Lead Sulfide Thin Films Research Articles

Effect of Pb:S molar ratio in precursor solution on the properties of lead sulphide thin films by ultrasonic spray pyrolysis

In this work, PbS thin films were deposited onto glass substrate at 225°C by spraying precursor solution prepared with different molar ratio of lead acetate and thiourea as a source of Pb2+ and S2- respectively in order to investigate the effect of Pb:S molar ratio in the precursor solution on the physical properties of PbS thin films. Structural investigations carried out by X-ray diffractometer have shown that all films have fcc cubic structure and the average crystal size increased from 11nm to 25nm with the increasing the thiourea ratio in the precursor solution. In order to analyze the surface morphology of PbS thin films, AFM and SEM images were taken and elemental analysis of the films was performed by EDS. Optical transmittance and absorption spectra show that all deposited films have fairly low transmittance and high absorbance in the visible region. Additionally, it was determined that optical band gap of the deposited films were varied between 1.18eV and 1.37eV. As a consequence of electrical investigations, it was seen that all films have p-type conductivity and electrical resistivity decreased by increasing thiourea molar ratio in the precursor solution. All examinations have revealed that the molar ratio of lead acetate and thiourea has a significant effect on the physical properties of PbS thin films.

Study of some physical properties of ultrasonically spray deposited silver doped lead sulphide thin films

In this study, undoped and Ag doped PbS thin films at different concentrations were deposited onto glass substrates at 225°C by using ultrasonic spray pyrolysis technique, in order to investigate the effect of Ag doping on the physical properties of PbS thin films. Structural investigations revealed that all doped PbS:Ag thin films have cubic structure and Ag doping enhances crystalline level of PbS thin films. It was determined that average crystallite size of PbS:Ag thin films increased from 24nm to 49nm by increasing Ag doping concentration. Morphological studies showed that surfaces of the films become denser after Ag doping. Optical transmittance and absorption spectra revealed that all deposited thin films have low transmission and high absorbance within the visible region and band gap energy of the PbS:Ag thin films were determined to be in the range of 1.37eV and 1.28eV by means of optical method. Electrical conductivity type of PbS:Ag films was determined to be p-type and calculated electrical resistivity was found to be lowest for Ag-doped PbS thin films at 2%.

Effective role of thickness on structural, electrical and optical properties of lead sulphide thin films for photovoltaic applications

The n-type lead sulphide thin films were deposited at 350°C substrate temperature on glass substrates using advanced spray pyrolysis technique. The thickness of the thin films played an important role to improve the properties of lead sulphide and to use in device fabrication apart from various deposition parameters. The films deposited at thickness of 520nm resulted in a well oriented polycrystalline with face-centered cubic structure. An enhancement in the crystallite size with increase in film thickness was evidenced by XRD and SEM. The variation in crystallite size of films associated with different thickness provides a significant control over optical and electrical properties. The resistivity of the thin films decreased with an increase in thickness was of the order of 102Ωcm. The activation energy and optical band gap of the films deposited at optimized condition were found to be 0.20eV and 1.22eV, respectively. The absorption coefficient of the films was found to be 106cm−1. Results prove that the lead sulphide films synthesized using spray technique appeal its adaptability for potential photovoltaic applications in solar cells.

Effect of doping concentration on the structural, morphological and optical properties of Ca-doped PbS thin films grown by CBD

Pure and calcium doped lead sulfide (PbS) thin films were prepared by chemical bath deposition (CBD) method. The effects of calcium doping content on their structural, morphological and optical properties were investigated by X-Ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and UV–vis spectroscopy measurements, respectively. According to X-Ray diffraction patterns all films were polycrystalline in nature, with a cubic crystal structure. It was observed from SEM analysis that calcium doping level affected the film morphology and surface roughness. Incorporation of Ca was confirmed from Energy dispersive X-Ray analysis results. Tauc method was used to estimate the optical band gap energies (Eg) of the pure and calcium doped films. UV–vis analysis showed that the transmittance of the samples varied between 15.3 and 20%. Also, it was observed that transmittance of deposited films increased with adding of calcium. Further, the optical energy band gap values were found to enhance (1.92–2.50eV) with increasing the Ca content in PbS films.

Optical, electrical, and photovoltaic properties of PbS thin films by anionic and cationic dopants

Lead sulfide (PbS) thin films were deposited by CVD method to examine the effects of anionic and cationic dopants on optical and electrical properties for photovoltaic applications. XRD diffractograms verified the formation of cubic phase of multicrystalline PbS thin films. FESEM images showed surface morphologies in nano-dimensions (rods and flowers). UV–Vis–NIR spectrum revealed absorbance in the visible and NIR regions for all samples, in which dopants decreased the intensity of absorbance. Se as an anionic dopant for PbS thin films increased electrical resistance, acceptor concentrations, and crystallite defects, and decreased flat-band voltage and depletion width. Finally, photovoltaic measurements indicated that Zn-doped PbS thin film, as a photovoltaic cell, exhibited higher conversion efficiency and external quantum efficiency (EQE).

Effect of annealing on the properties of spray-pyrolysed lead sulphide thin films for solar cell application

Annealing is the most important processing parameter perhaps as it directly affects the properties of the thin films. In the present article, lead sulphide thin films composed of (2 0 0) plane-oriented nano-rods were successfully synthesized on glass substrates using spray pyrolysis technique at annealing temperature 350 °C. Films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive analysis by X-ray (EDAX), UV–VIS–NIR spectrometry and two-probe experiments. The X-ray diffraction study confirmed that films exhibiting face-centred cubic structure with a preferred orientation along (2 0 0) plane were independent of annealing temperature. SEM photographs revealed the formation of nano-rods. The possible formation of nano-rods and its dependency on optical and electrical properties were discussed. Chemical composition in terms of atomic ratio of the constituents is determined from EDAX studies. The optical band gap of the lead sulphide thin films was found to decrease from 1.22 to 0.98 eV with an increase in annealing temperature. The electrical conductivity of the films at room temperature was of the order of 10−2 Ω−1 cm−1 with the low activation energy. Results prove that lead sulphide films grown by chemical method appeal its adoptability for potential solar cell applications.

Nanocrystalline Lead Sulphide Thin Films Deposited by Chemical Bath Deposition Technique

Nanocrystalline Lead Sulphide Thin Films Deposited by Chemical Bath Deposition Technique

Highly crystalline p-PbS thin films with tunable optical and hole transport parameters by chemical bath deposition

Lead sulfide (PbS) thin films, consisting of well faceted (up to 400 nm) cubic-nanocrystals and possessing significantly improved opto-electronic parameters essential for photovoltaic applications, are grown by utilizing chemical bath deposition (CBD) technique with bath concentrations of 10–200 mM. X-ray diffraction (XRD) and Raman studies confirm the highly crystalline and pure phase of PbS. FESEM and HRTEM studies show that all the films possess uniform and compact (111) oriented nanocubic morphology. Bath concentration change provides tunability of nanocube size from 100 to 400 nm and the direct optical band gap from 1.50 to 0.94 eV. The PbS films exhibit p-type semiconducting behavior with hitherto unreported concurrent highest mobility of 29.3 cm2V−1s−1 and high carrier concentration of ∼1018 cm−3 with the lowest room temperature resistivity of 0.26 Ω–cm. The 25 mM and 10 mM films show significant surface plasmon absorption in 1200–2400 nm range making them suitable as efficient infrared absorbers in excitonic and multi-junction solar cells.

Structural and Optical Properties of PbS Thin Films Deposited by Pulsed Laser Deposited (PLD) Technique at Different Annealing Temperature

Lead sulphide (PbS) thin films has attracted interest due to its potential applications in optoelectronics devices, gas sensors, solar cell technology and transparent conducting electrodes. Thin films were grown on glass substrates by pulsed laser deposition (PLD) technique at room temperature and different annealing temperatures (573, 673 and 773) K. The structural measurements for PbS thin film show face-centered-cubic structure. Atomic force microscopy (AFM) was used to examine PbS surface. The films exhibit more homogeneity. The root mean square(r.m.s), surface roughness and average grain size were increased After annealing. The optical properties of PbS thin films are studied as a function to wavelength in region (375 - 1100) nm. The optical transmittance of PbS thin films shown that the transparency decreases with increase of annealing temperature. The direct energy gap for PbS thin film was decreases with increasing of annealing temperature for all sample due to the growth of the crystallites. The optical constants such as refractive index, extinction coefficient and dielectric constant were also calculated.

Fabrication and characterization of Sr-doped PbS thin films grown by CBD

In this work, undoped and Strontium-doped lead sulfide (PbS) thin films were deposited on glass substrates by chemical bath deposition (CBD) technique. The effect of Sr doping concentration on the structural, morphological and optical properties of the PbS thin films was studied. Changing in crystallite size, microstrain, dislocation density and band gap energy values of the PbS thin films as a function of Sr concentration were investigated by scanning electron microscopy (SEM), X-Ray diffraction (XRD) and UV–visible spectroscopy measurements. Energy dispersive X-Ray analysis (EDS) results indicated that nanostructured PbS films is doped with Sr without causing much lattice strain. According to XRD experiments crystallite size of the films is decreasing from 17.90 to 9.14nm with increasing Sr-doping. UV–visible analysis showed that the band gap value of PbS thin films increased from 1.73ev to 2.19eV by changing Sr doping concentration from 0% to 5%.

Effect of Reaction Time and Temperature on Chemical, Structural, Optical, and Photoelectrical Properties of PbS Thin Films Chemically Deposited from the Pb(OAc)2–NaOH–TU–TEA Aqueous System

Lead sulfide (PbS) thin films have been deposited on float glass substrates by the chemical bath deposition technique using a Pb(CH3COO)2–NaOH–(NH2)2CS–N(CH2CH2OH)3 definite aqueous system. The chemical and structural characteristics, as well as the variation of the optical and photoelectrical properties, were studied as functions of reaction time and temperature. For this purpose, the following characterization techniques were employed: x-ray diffraction analysis, x-ray photoelectron spectroscopy, ultraviolet–visible–near infrared spectrophotometry, and dark and light current measurements. Based on the results, it was observed that increase in the reaction temperature increased the deposition rate of the PbS thin film (associated with the cubic crystalline structure); increase of this parameter from 40°C to 70°C (with reaction time of 60 min) led to an increase of the thickness from ∼129 nm to ∼459 nm and the crystallite size (D) from 15.3 nm to 20.2 nm; on the other hand, increase in temperature decreased the energy bandgap (Eg) from 1.66 eV to 0.51 eV and the relative photosensitivity factor (Sph) from 0.468 to 0.032. A similar effect was obtained with increase of the reaction time for given temperature.

Improved microstructure and performance of PbS thin films via in-situ thermal decomposition of lead xanthate precursors using self-assembling monolayer

Microstructure control is critical to achieve thin film-based devices with high performance. The surface properties of the substrates on which thin films grow are expected to greatly influence the morphology and the resulting performance. Generally, homogeneous, dense and highly crystalline films are required. However, “island” like structures are usually obtained mainly due to the non-uniform nucleation. In this article, the self-assembling monolayer (SAM) strategy was applied to efficiently realize the uniform nucleation and modulate the microstructure of lead sulfide (PbS) thin films, which were fabricated on the modified ZnO-coated substrates with 3-mercaptopropionic acid (MPA) SAM via in-situ thermal decomposition of lead xanthate precursors. The results showed that PbS thin films with reduced pin-holes and uniform crystalline grains were fabricated with the incorporation of MPA SAM. More importantly, PbS thin films modulated by MPA showed better photoelectric response.

Influence of Al doping on the structural, morphological and opto-electrical properties of spray deposited lead sulfide thin films

This paper reports the synthesis of Al-doped PbS (PbS:Al) thin films by spray pyrolysis technique on glass substrates. Al doping concentration is varied as 0, 2, 4, 6 and 8 at.% in undoped PbS. Undoped and doped films exhibit cubic crystal structure with a (2 0 0) preferential orientation. The 2θ value of the doped films shifts towards higher Bragg angles confirming a contraction in their unit cell volume. The crystallite size values determined using the Scherrer formula decreased from 27.88 to 25.79 nm with increase in Al doping concentration. EDX spectra confirmed the presence of Al in the doped films. Increased transparency and blue shift in the optical band gap is observed with Al doping. The resistivity range of all the films were found to be in the order of 102 Ω-cm. Increased transparency, widened band gap and decreased resistivity observed make PbS:Al films suitable for tandem solar cells which uses multilayered pn junctions.

Influencing the structural, microstructural and optical properties of PbS nanocrystalline thin films by Mg2+ doping

The aim of the current work is study the effect of Mg2+ doping (0–4%) on lead sulfide (PbS) thin films prepared using a simplest and cost effective chemical bath deposition (CBD) technique on glass substrates at ambient temperature and pressure. The effect of Mg2+ content on structural, morphological and optical properties of PbS thin films was studied. Powder X-ray diffraction and Atomic Force Microscopic results showed that all the deposited thin films exhibits both nanostructured and polycrystalline nature with cubic structure. The remarkable effect on optical transmittance and band gap was observed due to Mg2+ doping for all the films. The optical energy band gap values were found to enhance with increasing the Mg2+ content in PbS thin films. Further, the refractive index was calculated and a relationship with energy band gap was investigated and also the high frequency dielectric constant (ε∞) was determined using the energy band gap values as a function of the Mg2+ content.

Sulfide precursor concentration and lead source effect on PbS thin films properties

Lead sulfide (PbS) thin films were synthesized using chemical bath deposition (CBD). Bath solutions are formed of various concentrations of thiourea, sulfide source, ranged from 0.6 to 1.2 M and two different salts as Pb source (lead acetate and lead nitrate). From the growth mechanism, we inferred that PbS is formed through the ion by ion process when using acetate lead source, while, using nitrate source yields to films growth through the complex-decomposition process. Due to the difference in the involved growth process, lead acetate produces films with larger crystallite size (from 4 to 16 nm), smooth and dense films. However, lead nitrate produces rough films with smaller crystallite size (from 1 to 4 nm). Increasing the thiourea concentration results in crystallinity improvement when using lead acetate and, oppositely, in crystallinity degradation when using lead nitrate. Due to the quantum effect caused by the small crystallite sizes, the films optical gap is varied from 0.5 to 0.9 eV.

Effect of film thickness and texture morphology on the physical properties of lead sulfide thin films

Lead sulfide (PbS) thin films were prepared onto ultra-clean quartz substrate by the electron beam gun (EBG) evaporation method. The thicknesses of the thin films were 50, 100, 150 and 200 nm. They were annealed at 423 K for 2 h. Field emission scanning electron microscopy (FESEM) images of the thin films showed their texture morphology at the surface of the quartz substrate. X-ray diffraction (XRD) patterns of the thin films showed that they have a cubic phase and rock-salt structure after annealing. The average crystallite size for the thin films was in the range of 32–100 nm. Optical measurements confirmed that crystalline thin films have a direct band gap that increases by decreasing the film thickness. This blue shift of the band gap of thin films compared to the bulk structure can be attributed to the quantum confinement effects in the nanoparticles. A decrease in conductivity by increasing the temperature confirmed the positive temperature coefficient of resistance in the thin films that showed the dominant conduction mechanism is via a band-like transition. The density of localized states at the Fermi level increases by increasing the film thickness. Current–voltage behavior of the thin films showed an increase in both dark current and photocurrent by increasing the crystallite size which is discussed, based on the presence of trap states and barriers in nanostructures.

Synthesis and Optical Properties of Lead Sulfide And Copper Sulfide Thin Films Deposited By Chemical Bath Deposition Method

We report the synthesis and Optical properties of crystalline Copper sulfide and Lead sulfide thin films deposited on glass substrate using the chemical bath deposition method [CBD] at room temperature for 22 hours 23 minutes and 72 hours respectively. Copper sulfide was synthesized using copper sulphate and thiourea, while Lead nitrate and thiourea were used for the synthesis of lead sulfide thin films. Optical properties of the thin films were studied by spectrophotometer in the wavelength range of 200 nm - 800 nm. Band gap [Eg], absorbance [A] and absorption coefficients [α] were examined as a function of wavelength and photon energy. Further analysis revealed that Cu2S and PbS thin films had a band gap of 2.324 eV and 2.586 eV respectively, suitable for solar cell applications.

Effect of substrate temperature on the structural and electrical properties of spray deposited lead sulfide thin films

Lead sulfide (PbS) thin films were prepared by chemical spray pyrolysis method using lead acetate and thiourea as precursors of Pb+2 and S-2 ions. X-ray diffraction (XRD) technique, scanning electron microscope (SEM) and EDAX analysis were used for structural, morphological and compositional characterization. XRD analysis shows that the films are cubic in nature with a preferred orientation along (2 0 0). EDAX analysis shows that films deposited at 150°C are sulfur rich. An increase in the substrate temperature results in a decrease in the sulfur content of the prepared film. It has been observed that thin films deposited at or above 225°C are smooth & uniform morphologically. Beyond a substrate temperature of 275°C, the films become discontinuous and non-uniform. However, the films are sulfur rich, even at 275°C. Electrical conductivity of prepared thin films have been measured using silver contacts in coplanar geometry. Films are n - type as confirmed by hot probe technique. The electrical conductivity at room temperature (25°C) was in the order of 10-4 Ω-1cm-1 and was found to increase with increase in temperature showing the semiconducting nature of the films with the band gap of 0.39 eV.

The effect of short chain thiol ligand additives on chemical bath deposition of lead sulphide thin films: the unique behaviour of 1,2-ethanedithiol

Chemical bath deposition is an effective method for depositing semiconductor thin films with a wide range of compositions and microstructures. While it is widely accepted that organic additive molecules can play a very important role in chemical bath deposition, their role has not been systematically studied. In the present work, we have comparatively studied the effect of four common water-soluble molecules, 1,2-ethanedithiol, mercaptopropionic acid, cysteamine and mercaptoethanol, on the chemical bath deposition of lead sulfide. The effect of 1,2-ethanedithiol was shown to be markedly different, resulting in a significantly increased film thickness. We show the effect of each additive on the growth rate, microstructure and optical properties, and provide insights on their mechanism of operation.

Electrochemical approaches for rearrangement of lead sulfide thin films prepared by SILAR method

Potentiostatic and potentiodynamic approaches have been performed for rearrangement of lead sulfide thin films prepared by a successive ionic layer adsorption and desorption technique on Au electrodes. Potentiostatic processes have been applied by potential-controlled electrolyses at −450mV and potentiodynamic applications have been performed by cyclic voltammetry scanning potential between −800 and 50mV on lead sulfide modified Au electrodes in pH 5.9 solution. These potential values have been determined by considering underpotential deposition of both lead and sulfur as a result of cyclic voltammetry experiments of lead sulfide modified Au working electrodes. Scanning electron microscopy, scanning tunneling microscopy, and powder X-ray diffraction results show that electrochemical approaches cause a transformation from amorphous to polycrystalline structure for PbS thin films. UV–visible–near infrared spectroscopy investigation of the samples reveals that the optical properties of lead sulfide thin films are protected after electrochemical processes.