PbS Colloidal Quantum Dots Research Articles

P‐Type PbS Quantum Dot Solar Ink via Hydrogen‐Bonding Modulated Solvation for High‐Efficiency Photovoltaics

AbstractLigand modulation of the electrical properties and surface solvation plays a crucial role in the development of functionalized colloidal quantum dots (CQDs) inks for solution‐processed optoelectronics. While inorganic halide ionic ligands can facilitate the n‐type doping of PbS CQDs and establish an electrical double layer in polar solvents for stable high‐concentration n‐type CQD inks, a plausible solvation strategy is still lacking to stabilize p‐type PbS CQDs, thereby resulting in a tedious multi‐step deposition involving short‐chain dithiol molecular ligands for advanced heterojunction CQD solar cells. Here an effective hydrogen bonding solvation strategy is proposed using 2‐mercaptoethanol (ME) ligands to realize stable p‐type PbS CQD ink. This strategy enables DMSO to form a dense solvation layer surrounding the ME‐modified PbS CQDs. With this approach, the PbS‐ME CQD ink exhibits a photoluminescence quantum yield of 52.03%, which is the highest record for PbS CQD inks. Finally, one‐step deposition of a p‐type PbS‐ME layer for PbS CQD photovoltaics is successfully achieved with an impressive power conversion efficiency (PCE) of 10.91%. This p‐type solar ink facilitates the fabrication of ready‐to‐use devices, enabling extensive applications in large‐scale and flexible optoelectronic devices.

Enhancing the performance of PbS:CsPbBr3 bulk-heterojunction photodetectors by treating with imidazolium-based ionic liquids.

All-inorganic lead halide perovskites and quantum dots (QDs) have gained significant attention since their emergence, owing to their immense potential for applications in optoelectronic devices. Here, enhanced-performance broadband photodetectors based on the bulk-heterostructure of a CsPbBr3 perovskite and PbS colloidal quantum dots (CQDs) are presented, and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4) ionic liquids as a dual-purpose additive were introduced in the blended film to regulate the surface of QDs by facilitating surface passivation, adjusting energy levels, and coupling with longer alkyl chains as compared to iodide ions (I-). As a result, a superior-quality bulk-heterostructure based photodetector with long-term stability was obtained, showing outstanding performance in photodetection across the visible to near-infrared wavelength range, demonstrating a high photoresponsivity of 22.4 A W-1 with a response time of 16.2 ms and a specific detectivity of 1.58 × 1014 Jones under 405 nm illumination. Thus, this work provides a novel modification strategy for PbS:CsPbBr3 as a promising material for novel optoelectronics.

An ultra-sensitive colloidal quantum dot infrared photodiode exceeding 100 000% external quantum efficiency via photomultiplication.

In this study, we present ultrasensitive infrared photodiodes based on PbS colloidal quantum dots (CQDs) using a double photomultiplication strategy that utilizes the accumulation of both electron and hole carriers. While electron accumulation was induced by ZnO trap states that were created by treatment in a humid atmosphere, hole accumulation was achieved using a long-chain ligand that increased the barrier to hole collection. Interestingly, we obtained the highest responsivity in photo-multiplicative devices with the long ligands, which contradicts the conventional belief that shorter ligands are more effective for optoelectronic devices. Using these two charge accumulation effects, we achieved an ultrasensitive detector with a responsivity above 7.84 × 102 A W-1 and an external quantum efficiency above 105% in the infrared region. We believe that the photomultiplication effect has great potential for surveillance systems, bioimaging, remote sensing, and quantum communication.

Role of the ZnO electron transport layer in PbS colloidal quantum dot solar cell yield.

The development of lead sulfide (PbS) colloidal quantum dot (CQD) solar cells has led to significant power conversion efficiency (PCE) improvements in recent years, with record efficiencies now over 15%. Many of the recent advances in improving PCE have focused on improving the interface between the PbS CQD active layer and the zinc oxide (ZnO) electron transport layer (ETL). Proper optimization of the ZnO ETL also increases yield, or the percentage of functioning devices per fabrication run. Simultaneous improvements in both PCE and yield will be critical as the field approaches commercialization. This review highlights recent advances in the synthesis of ZnO ETLs and discusses the impact and critical role of ZnO synthesis conditions on the PCE and yield of PbS CQD solar cells.

Step-like 10-nm channel for high-performance PbS colloidal quantum dots near-infrared photodetector

The photodetector, featuring a 10-nm step-like channel, demonstrates a significantly improved responsivity of 23 A W−1 and an exceptionally high external quantum efficiency of 2800% upon spin-coating with PbS CQDs under 1000-nm illumination.

Thiol‐Free p‐Type Colloidal Quantum Dot for Efficient Broadband Optoelectronics

Colloidal quantum dots (CQDs) are promising semiconductors for optoelectronic applications owing to their bandgap tunability and solution processability. Historically, ethanedithiol has been widely employed as a surface ligand to form a p‐type CQD layer via a layer‐by‐layer process. However, the limited control of p‐type characteristics reduces the device performance, and the high reactivity of ligand and processing solvents degrade the underlying layer. In this study, a thiol‐free p‐type CQD is demonstrated by creating native p‐type CQDs during the synthesis process. Sulfurization of PbS CQD results in p‐type properties that enable the avoidance of any further thiol‐ligand treatment process. Further, alternative surface passivation of the sulfurized CQD using halide ligand yields a robust, p‐type, morphologically uniform, and trap‐suppressed film. The developed CQD film is then employed as a hole‐transporting layer (HTL) for both broadband solar cells and photodetectors. The resulting CQD devices exhibit improved performance with a 65.7% increase in photovoltaic efficiency and a 1.7‐fold improvement in responsivity for infrared photodetection. The devices also demonstrate higher ambient stability, retaining 85% of the initial performance after 1,000 hr owing to the uniform top HTL morphology, indicating the potential of the new p‐type layer to be utilized in various emerging optoelectronics.

Reducing the Open-Circuit Voltage Loss of PbS Quantum Dot Solar Cells via Hybrid Ligand Exchange Treatment.

The interface VOC loss between the active layer and the hole transport layer (HTL) of lead sulfide colloidal quantum dot (PbS-CQD) solar cells is a significant factor influencing the efficiency improvement of PbS colloidal quantum dot solar cells (PbS-CQDSCs). Currently, the most advanced solar cells adopt organic P-type HTLs (PbS-EDT) via solid-state ligand exchange with 1,2-ethanedithiol (EDT) on the CQD top active layer. However, EDT is unable to altogether remove the initial ligand oleic acid from the quantum dot surface, and its high reactivity leads to cracks in the HTL film caused by volume contractions, which inevitably results in significant VOC loss. These flaws prompted this research to develop a method involving hybrid organic ligand exchange using 3-mercaptopropionic acid (MPA) and 1,2-EDT (PbS-Hybrid) to overcome these drawbacks of VOC loss. The results indicated that the new exchange strategy improved the quality of the HTL film and benefited from the enhanced passivation of the quantum dot surface and better alignment of energy levels, and the average VOC of PbS-Hybrid devices is increased by approximately 25 mV compared to control devices. With the enhanced VOC, the average power conversion efficiency (PCE) of the devices is improved by 10%, with the highest PCE reaching 13.24%.

Investigation of suitable buffer layer for PbS-TBAI/PbS-EDT colloidal quantum dot solar cell using SCAPS-1D

Colloidal quantum dots (CQD) are emerging third-generation photovoltaic technologies because of their ability to link a wider range of the light spectrum compared to those of perovskite, crystalline, and copper indium gallium selenide (CIGS) solar cells. In this work, a Lead Sulphide (PbS) CQD solar cell architecture with Ag2S, CdS, ZnSe and ZnS buffer layer is presented. The device consisting of PbS-tetrabutyle ammonium iodide (PbS-TBAI) as an absorber layer, PbS-1,2-ethanedithiol (PbS-EDT) as a hole transport layer (HTL), TiO2 as an electron transport layer (ETL), and fluorine tin oxide (FTO) as an oxide layer. The electrical performances of the solar cells were simulated using SCAPS-1D while taking into account different buffer layers with increasing bandgap values. With ZnS acting as a buffer layer, the computational modelling and analysis of architectural PbS CQD solar cell result in an efficiency of 17.12%. Additionally, the parameters of the solar cell have been studied to be affected by the thickness and bandgap of the absorber and HTL layers, the effect of acceptor concentration with various buffer layers, the impact of temperature, the effect of HTL doping density, and the effect of absorber layer defect density. This study can serve as a guide for future PbS CQD solar cells.

Electronic sensitization by Mg doping gradient-induced functional interfaces: Large photocurrent in PbS/Zn1-xMgxO solar cells

We investigated doping gradient-mediated charge separation and carrier extraction in PbS/ZnMgO photovoltaic (PV) devices. We fabricated PbS/Zn(Mg)O/Al solar cells in which the Mg composition was systematically changed to form the PbS/Zn0.85Mg0.15O and PbS/ZnO interfaces where charge separation and extraction occur, respectively, during PV operation. The short-circuit current increased significantly with the Mg-doping gradient electron transport layer (ETL). The increased short-circuit current is attributed to the suppression of carrier recombination at the PbS/ Zn0.85Mg0.15O interface and the enhanced carrier extraction at the ZnO/Al interface resulting from the formation of Mg doping gradient in the ETL. The presented results provide insights into the synergistic effect of the doping gradient ETL and interface modification for the electronic sensitization of PbS colloidal quantum dot PV devices.

Double‐ended passivator enables dark‐current‐suppressed colloidal quantum dot photodiodes for CMOS‐integrated infrared imagers

AbstractLead sulfide (PbS) colloidal quantum dot (CQD) photodiodes integrated with silicon‐based readout integrated circuits (ROICs) offer a promising solution for the next‐generation short‐wave infrared (SWIR) imaging technology. Despite their potential, large‐size CQD photodiodes pose a challenge due to high dark currents resulting from surface states on non‐passivated (100) facets and trap states generated by CQD fusion. In this work, we present a novel approach to address this issue by introducing double‐ended ligands that supplementally passivate (100) facets of halide‐capped large‐size CQDs, leading to suppressed bandtail states and reduced defect concentration. Our results demonstrate that the dark current density is highly suppressed by about an order of magnitude to 9.6 nA cm−2 at −10 mV, which is among the lowest reported for PbS CQD photodiodes. Furthermore, the performance of the photodiodes is exemplary, yielding an external quantum efficiency of 50.8% (which corresponds to a responsivity of 0.532 A W−1) and a specific detectivity of 2.5 × 1012 Jones at 1300 nm. By integrating CQD photodiodes with CMOS ROICs, the CQD imager provides high‐resolution (640 × 512) SWIR imaging for infrared penetration and material discrimination.image

Colloidal PbS Quantum Dot Photodiode Imager with Suppressed Dark Current.

Lead sulfide (PbS) colloidal quantum dots (CQDs) for photodetectors (PDs) have garnered great attention due to their potential use as low-cost, high-performance, and large-area infrared focal plane arrays. The prevailing device architecture employed for PbS CQD PDs is the p-i-n structure, where PbS CQD films treated with thiol molecules, such as 1,2-ethanedithiol (EDT), are widely used as p-type layers due to their favorable band alignment. However, PbS-EDT films face a critical challenge associated with low film quality, resulting in many defects that curtail the device performance. Herein, a controlled oxidization process is developed for better surface passivation of the PbS-EDT transport layer. The dark current density (Jd) of PbS CQD PDs based on optimized PbS-EDT layer shows a dramatic decrease by nearly 2 orders of magnitude. The increase of carrier lifetime and suppression of carrier recombination via controlled oxidation in PbS-EDT CQDs were confirmed by transient absorption spectra and electrochemical impedance spectra. The device based on the optimized PbS-EDT hole transport layer (HTL) exhibits a specific detectivity (D*) that is 3.4 times higher compared to the control device. Finally, the CQD PD employing oxidization PbS-EDT CQDs is integrated with a thin film transistor (TFT) readout circuit, which successfully accomplishes material discrimination imaging, material occlusion imaging, and smoke penetration imaging. The controlled oxidization strategy verifies the significance of surface management of CQD solids and is expected to help advance infrared optoelectronic applications based on CQDs.

Interface Engineering to Drive High-Performance MXene/PbS Quantum Dot NIR Photodiode.

The realization of a controllable transparent conducting system with selective light transparency is crucial for exploring many of the most intriguing effects in top-illuminated optoelectronic devices. However, the performance is limited by insufficient electrical conductivity, low work function, and vulnerable interface of traditional transparent conducting materials, such as tin-doped indium oxide. Here, it is reported that two-dimensional (2D)titanium carbide (Ti3 C2 Tx ) MXene film acts as an efficient transparent conducting electrode for the lead sulfide (PbS) colloidal quantum dots (CQDs) photodiode with controllable near infrared transmittance. The solution-processed interface engineering of MXene and PbS layers remarkably reduces the interface defects of MXene/PbS CQDs and the carrier concentration in the PbS layer. The stable Ti3 C2 Tx /PbS CQDs photodiodes give rise to a high specific detectivity of 5.51×1012 cmW-1 Hz1/2 , a large dynamic response range of 140dB, and a large bandwidth of 0.76MHz at 940nm in the self-powered state, ranking among the most exceptional in terms of comprehensive performance among reported PbS CQDs photodiodes. In contrast with the traditional photodiode technologies, this efficient and stable approach opens a new horizon to construct widely used infrared photodiodes with CQDs and MXenes.

P-type NiOx ultrathin film as highly efficient hole extraction layer in n-type PbS quantum dots based NIR photodiode

Recently, the development of zero-dimensional (0D) materials has experienced significant growth. Among them, PbS colloidal quantum dots (CQDs) have received special attention due to their outstanding properties, including tunable optical absorption ranging from 600 to 2600 nm (size dependent bandgap) and easy solution synthesis. PbS CQDs are considered as one of the most promising materials for the next generation of infrared sensors. Hence, there is a growing interest in their use in industrial spheres. One of the major keys to obtaining high-performance devices is the realization of efficient charge extraction contacts on PbS CQDs films. In this work, we have demonstrated an efficient hole extraction layer (HEL) using NiOx ultra-thin film on infrared p-i-n photodiode based on only n-type PbS nanocrystals (CQDs). We compared the performance with the standard optimized MoOx. We obtained a significant gain in external quantum efficiency (EQE), a decrease of the operating bias, while keeping the same dark current level.

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

Self-formed interfacial oxide layer minimizes reverse bias dark current in PbS colloidal quantum dot photodiodes

PbS colloidal quantum dot (CQD) photodiodes possess high photoresponsivity and broad spectral sensitivity, making them tremendously attractive for low-cost short-wave infrared (SWIR) sensing. A critical challenge in achieving high detectivity in SWIR photodiodes is to minimize their reverse bias dark current density (Jdark) and elucidate the origin of Jdark. We demonstrate in this work how the self-formed AlOx at the ZnO/Al interface dramatically reduced Jdark of the PbS CQD SWIR photodiodes. In such a simple and controlled way, the interfacial states were thoroughly passivated by post-exposure to dry air, which could block the dominant pathways for minority hole injection from Al electrode. The treated photodiode showed low Jdark down to 1.58 × 10−7 A/cm2 at –0.5 V, high photoresponsivity of 0.62 A/W, and high specific detectivity of 2.05 × 1012 Jones at 1413 nm, establishing a readily approach to optimizing detectivity in PbS CQD SWIR photodetectors.

Photovoltaic performance enhancement on carbon counter electrode based PbS colloidal quantum dots solar cells with surface trap passivation via post-treatment process

Photovoltaic performance enhancement on carbon counter electrode based PbS colloidal quantum dots solar cells with surface trap passivation via post-treatment process

Advancing perovskite solar cell performance: Enhanced efficiency and stability through superimposed PbS QDs

This study investigates enhancing efficiency in thin-film photovoltaic devices by incorporating varying-sized superimposed PbS colloidal quantum dots (CQDs). These CQDs offer tunable near-infrared absorption, multiple exciton generation effects, and solution processability, rendering them promising for improved performance. Superimposing QDs of different sizes extends the device's absorption spectrum beyond conventional limits, utilizing tailored absorption coefficients for broader sunlight wavelength utilization and increased solar energy conversion efficiency. Each QD group exhibits a unique absorption coefficient, with a peak at its central wavelength from the Schrödinger equation solution. Spectral analysis reveals strategic enhancement in light absorption across visible and near-infrared regions, broadening the perovskite absorption range beyond 800 nm. These QDs enhance both infrared and visible spectra, improving light harvesting. Summing the absorption of single QD groups creates a continuous spectrum, enhancing perovskite film stability and morphology. Rigorous optical analysis and comprehensive electrical modeling investigate charge carrier interactions within the photovoltaic framework. The study verifies around 24 % efficacy enhancement compared to QD-absent configurations, surpassing uniformly dispersed QDs by 11 %. Optical and electrical analyses yield a short-circuit current of 26.7 mA/cm2, open-circuit voltage of 1.13 V, fill factor of 0.88, and overall efficiency of 25.12 % in superimposed configurations. Results underscore the significance of varied QD dimensions and layered structures for enhanced absorption, offering a promising route for advancing thin-film solar technology. The study showcases the potential of PbS CQDs with varying radii in photovoltaics, contributing to improved efficiency and stability, with implications for the future of solar energy technology.

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

Ultrafast Cascade Charge Transfer in Multibandgap Colloidal Quantum Dot Solids Enables Threshold Reduction for Optical Gain and Stimulated Emission.

Achieving low-threshold infrared stimulated emission in solution-processed quantum dots is critical to enable real-life applications including photonic integrated circuits (PICs), LIDAR application, and optical telecommunication. However, realization of low threshold infrared gain is fundamentally challenging due to high degeneracy of the first emissive state (e.g., 8-fold) and fast Auger recombination. In this Letter, we demonstrate ultra-low-threshold infrared stimulated emission with an onset of 110 μJ cm-2 employing cascade charge transfer (CT) in Pb-chalcogenide colloidal quantum dot (CQD) solids. In doing so, we investigate this idea in two different architectures including a mixture of multiband gap CQDs and a layer-by-layer (LBL) configuration. Using transient absorption spectroscopy, we show ultrafast cascade CT from large band gap PbS CQD to small band gap PbS/PbSSe core/shell CQDs in LBL (∼2 ps) and mixture (∼9 ps) configurations. These results indicate the feasibility of using cascade CT as an efficient method to reduce the optical gain threshold in CQD solid films.

Modeling and simulation of > 19% highly efficient PbS colloidal quantum dot solar cell: A step towards unleashing the prospect of quantum dot absorber

We used the SCAPS-1D simulation tool to maximize the performance of lead sulfide (PbS) solar cells. A PbS solar cell was first modeled and then experimentally verified from past research. The ZnO electron-transport layer (ETL) was then replaced with ZnO:Al ETL material. Additionally, the fluorine-doped tin oxide work function, PbS-TBAI, ZnO:Al layer thicknesses, ZnO:Al/PbS-TBAI, PbS-TBAI/PbS-EDT defect density, PbS-TBAI defect density, ZnO:Al, and PbS-TBAI doping concentration were optimized. Results showed a greater alignment of the absorber-layer valence band with the HOMO and LUMO of ZnO:Al than that of ZnO ETL. The PbS solar cell exhibited the greatest efficiency at the optimum values of 0.4 µm, 0.04 µm, 1019 cm–3, 4.0 eV, 1017 cm–3, 1014 cm–2, 1018 cm–2, and 3.8 eV for absorber thickness, ETL thickness, ETL doping concentration, work function of front contact, PbS-TBAI doping concentration, and electron affinity of ZnO:Al, respectively. The PbS solar cell also performed best at interface defect densities of 1014 and 1018 cm–2 for ZnO:Al/PbS-TBAI and PbS-TBAI/PbS-EDT, respectively. The PCE of ZnO:Al ETL-based device also increased from 15.036% before optimization to 19.169% after. The optimized result was found to be affected by temperature. The PbS-optimized device with inorganic hole-transport layers (HTLs) demonstrated higher performance than the device with organic HTL. This finding was attributed to the low hole mobility in the organic HTL than those of inorganic ones. Therefore, the ZnO:Al ETL-based device was more efficient than the ordinary ZnO ETL-based device.