Synergistic Effect of Ionic Liquid and Embedded QDs on 2D Ferroelectric Perovskite Films with Narrow Phase Distribution for Self-Powered and Broad-Band Photodetectors.

2D layered metal halide perovskites (MHPs) are a potential material for fabricating self-powered photodetectors (PDs). Nevertheless, 2D MHPs produced via solution techniques frequently exhibit multiple quantum wells, leading to notable degradation in the device performance. Besides, the wide band gap in 2D perovskites limits their potential for broad-band photodetection. Integrating narrow-band gap materials with perovskite matrices is a viable strategy for broad-band PDs. In this study, the use of methylamine acetate (MAAc) as an additive in 2D perovskite precursors can effectively control the width of the quantum wells (QWs). The amount of MAAc greatly affects the phase purity. Subsequently, PbSe QDs were embedded into the 2D perovskite matrix with a broadened absorption spectrum and no negative effects on ferroelectric properties. PM6:Y6 was combined with the hybrid ferroelectric perovskite films to create a self-powered and broad-band PD with enhanced performance due to a ferro-pyro-phototronic effect, reaching a peak responsivity of 2.4 A W-1 at 940 nm.

Robustly Boosting Thermoelectric Performance of N-Type PbSe via Lattice Plainification and Dynamic Doping.

Ideal thermoelectrics shall possess a high average ZT, which relies on high carrier mobility and appropriate carrier density at operating temperature. However, conventional doping usually results in a temperature-independent carrier concentration, making performance optimization over a wide temperature range be challenging. This work demonstrates the combination of lattice plainification and dynamic doping strategies is an effective route to boost the average ZT of N-type PbSe. Because Sn and Pb have similar ionic radii and electronegativity, this allows Sn to fill the intrinsic Pb vacancies and effectively improves the carrier mobility of PbSe to 1300 cm2 V-1 s-1. Furthermore, a trace amount of Cu is introduced into the Sn-filled PbSe to optimize the carrier concentration. The extra Cu is situated in the interstitial sides of the lattice, which undergoes a dissolution-precipitation process with temperature, leading to a strongly temperature-dependent carrier density in the material. This dynamic doping effectively improves the electrical transport properties and is also valid to suppress the lattice thermal conductivity. Ultimately, the resulting PbSn0.004Se+3‰Cu obtains a maximum ZT of ≈1.7 at 800 K and an average ZT of ≈1.0, with a 7.7% power generation efficiency in a single-arm device, showing significant potential for commercial application.

Enhanced Thermoelectric Performance of N-Type PbSe Through Semi-Coherent Nanostructure by AgCuTe Alloying.

N-type PbSe thermoelectric materials encounter challenges in improving the power factor due to the single-band structure near the Fermi level, which obstructs typical band convergence. The primary strategy for enhancing the thermoelectric figure of merit (ZT) for n-type PbSe involves reducing lattice thermal conductivity (κlat) by introducing various defect structures. However, lattice mismatches resulting from internal defects within the matrix can diminish carrier mobility, thereby affecting electrical transport properties. In this study, n-type AgCuTe-alloyed PbSe systems achieve a peak ZT value of ≈1.5 at 773 K. Transmission electron microscopy reveals nanoprecipitates of Ag2Te, the room temperature second phase of AgCuTe, within the PbSe matrix. Meanwhile, a unique semi-coherent phase boundary is observed between the PbSe matrix and the Ag2Te nanoprecipitates. This semi-coherent phase interface effectively scatters low-frequency phonons while minimizing damage to carrier mobility. Additionally, the dynamic doping effect of Cu atoms from the decomposition of AgCuTe within the matrix further optimize the high-temperature thermoelectric performance. Overall, these factors significantly enhance the ZT across the whole temperature range. The ZT value of ≈1.5 indicates high competitiveness compared to the latest reported n-type PbSe materials, suggesting that these findings hold promise for advancing the development of efficient thermoelectric systems.

Expanded Stability of Layered SnSe-PbSe Alloys and Evidence of Displacive Phase Transformation from Rocksalt in Heteroepitaxial Thin Films.

Bulk PbSnSe has a two-phase region, or miscibility gap, as the crystal changes from a van der Waals-bonded orthorhombic 2D layered structure in SnSe-rich compositions to the related 3D-bonded rocksalt structure in PbSe-rich compositions. This structural transition drives a large contrast in the electrical, optical, and thermal properties. We realize low temperature direct growth of epitaxial PbSnSe thin films on GaAs via molecular beam epitaxy using an in situ PbSe surface treatment and show a significantly reduced two-phase region by stabilizing the Pnma layered structure out to Pb0.45Sn0.55Se, beyond the bulk limit around Pb0.25Sn0.75Se at low temperatures. Pushing further, we directly access metastable two-phase films of layered and rocksalt grains that are nearly identical in composition around Pb0.50Sn0.50Se and entirely circumvent the miscibility gap. We present microstructural and compositional evidence for an incomplete displacive transformation from a rocksalt to layered structure in these films, which we speculate occurs during the sample cooling to room temperature after synthesis. In situ temperature-cycling experiments on a Pb0.58Sn0.42Se rocksalt film reproduce characteristic attributes of a displacive transition and show a modulation in electronic properties. We find well-defined orientation relationships between the phases formed and reveal unconventional strain relief mechanisms involved in the crystal structure transformation using transmission electron microscopy. Overall, our work adds a scalable thin film integration route to harness the dramatic contrast in material properties in PbSnSe across a potentially ultrafast crystalline-crystalline structural transition.

High Carrier Mobility and Promising Thermoelectric Module Performance of N-Type PbSe Crystals.

The scarcity of Te hampers the widespread use of Bi2Te3-based thermoelectric modules. Here, the thermoelectric module potential of PbSe is investigated by improving its carrier mobility. Initially, large PbSe crystals are grown with the temperature gradient method to mitigate grain boundary effects on carrier transport. Subsequently, light doping with <1mole‰ halogens (Cl/Br/I) increases room-temperature carrier mobility to ~1600 cm2 V-1 s-1, achieved by reducing carrier concentration compared to traditional heavy doping. Crystal growth design and light doping enhance carrier mobility without affecting effective mass, resulting in a high power factor ~40 µW cm-1 K-2 in PbSe-Cl/Br/I crystals at 300 K. Additionally, Cl/Br/I doping reduces thermal conductivity and bipolar diffusion, leading to significantly lower thermal conductivity at high temperature. Enhanced carrier mobility and suppressed bipolar effect boost ZT values across the entire temperature range in n-type PbSe-Cl/Br/I crystals. Specifically, ZT values of PbSe-Br crystal reach ~0.6 at 300 K, ~1.2 at 773 K, and the average ZT (ZTave) reaches ~1.0 at 300-773 K. Ultimately, ~5.8% power generation efficiency in a PbSe single leg with a maximum temperature cooling difference of 40 K with 7-pair modules is achieved. These results indicate the potential for cost-effective and high-performance thermoelectric cooling modules based on PbSe.

Lattice Plainification Leads to High Thermoelectric Performance of P-Type PbSe Crystals.

Thermoelectrics has applications in power generation and refrigeration. Since only commercial Bi2Te3 has a low abundance Te, PbSe gets attention. This work enhances the near-room temperature performance of p-type PbSe through enhancing carrier mobility via lattice plainification. Composition controlled and Cu-doped p-type PbSe crystals are grown through physical vapor deposition. Results exhibit an enhanced carrier mobility ≈2578 cm2 V-1 s-1 for Pb0.996Cu0.0004Se. Microstructure characterization and density functional theory calculations verify the introduced Cu atoms filled Pb vacancies, realizing lattice plainification and enhancing the carrier mobility. The Pb0.996Cu0.0004Se sample achieves a power factor ≈42 µW cm-1 K-2 and a ZT ≈ 0.7 at 300 K. The average ZT of it reaches ≈0.9 (300-573 K), resulting in a single-leg power generation efficiency of 7.1% at temperature difference of 270 K, comparable to that of p-type commercial Bi2Te3. A 7-pairs device paired the p-type Pb0.996Cu0.0004Se with the n-type commercial Bi2Te3 shows a maximum cooling temperature difference ≈42 K with the hot side at 300 K, ≈65% of that of the commercial Bi2Te3 device. This work highlights the potential of p-type PbSe for power generation and refrigeration near room temperature and hope to inspire researchers on replacing commercial Bi2Te3.

Realization of black phosphorus-like PbSe monolayer on Au(111) via epitaxial growth.

Lead selenide (PbSe) has been attracted a lot attention in fundamental research and industrial applications due to its excellent infrared optical and thermoelectric properties, toward reaching the two-dimensional limit. Herein, we realize the black phosphorus-like PbSe (α-phase PbSe) monolayer on Au(111) via epitaxial growth, where a characteristic rectangular superlattice of 5 Å × 9 Å corresponding to 1 × 2 reconstruction with respect to the pristine ofα-phase PbSe is observed by scanning tunneling microscopy. Corresponding density functional theory calculation confirmed the reconstruction and revealed the driven mechanism, the coupling between monolayer PbSe and Au(111) substrate. The metallic feature of differential conductance spectra as well as the transition of the density of states from semiconductor to metal further verified such coupling. As the unique anisotropic structure, our study provides a pathway towards the synthesis of BP-PbSe monolayer. In addition, it builds up an ideal platform for studying fundamental physics and also excellent prospects in PbSe-based device applications.

Prevalence of and Work-Related Factors Associated with Sickness Presenteeism among Nursing Care Providers in Selected Tertiary Hospitals in Bangalore City: A Cross-Sectional Study.

Introduction: Sickness presenteeism is a phenomenon where "workers go to work when ill." The objective of this study was to determine the prevalence of and work-related factors associated with presenteeism among nursing care providers in selected tertiary hospitals in Bangalore city. Methodology: Participants were selected using stratified sampling followed by simple random sampling. A questionnaire was designed to capture socio-demographic information, sickness-related behavior, performance-based self-esteem (PBSE), and selected work-related characteristics. Results: A total of 357 participants were enrolled in the study, 274 were staff nurses (S/N) and 83 were nursing assistants (N/A). About 75% of the participants reported presenteeism at least once in the last year, two-fifths did so in the last 4 weeks and nearly 15% were sick on the day of the interview. The mean Stanford Sickness Presenteeism Scale-6 score was 18.49 ± 3.84. The most frequent reason for presenteeism was "perceived mildness of the disease." In bivariate analysis, those who were younger, male, had children, higher qualifications, chronic ailment/s, financial commitments, lesser work experience, and higher PBSE had higher presenteeism scores. When introduced into a linear regression model, those S/N who had children [Standardized coefficient = 0.23 (0.40-1.97)], higher PBSE scores [Standardized coefficient = 0.385 (0.15-2.55)], and reported sickness absenteeism in the preceding 4 weeks [Standardized coefficient = 0.136 (0.12-1.01)] were significantly associated with higher presenteeism scores. Those N/A who had lesser work experience had higher presenteeism scores [Standardized coefficient = -0.33 (-0.02--0.004)]. Conclusion: Presenteeism is a common phenomenon among nursing care providers. It is imperative that both employers and employees be educated about its ill effects on the individual, fellow staff, and patients, followed by the adoption of preventive measures.

The Adsorption Effect of Methane Gas Molecules on Monolayer PbSe with and without Vacancy Defects: A First-Principles Study.

In this paper, the adsorption effect of methane (CH4) gas molecular on monolayer PbSe with and without vacancy defects is studied based on first-principles calculations. The effects of the adsorption of methane molecular on monolayer PbSe and on the Se vacancy (VSe) and Pb vacancy (VPb) of monolayer PbSe are also explored. Our results show that methane molecules exhibit a good physical adsorption effect on monolayer PbSe with and without vacancy defects. Moreover, our simulations indicate that the adsorption capacity of CH4 molecules on monolayer PbSe can be enhanced by applying strain. However, for the monolayer PbSe with Vse, the adsorption capacity of CH4 molecules on the strained system decreases sharply. This indicates that applying strain can promote the dissociation of CH4 from VSe. Our results show that the strain can be used as an effective means to regulate the interaction between the substrate material and the methane gas molecules.

Two Bulk-Heterojunctions Made of Blended Hybrid Nanocomposites for High-Performance Broadband, Self-Driven Photodetectors.

Heterojunctions based on low dimensional semiconducting materials are one of the most promising alternatives for next-generation optoelectronic devices. By choosing different dopants in high-quality semiconducting nanomaterials, p-n junctions can be realized with tailored energy band alignments. Also, p-n bulk-heterojunctions (BHJs) based photodetectors have shown high detectivity because of the suppressed dark current and high photocurrent, which are due to the larger built-in electric potential within the depletion region and can significantly improve the quantum efficiency by reducing the carriers' recombination. In this work, PbSe quantum dots (QDs) blended with ZnO nanocrystals (NCs) were used as the n-type layer, while CsPbBr3 NCs doped with P3HT were used as the p-type layer; as a result, a p-n BHJ was formed with a strong built-in electric field. Consequently, such a kind of p-n BHJ photodetector ITO/ZnO/PbSe:ZnO/CsPbBr3:P3HT/P3HT/Au showed a high ON/OFF current ratio of 105 with a photoresponsivity of 1.4 A/W and specific detectivity of 6.59 × 1014 Jones under 0.1 mW/cm2 532 nm illumination in self-driven mode. Moreover, the simulation performed by TCAD also agrees well with our experimental results, and the underlying physical mechanism for enhanced performance is discussed in detail for this type of p-n BHJ photodetector.

Preparation of Heavily Doped P-Type PbSe with High Thermoelectric Performance by the NaCl Salt-Assisted Approach.

Thermoelectric (TE) technology, which can convert scrap heat into electricity, has attracted considerable attention. However, broader applications of TE are hindered by lacking high-performance thermoelectric materials, which can be effectively progressed by regulating the carrier concentration. In this work, a series of PbSe(NaCl)x (x = 3, 3.5, 4, 4.5) samples were synthesized through the NaCl salt-assisted approach with Na+ and Cl- doped into their lattice. Both theoretical and experimental results demonstrate that manipulating the carrier concentration by adjusting the content of NaCl is conducive to upgrading the electrical transport properties of the materials. The carrier concentration elevated from 2.71 × 1019 cm-3 to 4.16 × 1019 cm-3, and the materials demonstrated a maximum power factor of 2.9 × 10-3 W m-1 K-2. Combined with an ultralow lattice thermal conductivity of 0.7 W m-1 K-1, a high thermoelectric figure of merit (ZT) with 1.26 at 690 K was attained in PbSe(NaCl)4.5. This study provides a guideline for chemical doping to improve the thermoelectric properties of PbSe further and promote its applications.

Epitaxial CdSe/PbSe Heterojunction Growth and MWIR Photovoltaic Detector.

A novel Epitaxial Cadmium Selenide (CdSe) on Lead Selenide (PbSe) type-II heterojunction photovoltaic detector has been demonstrated by Molecular Beam Epitaxy (MBE) growth of n-type CdSe on p-type PbSe single crystalline film. The use of Reflection High-Energy Electron Diffraction (RHEED) during the nucleation and growth of CdSe indicates high-quality single-phase cubic CdSe. This is a first-time demonstration of single crystalline and single phase CdSe growth on single crystalline PbSe, to the best of our knowledge. The current-voltage characteristic indicates a p-n junction diode with a rectifying factor over 50 at room temperature. The detector structure is characterized by radiometric measurement. A 30 µm × 30 µm pixel achieved a peak responsivity of 0.06 A/W and a specific detectivity (D*) of 6.5 × 108 Jones under a zero bias photovoltaic operation. With decreasing temperature, the optical signal increased by almost an order of magnitude as it approached 230 K (with thermoelectric cooling) while maintaining a similar level of noise, achieving a responsivity of 0.441 A/W and a D* of 4.4 × 109 Jones at 230 K.

Highly Responsive Mid-Infrared Metamaterial Enhanced Heterostructure Photodetector Formed out of Sintered PbSe/PbS Colloidal Quantum Dots.

Efficient and simple-to-fabricate light detectors in the mid infrared (MIR) spectral range are of great importance for various applications in existing and emerging technologies. Here, we demonstrate compact and efficient photodetectors operating at room temperature in a wavelength range of 2710-4250 nm with responsivities as high as 375 and 4 A/W. Key to the high performance is the combination of a sintered colloidal quantum dot (CQD) lead selenide (PbSe) and lead sulfide (PbS) heterojunction photoconductor with a metallic metasurface perfect absorber. The combination of this photoconductor stack with the metallic metasurface perfect absorber provides an overall ∼20-fold increase of the responsivity compared against reference sintered PbSe photoconductors. More precisely, the introduction of a PbSe/PbS heterojunction increases the responsivity by a factor of ∼2 and the metallic metasurface enhances the responsivity by an order of magnitude. The metasurface not only enhances the light-matter interaction but also acts as an electrode to the detector. Furthermore, fabrication of our devices relies on simple and inexpensive methods. This is in contrast to most of the currently available (state-of-the-art) MIR photodetectors that rely on rather expensive as well as nontrivial fabrication technologies that often require cooling for efficient operation.

Van der Waals epitaxial growth of two-dimensional PbSe and its high-performance heterostructure devices.

Inspired by the great success of ultrathin two-dimensional (2D) layered crystals, more and more attention is being paid to preparing 2D nanostructures from non-layered materials. They can significantly enrich the 2D materials and 2D heterostructures family, extend their application prospects, and bring us distinct properties from their bulk counterparts due to the strong 2D confinement effect. However, the realization of 2D non-layered semiconductors with strong light-harvesting capability and the ability to construct high-performance 2D heterostructures is still a critical challenge. Herein, we successfully synthesized 2D PbSe semiconductors with a large lateral dimension and ultrathin thickness via van der Waals epitaxy. The fabricated 2D PbSe device exhibits good electrical conductivity and superior multi-wavelength photoresponse performance with high responsivity (∼103 A/W) and impressive detectivity (∼2 × 1011 Jones). Furthermore, we demonstrate that 2D PbSe nanosheets can serve as component units for constructing high-performance heterostructure devices. With our strategy, ultrahigh current on/off ratio (∼108) and rectification ratio (∼106), as well as high responsivity (∼3 × 103 A/W) and detectivity (∼7 × 1012 Jones), can be achieved in PbSe/MoS2 back-gated transistors. These results indicate that 2D PbSe nanosheets and their heterostructures have tremendous applications potential in electrical and optoelectronic devices.

High-Mobility Hole Transport in Single-Grain PbSe Quantum Dot Superlattice Transistors.

Epitaxially-fused superlattices of colloidal quantum dots (QD epi-SLs) may exhibit electronic minibands and high-mobility charge transport, but electrical measurements of epi-SLs have been limited to large-area, polycrystalline samples in which superlattice grain boundaries and intragrain defects suppress/obscure miniband effects. Systematic measurements of charge transport in individual, highly-ordered epi-SL grains would facilitate the study of minibands in QD films. Here, we demonstrate the air-free fabrication of microscale field-effect transistors (µ-FETs) with channels consisting of single PbSe QD epi-SL grains (2-7 µm channel dimensions) and analyze charge transport in these single-grain devices. The eight devices studied show p-channel or ambipolar transport with a hole mobility as high as 3.5 cm2 V-1 s-1 at 290 K and 6.5 cm2 V-1 s-1 at 170-220 K, one order of magnitude larger than that of previous QD solids. The mobility peaks at 150-220 K, but device hysteresis at higher temperatures makes the true mobility-temperature curve uncertain and evidence for miniband transport inconclusive.

PbSe Quantum Dot Doped Mode-Locked Fiber Laser.

Herein, a PbSe quantum dot-doped-mode-locked fiber laser is experimentally demonstrated. A PbSe quantum dot-doped fiber is prepared using a melting method and induced as a gain medium in our mode-locked fiber laser. By increasing the pump power, a stable pulse train is obtained with a pulse duration of 36 ps, a pulse repetition rate of 4.5 MHz, an average laser power of 9.8 mW, and a central wavelength of 1214.5 nm. The pulse duration can be changed by adjusting the PC or increasing the pump power. The maximum laser power obtained was 42.7 mW under the pump power of 800 mW. Our results prove that a quantum dot-doped-mode-locked fiber laser is achievable, which provides a new scheme to solve wavelength problem of rare-earth-doped mode-locked fiber lasers.

Cation-Exchange Enables In Situ Preparation of PbSe Quantum Dot Ink for High Performance Solar Cells.

Lead selenide (PbSe) colloidal quantum dots (CQDs) are promising candidates for optoelectronic applications. To date, PbSe CQDs capped by halide ligands exhibit improved stability and solar cells using these CQDs as active layers have reported a remarkable power conversion efficiency (PCE) up to 10%. However, PbSe CQDs are more prone to oxidation, requiring delicate control over their processability and compromising their applications. Herein, an efficient strategy that addresses this issue by an in situ cation-exchange process is reported. This is achieved by a two-phase ligand exchange process where PbI2 serves as both a passivating ligand and cation-source inducing transformation of CdSe to PbSe. The defect density and carrier lifetime of PbSe CQD films are improved to 1.05 × 1016  cm-3 and 12.2 ns, whereas the traditional PbSe CQD films possess 1.9 × 1016  cm-3 defect density and 10.2 ns carrier lifetime. These improvements are translated into an enhancement of photovoltaic performance of PbSe solar cells, with a PCE of up to 11.6%, ≈10% higher than the previous record. Notably, the approach enables greatly improved stability and a two-month stability is successfully demonstrated. This strategy is expected to promote the fast development of PbSe CQD applications in low-cost and high-performance optoelectronic devices.

Atomic Level Defect Structure Engineering for Unusually High Average Thermoelectric Figure of Merit in n-Type PbSe Rivalling PbTe.

Realizing high average thermoelectric figure of merit (ZTave ) and power factor (PFave ) has been the utmost task in thermoelectrics. Here the new strategy to independently improve constituent factors in ZT is reported, giving exceptionally high ZTave and PFave in n-type PbSe. The nonstoichiometric, alloyed composition and resulting defect structures in new Pb1+ x Se0.8 Te0.2 (x = 0-0.125) system is key to this achievement. First, incorporating excess Pb unusually increases carrier mobility (µH ) and concentration (nH ) simultaneously in contrast to the general physics rule, thereby raising electrical conductivity (σ). Second, modifying charge scattering mechanism by the authors' synthesis process boosts a magnitude of Seebeck coefficient (S) above theoretical expectations. Detouring the innate inverse proportionality between nH and µH ; and σ and S enables independent control over them and change the typical trend of PF to temperature, giving remarkably high PFave ≈20 µW cm-1 K-2 from 300 to 823 K. The dual incorporation of Te and excess Pb generates unusual antisite Pb at the anionic site and displaced Pb from the ideal position, consequently suppressing lattice thermal conductivity. The best composition exhibits a ZTave of ≈1.2 from 400 to 823 K, one of the highest reported for all n-type PbQ (Q = chalcogens) materials.

Nanopore-Patterned CuSe Drives the Realization of the PbSe-CuSe Lateral Heterostructure.

Monolayer PbSe has been predicted to be a two-dimensional (2D) topological crystalline insulator (TCI) with crystalline symmetry-protected Dirac-cone-like edge states. Recently, few-layered epitaxial PbSe has been grown on the SrTiO3 substrate successfully, but the corresponding signature of the TCI was only observed for films not thinner than seven monolayers, largely due to interfacial strain. Here, we demonstrate a two-step method based on molecular beam epitaxy for the growth of the PbSe-CuSe lateral heterostructure on the Cu(111) substrate, in which we observe a nanopore-patterned CuSe layer that acts as the template for lateral epitaxial growth of PbSe. This further results in a PbSe-CuSe lateral heterostructure with an atomically sharp interface. Scanning tunneling microscopy and spectroscopy measurements reveal a fourfold symmetric square lattice of such PbSe with a quasi-particle band gap of 1.8 eV, a value highly comparable with the theoretical value of freestanding PbSe. The weak monolayer-substrate interaction is further supported by both density functional theory (DFT) and projected crystal orbital Hamilton population, with the former predicting the monolayer's anti-bond state to reside below the Fermi level. Our work demonstrates a practical strategy to fabricate a high-quality in-plane heterostructure, involving a monolayer TCI, which is viable for further exploration of the topology-derived quantum physics and phenomena in the monolayer limit.

Electron Paramagnetic Resonance Study of PbSe, PbTe, and PbTe:In Semiconductors Obtained by the Pulsed Laser Deposition Method.

The magnetic properties of lead selenide (PbSe) and indium-doped lead telluride (PbTe:In) composites have been studied by using the electron paramagnetic resonance (EPR) technique. The samples were obtained by using the pulsed laser deposition method (PLD). Temperature dependences of the EPR spectra were obtained. The analysis of the temperature dependencies of the integral intensity of the EPR spectra was performed using the Curie-Weiss law. In these materials, the paramagnetic centers of Pb1+ and Pb3+ ions were identified. The results are discussed.