PbSe Films Research Articles

Ternary Pb1−xCdxSe films grown by molecular beam epitaxy on GaAs/ZnTe hybrid substrates

Thin epitaxial Pb1−xCdxSe films with cadmium content x ≤ 0.36 have been grown by molecular beam epitaxy (MBE) on highly resistive, lattice matched (0 0 1) ZnTe/GaAs hybrid substrates. The High Resolution X-ray Diffraction (HRXRD) indicates that the films crystallize in the rock salt structure. Up to x = 0.12 the Pb1−xCdxSe films are (0 0 1) oriented and monocrystalline with negligible amount of other phases. The lattice constant of the films decreases proportionally to the Cd content. As evidenced by low-temperature photoluminescence (PL) the energy gap of Pb1−xCdxSe films increases with the increasing Cd content. The parameters of optical phonons and plasmons in the material are established by infrared reflectance measurements. The most interesting property of the Pb1−xCdxSe films is revealed by classical transport measurements. The alloying of PbSe with CdSe reduces the hole concentration in the material from a typical value of 3 × 1018 cm−3 in the pure PbSe film down to 3 × 1016 cm−3 in the film containing x = 0.052 of Cd. The reduction of the hole concentration by two orders of magnitude makes the Pb1−xCdxSe films very attractive for infrared detector applications. Simple photoresistors made of Pb1−xCdxSe films exhibit sensitivity to the infrared radiation up to the room temperature.

Electrical and optical characterization of extended SWIR detectors based on thin films of nano-columnar PbSe

There is an increasing demand for detectors with extended Short Wavelength Infrared (SWIR) absorption at wavelengths between 1.6 μm and 2.8 μm. Towards that end, PbSe absorber layers were grown by the Chemical-Bath-Deposition (CBD) technique in a nano-columnar morphology on n-type (1 0 0) oriented GaAs substrate, where the nano-columns are densely packed perpendicular to the substrate. The spectral absorption edge and photoluminescence (PL) peak of these layers were blue shifted from the bulk bandgap of 4.7 μm to 2.2 μm, i.e., within the extended SWIR range, due to quantum confinement effect. Current voltage (I-V) measurements were carried out in a vertical geometry of different circular mesa sizes (250–2000 μm in diameter). The area dependent current–voltage measurements indicate a densely packed layer with no apparent pinholes. On the other hand, it was found out that surface leakage currents on the mesa perimeters are the dominant mechanism of the dark current. A photo-response to SWIR illumination was evident, confirming the feasibility of using such structures as extended SWIR photodetectors upon minimizing leakage currents using surface treatments.

STUDY OF COMPOSITION FILM SYSTEM PB-SE AND CHANGE OF STRUCTURE UNDER TEMPERATURE ACTION

The Pb-Se film systems were obtained by solid-phase synthesis and investigated by Xray diffraction and X-ray photoelectron spectroscopy, electron Auger spectroscopy. It was found that the films are heterogeneous in structure and composition. To study the structural features under the influence of temperature, Raman spectra of samples at temperatures of 300 K and 373 K were investigated.

The electrical properties of carrier transport between lead selenide polycrystallites manipulated by iodine concentration

We provide the carrier transport properties of the polycrystalline PbSe material prepared by iodine concentration manipulation. We discover that the activation energy of the crystallite boundary barrier can be modulated the iodine concentrations. The electronic structure indicates some acceptor energy levels near the valence band at about -0.26 eV below the Fermi level. The temperature dependences of the conductivities with different iodine concentrations over the range 150–360 K reveal that a high crystalline boundary barrier is constructed with the activation energy as high as 108.2 meV induced by iodine treatment to reduce the dark current of the device. The carrier transport will all deviate from the Arrhenius thermally driven behavior below a transition temperature of 217.4 K, indicating the acceptor levels in the polycrystalline PbSe film with p-type surface microlayer. The structural and compositional properties reveal that the activation energy is highly affected by the phase orientations of PbSeO3 (002) and (110). We believe these results will be helpful for understanding the carrier transport across the crystallite boundaries, and may promote the material optimization of the polycrystalline lead chalcogenides in optoelectronics.

The Formation of Hollow Lead Structures on the Surface of PbSe Films Treated in Argon Plasma

Conditions for ion sputtering of a PbSe/CaF2/Si(111) epitaxial system in high-density inductively coupled plasma of high-frequency low-pressure discharge in argon have been established that ensure the formation of submicron-sized hollow lead structures on a lead-selenide surface. The surface was plasma-treated for time periods within 60–240 s at low energy (20–30 eV) of Ar+ ions, which is close to their sputtering threshold energy. The properties of the obtained material were studied by the techniques of scanning electron microscopy and energy-dispersive X-ray microanalysis. It is shown that the characteristic size, shape, and density of surface structures can be varied within broad limits depending on the time of plasma treatment and temperature of the material surface. Physical processes responsible for the formation of hollow lead structures under the proposed conditions of plasma sputtering are considered.

Effect of Ascorbic Acid Additions on the Mechanism Underlying the Growth of Nanostructured PbSe Films via Hydrochemical Deposition

The effect of ascorbic acid additions on the growth mechanism of thin PbSe films produced by hydrochemical deposition has been studied by atomic force microscopy (AFM). A fractal analysis of AFM images of the lead selenide films has shown that their formation follows the “cluster–particle” aggregation mechanism. The fractal dimension assessed by the box-counting method is 2.26 at an average grain size of ~150 nm. From the transmission spectra of the films grown at deposition times from 20 to 120 min, we have evaluated their optical band gap, which has been shown to decrease from 0.595 to 0.53 eV with increasing deposition time. These values are attributable to the manifestation of quantum size effects in the grown PbSe films.

Effect of oxygen annealing on the photoresponse of PbSe thin films fabricated by the pulsed laser deposition method

ABSTRACTIn this work, we have fabricated lead selenide (PbSe) thin films by the pulsed laser deposition method on Si/SiO2 substrates and investigated the effect of oxygen annealing (sensitization) in these films. The oxygen-sensitized films show high responsivity in the visible (VIS) and the near-infrared (NIR) region at room temperature without cooling. We also demonstrate the effective surface oxidation of PbSe thin films during the oxygen annealing process without treated with commonly used halogens that leads to a better photoresponse in these PbSe films.

Thermoelectric prospects of chemically deposited PbSe and SnSe thin films

Thin films of PbSe of 400–600 nm in thickness, were obtained via chemical deposition from a solution containing lead nitrate, thiourea and selenosufate. SnSe thin films of 90–180 nm in thickness, were also obtained by chemical deposition from a solution containing selenosulfate. Optical and electrical properties of these thin films were significantly altered by heating them in selenium vapor at 300 °C. Thin film PbSe has a bandgap (Eg) of 1.17 eV (direct gap, forbidden transitions), which decreases to 0.77 eV when it has been heated. Its electrical conductivity (σ) is p-type: 0.18 Ω−1 cm−1 (as-prepared), and 6.4 Ω−1 cm−1 when heated. Thin film SnSe is of orthorhombic crystalline structure which remains stable when heated at 300 °C, but its Eg increases from 1.12 eV (indirect) in as-prepared film to 1.5 eV (direct, forbidden transitions) upon heating. Its electrical conductivity is p-type, which increases from 0.3 Ω−1 cm−1 (as-prepared) to 1 Ω−1 cm−1 when heated (without Se-vapor). When SnSe film is heated at 300 °C in the presence of Se-vapor, they transform to SnSe2, with Eg of 1.5 eV (direct, forbidden) with n-type electrical conductivity, 11 Ω−1 cm−1. The Seebeck coefficient for the PbSe films is: +0.55 mV K−1 (as prepared) and +0.275 mV K−1 (heated); for SnSe films it is: +0.3 mV K−1 (as prepared) and +0.20 mV K−1 (heated); and for SnSe2 film, − 0.35 mV K−1. A five-element PbSe-SnSe2-PbSe-SnSe2-PbSe thermoelectric device demonstrated 50 mV for a temperature difference ΔT = 20 °C (2.5 mV K−1). For SnSe-SnSe2-SnSe-SnSe2-SnSe device, the value is 15 mV for ΔT = 20 °C (0.75 mV K−1). Prospect of these thin films in thermoelectric devices of hybrid materials, in which the coatings may be applied on distinct substrate and geometries is attractive.

Investigation of Micromechanical Properties of Thin Films of PbTe and PbSe

Investigation of Micromechanical Properties of Thin Films of PbTe and PbSe

Solution-processed fabrication of perfectly (2 0 0)-oriented lead selenide thin films

To the best of our knowledge, the solution-processed fabrication of perfectly (2 0 0)-oriented lead selenide (PbSe) films on various substrates, including glass, transparent conducting glass, and polyethylene terephthalate (PET) substrates, has been achieved for the first time. Herein, the effects of orientation parameters, including the acetate anion effect, crystallization temperature, and chemical composition, on solution-processed PbSe thin films were examined. Particularly, the presence of acetate anions in the precursor solution strongly affected the degree of orientation. X-ray diffraction analysis was employed, and X-ray diffraction pole-figure polar distance was scanned by rotating the sample about the incident beam direction. The experimental results confirmed the formation of perfectly (2 0 0)-oriented PbSe films.

PbSe mid-IR photoconductive thin films (part-II): Structural analysis of the functional layer

Photoconducting thin films on the basis of PbSe have been used as functional materials for infrared detectors. The photoconducting sensor function is established by annealing PbSe films in oxygen rich and iodine rich atmospheres. Under such conditions, new, chemically more complex phases are formed that yield outstanding photoconducting properties. Such thin films are investigated after annealing, the layer structure of these films consist of a bottom layer of PbSe (1 μm) and a top layer of Pb1 Sex Iy Oz about 400 nm thick.By electron diffraction, a pseudo-orthorhombic Bravais lattice could be assigned to the quaternary phase of the top layer, responsible for photoconductivity, which was about 400 nm thick. Lattice parameters were identified as a = 0.833 nm, b = 0.662 nm and c = 1.8 nm. The grain size of the top layer was 500–700 nm and yielded single-crystal like diffraction patterns for electron diffraction. Diffraction patterns were acquired in the [100], [010] and [111] poles and could be indexed. The Bravais lattice is simple orthorhombic, no centering was found. The single-grain diffraction patterns obtained here are more valuable than the poly-crystalline diffraction patterns shown in a previous paper (part I) and yield a pseudo-orthorhombic Bravais lattice for this phase. As a consequence, the X-ray diffractograms could be indexed with the assigned Bravais lattice for this phase. The chemical composition of the new phase was measured by EDX spectroscopy in the TEM. The elemental composition of this quaternary phase was determined as Pb1 Sex Iy Oz, for the mole fraction ratio of x = Se/Pb we found 0.17 ≤ x ≤ 0.5 and for y = I/Pb we found 0.2 ≤ y ≤ 0.5. Se and I can substitute each other and therefore a solid solution is formed. The mole fraction ratio of Pb/(Se + I) was found between 1.6 and 1.9. Electron energy-loss spectra revealed a double peak structure for the volume plasmon peak, energies of the quaternary phase lay between 15.7 and 16.3 eV (peak 1) and 23.1–23.2 eV (peak 2), respectively.

(Invited) Review of Recent Progress in Nanoscaled Thermoelectric Thin Films

In recent years, thermoelectric materials have received increasing attention due to their ability to generate electricity from waste heat recovery. The efficiency of thermoelectric materials systems to produce thermoelectric power is related to the figure of merit ZT and the power factor. The dimensionless thermoelectric figure of merit is expressed as ZT = S2σT/k, where S is the Seebeck coefficient, σ is the electrical conductivity, and k is the thermal conductivity. In the quest to enhance ZT values, a key strategy involves reduction in thermal conductivityk, resulting from phonon scattering by numerous interfaces in low dimensional structures. Promising advances have been achieved with phononic crystal (PnC) nanostructures in thermoelectric materials, because the thermal conductivity of PnC samples is lower compared to non-patterned thermoelectric samples due to phonon-boundary scattering. Metal telluride based compounds such as bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) alloys have reported some of the highest figures of merit and work best for thermoelectric devices used for the temperature range of 200 to 400 K, while lead chalcogenides such as PbTe, PbS, and PbSe are ideal for the temperature range of 350 to 600 K. Here we review advances in the ALD synthesis of composite thermoelectric nanolaminates of alternating Bi2Te3 and Sb2Te3 thin films, and PbSe and PbTe films. During our investigations, we have observed that PbTe/PbSe nanolaminates grown on porous templates have higher Seebeck coefficients than the ones grown on regular planar silicon wafers. The higher Seebeck values result from the lower thermal conductivity k in porous structures, which in turn lead to a higher figure of merit ZT. We demonstrate the feasibility to enhance the figure of merit ZT further by modulating the size and periodicity of the pattern and the thickness of the thermoelectric film in relation to the mean free path (MFP) of the phonons of the thermoelectric material. In our study PbTe and PbSe thin films and nanolaminates were synthesized by Atomic Layer Deposition (ALD) technology on regular planar silicon wafers and on porous templates. Various approaches to enhance the figure of merit ZT and the Seebeck coefficient for ALD PbTe & PbSe films are discussed that result in an effective reduction of the thermal conductivity. In this work, we report on the physical characterization and electrical characterization focusing on Seebeck coefficient measurements in PbTe/ PbSe nanolaminate structures synthesized by ALD on planar Si wafers and on porous Si templates.

Template Free Photoelectrodeposition of Highly Periodic Three-Dimensional PbSe Nanostructures

PbSe films with highly periodic nanoscale features were deposited over macroscale areas by utilizing a completely template-free photoelectrochemical deposition technique wherein the nature of the illumination directs the resultant material morphology. Highly-anisotropic lamellae were produced using linearly polarized light and the lamellae were oriented along the polarization axis; the pitch and width of these nanoscale features was observed to scale with the illumination wavelength. The deposition was simulated using a finite-difference time domain method to model light absorption and a Monte Carlo method for mass addition and the results of the simulation successfully reproduced the experimentally observed morphologies. The generation of polycrystalline PbSe was confirmed by energy dispersive X-ray spectroscopy and X-ray diffraction. Complete nanoscale patterning over square centimeter areas required only several minutes. Moreover, films were deposited from aqueous solution using oxidized precursors at room temperature and no lithographic processing or photomasks were utilized nor needed. Thus, this technique offers a method by which nanostructured semiconducting materials can be generated rapidly via a bottom-up approach capitalizing on the self-optimization of the material growth to maximize interfacial light absorption. Extension of this technique to generate other IV-VI as well as II-VI semiconductors is currently being explored.

(Invited) Thermoelectric Thin Films and Nanocomposites Synthesized Via Solution-Phase Chemistry

Solution-phase processing routes to thermoelectric materials have the potential to decrease costs and enable novel device architectures. The best thermoelectric materials are crystalline inorganic semiconductors, which makes finding solution-phase routes to these materials of high interest. Unfortunately, inorganic semiconductors are generally insoluble due to their strong covalent bonds. One way around this hurdle is to create soluble semiconductor precursors that can be transformed into crystalline semiconductors after deposition. Furthermore, these precursor chemistries can be combined with colloidal nanocrystals to create nanostructured thin films with controlled composition and microstructure. We first present the synthesis of CuSeS and Ag-doped CuSeS thin films via soluble precursors and then report their thermoelectric properties. Specifically, we study the effect of Cu vacancies, Se:S ratio, and Ag-doping. We find that Ag-doping leads to appreciable improvements in thermoelectric performance by increasing Seebeck coefficient and decreasing thermal conductivity, while having little to no change in electrical conductivity. Overall, we find that the room temperature thermoelectric properties of these solution-processed materials are comparable to measurements on CuSeS alloys made via conventional thermoelectric material processing methods. Achieving parity between solution-phase processing and conventional processing is an important milestone and demonstrates the promise of this approach to making thermoelectric materials. Next, we present new chemical syntheses for soluble PbSe, PbTe, SnSe, and SnTe precursors. These precursors are especially relevant because PbSe and PbTe are the best-performing conventional thermoelectric materials in the moderate-to-high temperature regime. This chemical discovery is also important because soluble precursor routes to PbSe and PbTe thin films have not been reported in the literature. In addition, SnSe has the highest thermoelectric figure of merit of any known material, which makes our SnSe synthesis of interest as well. Lastly, we combine these precursors with colloidal nanocrystals to create nanostructured thin films with controlled composition and microstructure. Colloidal nanocrystals are made via solution-phase chemistry and consist of an inorganic core with short ligand molecules bound to its surface. These nanocrystals can be made with excellent control over size, shape, and composition. We demonstrate that our precursors can replace the typical organic ligands used in colloidal nanocrystal synthesis. This creates new pathways to inorganic nanostructured thermoelectric thin films with controlled composition and microstructure, and we report on the thermoelectric properties of said films.

Simulation of Thermoelectric Generator Composed of Nanopatterned Thermoelement

The conversion efficiency of thermoelectric (TE) devices is determined by the dimensionless figure of merit ZT, which is expressed as ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature, respectively. The key strategy to enhance ZT is through decreasing the thermal conductivity of thermoelectric materials. In this study, finite element analysis was used to investigate the effect of stripe-patterned Si substrates on thermal properties of a thermoelectric thermoelement, which consists of PbSe and PbTe thin film layers grown on the periodic patterned Si substrates. The width and depth of the stripe patterns were varied from 10 µm to 0.5 µm to determine their effects on the heat transport in the thermoelement. The calculated results reveal that the depth and width of the stripe patterns play an important role in decreasing the thermal conductivity of the thermoelectric module. The effect of the dimension of the patterns on the effective thermal conductivity of the TE thermoelement was shown in figure 1. The thermal conductivity is lower with respect to the deeper and narrower stripe patterns. The decreased thermal conductivity results from the enhanced phonon-boundary scattering due to the presence of periodic patterns. The phonons can be scattered more extensively when the dimension of the patterns is comparable to the mean free path of TE materials. Therefore, we modeled a thermoelectric generator (TEG) composed of stripe-patterned TE thermoelements taking advantage of its lower thermal conductivity. The dimension of the patterns was optimized selected to generate to achieve a higher power output of TEG. This work demonstrated the feasibility of using nanopatterned thermoelectric (TE) thermoelements to improve TE generator performance. Figure 1

In-Plane ZT Measurements of PbTe/PbSe Superlattice Layers Deposited by Atomic Layer Deposition

The conversion efficiency of the thermoelectric (TE) device is determined by the dimensionless figure of merit ZT, which is expressed as ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. The key strategy to enhance ZT involves the reduction in thermal conductivity k of TE materials. This led to the synthesis of low-dimensional structured materials such as 2-D superlattice structure, 1-D nanowire, and 0-D quantum dots. The phonon transport was suppressed if the dimension of the film approaching the mean free path of the phonons, resulting in a reduction in thermal conductivity and consequently improves ZT. The direction of the measurement, either in-plane or vertical to the surface, plays an important role in determining TE properties of the anisotropic samples, such as superlattices and quantum well structures. It is essential to measure all the parameters in the same direction and simultaneously to obtain accurate ZT value. In this work, a novel Si-based test chip was utilized to perform in-plane ZT measurements of PbTe/PbSe superlattice films. Figure 1 (a) shows the pre-fabricated circuit on the chip for measuring simultaneously the Seebeck coefficient, electrical conductivity, and thermal conductivity [1]. The thermoelectric film was deposited in the red square area by using a shadow mask. All the parameters were measured in the temperature range of 120 K to 450 K with a 1 T magnet field. In our work, PbTe and PbSe thin films and superlattice layers were synthesized by Atomic Layer Deposition (ALD) technology directly on the pre-structured Si chip. Figure 1 (b) shows an SEM micrograph of the 30 nm thick PbSe film grown on the chip. The PbTe/PbSe superlattice was then deposited on the PbSe buffer layer using ALD by alternatively depositing PbTe and PbSe layers. A thin Al2O3protection and diffusion barrier layer was applied to avoid oxidation and degradation of PbTe/PbSe films. The period of superlattice structure was varied from 2 nm to 10 nm to observe optimized period for achieving highest ZT value. Reference: [1]. Linseis, V., Völklein, F., Reith, H., Woias, P., & Nielsch, K. Platform for in-plane ZT measurement and Hall coefficient determination of thin films in a temperature range from 120 K up to 450 K. Journal of Materials Research, 31(20), 3196-3204, (2016). Figure 1

Nanomorphology and performance of pure and doped lead selenide for infrared detector

Lead selenide (PbSe) has been studied as a promising material for room temperature midwave infrared detection. We have investigated pure PbSe, as well as tin (Tn) and cadmium (Cd)-doped PbSe, nanocrystalline materials produced using physical vapor transport methods on glass and high-resistivity silicon substrates. The morphologies were investigated by scanning electron microscopy and energy-dispersive x-ray analysis. Pure PbSe layers consisted of nanocrystals that change into cubes and cuboids upon annealing. Cuboids generally grew in [100] orientation and ultimately developed in nanorods. Growth on silicon and glass substrates showed different morphologies of pure PbSe material. Parabolic and elongated morphologies resulted in nanowires on the top of thin layers of PbSe nanofilm, which acted as the substrate. Under low gradient annealing conditions (<20 K/cm), elongated morphologies grew into nanorods. Annealing of these samples resulted in coarse nanomorphologies with higher resistivity. In the case of Tn-doped PbSe, annealing dissolved a Tn-rich phase observed in as-grown films. Cd- and iodine-doped films produced through the addition of Cd selenide and Cd iodide, respectively, showed higher resistivity than similarly treated pure PbSe films. Annealing of as-grown materials in the presence of oxygen or iodine showed increased resistivity and significant changes in optical characteristics.

Oxygen aided photoresponse enhancement of air-stable PbSe quantum dot based photoconductors

The recent success of the surface passivation of lead chalcogenide quantum dots for enhancing ambient stability offers further investigation of surface states in air. Here we studied the photoresponses due to surface passivation and oxygen, thus providing the relations of surface states and the photoresponse of PbSe QD films by monitoring the changes in QD film with air exposure. A dramatic near-infrared photoresponse was observed when the PbSe film stabilized through surface passivation was exposed to air. As a result of estimating the density of trap states from the FET characteristics, it was confirmed that the iodide-passivated PbSe film exposed to the air had more trap states than the nitrogen atmosphere. The increase of the trap state due to oxygen adsorption led to the increase of the trap-captured photogenerated electrons, which increased the photoconduction gain. Even though some trap states have a negative impact on device parameters such as charge mobility and response time, controlling the oxygen-related trap states on QD surface is expected to enhance the photoresponsivity on the QD-based photoconductive films without performance degradation in air.

PbSe mid-IR photoconductive thin films (part I): Phase analysis of the functional layer

Photoconductive thin films on the basis of PbSe have been used as functional materials for infrared (IR) detectors. High quality PbSe thin films were grown on glass substrates by chemical bath deposition (CBD) yielding a peak detectivity of 2.8 × 1010 cm Hz1/2 W−1 at room temperature. The photoconductive sensor function is established by a sensitization process by annealing PbSe films in oxygen and iodine rich atmospheres. By studying such sensitized PbSe layers we discovered that new, quaternary phases are formed at the top of the layered structure.We could show that after annealing the following layer structure had formed: a bottom layer of PbSe (1 μm) and a top layer of Pb-Se-O-I (400 nm), containing (i) a poly-crystalline and (ii) a nano-crystalline phase. The poly-crystalline phase was found to be a solid solution of Se and I and yielded an average Pb/I mole fraction ratio of 3.1 and Pb/Se of 3.9, respectively. It contained the largest iodine mole fraction of ∼20 at.% while the nano-crystalline phase yielded less iodine (<10 at.%). This proves the great efficiency of the reactive annealing for functionalizing the polycrystalline PbSe films. The d-spacings, the chemical composition and the plasmon energies of the phases were measured and bar code these phases. The quaternary Pb-Se-O-I phases in the top layer have large unit cells and d spacings exceeding 0.8 nm. The poly-crystalline phase yielded two sharp plasmon peaks at 17.2 eV and 23.8 eV, respectively. Therefore, it can be clearly distinguished from PbSe, which yields a plasmon energy of 15 eV and d spacings smaller than 0.353 nm.

Phase-Transfer Ligand Exchange of Lead Chalcogenide Quantum Dots for Direct Deposition of Thick, Highly Conductive Films.

The use of semiconductor nanocrystal quantum dots (QDs) in optoelectronic devices typically requires postsynthetic chemical surface treatments to enhance electronic coupling between QDs and allow for efficient charge transport in QD films. Despite their importance in solar cells and infrared (IR) light-emitting diodes and photodetectors, advances in these chemical treatments for lead chalcogenide (PbE; E = S, Se, Te) QDs have lagged behind those of, for instance, II-VI semiconductor QDs. Here, we introduce a method for fast and effective ligand exchange for PbE QDs in solution, resulting in QDs completely passivated by a wide range of small anionic ligands. Due to electrostatic stabilization, these QDs are readily dispersible in polar solvents, in which they form highly concentrated solutions that remain stable for months. QDs of all three Pb chalcogenides retain their photoluminescence, allowing for a detailed study of the effect of the surface ionic double layer on electronic passivation of QD surfaces, which we find can be explained using the hard/soft acid-base theory. Importantly, we prepare highly conductive films of PbS, PbSe, and PbTe QDs by directly casting from solution without further chemical treatment, as determined by field-effect transistor measurements. This method allows for precise control over the surface chemistry, and therefore the transport properties of deposited films. It also permits single-step deposition of films of unprecedented thickness via continuous processing techniques, as we demonstrate by preparing a dense, smooth, 5.3-μm-thick PbSe QD film via doctor-blading. As such, it offers important advantages over laborious layer-by-layer methods for solar cells and photodetectors, while opening the door to new possibilities in ionizing-radiation detectors.