Structural,optical, photocurrent and mechanism-induced photocatalytic properties of surface-modified ZnS thin films by chemical bath deposition

ZnS thin films were prepared by chemical bath codeposition using ZnSO₄–ZnCl₂ or Zn(CH₃COO)₂–ZnCl₂ as zinc ion sources. The presence of SO₄ ^2? favors the heterogeneous growth of ZnS thin film. The coexistence of two zinc salts impedes the formation of homogeneous precipitation and improves the growth rate of ZnS film. XRD and HRTEM results show that all the samples exhibit the cubic structure. EDS analysis shows that Zn/S atom ratios from the codeposition are closer to 1:1 than those deposited from a single zinc salt, and ZnS thin films of S3 and S7 are very uniform without stirring. FTIR reveals that –NH₂ group as a surface modifier is adsorbed on the surface of ZnS nanoparticles. Raman spectra further reveal that S3, S4 and S7 form the ZnS films, and ZnO phase is present in short or middle range of the S6 nanocrystal, indicating that different amounts of zinc salts affect the structure of ZnS films significantly after three 2.5 h deposition cycles. The grain sizes determined by FESEM are inversely proportional to RMS determined by AFM. The band gap values of ZnS thin films agree well with the results of HRTEM. The photocurrent responses of different samples are similar, indicating that different amounts of zinc salts have little effect on the photocurrent of ZnS films. The photocatalytic performance of S6 and S8 is much better than that of S1–S5. S6 decomposes 65 % of methyl orange within 3 h, and its K value is 4.78 × 10^?1 h^?1. The photocatalytic performance is induced by the growth mechanism, which determines the grain size of ZnS thin film. The tendency of grain sizes of ZnS films agrees well with that of photocatalytic performance, especially under the clusters by clusters deposition.     

Structural,optical and electrical properties of SnO<Subscript>2</Subscript>:F thin films deposited by spray pyrolysis for application in thin film solar cells

Fluorine doped tin oxide (FTO) thin films with adequate properties to be used as transparent electrical contact for PV solar cells were synthesised using the spray pyrolysis technique, which provides a low cost operation. The deposition temperature and the fluorine doping have been optimized for achieving a minimum resistivity and maximum optical transmittance. No post-deposition annealing treatments were carried out. The X-ray diffraction study showed that all the FTO films were polycrystalline with a tetragonal crystal structure and preferentially oriented along the (200) direction. The grain size ameliorates with the increase in substrate temperature. The samples deposited with the substrate temperature at 440 °C and fluorine content of 20 wt % exhibited the lowest electrical resistivity (1.8 × 10^?4 Ω cm), as measured by four-point probe. Room-temperature Hall measurements revealed that the 20 wt% films are degenerate and exhibit n-type electrical conductivity with carrier concentration of ~4.6 × 10²⁰ cm^?3, sheet resistance of 6.6 Ω/□ and a mobility of ~25 cm² V^?1 s^?1. In addition, the optimized growth conditions resulted in thin films (~500 nm thickness) with average visible transmittance of 89 % and optical band-gap of 3.90 eV. The electrical and optical characteristics of the deposited films revealed their excellent quality as a TCO material.     

Structural and optical characterization of CdS and CdHgTe thin films for the fabrication of CdHgTe/CdS structure

This article presents the deposition and characterization of CdS and CdHgTe thin films for the fabrication of CdHgTe/CdS structure. The growth of CdS and CdHgTe thin films on FTO-coated conducting glass substrates have been performed by chemical bath deposition (CBD) and electrodeposition methods, respectively. The deposition conditions have been optimized for getting better quality layers of CdS and CdHgTe. The grown layers of both CdS and CdHgTe have been characterized by photoelectrochemical cell (PEC) measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis spectrophotometer. Annealing effect of the deposited films has also been investigated. Finally the fabrication of CdHgTe/CdS structure has been performed and investigated by I–V characteristics. PEC, XRD, SEM and UV–vis spectrophotometer studies reveal that chemically deposited CdS layers are n-type with band gap values vary from 2.29 to 2.41 eV and cubic with (111) preferential orientation, and have spherical grain distributed over the surface. However, electrodeposited CdHgTe layers are p-type with band gap values varying from 1.50 to 1.53 eV and cubic with highly oriented CdHgTe crystallites with the (111) planes parallel to the substrate, and have uniform distribution of granular grains over the surface. The fabricated CdHgTe/CdS structure gave an open-circuit photovoltage and a short-circuit photocurrent of 510 mV and 13 mA/cm² respectively, under AM 1.5 illumination.     

Effect of annealing atmosphere (Ar vs. air) and temperature on the electrical and optical properties of spin-coated colloidal indium tin oxide films

Colloidal indium tin oxide (ITO) ~6 nm nanoparticles synthesized in-house were deposited by spin coating on fused silica substrates, resulting in high resistivity films due to the presence of passivating organics. These films were annealed at various temperatures ranging from 150 to 750 °C in air and argon atmospheres. The films are very transparent in the as-coated form, and they retain high transparency upon annealing, except the films annealed at 300 °C in argon, which became brown due to incomplete pyrolysis of the organics. Thermogravimetric analysis and Raman characterization showed that the removal of organics increases with an increase in the annealing temperature, and that this removal is more efficient in the oxidizing atmosphere of air, especially in the 300–450 °C temperature range than in Ar. Although ITO defect chemistry suggests that argon annealing should result in higher carrier concentration than air annealing, the faster removal of insulating organics upon annealing in air resulted in significantly lower film resistivity at intermediate annealing temperatures for films annealed in air than in Ar. At higher annealing temperatures, both Ar and air annealing, resulted in comparable film resistivities (the lowest achieved was ~10⁰ Ω cm).     

Effects of annealing temperature on the structural,morphology, optical properties and resistivity of sputtered CCTO thin film

CaCu₃Ti₄O₁₂ (CCTO) thin films with a thickness of 200 nm were deposited on ITO substrates by RF magnetron sputtering using a pure CCTO target. After the deposition, thin films were annealed at 400, 450, 500 and 550?°C, respectively, for 1 h. The effects of annealing temperature on the structural, surface morphology, optical properties and resistivity of (CCTO) thin films were investigated. The X-ray diffractometer results show that the thin films are polycrystalline in nature and are assigned to body-centered cubic perovskite configuration with a space group of Im-3. The intensity of the peaks and crystallinity gradually increased with the increase in annealing temperature. Microstructural investigation through FESEM showed that the grain size increased with increase in annealing temperature from 32 to 85 nm. The root mean square and roughness (Ra) were also enhanced with higher annealing temperatures, from 3.8 to 6.2 nm and from 4.7 to 7.7 nm, respectively, as confirmed by AFM. Increase in annealing temperature also affected the optical transmittance values which decreased to almost 60% at the visible range (550–850), as well as the optical energy band gap which decreased from 3.86 to 3.39 eV. The relevance between resistance behaviors and film microstructure is discussed. Therefore, it can be concluded that the desirable crystallinity, surface roughness, energy band gap and resistivity for 200 nm thick CCTO thin films deposited by RF magnetron sputtering can be achieved through the annealing process.     

Annealing effect on the structural,electrical and 1/f noise properties of Mn–Co–Ni–O thin films

Thin films of Mn_1.4Co_1.0Ni_0.6O₄ (MCN) spinel oxide are grown by radio frequency (RF) magnetron sputtering method on amorphous Al₂O₃ substrate. We investigate the annealing effect on the micro structural and electrical properties of RF sputtered MCN films. It is found that the crystallinity of MCN film is improved with increasing annealing time at 750 °C, and the annealed films present excellent cubic spinel (220) preferred orientation in X-ray diffraction patterns. Comparing to as-sputtered thin film, the annealed films show a decrease of 60 to 70 % in resistivity at 300 K. The annealed samples with post annealing time longer than 18 min acquire a negative temperature coefficient of resistance of about ?3.73 %K^?1 and resistivity of about 210–220 Ω cm at 300 K. 1/f noise of MCN films are also studied and the Hooge’s parameters (γ/n) are calculated. After annealing for 18 to 90 min, the γ/n values of the films are on the order of 10^?21 cm³, which ranks about two orders lower than that of amorphous silicon.     

Intrinsic defects and structural phase of ZnS nanocrystalline thin films: effects of substrate temperature

Fabrications of ZnS nanocrystalline thin films at different substrate temperatures (T_S) of 200, 300 and 400 °C by means of pulsed laser deposition are presented. Thin film deposited at T_S of 200 °C is in cubic zinc-blende (ZB) structure while those deposited at T_S of 300 and 400 °C are in hexagonal wurtzite (W) phase. The grain size, surface roughness and bandgap of the films increases with increasing T_S. The zinc vacancies and interstitials in the films increases while sulfur vacancies decreases with increasing T_S. The variation of zinc and sulfur vacancies in ZnS films with T_S is responsible for structural phase transition from ZB to W which causes the change in energy bandgap.     

Electrical characterization of nanocrystalline SnSe and ZnSe thin films: effect of annealing

In this paper, experimental data on the electrical properties of as deposited and annealed nanocrystalline SnSe and ZnSe thin films are reported. The thin films of SnSe and ZnSe are deposited on glass substrate by chemical bath deposition method. The films are studied before and after thermal annealing at temperatures 473 K for 1 h. This annealing is done in vacuum of 2?×?10^?3 mbar. The various electrical parameters like dark conductivity, photoconductivity, activation energy, photosensitivity and carrier life time have been measured on these films before and after annealing.     

Flexible CuInSe2 photovoltaic cells fabricated by non-vacuum techniques

In this work, CuInSe₂ based flexible photovoltaic cells have been fabricated completely using non-vacuum low-cost techniques. Thin films were deposited on molybdenum thin foil substrates by electrodeposition using a buffered aqueous electrolyte with the deposition of subsequent layers performed by spray pyrolysis. In addition, the buffer layer CdS was replaced with a wider bandgap ZnS (3.7 eV) and analysis undertaken of the fabrication pathway, morphological and compositional changes resulting from the different precursor route. The deposited films were annealed in a Se atmosphere at 450 °C. The influence of annealing temperature and time on the properties of the films are briefly discussed. Characterisation of thin films was performed using aqueous electrolyte contacts. Capacitance measurements were made as a function of applied bias on thin films deposited on metal substrates with blocking electrolyte contacts where analysis of the impedance gave values of the space charge capacitance from which the doping density and flat band potential were derived. The structural characterisation was carried out using X-ray diffraction and Raman spectroscopy. The structure and device properties of Mo (SS)/CuInSe₂/ZnS/n⁺-ZnO/Ni were characterized using current-voltage technique and photocurrent spectroscopy.     

Preparation and characterization of ZnS nanocrystalline thin films by low cost dip technique

Nanocrystalline ZnS semiconducting nanopowder and thin films have been deposited by simple low cost technique based on combination of dip coating and thermal reaction process. The deposited films and the prepared nanopowder have been characterized in the structurally, optically and electrically point of views. The effect of preparation conditions has been also optimized for good quality films. X-ray diffraction analysis performed the ZnS cubic phase in the reaction temperatures in the range 473–593 K. Above 593 K mixed cubic and hexagonal crystallographic phases have been resolved. Crystallite size and micro strain have been calculated to be 2.65 and 0.011 nm, respectively. The deposited film surface and cross section morphologies show that neither cracks nor peels have been observed and good film adhesion with the substrate was performed. Energy dispersive X-ray measurements of the film agree well with the calculated concentrations of the precursor components. Optical measurements confirm the optical characteristics of nanocrystalline ZnS film such as absorption and dispersion properties. Copper doped ZnS reduces the band gap while indium doped ZnS increases the band gap. Electrical characterization shows that copper doped ZnS increases the resistivity by one order of magnitude due to electron compensation process while indium doped ZnS decreases the resistivity three orders of magnitude due to increase of the carriers concentration. Hot probe thermoelectric quick test of ZnS:Cu and ZnS:In show opposite sign of thermoelectric voltage due to bipolar p and n types, respectively.     

Effect of sputtering power and annealing temperature on the properties of indium tin oxide thin films prepared from radio frequency sputtering using powder target

Indium tin oxide (ITO) thin films were deposited on quartz substrates by radio frequency (RF) sputtering with different RF power (100–250 W) using the powder target at room temperature. The effect of sputtering power on their structural, electrical and optical properties was systematically investigated. The intensity of (400) orientation clearly increases with the sputtering power increases, although the films have (222) preferred orientation. Increasing sputtering power is benefit for lower resistivity and transmittance. The films were annealed at different temperature (500–800 °C), then we explored the relationship between their electro-optical and structural properties and temperature. It has been observed that the annealed films tend to have (400) orientation and then show the lower resistivity and transmittance. The ITO thin film prepared by RF sputtering using powder target at 700 °C annealing temperature and 200 W sputtering power has the resistivity of 2.08 × 10^?4 Ω cm and the transmittance of 83.2 %, which specializes for the transparent conductive layers.     

Effect of rapid thermal annealing on Zn/ZnO layers

Zn/ZnO layers were deposited on SiO₂/Si substrate by magnetron sputtering at room temperature, and then these layers were annealed at various temperatures from 200 to 400 °C in nitrogen atmosphere for 1 min. The structural and electrical properties of the Zn/ZnO layers before and after annealing are systematically investigated by X-ray diffraction, scanning electron microscopy, current–voltage measurement system, and Auger electron spectroscopy. Current–voltage measurements show that the Zn/ZnO layers exhibit an Ohmic contact behavior. It is shown that, initially, the specific contact resistivity decreases with the increase of the annealing temperature and reaches a minimum value of 9.76 × 10^?5 Ω cm² at an annealing temperature of 300 °C. However, with a further increase of the annealing temperature, the Ohmic contact behavior degrades. This phenomenon can be explained by considering the diffusion of zinc interstitials and oxygen vacancies. It is also shown that Zn-rich ZnO thin films can be obtained by annealing Zn on the surface of ZnO film and that good Ohmic contact between Zn and ZnO layers can be observed when the annealing temperature was 300 °C.     

Effects of annealing on thermoelectric properties of Sb2Te3 thin films prepared by radio frequency magnetron sputtering

Antimony telluride (Sb₂Te₃) thin films were deposited on silicon substrates at room temperature (300 K) by radio frequency magnetron sputtering method. The effects of annealing in N₂ atmosphere on their thermoelectric properties were investigated. The microstructure and composition of these films were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. The electrical transport properties of the thin films, in terms of electrical conductivity and Seebeck coefficient were determined at room temperature. The carrier concentration and mobility were calculated from the Hall coefficient measurement. Both of the Seebeck coefficient and Hall coefficient measurement showed that the prepared Sb₂Te₃ thin films were p-type semiconductor materials. By optimizing the annealing temperature, the power factor achieved a maximum value of 18.02 μW cm^?1 K^?2 when the annealing temperature was increased to 523 K for 6 h with a maximum electrical conductivity (1.17 × 10³ S/cm) and moderate Seebeck coefficient (123.9 μV/K).     

PVD grown SnS thin films onto different substrate surfaces

Recent interests focus on tin mono sulphide as a potential candidate for an absorber layer in heterojunction solar cells. In the present investigation, SnS thin films have been deposited onto different substrates such as glass, ITO and Mo-coated glass substrate by thermal evaporation method. The compositional, microstructural and photoelectrochemical properties of the SnS films were analyzed depending upon the chemical nature of the substrates used. The SnS layers were polycrystalline with Herzbergite orthorhombic structure on all three substrates and had nearly stoichiometric elemental composition with a Sn/S ratio of ~1.01. The films grown on ITO and Mo-coated glass substrates exhibit (040) as preferred orientation whereas the films deposited on glass showed (111) plane as predominant. The layers were densely packed and well adherent to the substrate surface. The Raman spectra showed bands at 64, 163, 189 and 219 cm^?1, which corresponds to the single phase (SnS) composition of films. p-type conductivity of all the deposited films were determined by the photoresponse studies. The highest photoresponse for the films on the ITO substrate indicates their appropriateness for the solar cell application.     

Chemical bath deposition of SnS thin films on ZnS and CdS substrates

We illustrate that Tin sulfide (SnS) thin films of 110–500 nm in thickness may be deposited on ZnS and CdS substrates to simulate the requirement in developing window-buffer/SnS solar cells in the superstrate configuration. In the chemical bath deposition reported here, tin chloride and thiosulfate are the major constituents and the deposition is made at 25 °C. In a single deposition, film thickness of 110–170 nm is achieved and in two more successive depositions, the film thickness is 450–500 nm. The thicker films are composed of vertically stacked flakes, 100 nm across and 10–20 nm in thickness. The Sn/S elemental ratio is ~1 for the films 110–170 nm in thickness, but it slightly increases for thicker films. The crystalline structure is orthorhombic, similar to the mineral herzenbergite, and with crystallite diameters 13 nm (110–170 films) and 16 nm (450–500 nm films). The Raman bands at 94, 172 and 218 cm^?1 further confirm the SnS composition of the films. The optical band gap of SnS is 1.4–1.5 eV for the thinner films, but is 1.28–1.39 eV for the thicker films, the decrease being ascribed to the increase in the crystallite diameter. Uniform pin-hole free SnS thin films were successfully grown on two different substrates and can be applied in solar cell structures.     

Influence of annealing on the structural and electrical transport properties of Bi0.5Sb1.5Te3.0 thin films deposited by co-sputtering

Bi_0.5Sb_1.5Te_3.0 thin films were deposited on silicon substrates at room temperature by co-sputtering and the effects of annealing temperatures on structure and thermoelectric properties were investigated. The composition, crystallinity, and microstructure of these thin films were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction, and scanning electron microscopy. The crystalline quality of the thin films was enhanced with a rising annealing temperature. When annealed at 573 K, the layered structure of the Bi_0.5Sb_1.5Te_3.0 thin films with a preferred orientation along the (00l) plane was formed. However, excessive high annealing temperature caused the thin films to become porous due to the separation of substantial Sb-rich precipitates. The electrical transport properties of the thin films, in terms of electrical conductivity and Seebeck coefficient were determined at room temperature. The carrier concentration and mobility were calculated from the Hall coefficient measurement. By optimizing the annealing temperature and time to 573 K for 6 h, the thermoelectric power factor was enhanced to 22.54 μW/(cm K²) at its maximum with a moderate electrical conductivity of 6.21 × 10² S/cm and a maximum Seebeck coefficient of 190.6 μV/K.     

Improvement of hydrothermally synthesized MnO2 electrodes on Ni foams via facile annealing for supercapacitor applications

Nanostructured manganese dioxide (MnO₂) is deposited on nickel foams by a hydrothermal synthesis route. As-deposited MnO₂ thin films are largely amorphous. Facile post-deposition annealing significantly improves the electrochemical performance of the MnO₂ thin films via changing their morphology, phase, and crystallinity. The specific capacitance of the MnO₂ electrode increases with the annealing temperature and reaches an optimal value of 244 F g^?1 (at the current density of 1 A g^?1) in a neutral 1 M Na₂SO₄ electrolyte for a specimen annealed at 500 °C. Furthermore, when an alkaline 5 M KOH electrolyte is used, an exceptionally high capacitance of 950 F g^?1 is achieved at the current density of 2 A g^?1. The cost-effective facile synthesis, high specific capacitance, and good cycle stability of these MnO₂-based electrodes enable their applications in high-performance supercapacitors.     

Electrical,optical and magnetoresistive behavior of nanostructured ZnO:Cu thin films deposited by sputtering

Copper doped ZnO (ZnO:Cu) nanostructured films with magnetoresistive behavior were produced by growing ZnO/Cu/ZnO arrays at room temperature (RT) by the sputtering technique on corning glass substrates. The arrays were made with two electrical insulating ZnO films of 50 and 105 nm, and a Cu film of 5 nm, both materials were deposited at RT by the RF- and DC-sputtering technique, respectively. The processing method involves two stages that proceed in the course of the growth process, the main one is originated by the non-equilibrium regime of the sputtering technique, and the second is the diffusion-redistribution of the intermediate Cu film towards the neighborhood ZnO layers aided by the nanocrystalline films character. The influence of applying an additional annealing stage to the arrays in N₂ atmosphere at 250 and 350 °C by periods of 30 min were studied. The resistivity of the ZnO:Cu films can be varied from 0.0034 to 2.83 Ω-cm, corresponding to electron concentrations of 1.12?×?10²¹ and 7.85?×?10¹⁷ cm^?3 with carrier mobility of 1.6 and 2.8 cm²/V s. Measured changes on the magnetoresistance behavior of the films at RT were of ?R?~?3% for annealed samples with electron concentration of 1.12?×?10²¹ cm^?3. The X-ray diffraction measurements show that the films are comprised of nanocrystallites with dimensions between 13 and 20 nm in size with preferred (002) orientation. The transmittance of the films in the visible region was of 83% with an optical band gap of ~?3.3 eV for the low-resistivity samples.     

Bi1.5Zn1.0Nb1.5O7 thin films deposited at low temperature and post-annealed for crystallization

Near-stoichiometric Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were prepared on Pt/TiO₂/SiO₂/Si (100) substrates at 400 °C under an oxygen pressure of 10 Pa by using pulsed laser deposition process. The as-deposited BZN thin films were post-annealed at 700 °C for 30 min in situ vacuum chamber (in situ) and in oxygen ambient oven (ex situ). The crystallinity, microstructure and electrical properties of BZN thin films were investigated. The X-ray diffractometer results indicate that BZN thin films deposited at 400 °C are amorphous in nature and the post-annealed thin films exhibit a cubic pyrochlore structure. The as-deposited BZN thin films show permittivity of 68 and loss tangent of 0.0011 at 10 kHz, respectively. After a post-annealing at 700 °C for 30 min, the dielectric properties of thin films are significantly improved. Permittivity and loss tangent of the in situ annealed films are 127 and 0.005 at 10 kHz, respectively. And the films post-annealed in O₂ oven show the largest permittivity of 170 and tangent of 0.006. The improved dielectric properties can attribute to the crystallization of thin films. BZN thin films deposited at low temperature and crystallized at high temperature show the dielectric tunability without an electric breakdown to the maximum measurement bias voltage. And BZN thin films also show the excellent leakage current properties.     

Structural and optical properties of layer-by-layer solution deposited Cu2SnS3 films

Cu₂SnS₃ (CTS) is a simple and potential material for low-cost thin film solar cells. The present work incorporates the study of changes in structural and optical properties of layer-by-layer solution deposited CTS films with annealing. Raman spectroscopy is used to ascertain structural modification upon annealing. Increase in annealing temperature leads to a structural transition from tetragonal to cubic phase. Effect of annealing on optical properties of the films is evaluated in the wavelength range of 400–2,400 nm. It is proposed that layer-by-layer growth method fundamentally defines the optical behaviour of these films. Optical constants and parameters such as refractive indices, dielectric constants and electron energy loss function are calculated from transmittance and reflectance data. The refractive indices, n and k are determined to be in ranges of 1.8–2.2 and 0.18–1.2, respectively. The real and imaginary dielectric constants vary from 1.5 to 4.6 and 0.7 to 5, respectively. Dispersion of refractive index is analyzed using two different theoretical models of Wemple–diDomenico and Spitzer–Fan.