High-performance PbS Research Articles

Suppressing Charge Extraction Loss in Quantum Dot Infrared Photovoltaics by Optimizing the Charge Transport Layer.

Infrared solar cells (IRSCs), capable of converting low-energy infrared photons to electron-hole pairs, are promising infrared optoelectronic devices because of their extended utilization region of the solar to short-wavelength infrared region. For PbS QDs IRSCs, charge extraction loss, easily generated at the interfaces, has been one of the dominate obstacles impeding the improvement of device efficiencies due to too many trap states and mismatched energy levels between the photoactive layer and electron transport layer (ETL). Herein, an advanced ZnO ETL was developed to improve the extraction of photogenerated charges from the PbS QD photoactive layer to ETLs. The advanced ETL film exhibited effectively suppressed trap states and better-matched energy levels compared with the QD layer. As a consequence, high-performance PbS QD IRSCs with the highest infrared power conversion efficiencies of 1.26% under 1100 nm filtered solar illumination are achieved, suggesting an effective and facile route for enhancing the charge extraction in infrared photovoltaics.

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.

High-Performance PbS NCs-Graphene Phototransistor With Memory Function

High-Performance PbS NCs-Graphene Phototransistor With Memory Function

Effective Charge Collection of Electron Transport Layers for High-Performance Quantum Dot Infrared Solar Cells.

Infrared (IR) solar cells, capable of converting low-energy IR photons to electron-hole pairs, are promising optoelectronic devices by broadening the utilization range of the solar spectrum to the short-wavelength IR region. The emerging PbS colloidal quantum dot (QD) IR solar cells attract much attention due to their tunable band gaps in the IR region, potential multiple exciton generation, and facile solution processing. In PbS QD solar cells, ZnO is commonly utilized as an electron transport layer (ETL) to establish a depleted heterostructure with a QD photoactive layer. However, band gap shrinkage of large PbS QDs makes it necessary to tailor the behaviors of the ZnO ETL for efficient carrier extraction in the devices. Herein, the characteristics of ZnO ETL are efficiently and flexibly tailored to match the QD layer by handily adjusting the postannealing process of ZnO ETL. With a suitable temperature, the well-matched energy level alignment and suppressed trap states are simultaneously achieved in the ZnO ETL, effectively reducing the nonradiative recombination and accelerating the electron injection from the QD layer to ETL. As a consequence, a high-performance PbS QD photovoltaic device with power conversion efficiencies (PCEs) of 10.09% and 1.37% is obtained under AM 1.5 and 1100 nm filtered solar illumination, demonstrating a simple and effective approach for achieving high-performance IR photoelectric devices.

High-performance PbS detectors sensitized from one-step sensitization

Two-step sensitization is the key technique for achieving high-performance uncooled lead-salt infrared photoconductive detectors fabricated from vapor physic deposition (VPD) method. However, the commercialization of these devices is inhibited by the intricate sensitization processes, especially the iodination step, which requires precise control over high concentrations of iodine vapor. Herein, a one-step sensitization technique was proposed to improve the reliability of lead sulfide (PbS) detectors manufactured from VPD method. Moreover, the dependence of the detectivity on sensitization parameters involving the oxygen concentration, time, and temperature, was established and interpreted based on extensive studies on the sensitization of lead salt devices. The feasibility of the simplified sensitization was demonstrated by a room-temperature peak detectivity of 2.47 × 1010 cm Hz1/2 W−1 at 2.7 μm attained at 430 °C for 10 min in 50 % oxygen ambient. The evolution of phase, microstructure and electrical properties confirms the enhanced performance results from the improvement in PbS crystal quality as well as the formation of Pb3O2I2 and Pb2(SO4)O from high-temperature recrystallization. Therefore, the one-step sensitization paves a way for accelerating commercialization of lead-salt detectors fabricated by VPD technique.

Organic hole transport materials for high performance PbS quantum dot solar cells.

We developed a triazatruxene-based hole transport material (HTM), 3Ka-DBT-3Ka, aiming to enhance band alignment and augment charge generation and collection in devices, as an alternative for 1,2-ethanedithiol (EDT). The PbS CQD solar cells employing 3Ka-DBT-3Ka as the HTM achieve a peak efficiency of 11.4%, surpassing devices employing the conventional PbS-EDT HTM (8.9%).

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.

Charge Transport Layer Engineering toward Efficient and Stable Colloidal Quantum Dot Solar Cells.

Lead sulfide (PbS) colloidal quantum dot (CQD) solar cell, as a new type of solution-processed photovoltaic technology, have always attracted great interest. Early studies mainly focused on the surface passivation of CQDs and optimization of device structures. Recently, researchers further developed new charge transport layers and interfacial passivation strategies based on these foundations, which have significantly improved the device efficiency and stability. In this perspective, we summarize the important research progress in transport layer materials, structures, and interfacial passivation of CQD solar cells. We also discuss the remaining challenges and potential development directions for charge transport layers for high-performance and stable PbS CQD solar cells. We hope to draw attention to the enormous potential of charge transport layers in promoting CQD-based optoelectronics toward practical applications.

Flexible Microcomb Printed PbS Quantum Dot Film Enables Scalable Fabrication of Near Infrared Photodetector

AbstractColloidal PbS quantum dots (QDs) have attracted tremendous attention in near‐infrared photodetection for their superior optoelectronic properties. However, appropriate fabrication methods remain a challenge for scalable and high performance PbS QD photodetectors. Herein, a flexible microcomb printing (FMCP) technique is first introduced to fabricate PbS QD photoconductors without a layer‐by‐layer ligand exchange technique, and the detectors demonstrate a responsivity of 2.1 A W−1. A computational fluid dynamics model is built to simulate the flow field distribution and analyze the relationship between the key parameters of FMCP and QD film morphology. The QD ink flow field at the tip of the microcomb exhibits high shear rates that lead to a better crystallization configuration for solid QD films formation, which is verified by Grazing‐incidence small and wide‐angle X‐ray scattering. Moreover, the relationship between the intrinsic nature of the QD ink (viscosity and surface tension), substrate temperature, and printing speed are systematically analyzed to experimentally achieve high performance QD films. Benefiting from the good crystallization configuration, FMCP‐printed photodetectors using the direct PbS QD ink without ligand exchange show high responsivities. The results indicate that FMCP is a promising method for scalable and high‐performance PbS QD photodetectors.

The effect of the melt-drawing ratio on the microstructure and mechanical properties of poly(butylene succinate) cast films with row-nucleated lamellar structure

High-performance PBS films can be prepared by the melt-stretching method. The effect of the melt-drawing ratio (MDR) on the mechanical properties and microstructure of PBS cast films prepared by melt-stretching is studied in this paper. The elastic modulus, tensile stress, and strain hardening increase with increasing MDR. With an MDR of 25–50, the crystalline morphology changes from deformed spherulites to row-nucleated lamellar structure. The lateral size and orientation of the lamellae apparently improve with the MDR. When the MDR is within 50–125, the row-nucleated lamellar structure improves slightly by increasing the lateral size and orientation of the lamellae. The component fraction and thickness of the mobile (MAF) and rigid (RAF) amorphous fractions and crystalline phase are nearly unchanged within the whole MDR range. The increases in lateral size and orientation improve the mechanical properties of the films. Significantly, the linear relationship between the elastic modulus and orientation at MDRs from 50 to 125 indicates that the elastic modulus is determined by the crystal orientation in PBS cast films with row-nucleated lamellae. This work evaluates the importance of orientation for microstructure and properties of PBS films, which may guide the processing of high-performance PBS films.

Thermoelectric transport properties of PbS and its contrasting electronic band structures

In this work we investigated the thermoelectric transport behaviors of p-type PbS and n-type PbS with an emphasis on its contrasting electronic band structures. We found that the Seebeck coefficients of p-type PbS increased faster with rising temperature than that of n-type PbS with the same carrier concentration. The Density functional theory (DFT) calculation of the energy band structure of PbS as a function of temperature illustrates a significant contribution from multiple valence bands in K-doped p-type PbS. This work revealed one important information that manipulating electronic bands is also suitable in developing high-performance PbS thermoelectric systems.

Multiscale structure and band configuration tuning to achieve high thermoelectric properties in n-type PbS bulks

PbS shares several similar features with PbTe and PbSe, and it is much more earth-abundant and inexpensive, which is characteristic of promising Te/Se-free thermoelectric materials for intermediate temperature power generation. However, its thermal conductivity is much higher than those of PbTe and PbSe, which bring a big challenge for obtaining high-performance PbS. In this study, we rationally integrate multiscale structure involving point defects, nanoprecipitates, grain boundaries and dislocations in PbS by doping for decreasing lattice thermal conductivity and simultaneously tuning energy band configuration. Density functional theory (DFT) calculations demonstrate that the ClS–SbPb defects with the lowest formation energy create an obvious shallow donor band and push upward-moving Fermi level, in good agreement with high electrical transport properties. Remarkably, PbS-0.067%PbCl2-1.5%Sb sample presents outstanding ZT of ~1.0 at 823 K and averaged ZT of ~0.62 at 423–823 K due to a low lattice thermal conductivity and a high power factor.

Inverted Si:PbS Colloidal Quantum Dot Heterojunction-Based Infrared Photodetector.

Silicon and PbS colloidal quantum dot heterojunction photodetectors combine the advantages of the Si device and PbS CQDs, presenting a promising strategy for infrared light detecting. However, the construction of a high-quality CQDs:Si heterojunction remains a challenge. In this work, we introduce an inverted structure photodetector based on n-type Si and p-type PbS CQDs. Compared with the existing normal structure photodetector with p-type Si and n-type PbS CQDs, it has a lower energy band offset that provides more efficient charge extraction for the device. With the help of Si wafer surface passivation and the Si doping density optimization, the device delivers a high detectivity of 1.47 × 1011 Jones at 1540 nm without working bias, achieving the best performance in Si/PbS photodetectors in this region now. This work provides a new strategy to fabricate low-cost high-performance PbS CQDs photodetectors compatible with silicon arrays.

Improving Charge Collection from Colloidal Quantum Dot Photovoltaics by Single-Walled Carbon Nanotube Incorporation.

Improving charge collection is one of the key issues for high-performance PbS colloidal quantum dot photovoltaics (CQDPVs) due to the considerable charge loss resulting from the low mobility and large defect densities of the 1,2-ethanedithiol-treated PbS quantum dot hole-transporting layer (HTL). To overcome these limitations, single-walled carbon nanotubes (SWNTs) and C60-encapsulated SWNTs (C60@SWNTs) are incorporated into the HTL in CQDPVs. SWNT-incorporated CQDPV demonstrates a significantly improved short-circuit current density (JSC), and C60@SWNT-incorporated CQDPV exhibits an even higher JSC than that of pristine SWNT. Both result in improved power-conversion efficiencies. Hole-selective, photoinduced charge extraction with linearly increasing voltage measurements demonstrates that SWNT or C60@SWNT incorporation improves hole-transporting behavior, rendering suppressed charge recombination and enhanced mobility of the HTL. The enhanced p-type characteristics and the improved hole diffusion lengths of SWNT- or C60@SWNT-incorporated HTL bring improvement of the entire hole-transporting length and enable lossless hole collection, which results in the JSC enhancement of the CQDPVs.

Achieving high-performance PbS quantum dot solar cells by improving hole extraction through Ag doping

PbS quantum dot solar cells are promising candidates for low-cost and highly efficient light harvesting devices owing to their solution processability and bandgap tunability. The p-type ethanedithiol (EDT) treated PbS quantum dot film plays an important role in PbS quantum dot solar cells with an n-i-p junction device structure. However, despite their sulphur-rich surface the EDT-treated PbS quantum dot film still have a relatively low carrier concentration. Higher carrier concentrations in this layer are desirable to extend depletion regions and improve hole extraction. Also imbalances in the charge mobility between the intrinsic layer and the p-type layer may lead to charge build-up at this interface. These obstacles limit further improvement of the device performance. Herein, we utilize EDT-treated Ag-doped PbS quantum dots as a p-type layer to fabricate PbS quantum dot photovoltaic cells. The carrier carrier concentration, mobility and band extrema as well as Fermi energy levels of Ag doped PbS quantum dot film can be tailored by tuning the Ag/Pb mole ratio from 0.0% to 2.0% during fabrication. The device performance has been significantly improved from 9.1% to 10.6% power conversion efficiency largely due to improvements in carrier concentration in the PbS-EDT layer through the incorporation of silver impurities.

High-Performance Solid-State PbS Quantum Dot-Sensitized Solar Cells Prepared by Introduction of Hybrid Perovskite Interlayer.

High-performance solid-state PbS quantum dot-sensitized solar cells (QD-SSCs) with stable 9.2% power conversion efficiency at 1 Sun condition are demonstrated by introduction of hybrid perovskite interlayer. The PbS QDs formed on mesoscopic TiO2 (mp-TiO2) by spin-assisted successive precipitation and anionic exchange reaction method do not exhibit PbSO4 but have PbSO3 oxidation species. By introducing perovskite interlayer in between mp-TiO2/PbS QDs and poly-3-hexylthiophene, the PbSO3 oxidation species are fully removed in the PbS QDs and thereby the efficiency of PbS QD-SSCs is enhanced over 90% compared to the pristine PbS QD-SSCs.

High Performance PbS Colloidal Quantum Dot Solar Cells by Employing Solution‐Processed CdS Thin Films from a Single‐Source Precursor as the Electron Transport Layer

AbstractCdS thin films are a promising electron transport layer in PbS colloidal quantum dot (CQD) photovoltaic devices. Some traditional deposition techniques, such as chemical bath deposition and RF (radio frequency) magnetron sputtering, have been employed to fabricate CdS films and CdS/PbS CQD heterojunction photovoltaic devices. However, their power conversion efficiencies (PCEs) are moderate compared with ZnO/PbS and TiO2/PbS heterojunction CQD solar cells. Here, efficiencies have been improved substantially by employing solution‐processed CdS thin films from a single‐source precursor. The CdS film is deposited by a straightforward spin‐coating and annealing process, which is a simple, low‐cost, and high‐material‐usage fabrication process compared to chemical bath deposition and RF magnetron sputtering. The best CdS/PbS CQD heterojunction solar cell is fabricated using an optimized deposition and air‐annealing process achieved over 8% PCE, demonstrating the great potential of CdS thin films fabricated by the single‐source precursor for PbS CQDs solar cells.

Solvent Engineering for High-Performance PbS Quantum Dots Solar Cells

PbS colloidal quantum dots (CQDs) solar cells have already demonstrated very impressive advances in recent years due to the development of many different techniques to tailor the interface morphology and compactness in PbS CQDs thin film. Here, n-hexane, n-octane, n-heptane, isooctane and toluene or their hybrids are for the first time introduced as solvent for comparison of the dispersion of PbS CQDs. PbS CQDs solar cells with the configuration of PbS/TiO2 heterojunction are then fabricated by using different CQDs solution under ambient conditions. The performances of the PbS CQDs solar cells are found to be tuned by changing solvent and its content in the PbS CQDs solution. The best device could show a power conversion efficiency (PCE) of 7.64% under AM 1.5 G illumination at 100 mW cm−2 in a n-octane/isooctane (95%/5% v/v) hybrid solvent scheme, which shows a ~15% improvement compared to the control devices. These results offer important insight into the solvent engineering of high-performance PbS CQDs solar cells.

Constructing aligned single-crystalline TiO2 nanorod array photoelectrode for PbS quantum dot-sensitized solar cell with high fill factor

Low bandgap PbS quantum dots (QDs) have attracted special interests serving as promising sensitizers for developing high performance near-infrared responsive photovoltaics. However, the commonly studied successive ionic layer adsorption and reaction (SILAR) processed PbS QD-sensitized solar cells (QDSCs) constructed with mesoporous TiO2 nanoparticle-photoelectrodes generally experience poor fill factor (FF) values lower than 0.50, arising from severe interfacial charge recombination because of the structural disorder of nanoparticles. This work demonstrates the construction of aligned TiO2 nanorod arrays (NRAs), vertically grown on substrates, for SILAR processed PbS QDSCs with high FF. The microscopic, structural, and optical characterizations reveal a rutile phase of single-crystalline structure in nature for TiO2 NRAs. The as-designed solar cell affords the advantages of panchromatic absorption for adequate light harvesting, reasonable band structure for efficient electron injection, and one dimensional (1D) oriented architecture for radial directional charge transport. A solar cell based on a 1.9 μm TiO2 NRA photoelectrode yields a considerable power conversion efficiency of 1.15% under 1 sun, coupled with a significantly enhanced FF of 0.51 in contrast to a conventional TiO2 nanoparticle-based device (FF = 0.38). The high FF is attributed to the outstanding electron transport behavior from QD sensitizers to conducting substrates via a shortest pathway (i.e., through radial direction of NRAs), thereby suppressing charge recombinations in solar devices. Therefore, the architecture of aligned 1D TiO2 NRAs is of great prospect to construct high performance PbS QDSCs. The performance improvement is promisingly expected through fully understanding of the radial directional charge transport mechanism and further optimization of NRA photoelectrodes and QD assemblies.

High-performance PbS quantum dot vertical field-effect phototransistor using graphene as a transparent electrode

Solution processed photoactive PbS quantum dots (QDs) were used as channel in high-performance near-infrared vertical field-effect phototransistor (VFEpT) where monolayer graphene embedded as transparent electrode. In this vertical architecture, the PbS QD channel was sandwiched and naturally protected between the drain and source electrodes, which made the device ultrashort channel length (110 nm) simply the thickness of the channel layer. The VFEpT exhibited ambipolar operation with high mobilities of μe = 3.5 cm2/V s in n-channel operation and μh = 3.3 cm2/V s in p-channel operation at low operation voltages. By using the photoactive PbS QDs as channel material, the VFEpT exhibited good photoresponse properties with a responsivity of 4.2 × 102 A/W, an external quantum efficiency of 6.4 × 104% and a photodetectivity of 2.1 × 109 Jones at the light irradiance of 36 mW/cm2. Additionally, the VFEpT showed excellent on/off switching with good stability and reproducibility and fast response speed with a short rise time of 12 ms in n-channel operation and 10.6 ms in p-channel operation. These high mobilities, good photoresponse properties and simplistic fabrication of our VFEpTs provided a facile route to the high-performance inorganic photodetectors.