Quantum Dot Films Research Articles

Flexible Backlight and Quantum Dot Film for Photo-Dynamic Therapy

Flexible Backlight and Quantum Dot Film for Photo-Dynamic Therapy

In Situ Surface Reconstruction toward Planar Heterojunction for Efficient and Stable FAPbI3 Quantum Dot Solar Cells.

Pure-phase α-FAPbI3 quantum dots (QDs) are the focus of an increasing interest in photovoltaics due to their superior ambient stability, large absorption coefficient, and long charge-carrier lifetime. However, the trap states induced by the ligand-exchange process limit the photovoltaic performances. Here, a simple post treatment using methylamine thiocyanate is developed to reconstruct the FAPbI3 -QD film surface, in which a MAPbI3 capping layer with a thickness of 6.2 nm is formed on the film top. This planar perovskite heterojunction leads to a reduced density of trap-states, a decreased band gap, and a facilitated charge carrier transport. As a result, a record high power conversion efficiency (PCE) of 16.23% with negligible hysteresis is achieved for the FAPbI3 QD solar cell, and it retains over 90% of the initial PCE after being stored in ambient environment for 1000 h.

Photoelectric properties of thin layers of Ag2S quantum dots passivated with thiol-containing molecules

In this work, we studied the electrophysical properties of condensates of colloidal Ag2S quantum dots (QDs), passivated with thiol-containing molecules (thioglycolic acid and L-cysteine) (further, Ag2S/TGA QDs and Ag2S/L-Cys QDs) on indium tin oxide (ITO) substrates. The temperature dependences of the electrical characteristics (conductivity) are analyzed in the temperature range from 300 to 360 K. Facts of the formation of the Schottky barrier structures is obtained. Activation energies of 0.2 eV (Ag2S/L-Cys QDs) and 0.66 eV (Ag2S/TGA QDs) were obtained by the use of linear approximations of current–voltage (I–V) characteristics in Arrhenius coordinates. It is shown that the conductivity of ITO - Ag2S QDs film - Al structure is mainly determined by the Schottky barrier that is formed at the Al-Ag2S QDs film junction. The rectifying contact is formed at the Ag2S film -Al junction due to the lower work function of Al. The I–V characteristics under the optical radiation action were analyzed for the studied sandwich structures. They turned out to be similar for Ag2S/TGA and Ag2S/L-Cys QDs. When a reverse or forward bias voltage is applied to a sandwich structure, in the case of the optical radiation action with a wavelength starting from the its value, corresponding to the most probable exciton transition in the QDs absorption the photocurrent is observed. The found difference (by an order of magnitude) in the photocurrent values of the sandwich structure, based on Ag2S/TGA QDs and Ag2S/L-Cys QDs is related to the smaller thickness of the Ag2S/TGA QDs film.

Investigation of Ligand Exchange in Thin Films of PbS Colloidal Quantum Dots with FTIR-Spectroscopy

Investigation of Ligand Exchange in Thin Films of PbS Colloidal Quantum Dots with FTIR-Spectroscopy

Performance enhancement of PbS quantum dot solar cells employing a hybrid solid-state ligand exchange protocol

In this work, a hybrid (HB) solid-state ligand exchange strategy was developed for PbS quantum dots (QDs) films, incorporating a synergistic utilization of the popular inorganic ligand tetrabutylammonium iodide (TBAI) and the organic short bidentate linker 1, 2-Ethanedithiol (EDT) in a two-stage process. The two-stage process consisted of a primary solid-state ligand treatment with TBAI in a controlled manner followed by a second-stage ligand treatment with EDT. We could achieve an optimal iodine/EDT ligand passivation ratio for the QDs films by controlling the TBAI ligand treatment time. The method integrates the benefits of both the ligands and resolves the intrinsic incompleteness of the solid-state TBAI ligand exchange. The QDs films thus created have an optimal surface coverage and reduced inter-dot spacing due to an improved QDs close packing. This in turn led to lesser recombination routes due to reduced mid-bandgap trap states and an improved charge transport property through an enhanced electronic coupling between the QDs. A power conversion efficiency of 8.2 % has been achieved in the device with an optimized TBAI /EDT ligand passivation ratio for the QDs films with an EDT hole transport layer.

Stable PbS colloidal quantum dot inks enable blade-coating infrared solar cells

Infrared solar cells are more effective than normal bandgap solar cells at reducing the spectral loss in the near-infrared region, thus also at broadening the absorption spectra and improving power conversion efficiency. PbS colloidal quantum dots (QDs) with tunable bandgap are ideal infrared photovoltaic materials. However, QD solar cell production suffers from small-area-based spin-coating fabrication methods and unstable QD ink. Herein, the QD ink stability mechanism was fully investigated according to Lewis acid–base theory and colloid stability theory. We further studied a mixed solvent system using dimethylformamide and butylamine, compatible with the scalable manufacture of method-blade coating. Based on the ink system, 100 cm2 of uniform and dense near-infrared PbS QDs (~ 0.96 eV) film was successfully prepared by blade coating. The average efficiencies of above absorber-based devices reached 11.14% under AM1.5G illumination, and the 800 nm-filtered efficiency achieved 4.28%. Both were the top values among blade coating method based devices. The newly developed ink showed excellent stability, and the device performance based on the ink stored for 7 h was similar to that of fresh ink. The matched solvent system for stable PbS QD ink represents a crucial step toward large area blade coating photoelectric devices.Graphical

Resonant cavity phosphor

While phosphors play an immensely important role in solid-state lighting and full-colour displays, it has been noted lately that their performance can be largely improved via structural engineering. Here, phosphor material is synergistically merged with yet another structurally engineered platform, resonant cavity (RC). When a 40-nm-thick colloidal quantum dot (CQD) film is embedded in a tailored RC with a moderate cavity quality factor (Q ≈ 90), it gains the ability to absorb the majority (~87%) of excitation photons, resulting in significantly enhanced CQD fluorescence (~29×) across a reasonably broad linewidth (~13 nm). The colour gamut covered by red and green pixels implemented using the RC phosphor—along with a broad bandwidth (~20 nm) blue excitation source—exceeds that of the sRGB standard (~121%). The simple planar geometry facilitates design and implementation of the RC phosphor, making it promising for use in real applications.

Ligand‐Mediated Homojunction Structure for High‐Efficiency FAPbI3 Quantum Dot Solar Cells

AbstractFormamidinium lead iodide quantum dots (QDs) show great potential for solar cell applications but suffer from restricted charge transfer due to the insulating nature of their ligand shell. Management of the surface properties and resultant energy band alignment is the key to efficient and stable QD solar cells. Herein, an advance in QD surface passivation by introducing tailored multifunctional ligands (glycocyamine (GLA)) to the FAPbI3 QD surface is demonstrated. The incorporation of GLA ligands can partly substitute the native long‐chain insulating ligands and effectively reduce the non‐radiative recombination loss induced by surface trap states. Notably, the introduction of GLA ligands beneficially shifts the band offsets of the QD films and generates a homojunction structure with a cascading energy band alignment in the QD layers, promoting favorable charge transport and boosting the device's performance. As a result, a record‐high power conversion efficiency (PCE) of 15.34% with improved open‐circuit voltage and fill factor is achieved. Moreover, the GLA‐assisted surface passivation boosts the device stability, in which over 80% and 75% of the original PCEs are maintained after storing the devices for 5500 h in ambient air and 768 h under continuous 1‐sun illumination, respectively.

Photolithographic patterning on multi-wavelength quantum dot film of the improved conversion efficiency for digital holography.

A triple-wavelength patterned quantum dot film was fabricated for the light source of digital holography to improve both the axial measurement range and noise reduction. The patterned quantum dot film was fabricated after optimizing the photolithography process condition based on the UV-curable quantum dot solution, which was capable of multiple patterning processes. In addition, an optimized pattern structure was developed by adding TiO2 nanoparticles to both the quantum dot and bank layers to increase the scattering effect for the improved photoluminescence intensity. Finally, the newly developed light source with the balanced spectral distribution was applied to the digital holography, rendering it applicable as an improved light source.

Enhancing light use efficiency and tomato fruit yield with quantum dot films to modify the light spectrum

Enhancing light use efficiency and tomato fruit yield with quantum dot films to modify the light spectrum

Double‐Sided Indium Tin Oxide Photonic Crystal Glazing for All‐In‐One Multifunctional Rigid and Flexible Windows

AbstractFuturistic and high‐performance windows are required to perform multiple functions, occasionally including photo‐ and electricity‐associated functions. For each function, suitable components must be added, but this might result in complicated window structures that can impede the basic window function: high visibility. Therefore, platform technology is necessary to simplify window structures with minimal components for basic functions while adding specific desirable functions. This study proposes non‐close‐packed indium tin oxide (ITO) photonic crystals coated on both sides of rigid and flexible windows. Their photonic bandgap frequencies (stopbands) are tunable through the modulation of the ITO thickness or lattice constant, thereby manipulating the window light transmittances. When the stopband lies in bluelight (400–500 nm), the window can simultaneously block the bluelight and exhibit high transmittance (antireflection function) at 500–1500 nm. The dual functions are enhanced with double‐sided photonic crystal windows: the optical contrasts in solar irradiance transmittances (ΔTsol) between 500–1500 and 280–500 nm are maximally 37.1% and 47.2% for the glass and polyimide windows, respectively. Additionally, the windows can have dual stopbands. Moreover, the window stopbands can enhance the photoluminescence intensities of quantum dot films. This simplistic window is applicable to houses/buildings, automobiles, electronics, displays, and energy industries.

Optimized Design with Artificial Intelligence Quantum Dot White Mini LED Backlight Module Development

This study delves into the innovation of mini light-emitting diode (mini-LED) backlight module designs, a significant advancement in display technology. The module comprises a substrate, a receiving plane, and an LED structure, which uses a blue light with specific spectral characteristics. When combined with a red-green quantum dot (QD) film, it produces white light. For improved illumination uniformity, the Mini-LED structure was optimized with a focus on the thickness and concentration of layers, especially the TiO2 diffusion layer. A comprehensive design methodology using LightTools (8.6.0) optical simulation software was employed, linked with MATLAB (R2022a) for varied parameters and using the double deep Q-network (DDQN) algorithm via Python as a reinforcement learning agent. This approach facilitated optimal architecture design based on illumination uniformity. Also, the bidirectional scattering distribution function (BSDF) was employed to calculate the scattering properties of the backlight module’s surface, providing accurate simulation results. The DDQN algorithm enhanced the learning design, reducing simulation runs by 76.7% compared to traditional methods. The optimized solution achieved an impressive illumination uniformity of 83.8%, underscoring the benefits of integrating advanced algorithms into display technology optimization.

Color Rendering Index over 95 Achieved by Using Light Recycling Process Based on Hybrid Remote-Type Red Quantum-Dot Components Applied to Conventional LED Lighting Devices.

Red color conversion materials have often been used in conventional white LEDs (light-emitting diodes) to enhance the insufficient deep-red component and thus improve the color-rendering property. Quantum dots (QDs) are one of the candidates for this due to their flexibility in controlling the emission wavelength, which is attributed to the quantum confinement effect. Two types of remote QD components, i.e., QD films and QD caps, were prepared and applied to conventional white LED illumination to improve the color-rendering properties. Thanks to the red component near 630 nm caused by the QD components, the color rendering indices (CRIs) of both Ra and R9 could be increased to over 95. It was found that both the diffusing nature of the reflector and the light recycling process in the vertical cavity between the bottom reflector and the top optical films play important roles in improving the color conversion efficiency of remote QD components. The present study showed that the proper application of remote QDs combined with a suitable optical cavity can control the correlated color temperature of the illumination over a wide range, thus realizing different color appearances of white LED illumination. In addition, a high CRI of over 95 could be achieved due to the sufficient excitation from fewer QDs, due to the strong optical cavity effect.

Bilayer phosphine oxide modification toward efficient and large-area pure-blue perovskite quantum dot light-emitting diodes

Blue emissive halide perovskite light-emitting diodes (LEDs) are gaining increasing attention. Reducing defects in halide perovskites to improve the performance of the resulting LEDs is a main research direction, but there are limited passivation methods for achieving efficient and spectrally-stable pure-blue LEDs based on mixed-halide perovskites. In this work, double modification layers containing phosphine oxides, i.e., diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide (TSPO1) and 2,7-bis(diphenylphosphoryl)-9,9′-spirobifluorene (SPPO13), are developed to passivate mixed-halide perovskite quantum dot (QD) films. The comprehensive spectroscopic and structural characterization results indicate the presence of strong interactions between TSPO1/SPPO13 and the QDs. Besides, the combination of the bilayer exhibits a synergistic hole-blocking effect, improving the charge balance of the LEDs. LEDs based on the QD/TSPO1/SPPO13 films deliver stable electroluminesence at 469 nm and present a maximum external quantum efficiency (EQE) and luminance of 4.87% and 560 cd m−2, respectively. Benefiting from the uniform QD/TSPO1/SPPO13 film over a large area, LEDs with an area of 64 mm2 show a maximum EQE of 3.91%, which represents the first efficient large-area mixed-halide perovskite LED with stable pure-blue emission. This work provides a method to improve the perovskite QDs-based film quality and optoelectronic properties, and is a step toward the fabrication of highly-efficient large-area blue perovskite LEDs.

Ultra-thick inkjet-printed quantum dots layer for full-color micro-LED displays.

Micro-LEDs have promising development potential in display applications because of their outstanding performance. Achieving a full-color display based on micro-LEDs is one of the most important issues in commercial applications. In this paper, an effective method based on quantum dots and blue micro-LEDs was developed. Using an etching method, a thick black matrix was fabricated to reduce crosstalk and form a thick bank for quantum dots. Quantum dots were deposited in a thick black matrix using inkjet printing technology. With blue micro-LEDs, inkjet-printed quantum dot films can realize effective color conversion. The integrated blue micro-LEDs and red/green quantum dot films can achieve full-color displays without color filters, because the blue light leakage in the color conversion film can be reduced by the quantum dots themselves. The results suggest that inkjet-printed quantum dots are a promising way to achieve full-color micro-LED displays.

Enhancing performance of inverted quantum-dot light-emitting diodes based on a solution-processed hole transport layer via ligand treatment

The performance of inverted quantum-dot light-emitting diodes (QLEDs) based on solution-processed hole transport layers (HTLs) has been limited by the solvent-induced damage to the quantum dot (QD) layer during the spin-coating of the HTL. The lack of compatibility between the HTL's solvent and the QD layer results in an uneven surface, which negatively impacts the overall device performance. In this work, we develop a novel method to solve this problem by modifying the QD film with 1,8-diaminooctane to improve the resistance of the QD layer for the HTL’s solvent. The uniform QD layer leads the inverted red QLED device to achieve a low turn-on voltage of 1.8 V, a high maximum luminance of 105 500 cd/m2, and a remarkable maximum external quantum efficiency of 13.34%. This approach releases the considerable potential of HTL materials selection and offers a promising avenue for the development of high-performance inverted QLEDs.

Ultrathin Dimethylammonium Iodide Matrix: Suppressing Octahedral Distortion and Reconstructing Surface Ligands for Efficient CsPbI3 Quantum Dot Photovoltaics

Inorganic CsPbI3 quantum dots (QDs) have received increasing attention for their application in new‐generation solar cells. However, their poor phase stability due to the small ionic radius of Cs and their inhomogeneous energy landscape on the QD surface during ligand exchange remain as bottlenecks for the practical application of CsPbI3 QD photovoltaics. Herein, the unfavorable octahedral distortion is effectively suppressed by riveting dimethylammonium hydroiodide (DMAI) into the lattice structure. Moreover, DMAI reconstructs the surface ligands to create an ultrathin matrix that encloses the QDs. The ultrathin DMAI matrix effectively passivates the vacancy defects and allows efficient coupling and charge transport in the QD films. As a result, the CsPbI3 QD solar cell yields an efficiency approaching 15%. In addition, the increase in the Goldschmidt tolerance factor enhances the stability of the octahedral structure, resulting in significantly improved device stability.

Fluorescence properties and laser-induced enhancement of CsPbBr3 quantum dot with three different ligand amine systems

Inorganic perovskites have attracted much attention due to their excellent optical properties, making them a potential material for optoelectronic devices. In order to better apply it to optoelectronic devices, researchers have developed many synthesis schemes, for example, hot injection method, ligand-assisted reprecipitation method, template method, etc. to accurately control chemical composition, dimension, size, photoelectric and other properties. Here, we used oleylamine, octylamine, and phenylethylamine as amine ligands, and synthesized quantum dots (QDs) through the hot injection method. We found that quantum dot solutions prepared with long-chain ligands exhibit better luminescence performance, while quantum dot films prepared with shorter-chain phenethylamine ligands exhibit better luminescence performance, revealing the regulatory mechanism of amine ligands in the quantum dot growth process. In addition, we have enhanced the optical properties of perovskite films through laser direct writing, providing a reference for the synthesis and control of perovskite materials and their applications in the display.

Patterning Quantum Dots via Photolithography: A Review.

Pixelating patterns of red, green, and blue quantum dots (QDs) is a critical challenge for realizing high-end displays with bright and vivid images for virtual, augmented, and mixed reality. Since QDs must be processed from a solution, their patterning process is completely different from the conventional techniques used in the organic light-emitting diode and liquid crystal display industries. Although innovative QD patterning technologies are being developed, photopatterning based on the light-induced chemical conversion of QD films is considered one of the most promising methods for forming micrometer-scale QD patterns that satisfy the precision and fidelity required for commercialization. Moreover, the practical impact will be significant as it directly exploits mature photolithography technologies and facilities that are widely available in the semiconductor industry. This article reviews recent progress in the effort to form QD patterns via photolithography. The review begins with a general description of the photolithography process. Subsequently, different types of photolithographical methods applicable to QD patterning are introduced, followed by recent achievements using these methods in forming high-resolution QD patterns. The paper also discusses prospects for future research directions.

Effect of silica encapsulation on the stability and photoluminescence emission of FAxCs1-xPbX3 quantum dots for white mini light emitting diodes

Development of wide-color gamut white light-emitting diodes (WLEDs) for displays, with nitride-based phosphors and conventional core-shell quantum dots (QDs) such as InP, CdSe, and all-inorganic CsPbI3 perovskite quantum dots due to their excellent optoelectronic properties performance, is an excellent candidate for new optoelectronic applications.However, in backlight applications, the color gamut of perovskite quantum dots will be reduced due to the matching degree of color filter, which will limit its application in wide color gamut. To address these issues, in this paper, we propose a novel approach, namely, formamidine acetate (FA+) cationic doping, in CsPbI3 system synthesized at room temperature by organic-inorganic ligand passivation method which can effectively maintain structural stability. At the same time, the PL emission band of CsPbI3 is increased by doping FA + cations and the color gamut range is improved. We will discuss this change in detail, and quantum dot films using spin coating method can be maintained for a month in atmospheric conditions. For practical applications, the color gamut range can reach 133%. Therefore, our proposed perovskite quantum dots, FAxCs1-xPbI3, have great potential for application in wide color gamut displays.