Improvement of structural and optoelectrical properties by post-deposition electron beam annealing of ITO thin films

Sn-doped In₂O₃ (ITO) thin films were deposited on a glass substrate with reactive RF magnetron sputtering and then post-deposition electro-annealed. The electron accelerating voltage was varied from 300 to 900 V, and the substrate temperature was increased to 250 °C with an electron accelerating voltage of 900 V for 20 min in a 4 × 10^?1 Pa vacuum. As-deposited and ITO films electro-annealed at low energy (≤600 eV) were found to be in the amorphous phase, while ITO films electro-annealed at 900 eV showed diffraction peaks of the ITO (222) and (400) planes. As the electron accelerating voltage increased, the electrical resistivity decreased to as low as 6 × 10^?4 Ωcm, and the mean optical transmittance also increased from 79 to 82% in the visible wavelengths. The electro-annealed films showed a higher figure of merit (1.8 × 10^?3 Ω^?1) than the as-deposited ITO films (6.7 × 10^?3 Ω^?1), indicating that electro-annealed ITO films have better optoelectrical performance than as-deposited films.     

Structural, optical and luminescent characteristics of sprayed fluorine-doped In2O3 thin films for solar cells

Fluorine-doped indium oxide thin films, F-In₂O₃, prepared by the spray pyrolysis technique on glass substrates have been studied using cathodoluminescence spectroscopy, X-ray diffraction and spectrophotometry. These films, deposited at the optimal substrate temperature (T_s=450 °C), crystallize in a cubic structure with a preferential orientation along the (4 0 0) direction. For this temperature, the electrical resistivity is in the order of 6×10⁻³ Ω cm and the average optical transmission in the visible region is larger than 95%. At room temperature, the cathodoluminescence spectra of F-In₂O₃ present two emission peaks: blue indirect band gap peak at 410 nm and a red emission at 650 nm.     

Substrate temperature and thickness dependence of properties of boron and gallium co-doped ZnO films

Transparent conducting oxide films of boron and gallium co-doped ZnO (BGZO) were prepared on glass substrates by radio frequency magnetron sputtering at room temperature and 200°C, respectively. The dependence of structural, electrical and optical properties on the thickness and substrate temperature were investigated. All films demonstrated c-axis preferred orientation and showed highly transparent in the visible wavelength region. With the increase thickness and substrate temperature, the grain size of BGZO films increased and the full width at half maximum decreased, the carrier mobility increased and resistivity decreased, which indicated that the crystallinity and conductivity of films were improved. The research also found that the optical band gap (E_g) of BGZO thin films decreased with increased substrate temperature and thickness.     

Influence of substrate temperature on the properties of laser ablated indium tin oxide films

Nanocrystalline indium tin oxide films are deposited in a reactive oxygen atmosphere with background pressure at 0.02 mbar on glass substrate at different substrate temperatures (T_s) ranging from 300 to 573 K using pulsed laser deposition technique. The films are characterized using GIXRD, AFM and UV–visible spectroscopy to study the effect of substrate temperature on the structural and optical properties of films. The XRD patterns suggest that the films deposited at room temperature are amorphous in nature and the crystalline nature of the films increases with increase in substrate temperature. The thickness of the film decreases with increase in substrate temperature. The AFM data show that substrate temperature plays a dominant role on the surface morphology of the films. UV–visible spectra show that all the deposited ITO films exhibit a direct allowed transition. The higher value of optical band gap obtained for the films may be attributed to quantum confinement effect. The films deposited at higher substrate temperatures show higher value of transmittance.     

Sprayed CeO2 thin films for electrochromic applications

Cerium dioxide (CeO₂) thin films were prepared by spray pyrolysis using hydrated cerium chloride (CeCl₃·7H₂O) as source compound. The films prepared at substrate temperatures below 300°C were amorphous, while those prepared at optimal conditions (T_s=500°C,s=5 ml/min) were polycrystalline, cubic in structure, preferentially oriented along the (2 0 0) direction and exhibited a transmittance value greater than 80% in the visible range. The cyclic voltammetry study showed that films of CeO₂ deposited on ITO pre-coated glass substrates were capable of charge insertion/extraction when immersed in an electrolyte of propylene carbonate with 1 M LiClO₄.These films also remained fully transparent after Li+ intercalation/deintercalation.     

Preparation of In2O3:F thin films grown by spray pyrolysis technique

Transparent conducting fluorine doped indium oxide (In₂O₃:F) thin films have been deposited on Corning 7059 glass substrates by the spray pyrolysis technique. The structural, electrical, and optical properties of these films were investigated as a function of substrate temperature. The X-ray diffraction pattern of the films deposited at lower substrate temperature (T_s=300 °C) showed no peaks of In₂O₃:F. In the useful range for deposition (i.e. 425–600 °C), the orientation of the films was predominantly [400]. For the 4500 Å thick In₂O₃:F deposited with an F content of 10-wt%, the minimum sheet resistance was 120 Ω and average transmission in the visible wavelength rang (400–700 nm) was 88%.     

Optical and structural properties of the sol-gel-prepared ZnO thin films and their effect on the photocatalytic activity

ZnO thin films were obtained by the sol-gel method, using the dip-coating procedure. Glass slides were used as substrates. The sintering temperature (T_s) was varied in the range of 200-600 °C in intervals of 50 °C, in an open atmosphere. Films with 1 and 5 coatings were prepared for each T_s. An increase of the grain size from 10 to 34 nm as the T_s increased was observed from X-ray diffraction measurements. The thickness of the films prepared starting from five coatings, decreased by 36% when T_s increased, and denser films were obtained. This result was corroborated with the refractive index values, calculated from the UV-Vis transmission spectra. The films were tested as a photocatalyst by the photobleaching of methylene blue in an aqueous solution under UV light exposure during 5 h. The photocatalytic activity (PA) increased with T_s, around 72% for the films with one coating and 66% for those with five coatings. The samples with one coating and a T_s=500 °C showed the best PA. However, the glass substrate had a negative effect on the PA for T_s>500 °C, even when the surface morphology of the samples showed an increase in roughness when T_s increased. The observed negative effect can be due to the presence of an amorphous compound formed by Si, Zn and O at the glass-ZnO interface.     

Wide-optical bandgap with improved conductivity p-μc-Si:Ox:H films prepared by Cat-CVD

Boron-doped hydrogenated microcrystalline silicon oxide (p-μc-Si:O_x:H) films have been deposited using catalytic chemical vapor deposition (Cat-CVD). The single-coiled tungsten catalyst temperature (T_fil) was varied from 1850 to 2100 °C and films were deposited on glass substrates at the temperatures (T_sub) of 100–300 °C. Different catalyst-to-substrate distances of 3–5 cm and deposition pressures from 0.1 to 0.6 Torr were considered.Optical and electrical characterizations have been made for the deposited samples. The sample transmittance measurement shows an optical-bandgap (Eg_opt) variation from 1.74 to 2.10 eV as a function of the catalyst and substrate temperatures. One of the best window materials was obtained at T_sub=100 °C and T_fil=2050 °C, with Eg_opt=2.10 eV, dark conductivity of 3.0×10^?3 S cm^?1 and 0.3 nm s^?1 deposition rate.     

Optical, electrical and structural properties of indium-doped cadmium oxide films obtained by the sol-gel technique

Indium-doped cadmium oxide films were obtained by mixing cadmium oxide and indium oxide precursor solutions by the sol-gel technique. The indium atomic concentrations in solution (x) studied were 0, 2, 5 and 10 at%. The films were sintered at two different sintering temperatures (T_s) 350 and 450 °C, and after that annealed in a 96:4 N₂/H₂ gas mixture atmosphere at 350 °C. X-ray diffraction patterns showed that all films sintered at T_s=350 °C only consisted of cadmium oxide crystals. The films sintered at T_s=450 °C consisted of cadmium oxide crystals also; however, for the highest indium atomic concentration (10 at%) the formation of cadmium indate oxide crystals was evident. All films show high optical transmission (>85%) and an increase of the direct band gap value from 2.4 to 3.1 eV, as the indium atomic concentration in solution increases. The minimum resistivity value obtained was 6.3×10⁻⁴ Ω cm for the films with x=5 at%, T_s=450 °C and annealed at 350 °C.     

A novel Al and Y codoped ZnO/n-Si heterojunction solar cells fabricated by pulsed laser deposition

Al and Y codoped ZnO (AZOY) transparent conducting oxide (TCO) thin films were first deposited on n-Si substrates by pulsed laser deposition (PLD) to form AZOY/n-Si heterojunction solar cells. However, the properties of the AZOY emitter layers are critical to the performance of AZOY/n-Si heterojunction solar cells. To estimate the properties of AZOY thin films, films deposited on glass substrates with various substrate temperatures (T_s) were analyzed. Based on the experimental results, optimal electrical properties (resistivity of 2.8 ± 0.14 × 10^?4 Ω cm, carrier mobility of 27.5 ± 0.55 cm²/Vs, and carrier concentration of 8.0 ± 0.24 × 10²⁰ cm^?3) of the AZOY thin films can be achieved at a T_s of 400 °C, and a high optical transmittance of AZOY is estimated to be >80% (with glass substrate) in the visible region under the same T_s. For the AZOY/n-Si heterojunction solar cells, the AZOY thin films acted not only as an emitter layer material, but also as an anti-reflected coating thin film. Thus, a notably high short-circuit current density (J_sc) of 31.51 ± 0.186 mA/cm² was achieved for the AZOY/n-Si heterojunction solar cells. Under an AM1.5 illumination condition, the conversion efficiency of the cells is estimated at only approximately 4% (a very low open-circuit voltage (V_oc) of 0.24 ± 0.001 V and a fill factor (FF) of 0.51 ± 0.011) without any optimization of the device structure.     

Cigs flexible nano solar cell by inert argon gas condensation

The Cu(In_0.7Ga_0.3)Se₂ nano solar cell pn junction structure consist of six layers of Al/CIGS/nano-CIGS/CdS/ITO/PET with thicknesses about 200, 500, 70, 100, 150 nm and 170 um were deposited by thermal evaporation technique at vacuum pressure 2 × 10^–5 mbar respectively. where the ITO/PET conductive flexible substrate with sheet resistance 15 Ohms per sq. The X-ray diffraction analysis showed that as-deposited thin films CIGS and CdS are polycrystalline where optical energy gap and carrier concentration are found that 1.15 and 2.38 eV with p = 3.58 × 10¹⁰ cm^–3 and n = 3.11 × 10¹³ cm^–3 respectively. CIGS nano solar cell thin films are deposited on CdS/ITO/PET with assistance of inlet Argon gas vacuum pressure at 1, 5, 20 mbar by thermal evaporation technique at room temperature by using Inert gas condensation (IGC) is the method by which one can deposit films with high purity as deposition is done in low vacuum. The high magnification SEM image of CIGS nano-structures synthesized at 20 mbar revealed that the particles have exact spherical shape with sizes ranged from few nanometers to hundreds nanometers due to agglomeration effect. It was found that the grain size and the root mean square of surface roughness increases as Argon gas pressure increase. Therefore the structure of CIGS thin films has been changed from polycrystalline to nanostructure and have been found with increase Argon gas vacuum pressure from 1mbar to 5 mbar and then 20 mbar will increase grain size at 2θ = 32° from 15.9, 18.9 and 25.7 nm with decrease optical energy gap from 1.54, 1.44 and 1.26 eV respectively. The results showed the efficiency increase from 1.37% of CIGS/CdS to 2.01% of CIGS nano thin films of solar cells.     

Deposition and characterization of earth abundant CuZnS ternary thin films by vacuum spray pyrolysis and fabrication of p-CZS/n-AZO heterojunction solar cells

We report fabrication of solar cell device <ITO/AZO/i-ZnO/CZS/Al> with Copper Zinc Sulfide (CZS) thin films as absorber layer. CZS thin films prepared using chemical spray pyrolysis technique at a pressure of 10⁻³ mbar at different substrate temperatures. Structural, morphological, optical, compositional and electrical properties of as prepared films are investigated. Structural analysis shows crystalline nature with mixed phase containing CuS-ZnS binary composite. Atomic Force Microscopy analysis shows the average particle size of 88 nm. Value of work function obtained from ultraviolet photoelectron spectroscopy is 4.58 eV. The band gap of the as-prepared films varies from 1.62 to 2.06 eV. Hall effect measurement proves the p-type nature for all the deposited films. Samples deposited at 350°C shows carrier concentration of 10²¹ cm⁻³ and electrical conductivity of 526 S cm⁻¹. Solar cell device structure of <ITO/AZO/i-ZnO/CZS/Al> has been fabricated using the CZS sample deposited at 350°C. The cell parameters obtained are V_oc = 0.505 V, I_sc = 4.97 mA/cm², FF = 64.28% and η = 1.6 ± 0.05%.     

Influence of the growth parameters of p-CdTe thin films on the performance of Au-Cu/p-CdTe/n-CdO type solar cells

R.F. sputter deposition of Sb doped CdTe thin films was carried out with targets containing different amounts of antimony (C_T: 0, 2.5, 10 and 20 at.%). The substrates were kept at different temperatures (T_s) of 200, 275, 350 and 450 °C. Three different argon pressure values: 2.5, 5 and 15 mTorr were used. The lowest dark resistivity (ρ) at room temperature (RT) was 9.0 × 10⁵ Ω cm, which is one of the lowest values reported in the literature for Sb doped CdTe. Highly transparent (∼90%) and conductive (ρ = 3.7 × 10⁻⁴ Ω cm) F doped CdO (n-type) thin films, prepared at room temperature by the sol-gel method, were employed as window and top-contact. The configuration of the fabricated solar cell was (Au-Cu)/p-CdTe/n-CdO/glass. Open-circuit voltage (V_oc) and short-circuit current density (J_sc) at room temperature have the highest values for high T_s, low P_g and C_T = 10 at.%. Despite the fact that V_oc and J_sc are lower than those reported in the literature, we think this work is useful as a basis for the search of more competitive CdTe/CdO based PV devices.     

Synthesis,characterization, and photoelectrochemical study of Cd1−xZnxS solid solution thin films deposited by spray pyrolysis for water splitting

A series of Cd_1−xZn_xS thin films were deposited onto indium-doped tin oxide (ITO) coated glass substrates by ultrasonic spray pyrolysis CdCl₂, ZnCl₂, and CS(NH₂)₂ aqueous solutions. The XRD patterns revealed that these films processed a wurtzite structure and a series of solid solutions of CdS and ZnS formed. The lattice constants decreased as the x value increased. From the transmittance and reflectance, the optical band gap was estimated to be between 2.45 eV and 3.72 eV, and the band gap increased as the x value increased according to a near linear relationship with the x value. The Mott-Schottky tests revealed that the flat potential shifted negatively as the x value increased. The photo responses agreed with the optical absorption of these films quite well. The current–potential measurements under chopped Xe lamp light irradiation show that the CdS deposited at 300 °C had best photoresponse. Its photoelectrochemical efficiency was estimated to be about 0.95% under 0.73 V bias from two electrodes current–potential tests.     

Tin-doped indium oxide (ITO) film deposition by ion beam sputtering

Indium tin oxide (ITO) thin films were deposited by ion beam sputtering. This paper aimed at the reach of high conductivity and high transmittance simultaneously at relatively low substrate temperature. In order to reach the objects, the influences of substrate temperature, ion beam energy, and oxygen gas flowing rate on the properties of deposited ITO films were investigated. Resistivity showed the lowest value of 1.5×10⁻⁴ Ω cm on the films deposited by 1.3 keV Ar ions at 100°C. The microstructure of the films was sub-grain (domain) structure. The ITO films have above 80% of transmittance in the visible wavelength including that of the glass substrate.     

Structure, composition and optical properties of Cu2ZnSnS4 thin films deposited by Pulsed Laser Deposition method

Polycrystalline Cu₂ZnSnS₄ (CZTS) thin films have been directly deposited on heating Mo-coated glass substrates by Pulsed Laser Deposition (PLD) method. The results of energy dispersive X-ray spectroscopy (EDX) indicate that these CZTS thin films are Cu-rich and S-poor. The combination of X-ray diffraction (XRD) results and Raman spectroscopy reveals that these thin films exhibit strong preferential orientation of grains along [1 1 2] direction and small Cu_2−xS phase easily exists in CZTS thin films. The lattice parameters and grain sizes have been examined based on XRD patterns and Atom Force Microscopy (AFM). The band gap (E_g) of CZTS thin films, which are determined by reflection spectroscopy varies from 1.53 to 1.98 eV, depending on substrate temperature (T_sub). The optical absorption coefficient of CZTS thin film (T_sub=450 °C) measured by spectroscopic ellipsometry (SE) is above 10⁴ cm⁻¹.     

Effects of step-deposition on structures and properties of transparent conducting aluminum-doped zinc oxide films prepared by DC magnetron sputtering

The 2 wt% aluminum-doped zinc oxide films (AZO) was sputtered on corning glass plate at temperatures of 30–200 °C by DC magnetron sputtering using ceramic target. The microstructures and electrical resistivity of thin films were investigated by scanning electron microscope (SEM) and the van der Pauw method. The optical transmittances of films were measured by UV visible spectrophotometer in the wavelength of 300–900 nm. It was found that the average optical transmittances of specimens were 88%. Highly oriented AZO films in the (0 0 2) direction was observed in specimens as increasing of the substrate temperature. The dense film increased as the temperature increases. In addition, craters of greater depth with more compactness were obtained by step-deposition. The lowest resistivity of 9×10⁻⁴ Ω cm with film thickness of 700 nm was found in specimen grown by step-deposition at 200 °C.     

Enhanced hydrogen storage by a variable temperature process

We present a simple method of variable temperature process that can potentially enhance the hydrogen storage properties of a large variety of solid state materials. In this approach, hydrogen gas is first introduced at about room temperature, which is followed by a gradual increase to a preset maximum temperature value, T_max. Using this approach, we investigated hydrogen absorption properties of vertically aligned arrays of magnesium nanotrees and nanoblades fabricated by glancing angle deposition (GLAD) technique, and conventional Mg thin film. Weight percentage (wt%) storage values were measured by quartz crystal microbalance (QCM). After exposing Mg samples to H₂ at 30 bar and 30 °C, dynamic absorption measurements were conducted as the temperature was increased from 30 °C to maximum values of T_max = 100, 200, and 300 ^°C all within 150 min. QCM measurements revealed that variable temperature method results in significant improvements in hydrogen storage values over the ones obtained by conventional constant temperature process. At a low effective temperature T_eff = 165 °C (T_max = 300 °C), we achieved storage values of 6.19, 4.76, and 2.79 wt% for Mg nanotrees, nanoblades, and thin film, respectively.     

Brush electrodeposited CdSexTe1−x thin films and their properties

CdSe_xTe_1−x thin films were brush plated on titanium and conducting glass substrates from the precursors at different substrate temperatures in the range of 30-80 °C. X-ray diffraction studies indicated the films to possess hexagonal structure irrespective of composition. The strain and dislocation density decrease with increase of substrate temperature. The crystallite size increased from 30 to 100 nm as the substrate temperature increased. The resistivity of the films decreased with increase of substrate temperature. The carrier density and mobility increased with substrate temperature. Optical band gap of the films varied in the range of 1.45-1.72 eV. Higher photosensitivity was obtained compared to earlier reports.