Lead Sulfide Quantum Dots Research Articles

Interface-resolved photovoltage generation dynamics and band structure evolution in a PbS quantum dot solar cell.

For directed development of solar cells using nanomaterials such as quantum dots, there is a need to understand the device function in detail. Understanding where photovoltage is generated in a device and where energy losses occur is a key aspect of this, and development of methods which can provide this information is needed. We have previously shown that time-resolved photoelectron spectroscopy of core levels can be used to follow the photovoltage dynamics at a specific interface of a lead sulfide quantum dot solar cell. Here, we use the method's selectivity and sample design to investigate the photovoltage generation in different parts of this solar cell and determine how the different layers (including the absorber layer thickness) contribute to charge separation. We show that all layers contribute to photovoltage generation and that a gold contact deposited on the quantum dots is necessary for full photovoltage generation and slow charge recombination. By combining the information obtained, we are able to experimentally follow the time evolution of the solar cell band structure during the charge separation process. Furthermore, we can identify which specific layers need to be optimized for an overall improvement of quantum dot cells. In the future, this methodology can be applied to other types of devices to provide insights into photovoltage generation mechanisms.

Enhanced carrier transfer performance on blade-coating PbS quantum dot solar cells by coordinated operation of iodine ligands

The significant breakthrough in the photovoltaic conversion efficiency of lead sulfide (PbS) quantum dot solar cells has primarily been achieved on small substrates using the spin-coating method. However, the blade-coating technique offers a scalable alternative for large-scale fabrication of absorption film, addressing the limitations of spin-coating for commercial applications. Given the inherent challenges of the blade-coating method, which often produces low-quality and defective films. Thus, an iodide ligand passivation strategy to realize the formation of high-quality films with reduced trap states was proposed. Typically, the iodide ligand is incorporated into the precursor solution with the aim of fine-tuning the nanoparticle’s functionality, facilitating the formation of systematically aligned and densely coupled film configurations during the blade coating procedure. The functional mechanisms of the aligned and compact-coupled configurations, as well as the effect of iodide introduction on defect mitigation, have been systematically investigated. The results reveal that iodide ligand introduction modulates the interparticle electrostatic potential and inter-dot space, facilitating the formation of a uniform structure with enhanced energy level alignment and reduced trap states. The highly aligned and compact structure improves interfacial integration with the ZnO electron transport layer, enabling efficient photon-electron extraction and transfer. As a result, PbS quantum dot solar cells fabricated using the blade coating technique have achieved an optimized efficiency of 4.68 %, offering significant potential for the development and production of directly-synthesized ink for quantum dot solar cells.

Lead sulfide quantum dots in an organic solar cell active layer

Organic solar cells have been fabricated using various concentrations of lead sulfide quantum dots. Data from Mott–Schottky analysis revealed intriguing changes in the bulk heterojunction layer of the solar cells that were directly related to the addition of the quantum dots. Notably, the highest power conversion efficiency of 5.15% was achieved with the addition of 0.4 wt% lead sulfide quantum dots.

Chlorine passivation of PbS quantum dots in all solid glass matrix for high efficiency luminescence

Lead sulfide quantum dots (PbS QDs) show great potential application in near infrared range, and incorporation of PbS QDs into all solid glass matrix improves both their chemical and thermal stabilities as well as the shaping ability. However, the incorporation of PbS QDs into all solid glass matrix makes it difficult to modify their surface, resulting in the relatively low absolute photoluminescence quantum yield (PL QY) caused by the surface defects. Here, PbS QDs with tunable photoluminescence band in near-infrared range in silicate glasses were prepared by melting-quenching method. By addition of chloride and forming PbClx shell around PbS QDs in glass, defects induced by surficial lead ions of above PbS QDs can be effectively passivated, reducing subsequent trapping of photo-generated electrons accordingly. PL QY of PbS QDs inbuilt glasses is enhanced eventually and achieved as high as 49.3 %. Furthermore, thermo- and photo-stabilities of PbS QDs in glass are greatly improved compared with those without surface chlorine passivation. These high performance PbS QDs embedded glasses with excellent stability show significant potential in light-emitting diodes, lasers and fiber amplifiers in near-infrared range.

(Invited) Surface State Modulation of Colloidal Quantum Dots and Construction of Quantum Dot Based Infrared Detectors

Near-infrared photodetection and imaging devices play an important role in fields such as biological detection, information communication, military meteorology, etc. Traditional imaging devices require integration with readout circuits, and the complex integration process limits the development of infrared imaging systems. Lead sulfide colloidal quantum dots have excellent photoelectric properties in the infrared region, with a tunable bandgap width ranging from 0.4 to 1.5 eV, and spectral response covering below 2400 nm. Lead sulfide quantum dot films exhibit high absorption coefficients in the infrared region and excellent carrier mobility. In recent years, the performance of infrared detectors based on quantum dot systems has rapidly improved, and they are expected to develop into a new type of infrared detection and imaging technology. The speaker's team has combined infrared quantum dots with visible light quantum dots to prepare a simple, low-cost, and efficient infrared upconversion imaging device. By using the method of inducing band bending through interface electron storage, the efficiency of carrier tunneling and photon conversion has been improved, and the application of this technology in biological imaging has been preliminarily demonstrated. This report will introduce the development of quantum dot infrared detection materials and devices in recent years, as well as the research progress of the speaker's team in this area.

Synthesis and Processing Strategy for High-Bandgap PbS Quantum Dots: A Promising Candidate for Harvesting High-Energy Photons in Solar Cells.

The wide tunability of the energy bandgap of colloidal lead sulfide (PbS) quantum dots (QDs) has uniquely positioned them for the development of single junction and tandem solar cells. While there have been substantial advancements in moderate and narrow bandgap PbS QDs-ideal for single junction solar cells and the bottom cell in tandem solar cells, respectively; progress has been limited in high-bandgap PbS QDs that are ideally suited for the formation of the top cell in tandem solar cells. The development of appropriate high bandgap PbS QDs would be a major advancement toward realizing efficient all-QD tandem solar cells utilizing different sizes of PbS QDs. Here, we report a comprehensive approach encompassing synthetic strategy, ligand engineering, and hole transport layer (HTL) modification to implement high-bandgap PbS QDs into solar cell devices. We achieved a greater degree of size homogeneity in high-bandgap PbS QDs through the use of a growth retarding agent and a partial passivation strategy. By adjusting the ligand polarity, we successfully grow HTL over the QD film to fabricate solar cells. With the aid of an interface modifying layer, we incorporated an organic HTL for the realization of high-performance solar cells. These solar cells exhibited an impressive open-circuit voltage of 0.824 V and a power conversion efficiency of 10.7%, marking a 360% improvement over previous results.

One-pot, easy and scalable synthesis of large-size short wave length IR emitting PbS quantum dots.

This study presents a versatile and efficient method to synthesize large-size lead sulfide (PbS) quantum dots (QDs) that display emission in the short-wave infrared (SWIR) region, using accessible and stable diethylammonium diethyldithiocarbamate (C2)2DTCA and octylammonium octyldithiocarbamate (C8DTCA) as sulfur sources. As these sulfur sources enable the formation of well-dispersed, large-size PbS QDs in a very convenient way, this method can further be taken up for scale-up studies. Importantly, this approach allows precise control over QD sizes, thereby enhancing their SWIR optical properties. By adjusting the hot injection temperatures and sulfur source concentrations, different synthesis routes are explored, providing flexibility for the desired QD characteristics. The results presented here offer a promising opportunity to leverage the synthesized PbS QDs in applications such as optoelectronics, sensors, and imaging technology.

Efficient PbS quantum dots tandem solar cells through compatible interconnection layer

Lead sulfide quantum dots (PbS QDs) hold unique characteristics, including bandgap tunability, solution-processability etc., which make them highly applicable in tandem solar cells (TSCs). In all QD TSCs, its efficiency lags much behind to their single junction counterparts due to the deficient interconnection layer (ICL) and defective subcells. To improve TSCs performance, we developed three kinds of ICL structures based on 1.34 and 0.96 eV PbS QDs subcells. The control, 1,2-ethanedithiol capped PbS QDs (PbS-EDT)/Au/tin dioxide (SnO2)/zinc oxide (ZnO), utilized SnO2 layer to obtain high surface compactness. However, its energy level mismatch causes incomplete recombination. Bypassing it, the second ICL (PbS-EDT/Au/ZnO) removed SnO2 and boosted the power conversion efficiency (PCE) from 5.75% to 8.69%. In the third ICL (PbS-EDT/poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)/Au/ZnO), a thin layer of PTAA can effectively fill fissures on the surface of PbS-EDT and also protect the front cells from solvent penetration. This TSC obtained a PCE of 9.49% with an open circuit voltage of 0.91 V, a short circuit current density of 15.47 mA/cm2, and a fill factor of 67.7%. To the best of our knowledge, this was the highest PCE achieved by all PbS QD TSCs reported to date. These TSCs maintained stable performance for a long working time under ambient conditions.

P‐134: Organic Buffer Layer Depressed Dark Current of Short‐Wave Infrared PbS Quantum Dot Photodetector

Lead Sulfide Quantum Dots (PbS QDs) are promising in shortwave infrared (SWIR) photodetectors. This work introduces organic polymer PM6 in hole transport layer of photodetectors and we obtain a decreased dark current density below 150 nA/cm2 and an increased external quantum efficiency at 60% of the QD SWIR photodetectors.

26‐4: PbS Quantum Dot Photodetector for High Resolution and Low Light Night Vision of Phone Camera

Our recent advancement employs lead sulfide (PbS) quantum dots (QDs) in short‐wave infrared (SWIR) photodetector towards low light night vision (LLNV). The as prepared QD SWIR photodetector showcases low dark current density(< 200 nA/cm2) and high efficiency (EQE > 50%), demonstrating QDs’ potential for superior LLNV in mobile devices.

Controlled growth of uniform and dense perovskite layers on SnO2 via interface passivation by PbS quantum dots

AbstractFormamidinium lead iodide (FAPbI3) and SnO2 are a promising pair of halide perovskite and electron transport layer (ETL). However, FAPbI3 and SnO2 have inherent problems such as high crystallization temperature of FAPbI3 and surface defects of SnO2 like oxygen vacancies. They cause low crystallinity, non‐uniform grain growth, and more interface defects, leading to carrier recombination and leakage current. The passivation of the interface between FAPbI3 and SnO2 is an effective process to address these materials issues. Herein, a dual role of lead sulfide (PbS) quantum dots (QDs) in the interface passivation is explored. PbS QDs which are introduced to the interface between FAPbI3 and ETL, link to Sn‐dangling bonds of SnO2 ETLs and anchor the iodine atoms of FAPbI3. This changes considerably lower nonradiative recombination, achieve a better energetic alignment between ETL and PbI3, and facilitate electron extraction, leading to a power conversion efficiency of 21.66%.image

Lead sulfide quantum dot-linear low-density polyethylene composites for near-infrared Mini-LEDs

Lead sulfide quantum dots (QDs), presenting near-infrared (NIR) emissions, have gained extensive interest within the realm of NIR light-emitting diodes (LEDs). However, the intricate surface defect passivation poses a major impediment that curbs broader applications of PbS QDs. To address it, we introduce linear low-density polyethylene (LLDPE) as a facilitating agent for the aggregation of PbS QDs, aiming to improve their optical properties by harnessing a stress-inducing effect. Compared to the bare PbS QDs that are luminescence silent, the PbS aggregates formed with the addition of LLDPE show a notable photoluminescence quantum yield (PLQY) as high as 20.7 %. Moreover, the presence of LLDPE mitigates the oxidative degradation of lead ions on the PbS QD surface, thereby enhancing the stability of the PbS QDs through steric hindrance. Near-infrared nini-LEDs are demonstrated by combining the PbS QD/LLDPE composites with blue mini-LED chips, which show an emission maximum of 1517.9 nm, a full width at half maximum (FWHM) of 297.6 nm and an energy conversion efficiency (ECE) of 14.6 %. The proposed method opens up new avenues for enhancing the optical properties of PbS QDs without using traditional passivation procedures.

High Volumetric Energy Density Supercapacitor of Additive-Free Quantum Dot Hierarchical Nanopore Structure.

The high surface-area-to-volume ratio of colloidal quantum dots (QDs) positions them as promising materials for high-performance supercapacitor electrodes. However, the challenge lies in achieving a highly accessible surface area, while maintaining good electrical conductivity. An efficient supercapacitor demands a dense yet highly porous structure that facilitates efficient ion-surface interactions and supports fast charge mobility. Here we demonstrate the successful development of additive-free ultrahigh energy density electric double-layer capacitors based on quantum dot hierarchical nanopore (QDHN) structures. Lead sulfide QDs are assembled into QDHN structures that strike a balance between electrical conductivity and efficient ion diffusion by employing meticulous control over inter-QD distances without any additives. Using ionic liquid as the electrolyte, the high-voltage ultrathin-film microsupercapacitors achieve a remarkable combination of volumetric energy density (95.6 mWh cm-3) and power density (13.5 W cm-3). This achievement is attributed to the intrinsic capability of QDHN structures to accumulate charge carriers efficiently. These findings introduce innovative concepts for leveraging colloidal nanomaterials in the advancement of high-performance energy storage devices.

Mixed quantum dot film for dual-band infrared detection

Dual-band infrared detection offers enhanced spectral information crucial for improved target identification. Traditional dual-band infrared photodetectors have often relied on expensive epitaxial growth bulk materials, limiting their widespread use in civilian applications. Colloidal quantum dots present an affordable alternative for dual-band infrared detection, owing to their spectral tunability and solution processability. In this study, we have developed an approach utilizing mixed lead sulfide quantum dot films to achieve dual-band infrared detection spanning the NIR (Near Infrared) and SWIR (Short Wave Infrared) ranges. These films exhibit a broad absorption spectrum, ranging from 400 to 1600 nm. When operating within the near-infrared band, the device based on mixed quantum dot films demonstrates an responsivity of 0.18A/W and specific detectivity of 2.38 × 109cm∙Hz1/2/W near 900 nm.While operated in the SWIR band, the detector has responsivity of 0.17A/W and specific detectivity of 2.11 × 109cm∙Hz1/2/W near 1600 nm.

Stronger Coupling of Quantum Dots in Hole Transport Layer Through Intermediate Ligand Exchange to Enhance the Efficiency of PbS Quantum Dot Solar Cells.

Nowadays, the extensively used lead sulfide (PbS) quantum dot (QD) hole transport layer (HTL) relies on layer-by-layer method to replace long chain oleic acid (OA) ligands with short 1,2-ethanedithiol (EDT) ligands for preparation. However, the inevitable significant volume shrinkage caused by this traditional method will result in undesired cracks and disordered QD arrangement in the film, along with adverse increased defect density and inhomogeneous energy landscape. To solve the problem, a novel method for EDT passivated PbS QD (PbS-EDT) HTL preparation using small-sized benzoic acid (BA) as intermediate ligands is proposed in this work. BA is substituted for OA ligands in solution followed by ligand exchange with EDT layer by layer. With the new method, smoother PbS-EDT films with more ordered and closer QD packing are gained. It is demonstrated stronger coupling between QDs and reduced defects in the QD HTL owing to the intermediate BA ligand exchange. As a result, the suppressed nonradiative recombination and enhanced carrier mobility are achieved, contributing to ≈20% growth in short circuit current density (Jsc) and a 23.4% higher power conversion efficiency (PCE) of 13.2%. This work provides a general framework for layer-by-layer QD film manufacturing optimization.

Autonomous self-healing hybrid energy harvester based on the combination of triboelectric nanogenerator and quantum dot solar cell

Realization of multi-source energy harvesting with one single device would maximize power output. Thus, it is emerging as a promising strategy towards renewable energy generation and has attracted worldwide attention in the past decades. Capable of capturing mechanical energy that is ubiquitous in the ambient environment, triboelectric nanogenerator (TENG) has been considered a novel yet effective source towards next-generation energy harvesting. In this work, a flexible hybrid energy harvester (HEH) is developed via the rational integration of autonomous self-healing TENG and high bending-stable lead sulfide quantum dot (PbS QD) solar cell, enabling independent electricity generation by two different mechanisms. The single-electrode mode TENG component with self-healing is realized by a polydimethylsiloxane/Triton X-100 (PDMS/TX100) mixture as the dielectric layer and the shared gold (Au) electrode, which generates 0.39 µA of output current (Iout), 24.6 V of output voltages (Vout), 15.4 nC of transfer charges (Qsc), and 7.80 mW m−2 of output power peak density. The thin-film solar cell component is based on a PbS QD layer as the light absorber with a planar structure fabricated under low-cost and compatible conditions, achieving 22.8 mA cm−2 of short-circuit current density (Jsc) and 4.92% of power conversion efficiency (PCE). As a proof of concept, an electronic watch is successfully powered by harnessing ambient mechanical and solar energy with a hybridized energy cell. This approach will offer more opportunities to construct a versatile platform towards remote monitoring and smart home systems.

The Role of PbCoS Quantum Dots in Improved Photovoltaic Efficiency

<p>The quest for efficient, sustainable solar energy solutions has propelled the exploration of novel materials with enhanced photovoltaic properties. This study delves into the synthesis, characterization, and photovoltaic application of cobalt-doped lead sulfide (PbCoS) quantum dots (QDs) deposited on titanium dioxide (TiO2) substrates. Employing a hot-injection method, we synthesized PbCoS QDs and characterized their structural, compositional, and optical properties using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and UV-Visible absorption spectroscopy. The QDs demonstrated a cubic crystal structure with an average size of 20.12 nm and exhibited a direct band gap of 1.91 eV, indicative of quantum confinement effects and improved absorption in the visible spectrum. The photovoltaic performance of quantum dot-sensitized solar cells (QDSSCs) incorporating PbCoS QDs was assessed through current density-voltage (J-V) measurements, revealing a power conversion efficiency (PCE) of 2.17%. This efficiency highlights the potential of PbCoS QDs to enhance the performance of QDSSCs, partly attributed to the impact of cobalt doping on the electronic structure and photovoltaic properties of the material. The study identifies gaps in current research, such as the optimization of cobalt doping levels and the exploration of interface engineering between QDs and substrates, pointing towards future directions for enhancing the efficiency and applicability of PbCoS-based photovoltaic devices.</p>

A deep learning approach for quantum dots sizing from wide-angle X-ray scattering data

AbstractDisclosing the full potential of functional nanomaterials requires the optimization of synthetic protocols and an effective size screening tool, aiming at triggering their size-dependent properties. Here we demonstrate the successful combination of a wide-angle X-ray total scattering approach with a deep learning classifier for quantum dots sizing in both colloidal and dry states. This work offers a compelling alternative to the lengthy process of deriving sizing curves from transmission electron microscopy coupled with spectroscopic measurements, especially in the ultra-small size regime, where empirical functions exhibit larger discrepancies. The core of our algorithm is an all-convolutional neural network trained on Debye scattering equation simulations, incorporating atomistic models to capture structural and morphological features, and augmented with physics-informed perturbations to account for different predictable experimental conditions. The model performances are evaluated using both wide-angle X-ray total scattering simulations and experimental datasets collected on lead sulfide quantum dots, resulting in size classification accuracies surpassing 97%. With the developed deep learning size classifier, we overcome the need for calibration curves for quantum dots sizing and thanks to the unified modeling approach at the basis of the total scattering method implemented, we include simultaneously structural and microstructural aspects in the classification process. This algorithm can be complemented by incorporating input information from other experimental observations (e.g., small angle X-ray scattering data) and, after proper training with the pertinent simulations, can be extended to other classes of quantum dots, providing the nanoscience community with a powerful and broad tool to accelerate the development of functional (nano)materials.

Size-tunable and monodisperse lead sulfide quantum dots for broadband photodetectors

Lead sulfide quantum dots (PbS QDs) are used in broadband photodetectors due to their excellent size tunability, photosensitivity, and solution processability. However, due to the risk of Ostwald ripening, synthesizing high-quality PbS QDs with absorption peaks over 2000 nm with high monodispersity is a challenge. In this study, by controlling the molar ratio of Pb to S and the number of injections of S precursor, we successfully prepared large PbS QDs with an absorption peak at 2122 nm, corresponding to an average diameter of 11.42 nm, with a super-mono-dispersity of 5.50%. Broadband photodetectors ranging from visible light to short-wave infrared are prepared using the large PbS QDs, corresponding to a response rate of 5.98 mA/W at 1940 nm.

Optimizing Surface Passivation of n‐Type Quantum Dots for Efficient PbS Quantum Dot Solar Cells

The n‐type quantum dot (QD) active layer is the core component of lead sulfide QD solar cells (PbS QDSCs). In the state‐of‐the‐art PbS QDSCs, the active layer is commonly obtained through liquid‐phase ligand exchange (LPLE). Due to the intricate chemical state of the ligand exchange solution providing halide ligand, therefore, the PbS‐OAQD solutions is used at concentrations of 20, 30, and 40 mg mL−1 for LPLE, aiming to investigate the reasons for different surface states post‐exchange and their impact on device performance. The results indicate that when the concentration of the PbS‐OA QD solution is 30 mg mL−1, the exchanged QDs exhibit complete removal of surface OA, a higher content of short‐chain ligand PbX2 (X = I, Br), Consequently, devices fabricated using PbS‐PbX2 QD obtained through the exchange of 30 mg mL−1 PbS‐OA QD solution achieve a higher power conversion efficiency (PCE) of 12.53%. This study presents a simple and effective strategy to enhance the performance of PbS QDSCs.