Quantum Dot Films Research Articles

High-sensitivity NO2 fluorescence sensor based on a QDs@Aerogels/SM composite nanofilm

Quantum dots (QDs) exhibit excellent optical and chemical properties, making them advantageous for fluorescence sensing. However, gas sensor using QDs is often hampered by challenges such as gas diffusion and low concentration. This work describes the development of a nitrogen dioxide (NO2) fluorescence gas sensor that utilizes a QDs@Aerogels/SM composite nanofilm containing CdTe QDs modified by reduced glutathione (GSH), silica microspheres (SMs), and silica aerogel. The SM and porous aerogels create a uniform porous structure that enhances the distribution of QDs. Compared to the pure QDs film, the QDs@Aerogels/SM composite film exhibits enhanced fluorescence intensity. The porous structure promotes the adsorption of NO2, which improves the detection sensitivity. The QDs@Aerogels/SM composite film was applied in a portable gas sensor. The sensor demonstrates a good linear response to NO2 gas in the range of 0–10 ppm, with an ultra-low detection limit of 0.096 ppm and high selectivity. The uniform distribution of aerogel and SM enhances the stability of the composite nanofilm, and the fluorescence of the films remains virtually unchanged over a period of 60 days which ensures its optimal performance over extended periods of use. The fluorescent NO2 sensor demonstrated selective and sensitive quenching upon exposure to NO2, making it ideal for environmental monitoring and further applications.

Fabrication of a uniform quantum dot film with a high quantum yield

We present a method that uses viscosity-lowering materials to fabricate flexible polydimethylsiloxane-based quantum dot (QD) films with high quantum yield (QY) and improved uniformity. We found that the aggregation of individual QDs was prevented, and the QY improved simultaneously in films that contained surfactants. These films showed an improved absorption of approximately 27% in the near-UV and blue light regions, along with an improved photoluminescence of approximately 18%, indicating improved light conversion from the UV to the visible frequency region.

Gradient Hole Injection Inducing Efficient Exciton Recombination in Blue (475 nm) Perovskite QLEDs.

Perovskite quantum dots (QDs) are emerging as excellent light sources for light-emitting diodes (LEDs). However, the performance of blue perovskite QD-based LEDs (QLEDs) still lags behind that of red and green counterparts, which is hindered by blue perovskite QDs with broad bandgaps that tend to increase nonradiative recombination. Here, we designed a gradient energy for hole injection utilizing multiple hole injection layers (HTLs) combined with carbazole-based small-molecule modification to reduce the hole injection barrier between HTLs and QD layers and improve the hole injection efficiency, realizing efficient exciton recombination in blue perovskite QLEDs. Moreover, the QD film on the designed HTLs demonstrates a lower surface roughness and improved photoluminescence properties. The optimized blue CsPbCl3-xBrx QLEDs exhibit an impressive external quantum efficiency of 20.7% with an electroluminescence peak at 475 nm and a turn-on voltage of 2.6 V, representing the state-of-the-art for blue perovskite LEDs emitting in the range of 460-480 nm.

Special-point approach for optical absorption coefficient calculations on two-dimensional self-assemblies of type-II perovskite quantum dots

All-inorganic perovskite quantum dots with the usual cubic shape have emerged as a successful and low-cost alternative to electronically functional nanomaterials motivating various fields of applications, including high-efficiency photovoltaics. Here, we present an efficient and almost analytic approach for optical absorption coefficient calculation on self-assembled perovskite quantum dot films with type-II band alignment. The approach takes advantage of the special point technique for integration over the two-dimensional Brillouin zone, which minimizes the computational cost. The set of special wave-vector points is generated using the Monkhorst and Pack method. The optical absorption spectrum for phenyl-C60-butyric acid methyl ester (PCBM)/CsPbI3quantum dot films is computed, in good agreement with the experiment assuming a homogeneous linewidth of 50 meV and considering a ten special-point set. We show that light absorption in these systems is a cooperative optoelectronic property resulting from the quantum-mechanical coupling between perovskite nanocubes, leading to extended system states. The generality of this approach makes it suitable for calculating the optical absorption coefficient in a broad class of perovskite quantum dot systems.

Synergistic effect of 2D covalent organic frameworks confined 0D carbon quantum dots film: Toward molecularly imprinted cathodic photoelectrochemical platform for detection of tetracycline

The development of high photoactive cathode materials combined with the formation of a stable interface are considered important factors for the selective and sensitive photoelectrochemical (PEC) detection of tetracycline (TC). Along these lines, in this work, a novel type II heterostructure composed of two-dimensional (2D) covalent organic frameworks confined to zero-dimensional (0D) carbon quantum dots (CDs/COFs) film was successfully synthesized using the rapid in-situ polymerization method at room temperature. The PEC signal of CDs/COFs was significantly amplified by improving the light absorption and electron transfer capabilities. Furthermore, a cathodic molecularly imprinted PEC sensor (MIP-PEC) for the detection of TC was constructed through fast in-situ Ultraviolet (UV) photopolymerization on the electrode. Finally, a “turn-off” PEC cathodic signal was achieved based on the selective recognition of the imprinted cavity and the mechanism of steric hindrance increase. Under optimal conditions, the proposed sensor demonstrated a wide linear relationship with TC in the concentration range of 5.00 × 10−12–1.00 × 10−5 M, with a detection limit as low as 6.00 × 10−13 M. Meanwhile, excellent stability, selectivity, reproducibility, and applicability in real river samples was recorded. Our work provides an effective and rapid in situ construction method for fabricating highly photoactive cathode heterojunctions and uniform stable selective MIP-PEC sensing interfaces, yielding accurate antibiotics detection in the environment.

Siloxane-based oligomer ligands of indium phosphide quantum dots for improving dispersion in a siloxane matrix

The ligands of indium phosphide (InP) quantum dots (QDs) were modified with siloxane-based oligomers in a two-step process to improve the dispersion of InP QDs in a siloxane-based matrix. Oleic acid ligands on InP QDs (InP-OA) were exchanged with 6-mercapto-1-hexanol. Then, the hydroxyl functional groups (–OH) of the ligands were induced to react with poly(dimethylsiloxane), diglycidyl ether terminated (PDMS-DGE) by a ring-opening reaction of epoxide. The chemical bonding between the hydroxyl groups and PDMS-DGE was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The synthesized InP QDs with PDMS-DGE ligands (InP-PDMS-DGE) were blended with acrylate-siloxane polymers to produce color conversion QD films. The photoluminescence (PL) intensity of the QD films with the InP-PDMS-DGE QDs was improved by 2.3 times compared with that of InP-OA QDs. The color conversion efficiency of the QD films was determined using a blue light-emitting diode (LED), and the QD film containing InP-PDMS-DGE QDs demonstrated a conversion efficiency of 21%, compared to a lower efficiency of 17% for a film containing InP-OA QDs. The stability of the InP-PDMS-DGE film was tested at 85°C with a relative humidity (RH) of 85%, demonstrating an improvement of 28% compared to that with an InP-OA film.

Flexible polyaniline/carbon quantum dots films for enhanced electrochromic performance

Polyaniline (PANI) conducting polymers exhibit potential electrochromic properties. However, the electrochromic response of PANI films in the infrared (IR) ranges is restricted by their dense structure. Herein, the polyaniline/carbon quantum dots (PANI/CQDs) films were synthesized with sulfuric acid (SA) and CQDs as the dopants. The tetrahedral structures of SA contribute to the formation of highly oriented lamellar PANI. The synergistic effect between CQDs and PANI promotes the loose and porous surface morphology, thereby improving the electrochromic performance of PANI film. The PANI/CQDs porous film for the polymerization charge of 0.5C (PANI/CQDs-5) shows the optimal electrochromic properties and IR modulation capacity, achieving an optical contrast (ΔT) values of 53 % at 850 nm, and with the emittance variation (Δε) values of 0.41, 0.46 and 0.42 in 3–5 μm, 8–14 μm, and 2.5–25 μm, respectively. Furthermore, the switching time of the PANI/CQDs-5 films for coloration and blanching are 2.5 s and 3.6 s, respectively, with over 95 % retention after 100 cycles. Theoretical calculations verified that PANI/CQDs composite films displayed outstanding electron and ion transfer kinetics, facilitating superior electrochromic properties.

Anion-Driven Bandgap Tuning of AgIn(SxSe1-x)2 Quantum Dots.

Accurate tuning of the electronic and photophysical properties of quantum dots is required to maximize the light conversion efficiencies in semiconductor-assisted processes. Herein, we report a facile synthetic procedure for AgIn(SxSe1-x)2 quantum dots with S content (x) ranging from 1 to 0. This simple approach allowed us to tune the bandgap (2.6-1.9 eV) and extend the absorption of AgIn(SxSe1-x)2 quantum dots to lower photon energies (near-IR) while maintaining a small QD size (∼5 nm). Ultraviolet spectroscopy studies revealed that the change in the bandgap is modulated by the electronic shifts in both the valence band and the conduction band positions. The negative overall charge of the as-synthesized quantum dots enabled us to make films of quantum dots on mesoscopic TiO2. Excited state studies of the AgIn(SxSe1-x)2 quantum dot films demonstrated a fast charge injection to TiO2, and the electron transfer rate constant was found to be 1.5-3.5 × 1011 s-1. The results of this work present AgIn(SxSe1-x)2 quantum dots synthesized by the one-step method as a potential candidate for designing light-harvesting assemblies.

Stable random laser of perovskite quantum dots based on SiO2-QDs-SiO2 composite nanostructure

In recent years, metal halide perovskite has gradually become a hotspot in the field of optoelectronics. However, the inherent instability of CsPbX3 quantum dots (QDs) seriously affects the amplified spontaneous emission (ASE) or lasing performance. Herein, the highly stable CsPbBr3 random laser is realized in SiO2-QDs-SiO2 (SQS) composite nanostructure doped with Ag nanoislands. The strong scattering generated by SQS composite nanostructure and the localized surface plasmon resonance (LSPR) of metal silver nanoislands provide optical feedback for the formation of random laser. Then a coherent random laser with low threshold (∼2.2 mJ/cm2) is obtained. SiO2 microspheres anchor QDs to avoid photoinduced regeneration and fluorescence quenching caused by QDs clusters. The inner QDs of SQS are effectively protected from water erosion, thus resulting that the samples have higher water resistance. The luminescence intensity still maintains 70 % of the original intensity after 40 days with the addition of pure water. Our research provides an effective method for improving the water stability of perovskite QDs. The highly stable random laser based on perovskite quantum dot film has a wide application prospect in integrated optoelectronics, display imaging and sensing measurement.

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.

Non-contact and non-destructive in-situ inspection for CdSe quantum dot film based on the principle of field-induced photoluminescence quenching

Non-contact and non-destructive in-situ inspection for CdSe quantum dot film based on the principle of field-induced photoluminescence quenching

High-Performance CsPbI3 Quantum Dot Photodetector with a Vertical Structure Based on the Frenkel-Poole Emission Effect.

The selection of photoactive materials and the design of device structures are critical to the photoelectronic performance of photodetectors. This study reports on a vertically structured photodetector device with rapid, stable, and efficient photoelectric performance across the UV-visible broadband range based on the Si++/SiO2/Au/single-layer graphene/CsPbI3 quantum dots (QDs) configuration. In this specific device structure, a relatively high conductivity Si++/SiO2 wafer was used as the substrate, a CsPbI3 QD film with high light absorption was used as the photoactive layer, and a monolayer graphene with high conductivity was inserted between the substrate and the CsPbI3 QD film to form a heterojunction with the QD film. Based on the Frenkel-Poole emission effect arising from the high trap state density within the SiO2 layer, the device exhibited excellent photoelectric performances. Especially at a wavelength of 365 nm, a photocurrent responsivity of 2319 A/W, a specific detectivity of 1.15 × 1014 Jones, an external quantum efficiency of 7883%, and an on/off time of 39/36 ms at a Si++ terminal voltage of -80 V and an optical power density of 84.03 nW/cm2 can be achieved.

Enhancing the reliability of InP-based QD color conversion layer through a uniform organic encapsulation layer via inkjet printing

Quantum dot (QD) as a color conversion layer (CCL) is gaining increasing attention for use in next generation displays. However, QD CCL, especially those based on indium phosphide (InP) materials, are vulnerable to oxygen and moisture. Accordingly, even in CCL technology, encapsulation is essential to mitigate performance reduction due to the degradation of color conversion efficiency (CCE). Herein, we employed only acrylic-based resin to produce a uniform encapsulation layer on a CCL, enhancing the CCE reliability of the QD CCL under ambient conditions. To print a uniform encapsulation layer, we confirmed the significance of the minimized surface energy differences on glass, bank, and QD film through O2 plasma treatment. We also investigated coating characteristics through adjustment of the drop spacing to analyze the reliability of the CCL. Compared to the CCL without an encapsulation layer, the CCE only showed a decrease of 1.96 % at green and 3.6 % at red light, after 168 h. The T95 (time to 95 % of the initial luminance) was improved from 5.25 h to 75.02 h by applying the encapsulation layer. As a result, we enhanced the stability of the InP-based QD CCL by printing only an organic encapsulation layer using the inkjet printing process.

Ligand‐Solvent Coordination Enables Comprehensive Trap Passivation for Efficient Near‐Infrared Quantum Dot Light‐Emitting Diodes

AbstractNear‐infrared light‐emitting diodes (NIR LEDs) based on perovskite quantum dots (QDs) have produced external quantum efficiency (EQE) of ~15 %. However, these high‐performance NIR‐QLEDs suffer from immediate carrier quenching because of the accumulation of migratable ions at the surface of the QDs. These uncoordinated ions and carriers—if not bound to the nanocrystal surface—serve as centers for exciton quenching and device degradation. In this work, we overcome this issue and fabricate high‐performance NIR QLEDs by devising a ligand anchoring strategy, which entails dissolving the strong‐binding ligand (Guanidine Hydroiodide, GAI) in the mediate‐polar solvent. By employing the dye‐sensitized device structure (phosphorescent indicator), we demonstrate the elimination of the interface defects. The treated QDs films exhibit an exciton binding energy of 117 meV: this represents a 1.5‐fold increase compared to that of the control (74 meV). We report, as a result, the NIR QLEDs with an EQE of 21 % which is a record among NIR perovskite QLEDs. These QLEDs also exhibit a 7‐fold higher operational stability than that of the best previously reported NIR QLEDs. Furthermore, we demonstrate that the QDs are compatible with large‐area QLEDs: we showcase 900 mm2 QLEDs with EQE approaching 20 %.

Ligand-Solvent Coordination Enables Comprehensive Trap Passivation for Efficient Near-Infrared Quantum Dot Light-Emitting Diodes.

Near-infrared light-emitting diodes (NIR LEDs) based on perovskite quantum dots (QDs) have produced external quantum efficiency (EQE) of ~15 %. However, these high-performance NIR-QLEDs suffer from immediate carrier quenching because of the accumulation of migratable ions at the surface of the QDs. These uncoordinated ions and carriers-if not bound to the nanocrystal surface-serve as centers for exciton quenching and device degradation. In this work, we overcome this issue and fabricate high-performance NIR QLEDs by devising a ligand anchoring strategy, which entails dissolving the strong-binding ligand (Guanidine Hydroiodide, GAI) in the mediate-polar solvent. By employing the dye-sensitized device structure (phosphorescent indicator), we demonstrate the elimination of the interface defects. The treated QDs films exhibit an exciton binding energy of 117 meV: this represents a 1.5-fold increase compared to that of the control (74 meV). We report, as a result, the NIR QLEDs with an EQE of 21 % which is a record among NIR perovskite QLEDs. These QLEDs also exhibit a 7-fold higher operational stability than that of the best previously reported NIR QLEDs. Furthermore, we demonstrate that the QDs are compatible with large-area QLEDs: we showcase 900 mm2 QLEDs with EQE approaching 20 %.

High performance pixelated quantum dots array on Micro-LED by inkjet printing

Micro-LED display has risen to prominence in research and industry, distinguished by their numerous advantages. Quantum dots (QDs) film, serving as color conversion layers (CCLs) for Micro-LED, are considered a leading candidate for the next generation of displays, owing to their low power consumption and broad color gamut. Inkjet printing stands out as a feasible approach for crafting QDs CCLs. The essence of the process hinges on attaining a printed QDs film that boasts both uniformity and high-precision QDs array. However, the unstable printing of QDs ink significantly impacts the surface morphology of QDs arrays and the display performance of Micro-LEDs. Therefore, elucidating the mechanism behind the unstable printing of QDs in inkjet printing and fabricating QDs is of paramount importance. In this study, through the simulation of unstable printing with conventional QDs ink, we identified nozzle blockage and the rapid evaporation of low-boiling-point ink as the primary causes of unstable printing. This leads to aggregation and deposition of QDs, obstructing the nozzle and altering the fluid path. A novel binary organic composite ink was employed to print the QDs array on the substrate with ultra-stability, achieving a high yield and greatly reduced coffee-ring effect Micro-LED full-color display.

Multi‐Mode Elastic Full‐Color Fluorescent Patterns for Multi‐Visual Encryption

AbstractThe development of multi‐mode fluorescent patterns has attracted widespread attention, particularly for applications in high‐density information storage and highly secure encryption. However, the fabrication process of multi‐mode fluorescent patterns generally involves tedious and expensive steps. Specifically, in the fabrication technology of elastic full‐color fluorescent patterns, there is still a lack of ideal patterning preparation technology that can overcome the solvent orthogonality problem associated with multi‐color fabrication while ensuring both high elasticity and luminescence efficiency of the pattern. Herein, the multi‐mode elastic fluorescent patterns are successfully fabricated by multiple transferring of the quantum dots (QDs) from the carrier substrates to the elastomeric PDMS substrate via femtosecond laser‐induced forward transfer (FsLIFT) technology. Due to its solvent‐free nature, absence of masking requirements, and no need for annealing during FsLIFT processing, the multiple transferred QD films achieve independent patterns and does not interfere with each other, providing a strong promise for the fabrication of multi‐mode elastic full‐color patterns. Based on these stretchable fluorescent patterns, multi‐visual encryption techniques are successfully demonstrated. The proposed FsLIFT technology offers an efficient and straightforward strategy for fabricating multi‐mode fluorescent patterns with potential applications in advanced commercial security information encryption and dynamic camouflage.

Solution-processed ZnO quantum dot thin films with low solvent residues and ultra-flat surfaces

ZnO quantum dots are considered a desirable material for the electron transport layer (ETL) in thin-film optoelectronic devices, determining their efficiency and stability. Solution-processed ZnO quantum dot films are fascinating due to the potential for low-cost manufacture of large-area devices and the compatibility with flexible substrates. However, eliminating solvent residues from solution-derived ZnO films remains a challenge, as their presence can significantly impact the efficiency and performance of the devices. Herein, we reported a straightforward and controllable strategy to overcome the above problem, aiming to achieve low solvent residues and ultra-flat ZnO films. Methanol, with its low boiling point and high relative evaporation rate, is utilized as a dispersing solvent for ZnO quantum dots, the resulting thin films exhibit low solvent residue, as confirmed by TGA and NMR analyses. Moreover, we achieved a stable monodisperse state of ZnO quantum dots in methanol solvent for three months by a simple temperature control method. The ZnO film prepared using a low-temperature spin-coating technique demonstrates extremely low surface roughness (RMS less than 1 nm).

Correlation between Photoluminescence Features and Enhanced Performance in Formamidinium Lead Triiodide Quantum Dot Solar Cells by Replacement of Octadecene

In this study, an innovative approach is developed for fabricating formamidinium lead triiodide (FAPbI3) quantum dots (QDs) by substitution of octadecene (ODE). The results showcase the formation of superior‐quality FAPbI3 QD films, boasting enhanced photoluminescence (PL) and transport properties. Specifically, ODE has been replaced with octene (OCE), a shorter linear alpha olefin. Comparisons are drawn between the novel synthesis method and the conventional ODE‐based QD films, scrutinizing their optical properties and applicability in QD solar cells. The outcomes highlight distinctions in temperature‐dependent PL emission characteristics, revealing an unprecedented absolute PL QY of up to 84%, a notable improvement from the 70% achieved with ODE, along with enhanced transport properties. Furthermore, the performance of both systems in QD solar cells is evaluated for two values of layer thickness, 100 and 200 nm, to investigate the transport properties at the device level. The results exhibit a remarkable improvement from 200% to 150% in average power conversion efficiency (PCE) and consistently higher values for open‐circuit voltage and short‐circuit current density for the OCE‐based solar cell compared to an ODE‐based counterpart for both thickness values, reaching a striking 6.7% PCE for the best‐performing device despite the nonideal conditions.

Surface Engineering Enables Efficient AgBiS2 Quantum Dot Solar Cells.

Surface ligand chemistry is vital to control the synthesis, diminish surface defects, and improve the electronic coupling of quantum dots (QDs) toward emerging applications in optoelectronic devices. Here, we successfully develop highly homogeneous and dispersed AgBiS2 QDs, focus on the control of interdot spacing, and substitute the long-chain ligands with ammonium iodide in solution. This results in improved electronic coupling of AgBiS2 QDs with excellent surface passivation, which greatly facilitates carrier transport within the QD films. Based on the stable AgBiS2 QD dispersion with the optimal ligand state, a homogeneous and densely packed QD film is prepared by a facile one-step coating process, delivering a champion power conversion efficiency of approximately 8% in the QD solar cells with outstanding shelf life stability. The proposed surface engineering strategy holds the potential to become a universal preprocessing step in the realm of high-performance QD optoelectronic devices.