Colloidal Quantum Dots Research Articles

Optical Applications of CuInSe2 Colloidal Quantum Dots.

The distinctive chemical, physical, electrical, and optical properties of semiconductor quantum dots (QDs) make them a highly fascinating nanomaterial that has been extensively studied. The CuInSe2 (CIS) QDs demonstrates great potential as a nontoxic alternative to CdSe and PbSe QDs for realizing high-performance solution-processed semiconductor devices. The CIS QDs show strong light absorption and bright emission across the visible and infrared spectrum and have been designed to exhibit optical gain. The special characteristics of these properties are of great significance in the fields of solar energy conversion, display, and electronic devices. Here, we present a comprehensive overview of the potential applications of colloidal CIS QDs in various fields, with a particular focus on solar energy conversion (such as QD solar cells, QD-sensitized solar cells, and QD luminescence solar concentrators), solar-to-hydrogen production (such as photocatalytic and photoelectrochemical H2 production), and QD electronics (such as QD transistors, QD light-emitting diodes, and QD photodetectors). Furthermore, we offer our insights into the current challenges and future opportunities associated with CIS QDs for further research.

Modulating lifetime distribution through variable excitation pulse length and power: a case study on colloidal PbS quantum dots

Modulating lifetime distribution through variable excitation pulse length and power: a case study on colloidal PbS quantum dots

Surface-Reconstructed InAs Colloidal Nanorod Quantum Dots for Efficient Deep-Shortwave Infrared Emission and Photodetection.

Shortwave infrared (SWIR) light emitters and detectors are crucial in numerous applications. Conventionally, SWIR devices rely on epitaxially grown narrow bandgap semiconductors, such as InGaAs, which are expensive to fabricate and difficult to integrate with silicon complementary metal-oxide-semiconductors (CMOS). Colloidal quantum dots (CQDs) have emerged as low-cost alternatives to epitaxially grown semiconductors, offering integration with CMOS through solution-processing methods. However, the predominant SWIR-active CQD systems rely on heavy-metal-containing compositions (PbS and HgTe), hindering the adoption of CQD SWIR technology. InAs CQDs are promising substitutes in SWIR applications. However, synthesizing SWIR-active InAs CQDs is challenging, often constraining them to the visible or near-infrared regions. To achieve SWIR bandgaps, large InAs CQDs are typically required; such CQDs are prone to having surface traps that quench photogenerated charge carriers, adversely affecting device performance. Here, we report a two-step synthesis of surface-passivated SWIR-active InAs/ZnSe core/shell colloidal nanorod quantum dots (CNQDs). These surface-passivated CNQDs are highly emissive and tunable over the entire technologically important region (1200-1800 nm) of the SWIR window with photoluminescence quantum yields as high as 60%. Using these SWIR-active InAs/ZnSe CNQDs, we demonstrated an SWIR-active InAs CQD photodetector, achieving a record high external quantum efficiency of ∼15% at ∼1450 nm and a low dark current of ∼10-2 mA/cm2.

Direct Photopatterning of Colloidal Quantum Dots with Electronically Optimized Diazirine Cross-Linkers.

Colloidal quantum dots (QDs) with a wide color gamut and high luminescent efficiency are promising for next-generation electronic and photonic devices. However, precise and scalable patterning of QDs without degrading their properties and their integration into commercially relevant devices, such as digitally addressable QD light-emitting diode (QLED) displays, remain challenging. Here, we develop electronically optimized diazirine-based cross-linkers for nondestructive, direct photopatterning of QDs and, ultimately, building the active-matrix QLED displays. The key to the cross-linker design is the introduction of electron-donating substituents that permit the formation of ground-state singlet carbenes for air-stable and benign QD photopatterning. Under ambient conditions, these cross-linkers enable the patterning of heavy metal-free QDs at a resolution of over 13,000 pixels per inch using commercial i-line photolithography. The patterned QD layers fully preserved their optical and optoelectronic properties. Pixelated electroluminescent devices with patterned InP/ZnSe/ZnS QD layers show a peak external quantum efficiency of 15.3% and a maximum luminance of about 40,000 cd m-2, outperforming those made by existing QD patterning approaches. We further show the seamless integration of patterned QLEDs with thin-film transistor circuits and the fabrication of dual-color active-matrix displays. These results underscore the importance of designing photochemistry for QD patterning, and promise the implementation of direct photopatterning methods in manufacturing commercial QLED displays and other integrated QD device platforms.

High Performance Infrared InAs Colloidal Quantum Dot Photodetector with 79% EQE Enabled by an Extended Absorber Layer

AbstractColloidal quantum dots (CQDs) with tunable bandgaps in the NIR‐SWIR range are highly valued for infrared applications including LiDAR, interactive displays, and biometrics. Particularly, for environmental considerations, photodetectors (PDs) using InAs CQDs are actively being explored. However, their performance still lags behind that of Pb‐based devices. Herein, an effective strategy to improve the photodetection characteristics of InAs CQD PDs by enhancing the incident photon usage is presented. By engineering the solvent of InAs CQD ink to increase volatility, the controllable range of absorber layer thickness is substantially extended. Then, the thickness‐ and bias‐dependent performance of InAs CQD PDs are systematically studied, guided by optical simulations. Under optimal conditions, an external quantum efficiency (EQE) of 79%, a responsivity of 0.6 AW−1–the highest reported for InAs CQD photodiodes, and a detectivity of 3.1 × 1011 Jones at 940 nm are achieved. Furthermore, it is found that increasing the absorber layer thickness reduces device capacitance, resulting in a faster response time of 46 ns. This study provides optical and electrical insights into how absorber layer thickness affects InAs CQD PD performance and outlines design principles for high‐performance optoelectronic devices with specified light‐absorbing layers, paving the way for the development of advanced optoelectronic devices.

Silver Telluride Colloidal Quantum Dot Solid for Fast Extended Shortwave Infrared Photodetector.

Extended shortwave infrared (eSWIR) photodetectors that employ solution-processable semiconductors have attracted attention for use in applications such as ranging, night vision, and gas detection. Colloidal quantum dots (CQDs) are promising materials with facile bandgap tunability across the visible-to-mid-infrared wavelengths. However, toxic elements, such as Hg and Pb, and the slow response time of CQD-based IR photodetectors, limit their commercial viability. This article presents a novel eSWIR photodetector that is fabricated using silver telluride (Ag2Te) CQDs. Effective thiolate ligand exchange enables a lower trap density and improved carrier mobility in CQD solids. Furthermore, a vertical p-n photodiode architecture with a favorable energy-level landscape is utilized to facilitate charge extraction, resulting in a fast, room-temperature-operable, and toxic-element-free CQD photodetector. The best eSWIR Ag2Te CQD photodetector exhibits a fall time of 72ns, representing the fastest response time among all prior CQD-based eSWIR photodetectors, including those containing toxic elements, such as Pb and Hg.

Extended Short-Wavelength Infrared Ink by Surface-Tuned Silver Telluride Colloidal Quantum Dots and Their Infrared Photodetection

Extended Short-Wavelength Infrared Ink by Surface-Tuned Silver Telluride Colloidal Quantum Dots and Their Infrared Photodetection

Ultrafast and Highly Collimated Radially Polarized Photons at Room Temperature from a Colloidal Quantum Dot Coupled to a Hybrid Nanoantenna

Ultrafast and Highly Collimated Radially Polarized Photons at Room Temperature from a Colloidal Quantum Dot Coupled to a Hybrid Nanoantenna

Analysis on the shape of α-Sn CQDs

In the search for materials alternate to bulk HgCdTe for high performance infrared imaging applications, colloidal quantum dots (CQDs), particularly HgTe CQDs, have gained traction owing to acceptable detector performance with easy preparation and low cost. In this article, we evaluate α-Sn CQDs, an environmentally less reactive and less toxic alternative to HgTe, for infrared sensing applications. Ab initio density functional theory calculations are used to study the shape-dependent stability, electronic bandgap, and absorption coefficient of α-Sn CQD nanoparticles (NPs). We consider three possible CQD shape constructions—Wulff, shell-by-shell, and spherical. The CQD of Wulff construction is predicted to be the most stable. However, we find that the size, not the shape, of the NP has a strong effect on the bandgap and absorption coefficient. Consequently, a sharp absorption edge is expected even in an ensemble of CQDs with different shapes. Importantly, the shape determines the position of the band edges with respect to vacuum, and thus offers a possibility of choosing the shape to improve alignment with the energy levels of ligands to enable efficient drift transport, instead of a slower and less efficient hopping transport.

3D-printed copolymer semi-cavity sensor with inner optical filter-effecting quantum dots photoluminescence for multiple drugs and amino acids detection

Here, we demonstrate a prototype for a novel optical sensor based on 3D-printed copolymer semi-cavity embedded with colloidal ZnCuInS (ZCIS) quantum dots (QDs) and utilizing the optical filter-effect in the QDs photoluminescence excitation pathway by analytes in the solution. First, in situ copolymerization of styrene and n-butyl methacrylate (P(S-BMA)) with colloidal ZCIS QDs allowed formation of solid P(S-BMA) matrix homogeneously impregnated with QDs. Then QDs@P(S-BMA) mixed with polylactic acid (PLA) has been processed into QDs@P(S-BMA)@PLA hybrid filaments using extruder. Then, a semi-cavity optical cell was 3D-printed out of QDs@P(S-BMA)@PLA filaments. Such 3D-printed semi-cavity cell can be used as the optical sensor on various molecules utilizing the optical absorption by analyte molecules through inner filter effect (IFE) of a properly selected QDs excitation beam. The multiple drug and amino acid molecules have been utilized having selective UV absorption to examine our proof of concept.

Advancing the Coupling of III–V Quantum Dots to Photonic Structures to Shape Their Emission Diagram

AbstractThe development of optoelectronic devices based on III–V semiconductor colloidal quantum dots (CQDs) is highly sought after due to their reduced toxicity. While devices based on conventional CQDs (II–VI semiconductors, halide perovskites) have achieved impressive technological leaps since their discovery, the most mature of these compounds contain toxic heavy metal elements (Cd, Hg, or Pb), which are highly undesirable for safe industrial scale applications. The strong covalent bonds of III–V compounds like InP, InAs, or InSb prevent the release of their toxic atoms, making them safer. However, these same bonds create severe material constraints. Namely, their harsher reaction conditions and increased sensitivity to oxidation have kept most of the research focused on material development. Meanwhile, their integration into devices and their coupling to photonic structures lag behind. Here, the integration of InAs/ZnSe core‐shell CQDs is advanced. First, the material parameters necessary to design plasmonic gratings coupled to the CQDs are elucidated and those gratings are fabricated. Angle‐resolved spectroscopy shows that the plasmon modes successfully couple to the CQD layer's emission leading to a tunable directivity with a 15° linewidth. A 3‐fold increase of the PL signal is achieved at normal incidence, thus advancing toward the goal of efficient outcoupling in LEDs.

Modulating Eco-friendly Colloidal AgGaS2 Quantum Dots for Highly Efficient Photodetection and Image Sensing via Direct Growth of Ternary AgInS2 Shell.

Tailoring the optoelectronic characteristics of colloidal quantum dots (QDs) by constructing a core/shell structure offers the potential to achieve high-performing solution-processed photoelectric conversion and information processing applications. In this work, the direct growth of wurtzite ternary AgInS2 (AIS) shell on eco-friendly AgGaS2 (AGS) core QDs is realized, giving rise to broadened visible light absorption, prolonged exciton lifetime and enhanced photoluminescence quantum yield (PLQY). Ultrafast transient absorption spectroscopy demonstrats that the photoinduced carrier separation and transfer kinetics of AGS QDs are significantly optimized following the AIS shell coating. As-synthesized environmentally benign AGS/AIS core/shell QDs are employed to fabricate photodetectors (PDs), showing a remarkable responsivity of 38.4 AW-1 and a detectivity of 2.4×1012 Jones under visible light illumination (405 nm). Moreover, the fabricated QDs-PDs exhibit superior image-sensing capability to record complex patterns with high resolution (160×160 pixels) under visible light illumination at 405 and 532 nm. The findings indicate that the direct growth of multinary narrow-band shell materials on eco-friendly QDs holds great promise to implement future "green", cost-effective and high-performance optoelectronic sensing/imaging systems.

Hydrogen chloride treated InAs quantum dot thin film phototransistor for ultrahigh responsivity

Indium Arsenide (InAs) colloidal quantum dots (CQDs) are emerging candidates for infrared photodetector applications owing to their excellent optoelectronic properties and low toxicity. However, low electron mobility stemming from its unique surface chemistry hinders its practical application. Through comprehensive structural and chemical analyses, we optimized the one-step HCl treatment to achieve stoichiometric balance, a well-passivated surface with low defect density, and an improved coupling effect by reducing the interparticle distance. Subsequently, a near infrared photodetector at a wavelength of 980 nm was fabricated with the modified InAs QDs in thin film transistor structure by all-solution process, showing remarkable electron mobility enhancement of up to 3.15 cm2/V∙s. The thin film phototransistor exhibited excellent photoresponse with a responsivity of 5.45 × 103 A/W, external quantum efficiency of 6.90 × 105%, and a linear dynamic range of 50 dB. This achievement represents the highest responsivity observed in an InAs QD-based phototransistor device, demonstrating its potential for lead-free infrared (IR) region optoelectronic applications.

A Review on Pulsed Laser Preparation of Quantum Dots in Colloids for the Optimization of Perovskite Solar Cells: Advantages, Challenges, and Prospects.

In recent years, academic research on perovskite solar cells (PSCs) has attracted remarkable attention, and one of the most crucial issues is promoting the power conversion efficiency (PCE) and operational stability of PSCs. Generally, modification of the electron or hole transport layers between the perovskite layers and electrodes via surface engineering is considered an effective strategy because the inherent structural defects between charge carrier transport layers and perovskite layers can be reshaped and modified by adopting the functional nanomaterials, and thus the charge recombination rate can be naturally decreased. At present, large amounts of available nanomaterials for surface modification of the perovskite films are extensively investigated, mainly including nanocrystals, nanorods, nanoarrays, and even colloidal quantum dots (QDs). In particular, as unique size-dependent nanomaterials, the diverse quantum properties of colloidal QDs are different from other nanomaterials, such as their quantum confinement effects, quantum-tunable effects, and quantum surface effects, which display great potential in promoting the PCE and operational stability of PSCs as the charge carriers in perovskite layers can be effectively tuned by these quantum effects. However, preparing QDs with a neat and desirable size remains a technical difficulty, even though the present chemical engineering is highly advanced. Fortunately, the rapid advances in laser technology have provided new insight into the precise preparation of QDs. In this review, we introduce a new approach for preparing the QDs, namely pulsed laser irradiation in colloids (PLIC), and briefly highlight the innovative works on PLIC-prepared QDs for the optimization of PSCs. This review not only highlights the advantages of PLIC for QD preparation but also critically points out the challenges and prospects of QD-based PSCs.

Intraband cascade electroluminescence with weakly n-doped HgTe colloidal quantum dots.

Room temperature 6μm intraband cascade electroluminescence (EL) is demonstrated with lightly n-doped HgTe colloidal quantum dots of ∼8nm diameter deposited on interdigitated electrodes in a metal-insulator-metal device. With quantum dot films of ∼150nm thickness made by solid-state-ligand-exchange, the devices emit at 1600cm-1 (6.25μm), with a spectral width of 200cm-1, determined by the overlap of the 1Se-1Pe intraband transition of the quantum dots and the substrate photonic resonance. At the maximum current used of 20 mA, the bias was 30V, the external quantum efficiency was 2.7%, and the power conversion efficiency was 0.025%. Adding gold nano-antennas between the electrodes broadened the emission and increased the quantum efficiency to 4.4% and the power efficiency to 0.036%. For these films, the doping was about 0.1 electron/dot, the electron mobility was 0.02cm2V-1s-1, and the maximum current density was 0.04kAcm-2. Higher mobility films made by solution ligand exchange show a 20-fold increase in current density and a 10-fold decrease in EL efficiencies. Electroluminescence with weak doping is interesting for eventually achieving electrically driven stimulated emission, and the requirements for population inversion and lasing are discussed.

Coherent random fiber laser emission from CdSe/ZnS quantum dots.

We experimentally demonstrate the coherent random laser emission by combining CdSe/ZnS colloidal quantum dots (CQDs) with hollow optical fiber. Through the localized surface plasmon resonance (LSPR) induced by Ag nanoparticles (NPs), well-distinguished discrete spikes are observed from the Ag modified hollow fiber loaded with CdSe/ZnS QDs solution. In addition, coherent random laser action with low threshold is also realized in the hollow optical fiber filled with high packing-density CdSe/ZnS QDs even if the Ag NPs is not introduced. The self-assembled clusters of CdSe/ZnS QDs serve as the optical gain media as well as the strong scattering centers. The angle measurement experiments show that the directional emission of random laser can be adjusted by using different pumping manners. This facile, inexpensive, low pump threshold random laser could be widely used in photonic devices and display imaging.&#xD.

In-Situ Surface Repair of FAPbBr3 Quantum Dots toward High-Performance Pure-Green Perovskite Light-Emitting Diodes.

Metal halide perovskite light-emitting diodes (PeLEDs) are ideal for high-resolution displays due to their tunable emission, narrow spectra, and low-cost processing. Colloidal FAPbBr3 perovskite quantum dots (PeQDs) enhance radiative recombination, making them efficient for pure-green PeLEDs. However, their low stability and surface defects limit their practical application. Here, we address these challenges by proposing an in situ surface repair strategy using benzhydroxamic acid (BHA) as a modifier. We demonstrated that BHA can coordinate with Pb2+ ions and form hydrogen bonds with FA+ and halide ions, effectively reducing nonradiative recombination and maintaining the integrity of the PeQDs. High-quality FAPbBr3 PeQDs with a photoluminescence quantum yield (PLQY) of up to 92.5% were achieved, leading to pure-green PeLEDs with an external quantum efficiency (EQE) of 24.8% and a maximum luminance of 40,231 cd m-2, providing a feasible and promising perspective for advanced solid-state lighting and displays.

Inserting colloidal quantum dots into GaN mesa-array subsurface porous structures through electrochemical etching for display color conversion application

High-efficiency photon color conversion is an approach of great potential for implementing color display. Inspired by the observation of emission enhancement in a nanoscale cavity, a novel technique to fabricate an array of color converter by mixing colloidal quantum dots (QDs) with the electrolyte of an electrochemical etching (ECE) process is demonstrated. In this process, QDs flow with the electrolyte into the etched subsurface nanoscale porous structure (PS) and settle inside. Since the PS formation and hence QD insertion are controlled by the flow path of the applied electric current in the ECE process, this technique can be used for fabricating any graphic pattern. The nanostructure of such a QD-inserted mesa is examined to confirm QD insertion. Although only single-color mesa arrays are demonstrated in this paper, this technique can be used for fabricating a multiple-color mesa array if a QD or a light-emitting nanoparticle of higher thermal stability is available.

Increase the efficiency of lead sulfide colloidal quantum dots solar cells by incorporating In2O3 and NiO interlayers

Substantial advancements have been made in PbS colloidal quantum dot solar cells (CQDSCs) by focusing on device architecture, manipulating band alignment, and refining the surface chemistry of colloidal quantum dots (CQDs). Nevertheless, creating an incredibly stable and efficient solar cell remains a challenging problem for researchers in this field. This study reveals that the efficiency of PbS CQDSCs can be improved by incorporating ultrathin In2O3 (between ITO electrode & indium-doped zinc oxide ETL) and NiO (between PbS-EDT HTL and Au electrode) nanocrystalline interlayers. The enhanced power conversion efficiency (PCE), which increases from 11.5 % to 13.6 %, is attributed to the improved surface smoothness and well-matched energy bandgap. Furthermore, following a heating period of 90 min at a temperature of 80 °C and 50 days of storage in the air, the solar cells containing these interlayers retained 98 % and 99 % of their initial efficiency, respectively. In distinction, the control device without these interlayers maintained only 85 % and 91 % of their initial efficiency under identical testing environments.

Colloidal 2D Layered SiC Quantum Dots from a Liquid Precursor: Surface Passivation, Bright Photoluminescence, and Planar Self-Assembly.

We report the bottom-up synthesis of colloidal two-dimensional (2D) layered silicon carbide (SiC) quantum dots with a cubic structure, lateral size of 5-10 nm, ⟨110⟩ exfoliation to few atomic layers, and surface passivation with 1-dodecene. Samples shielded from oxygen and plasma-annealed for purity exhibit narrow blue photoluminescence (PL) with quantum yields (QYs) over 60% in exceptional cases, while unshielded nanocrystals (NCs) exhibit broad blue/green/white PL with 10-15% QY. The latter scenario is attributed to excess surface carbon and oxygen accrued during synthesis and processing, with size separation through ultracentrifugation revealing size-dependent impurity emission. In contrast, the shape of the bright narrow blue PL shows little variation with NC size, while in both scenarios, the maximum QY occurs near four atomic layers. When dried under heat, the disk-like NC suspensions are observed to aggregate into microscale domains, with further self-assembly into planar superlattice domains with common crystalline orientation. The results are compared with photophysical simulations and bring clarity to the broad emission commonly reported for top-down approaches, while inspiring bottom-up schemes directed at improved material quality.