N-type PbS Research Articles

Unveiling the potential of direct synthesized PbS CQD ink based solar cells through numerical simulation

Studies on lead sulfide-PbS quantum dot-QD based solar cells have gained considerable attention in recent years. A direct synthesis-DS method has emerged that makes it possible to obtain PbS ink in a single step by eliminating complex synthesis and ligand exchange processes, thus reducing the production cost and time. However, the limited number of studies on cells obtained with this method obscures the high potential of this technique. In this study, various electron-ETL and hole transport layers-HTL were systematically brought together in the SCAPS-1D environment to determine the architecture of the cell with record performance. A photoconversion efficiency-PCE of over 20% was achieved with a cell in which n-type DS PbS inks were combined with TiO2 ETL and MoO3 HTL. Moreover, we found that p-type DS PbS inks have a much higher potential than n-type inks, with a PCE of up to 36%, and most importantly, they are more resistant to increased defect density. We believe that this study, in which the device architecture for DS PbS inks was optimized and structured for the first time and the importance of p-type DS PbS inks was emphasized, will shed light on future studies in the field of solar cell technologies.

Top-Down Synthesis of N-Type PbS Quantum Dots with High Photoluminescence Quantum Yield from Microsized Pb(OH)Cl.

Synthesis of PbS quantum dots (QDs) with uniform and controllable size is of great importance in realizing functionality manipulation, as well as building advanced devices, and these QDs have been normally synthesized via "bottom-up" colloidal chemistry. However, the problems of complicated techniques and the relative high cost of the "bottom-up" methods still need to be overcome. Herein, we present a facile and cost-effective "top-down" strategy for the production of PbS QDs with controllable sizes and narrow dispersions (4.8% < σ < 7%) based on the sulfuration reaction of highly active lead oxide and oxychloride intermediates. We investigated the two-step reaction mechanism of the QD synthesis. Initially, Pb(OH)Cl undergoes a reaction with oleic acid in the presence of oleylamine as an activator, leading to the formation of active lead oxide/oxychloride intermediates. Notably, this distinctive reaction induces the creation of numerous cracks within the intermediates, thereby augmenting the active sites available for the subsequent sulfuration reactions. In that, the sulfur precursor reacts with the intermediates, resulting in the rapid generation of a substantial number of PbS fragments. Over time, these small fragments undergo "ripening" until reaching the "critical" size threshold. Different from the ones obtained by the traditional "bottom-up" method, our synthesized colloidal QDs exhibit a S-rich surface and are confirmed to be N-type. In addition, size-tunable near-infrared photoluminescence renders these QDs a promising material for various applications.

Realizing thermoelectric cooling and power generation in N-type PbS0.6Se0.4 via lattice plainification and interstitial doping

Thermoelectrics have great potential for use in waste heat recovery to improve energy utilization. Moreover, serving as a solid-state heat pump, they have found practical application in cooling electronic products. Nevertheless, the scarcity of commercial Bi2Te3 raw materials has impeded the sustainable and widespread application of thermoelectric technology. In this study, we developed a low-cost and earth-abundant PbS compound with impressive thermoelectric performance. The optimized n-type PbS material achieved a record-high room temperature ZT of 0.64 in this system. Additionally, the first thermoelectric cooling device based on n-type PbS was fabricated, which exhibits a remarkable cooling temperature difference of ~36.9 K at room temperature. Meanwhile, the power generation efficiency of a single-leg device employing our n-type PbS material reaches ~8%, showing significant potential in harvesting waste heat into valuable electrical power. This study demonstrates the feasibility of sustainable n-type PbS as a viable alternative to commercial Bi2Te3, thereby extending the application of thermoelectrics.

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.

Thermoelectric enhancement for n-type PbS via synergistic effect of Ti doping and Cu2S compositing

PbS is identified as a potential alternative candidate material for thermoelectric power generation and refrigeration, owing to the resemblance with PbTe in crystal and band structures. However, the thermoelectric performance has reached a bottleneck because of its inferior electronic structure and high lattice thermal conductivity. This work focuses on optimizing the electron–phonon transport by the synergistic effect of Ti and Cu2S in n-type PbS. The first-principles calculation, single Kane band model, and Debye model reveal the physical origin of thermoelectric enhancement. The Ti doping introduces a donor-defect state, leading to a high electrical conductivity and a suppression of bipolar diffusion. However, the band structure of PbS is not ideally optimized due to the localization effect of the Ti resonant impurity states. Furthermore, the co-added Cu2S induces additional point defects, multiscale secondary phases, and Cu-rich precipitates at grain boundaries, which significantly scatter phonons in a wide frequency range and reduce the lattice thermal conductivity. As a result, the maximum zT of ∼0.8 at 823 K and the average zTave of ∼0.46 from 300 to 623 K are achieved in n-type Pb0.99Ti0.01S–2%Cu2S, demonstrating the important roles of Ti and Cu2S on improving thermoelectrics in n-type PbS.

GaSb doping facilitates conduction band convergence and improves thermoelectric performance in n-type PbS

We improve n-type lead chalcogenides by adding GaSb to reduce lattice thermal conductivity and achieve conduction band convergence. This significantly enhances the thermoelectric performance of n-type PbS, making it comparable to its p-type counterpart.

Valence Disproportionation of GeS in the PbS Matrix Forms Pb5Ge5S12 Inclusions with Conduction Band Alignment Leading to High n-Type Thermoelectric Performance.

Converting waste heat into useful electricity using solid-state thermoelectrics has a potential for enormous global energy savings. Lead chalcogenides are among the most prominent thermoelectric materials, whose performance decreases with an increase in chalcogen amounts (e.g., PbTe > PbSe > PbS). Herein, we demonstrate the simultaneous optimization of the electrical and thermal transport properties of PbS-based compounds by alloying with GeS. The addition of GeS triggers a complex cascade of beneficial events as follows: Ge2+ substitution in Pb2+ and discordant off-center behavior; formation of Pb5Ge5S12 as stable second-phase inclusions through valence disproportionation of Ge2+ to Ge0 and Ge4+. PbS and Pb5Ge5S12 exhibit good conduction band energy alignment that preserves the high electron mobility; the formation of Pb5Ge5S12 increases the electron carrier concentration by introducing S vacancies. Sb doping as the electron donor produces a large power factor and low lattice thermal conductivity (κlat) of ∼0.61 W m-1 K-1. The highest performance was obtained for the 14% GeS-alloyed samples, which exhibited an increased room-temperature electron mobility of ∼121 cm2 V-1 s-1 for 3 × 1019 cm-3 carrier density and a ZT of 1.32 at 923 K. This is ∼55% greater than the corresponding Sb-doped PbS sample and is one of the highest reported for the n-type PbS system. Moreover, the average ZT (ZTavg) of ∼0.76 from 400 to 923 K is the highest for PbS-based systems.

High thermoelectric properties with low thermal conductivity due to the porous structure induced by the dendritic branching in n-type PbS

High thermoelectric properties with low thermal conductivity due to the porous structure induced by the dendritic branching in n-type PbS

Enhanced covalency and nanostructured-phonon scattering lead to high thermoelectric performance in n-type PbS

High thermoelectric performance can be achieved either by tuning the electronic structure or by enhancement in scattering the heat-carrying phonons, which often affect each other. Thereby, a leap in the performance can be achieved by simultaneous modulation of electronic structure and lowering of thermal conductivity. Herein, we demonstrate a high thermoelectric figure of merit (zT) of 1.45 at 900 K for Ge doped (4–10 mol%) n-type PbS, which is the one of the highest values among all n-type PbS-based thermoelectric materials. This high performance is achieved by simultaneous (a) enhancement of covalency in chemical bonding which increases the electrical conductivity, and (b) reduction of lattice thermal conductivity (κlat) to an ultra-low value of 0.56 W m−1K−1 at 900 K by the introduction of nanometer-sized (5–10 nm) precipitates of Pb2GeS4 in PbS matrix which strongly scatter the heat-carrying phonons. The presence of low-lying transverse acoustic (TA) and longitudinal acoustic (LA) phonon modes at 48.24 cm−1 and 91.83 cm−1, respectively are experimentally revealed from inelastic neutron scattering (INS) experiments. The softening of low-frequency modes at a higher temperature and ultra-short phonon lifetime (1–4.5 ps) further explain the ultra-low κlat. Electron localization function (ELF) analysis confirms chemical bonding hierarchy and increased covalent bonding due to the presence of Ge in PbS. The increase in bond covalency upon Ge doping in n-type PbS weakens electron–phonon coupling, thereby increasing the electrical transport.

Characterization of carrier transport using a bifacial structure for rational design of p-n junction PbS solar cells

In this study, a difference in the mobility of holes and electrons as a minority carrier has been systematically characterized in PbS quantum dot (QD) solar cells. While the mobility of electrons and holes is important in designing the p-n junction solar cells, it is still challenging to measure them during the normal operation of QD solar cells. When the solar includes only one transparent contact, it is difficult to separate the transport of electrons from that of holes during the normal operation of the device. We fabricated the bifacial solar cells and characterized the carrier transport by measuring the decay of photocurrent under pulsed illumination. The electron and hole mobility of p-type, n-type, and p-n junction type PbS QD film was examined and its connection to the performance of the solar cells was studied. In n-type PbS layer, the diffusion length of both electron and hole is ∼300 nm. In contrast, the diffusion length of hole and electron of p-type PbS layer is 250 nm and 175 nm. The asymmetric charge kinetics between holes and electrons in p-type PbS is systematically discussed. This result offers a rationale design rule of p-n junction type QD solar cells. 1) A difference in the mobility of holes and electrons is measured. 2) In n-type PbS layer, the diffusion length of both electron and hole is ∼300 nm 3) In p-type PbS, the asymmetric charge kinetics between holes and electrons is observed. 4) This study guides the design of the p-n junction type solar cells.

Enhancement of thermoelectric performance for n-type PbS via synergy of CuSbS2 alloying and Cl doping

Lead sulfide has attracted extensive attention as an outstanding thermoelectric material with practical energy conversion applications at intermediate temperature scope due to its cost-effectiveness and earth-abundant constituent elements. However, the naturally low carrier concentration and high thermal conductivity greatly restrict the thermoelectric performance of PbS-based materials. Herein, we present a significantly promoted thermoelectric performance in n-type PbS through synergistically promoting the electrical conductivity and suppressing lattice thermal conductivity with Cl doping and CuSbS2 alloying. The alloying with CuSbS2 lowers lattice thermal conductivity of PbS, which is essentially ascribed to point defect scattering. While the substitution of Cl for S in lattice significantly increases the Hall carrier concentration and carrier mobility, which prominently boosts electrical conductivity and thus results in high power factor of ~1.38 mW/mK2 at 723 K. Finally, compound with the nominal composition of (PbS0.98Cl0.02)0.95(CuSbS2)0.05 reaches a peak zT of ~0.76 at 773 K.

DETERMINATION AND MODELING OF THE LIQUIDUS SURFACE, VAPOR PRESSURE AND IMMISCIBILITY BOUNDARIES IN THE Cu–Pb–S SYSTEM

For the first time using a membrane zero-manometer, the vapor pressure S2 over the surface of the PbS liquidus in the ternary system Cu–Pb–S were determined in the range 1100÷1400 K and 0÷760 mm Hg. Based on the thermodynamic calculation, the boundaries of the immiscibility of liquid alloys of the Cu–S, Pb–S, and Cu–Pb–S systems were determined and analytically described. Critical temperatures and pressures for immiscibility regions of sulfur-rich liquid alloys are characterized by high values: Tcr= 1520÷1880 K; Pcr=170÷510 atm. The crystallization surfaces of lead sulfide with electronic conductivity (p-type PbS) and with hole conductivity (n-type PbS) are calculated and analytically de-scribed, as well as the corresponding values of sulfur vapor pressure over the crystallization surface of lead sulfide. All analytical dependencies for 3D modeling were obtained and visualized using the OriginLab computer program

Bridging the miscibility gap towards higher thermoelectric performance of PbS

Forming solid solutions between two isostructural compounds is an important strategy of regulating thermal transport in solids and boosting thermoelectric performance of narrow gap semiconductors. However, its full potential is not reached in a large variety of systems because of the known miscibility gap. A typical example includes PbS-PbTe where a limited solubility is demonstrated for one in another. Here in this study we show that the miscibility gap between PbS and PbTe is well bridged by introducing 30 mol% PbSe. This considerably extends the solubility limit of PbTe from only ∼4 mol% in PbS to at least 16 mol% in PbS0.7Se0.3, thus remarkably reducing the lattice thermal conductivity from a solid solution point of view. More importantly, it is found that carrier mobility of PbS is negligibly affected by this heavy alloying process, which is against conventional knowledge that higher concentration of defects leads to stronger carrier scattering. Our electron localization functions (ELF) mapping calculation results suggest an increased overlap of the adjacent electron clouds and decreased periodic potential fluctuations when the miscibility gap between PbS and PbTe gets bridged by PbSe. Therefore, the strengthened chemical bond covalency of PbS upon PbSe/PbTe alloying is responsible for the well reserved carrier mobilities. The simultaneous optimization of electron and phonon transport enabled by miscibility gap engineering (also applicable to many other technologically important thermoelectric materials) greatly boosts the thermoelectric performance of n-type Ga-doped PbS, leading to an excellent peak ZT of ∼1.1 at ∼723 K together with a record high average ZT value of 0.73 (300-723 K) in the samples of Pb0.99Ga0.01S0.7-xSe0.3Tex (x ≥ 0.12).

Contrasting Thermoelectric Transport Properties of n-Type PbS Induced by Adding Ni and Zn

Introducing small metallic atoms is an effective approach to enhance thermoelectric performance. In this research, we investigate the impacts of Ni and Zn on the thermoelectric performance of n-type PbS. We find that adding Ni is superior to that of Zn. Both experimental and theoretical results show that the extra Ni could bring a new impurity level among the Fermi energy, thus the electrons can be easily excited from defect states, leading to enhanced carrier mobility. Above all, adding Ni can boost the thermoelectric performance of n-type PbS dramatically. A peak ZT value at 823 K and a ZTave value of Pb0.995In0.005S + 5% Ni were achieved as ∼1.0 and ∼0.66, respectively.

Enhanced thermoelectric properties of PbTe0.95via N-type PbS nano-inclusions using a conventional sintering method

The successful synthesis of n-type nano PbS particles as sintering additives that highly promote densified PbTe0.95/PbS thermoelectric composites using the conventional sintering method, largely enhancing the zT value.

Enhanced thermoelectric performance of hot-press Bi-doped n-type polycrystalline PbS

Lead sulfide (PbS) is a type of promising thermoelectric materials which is consist of elements with high natural abundance. However, the relatively low conversion efficiency limits its further application due to the high lattice thermal conductivity of PbS compared with that of PbTe. It has been widely accepted that nanostructuring and doping are effective ways to enhance the thermoelectric properties. Herein, nano/micro structure Bi doped PbS materials have beensynthesized by a facile method of hydrothermal synthesis. The nano/micro structure material systems exist abundant interface which could scatter mid- and low-frequency phonons effectively, combined with point defect such as Bi–Pb scattering high-frequency phonons, and thus the results show that the lattice thermal conductivity of PbS decreases with the increasing concentration of Bi3+ doping as expected. Moreover, the optimal power factor (PF) can be obtained by tuning the carrier concentration and mobility at the same time. The optimal thermoelectric figure of merit (ZT) can reach 0.89 for Pb0.96Bi0.04S at 773K and rises with the increase of the temperature without sign of saturation. Our work may shed light to further possible and environmentally friendly application of PbS-based thermoelectric materials.

Boosting thermoelectric performance of n-type PbS through synergistically integrating In resonant level and Cu dynamic doping

PbS has attracted much attention as an excellent thermoelectric material with high development space at middle temperature scope. The thermoelectric performance for n-type PbS was boosted by the cooperative effects of resonance level and Cu dynamic doping in our research. In the first place, In doping improved the electrical transport performance of n-type PbS effectively on account of optimal carrier concentration and resonant level effects, and reduced the lattice thermal conductivity by reason of heightened phonon scattering through impurity atoms scattering simultaneously. Secondly, Cu dynamic doping further increased average power factor to ~18.8 μW cm−1 K−2 at 423 K- 823 K of Pb0.995In0.005S+3%Cu owing to higher Seebeck coefficients and suppressed electronic thermal transports at vast temperature span. In result, the best thermoelectric figure of merit (ZT) of Pb0.995In0.005S+3%Cu at 723 K reached ~1.1 and a record large average ZT (ZTave) of Pb0.995In0.005S+3%Cu was achieved ~ 0.8 at 423 K-823 K, which is vital in the implementation of thermoelectric technology.

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.