improving the stability of colloidal CsPbBr3 quantum dots with ZnO as surface modifier

How to suppress the development of magic-size clusters (MSCs) in reactions of colloidal semiconductor quantum dots (QDs) remains an outstanding challenge. Using the reaction of Cd(OAc)2/OLA (made from cadmium acetate and oleylamine) and TeTOP (tri-n-octylphosphine telluride) as a model system, we show that when tri-n-octylamine (TOA) was used as a reaction medium, MSCs did not form, but QDs did. When OLA was used, MSCs and QDs evolved together. To explain the effect of reaction media, we suggest that prenucleation clusters (PNCs) form first via chemical self-assembly of Cd(OAc)2/OLA and TeTOP. Afterward, the PNC-QD and/or PNC-MSC transformation occurs. The former is favored by a less polar environment (TOA), while the latter by a more polar environment (OLA). Paving the avenue to the inhibition of MSCs in the QD synthesis, this work brings deeper insight into the two-step model, showing that the reaction medium affects the formation and transformation of the PNC.