Properties Of CdTe Thin Films Research Articles

Morphological, Optical, and Electrical Studies of PVD CdTe Thin Films for Photovoltaic Applications

Nano-crystalline CdTe films were coated on glass and silicon substrates using the vacuum evaporation (PVD) technique, with annealing temperatures of 25, 100, 150, and 200 °C. This study aims to create a simple photoelectric cell using the effective light-absorbing layer CdTe as a thin film and Si as an n-type semiconductor. Additionally, it investigates the properties of CdTe thin films annealed at various temperatures. The following equipment was used: XRD, UV-visible spectrophotometer, SEM, and AFM. Moreover, the electrical characteristics of the fully designed devices were tested using I-V measurements and the Hall effect. Thin-film photovoltaics could become the primary source of global electricity. The CdTe thin films were coated using thermal evaporation. The best efficiency was 0.99% for the CdTe/Si structure with Voc = 5.0 x 10-1 V, Jsc = 51.0 x 10-2 mA/cm2, FF = 0.39, at 25 °C, and the efficiency decreased with increasing temperature. It has been found that annealing temperatures have an impact on the size of crystallites, the values of energy gaps, and the electrical properties of CdTe thin films.

Photodegradation of CdTe thin film via PVD for water splitting to generate hydrogen energy

The cost-effective catalysts are attracting attention in the field of water-splitting hydrogen generation for their effective light utilization and charge separation activity. In this work, CdTe has introduced this promising photocathodic material among the few photocatalysts with a low band gap. This photocatalyst has a high activity for the PEC hydrogen evolution under simulated sunlight irradiation. XRD study reveals the confirmation of the prepared CdTe thin film. SEM study provided the morphology and surface structure for the absorption of the solar spectra, the optical properties of CdTe thin film confirmed the absorption of solar spectra for the hydrogen production. FTIR provided the functional group of the CdTe thin film. Electrochemical impedance spectroscopy showed that the charge transfer at the electrode–electrolyte interface for CdTe thin film is much better than another semiconductor. The LSV for STH% was noted to be 1.07% for CdTe thin film and the production of hydrogen generation of CdTe thin film was observed at 4953.21 mol.g−1.h−1.

Influence of growth time on the properties of CdTe thin films grown by electrodeposition using acetate precursor for solar energy application

Cadmium telluride (CdTe) thin films were deposited using a two–electrode electrodeposition (ED) configuration from an aqueous acidic solution. The electrolyte solution contains 1 M of cadmium acetate dihydrate (Cd (CH3OO) 2.2H2O) as cadmium precursor and 1 ml of tellurium dioxide (TeO2) as tellurium precursor. The thin films were grown for different deposition times of 60, 120, 180, 240, and 300 min to investigate the effect of the deposition period on the structural, optical, electrical, surface morphology, elemental composition, and surface roughness properties of the CdTe thin films in both as–deposited and heat–treated forms. X-ray diffraction (XRD) analysis indicates that the CdTe thin films have polycrystalline cubic zinc blend, orthorhombic and hexagonal structures. The result confirmed that the cubic phase is dominant and the peak for preferred orientation is along the (111) plane. Ultraviolet-visible (UV–vis) spectrophotometry study shows that the band gap of the as-deposited thin films varies from (1.41–1.45) eV, and after heat treatment, the band gap decreased to (1.39–1.42) eV. Photoelectrochemical cell (PEC) measurements show that CdTe thin films haven-type conductivity in both as–deposited and annealed forms. Scanning electron microscopy (SEM) analysis shows that the surface morphology of CdTe thin films changed as the deposition period increases. After heat treatment, increase in grain size was observed. Energy–dispersive x-ray spectroscopy (EDS) analysis shows that the percentage composition of as–deposited and heat-treated CdTe thin films varied with deposition time. After post–deposition treatment (PDT), the concentration of Te decreased, while that of Cd increased due to recrystallization during annealing. For the film deposited for 120 min, stoichiometric composition of CdTe was observed after heat treatment. Scanning probe microscopy (SPM) measurements revealed that the average surface roughness of the thin films varied with deposition time. The maximum average surface roughness was recorded when the film was deposited for 120 min. These results show that the prepared CdTe thin films have potential application as absorber layers in thin film solar cells.

Microstructure and optical properties of CdTe thin films prepared by close spaced sublimation method at various growth temperatures

Cadmium telluride (CdTe) is an important Ⅱ-Ⅵ multifunctional semiconductor, often used as the light absorption layer in photovoltaic solar cells or the core layer in γ-ray detection. The deposition temperature has a great greatly influences on the microstructure and morphology of the thin films during their growth. Here, close spaced sublimation method is used for depositing CdTe thin films on glass substrate at various temperatures conditions. The microstructure, morphology, optical and luminescent properties of the CdTe thin films were systematically characterized. CdTe thin films with a high preferred crystal orientation, large grain size, low micro-stress, and strong luminescence performance were obtained. And the origin of luminescent peaks is analyzed in detail by low-temperature photoluminescence spectroscopy.

Low-temperature growth of CdTe thin films as passivation layers for IR and THz functional elements

Low-temperature modes of growing thin (dCdTe = 80–360 nm) CdTe layers by the “hot-wall” method with a high degree of adhesion to CdHgTe epitaxial layers were implemented. Growth parameters (source and substrate temperatures 650 K and 373 K, respectively, deposition time 60 min), at which the film is optimal when used as a protective passivation coating for the functional elements of the IR and THz photoelectronics were selected. The study of morphology, chemical composition and electrical properties of CdTe thin films depending on temperature and growth time were carried out. It is shown that the CdTe semiconductor film on the CdHgTe surface grows in columns that aggregate with increasing deposition time. The study of capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of CdTe/p-Si structures demonstrated the controllability of the space charge region in silicon by the voltage applied to CdTe, which indicates good dielectric properties of CdTe with low surface density at the CdTe/p-Si boundary (4.5 × 1010 сm−2) and small leakage currents through the dielectric.

Study of structural and optical properties of CdTe:Yb thin films

In this work, the crystal structure and optical properties of CdTe thin films were investigated depending on the technological conditions of their deposition. In addition to structural measurements, the exciton was also used as a probe for the defect structure and optical quality of these films. The films growth mechanism was determined. Microstructural characteristics of CdTe:Yb thin films were obtained. It is shown that the photoionization energy of complex acceptor centers including noble metal ions and Yb3+ ions is about 100 meV. The accurate values of the band gap for CdTe:Yb thin films were obtained based on exciton spectra. A correlation was established between the microstructural parameters of the films and the behavior of their exciton spectra. These results make it possible to significantly improve the structural and optical properties of CdTe thin films in order to obtain a material with controlled electronic characteristics, suitable for modern optoelectronic applications.

Optical properties of CdTe thin film obtained by high-frequency magnetron sputtering method

Cadmium telluride (CdTe) thin films relate to AII BVI compounds and show semiconductor behaviour. They present an important research field because of their wide application in various optoelectronic devices. CdTe-based solar cells attract attention since CdTe is characterised by the direct energy bandgap Eg and high absorbance, which makes it an excellent light-absorbing layer of solar cells. Material evaporation in vacuum by using the high-frequency magnetron sputtering method is one of the most advantageous methods for obtaining uniform films. The present work is dedicated to the investigation of the optical properties of CdTe thin film, which is produced on quarts substrate by the high-frequency magnetro sputtering method. The optical transmission, reflectivity, and μ-Raman spectra of the CdTe thin film have been determined. Linearity of the spectral dependence of the coefficient of optical absorption α of CdTe thin film in the coordinates (αhν)2 vs hν indicates for the direct character of optical transitions corresponding to the long-wavelength edge of fundamental absorption. The optical bandgap of the studied CdTe thin film is found to be Eg = 1.53 eV. The peaks of the experimental m-Raman spectra at 121; 139; 142; 167 and 331 cm–1 are attributed to the phonons in crystalline CdTe and Te.

Impact of CdCl2 Treatment in CdTe Thin Film Grown on Ultra-Thin Glass Substrate via Close Spaced Sublimation

In this study, close-spaced sublimation (CSS) grown cadmium telluride (CdTe) thin films with good adhesion to 100 µm thin Schott D263T ultra-thin glass (UTG) were investigated. Cadmium chloride (CdCl2) treatment in vacuum ambient was executed to enhance the film quality and optoelectrical properties of CdTe thin film. The post-deposition annealing temperature ranging from 360–420 °C was examined to improve the CdTe film quality on UTG substrate. Various characterization techniques have been used to observe the compositional, morphological, optical, as well as electrical properties. Scanning electron microscopy (SEM) verified that the CdTe morphology and grain size could be controlled via CdCl2 treatment temperature. Energy Dispersive X-Ray Analysis (EDX) results confirmed that the annealing temperature range of 375–390 °C yielded the stoichiometric CdTe films. UV-Vis analysis estimated the post-treatment bandgap energy in the range of 1.39–1.46 eV. Carrier concentration and resistivity were obtained in the order of 1013 cm−3 and 104 Ω-cm, respectively. All the experimental results established that the CdCl2 treatment temperature range of 390–405 °C might be considered as the optimum process temperature for the deposition of CdTe solar cell on UTG substrate in close-spaced sublimation (CSS) method.

Effect of high-pressure annealing on the physical properties of CdTe thin films

In the present work, the CdTe thin films were fabricated on the Ag substrate using thermal evaporation technique. The effect of post-deposition high-pressure annealing (PDHPA) of 0.2, 0.5 and 1 MPa at 500 °C on physical properties of CdTe thin films was studied. The structural, optical, and electrical properties of films were considered using grazing incidence X-ray diffraction, ultraviolet–visible spectrophotometer (UV–Vis), scanning electron microscopy, and transverse current–voltage (I–V) test. The structural analysis shows that both pristine and treated films have zinc blende crystal structure with strong preferred (220) orientation. The optical analysis revealed the enhancement of optical absorbance and decrement of the energy band gap of films with PDHPA. Moreover, our analysis indicates that the electrical conductivity of CdTe films increases with PDHPA. The SEM images show that the untreated films are uniform and homogeneous. Our results indicate that the cracking is observed in treated films with PDHPA. This study shows that the treated films at the pressure of 1 MPa can be used as suitable absorber layer to fabricate CdTe solar cell devices.

Study the effect of type of substrates on the microstructure and optical properties of CdTe Thin Films

Cadmium telluride (CdTe) thin films are deposited on an ultrasonically cleaned substrate of different types by using thermal evaporation technique under pressure 2 × 10-5 mbar. The structural and morphological studies of all the films are accomplished using the X-ray diffraction method (XRD) and field emission scanning electron microscope (FE-SEM). CdTe found to has a polycrystalline structure. The grains were very uneven and the grain shape was irregular. A Jasco V-570 UV- visible - NIR spectrometer has been used to measure the optical properties in the range of wavelength from 200 to 2500 nm at normal incidence. The optical energy gap (Eg) is determined by using the Tauc’s equation. The optical parameters such as; refractive index (n), static refractive index (no), infinite dielectric constant (ε∞), dispersion energy (Ed), single oscillating energy (E0), static dielectric constant (εs), free carrier concentration (N), plasma frequency (ωp), relaxation time (τ), oscillator wavelength (λo), oscillator strength (S0) and electronic polarizability (αp) respectively are calculated. The optical measurements for CdTe films deposited on FTO substrate were property used as absorber material for solar cell applications. Inversely, CdTe films deposited on a glass substrate is more suitable for a window in solar cell applications.

Temperature difference in close-spaced sublimation (CSS) growth of CdTe thin film on ultra-thin glass substrate

In this study, cadmium telluride (CdTe) thin films were grown for the first time ever on ultra-thin (100 µm) Schott D263T glass substrates via high temperature deposition process namely close-spaced sublimation (CSS). CdTe thin films were deposited under different source and substrate temperatures ranging from 500 ℃ to 700 ℃ to investigate the influence of deposition temperature on the properties of CdTe thin films grown on ultra-thin Schott glass substrates. X-ray diffraction (XRD) analysis illustrated cubic CdTe structure with a sharp peak at (111) orientation. The scanning electron microscope (SEM) study elucidated that the grain growth and surface morphology were highly dependent on the deposition temperature. UV–Vis results showed approximate optical band gap range of 1.61–1.66 eV. Carrier concentration and resistivity were found in the order of 1013 cm−3 and 105 Ω-cm, respectively. Structural and opto-electronic characteristics were optimized for the best temperature range to be used for CdTe film deposition in CSS growth. Optimum conditions for CdTe film growth on ultra-thin (100 µm) substrate were found in the range of 500 ℃–600 ℃ for substrate and source temperature.

Optical properties of CdTe thin films obtained by the method of high-frequency magnetron sputtering

Optical properties of CdTe thin films obtained by the method of high-frequency magnetron sputtering

Studying the effect of deposition time on physical properties of CdTe thin films; Influence of CdTe electrical properties on CdS/CdTe heterojunction rectifying behavior

CdTe nanostructured thin films were grown on glass substrates by RF-magnetron sputtering at different deposition time periods (10, 20 and 30 min). The layers were characterized by FESEM, EDAX, XRD, Raman, UV–vis., PL spectra, also Seebeck effect and I–V-T measurements. It is found with increasing the deposition time: the size of cubic phase CdTe nano-grains were gradually increased and the stoichiometry of the layers improved, as consistent with the PL spectra of layers. The synthesized CdTe layers were then put in contact with an optimized CdS layer. The analysis of dark I–V data showed that the electrical properties of CdTe layer has crucial impact on rectifying ration (RR) of the prepared CdS/CdTe heterojunction diodes.

Electrodeposition of CdTe Thin Films for Solar Energy Water Splitting.

CdTe thin films have been prepared by electrochemical deposition. The morphological, structural, and optical properties of CdTe thin films deposited with different deposition time were investigated, and the influence of film thickness on the photoelectric characteristics of CdTe thin films was studied. At the deposition time of 1.5 h, CdTe thin films had good optical properties and the photocurrent reached 20 μAcm−2. Furthermore, the Pt/CdS/CdTe/FTO structure was prepared to improve its PEC stability and the photocurrent of 240 μAcm−2 had been achieved.

The Features of the Photoconductivity Activation of CdTe Thin Films by Cadmium Halide Mixtures

The effect of the annealing temperature in the presence of mixtures of cadmium chloride and cadmium iodide of different compositions on the electrophysical properties of CdTe thin films is studied. This process, in which, as a rule, cadmium chloride is used, is called activation. It allows us to significantly improve the efficiency of solar cells based on CdTe. It is found that the temperature of this process can be reduced from 450 to 300°C by replacing CdCl2 with a mixture of the composition of ~60 mol % CdCl2 to ~40 mol % CdI2.

Structural and Optical Properties of RF-Sputtered CdTe Thin Films Grown on CdS:O/CdS Bilayers

In this work, we report the structural and optical properties of CdTe thin films on oxygenated Cadmium Sulfide (CdS:O)/Cadmium sulfide(CdS) bilayer using RF magnetron sputtering for different substrate temperatures ( 150, 200, 250, 300 and 350 °C) in Argon ambient. The XRD spectra reveal the polycrystalline nature of all the CdTe thin films with preferential cubic orientation along (111) direction. Raman Spectra show a dominant peak at 163.5 cm -1  and its overtone at 328.7 cm -1  which corresponded to the longitudinal optical (LO) phonon of CdTe. The SEM microscopy exhibits the uniform growth of CdTe films onto the entire glass substrate. The optical transmission of the CdTe films begin at the edge of 800 nm wavelength and showed interference fringe in the transmission spectra. The thickness of the deposited films and the optical constants were calculated from the fringe pattern. The thicknesses of the CdTe films are found to be increasing from 2.34 I¼m to 2.82 I¼m with increasing the substrate temperature i.e. from 150 to 250°C. Thereafter, the CdTe film thickness decreased to 2.24 I¼m while the temperature increased further up to 350°C. The optical bandgap of the deposited CdTe films follows an increasing trend of 1.46 eV to 152 eV with the increase of substrate temperature 150 to 250°C after that the bandgap decrease to 1.50 for 350°C. Hence the obtained structural and optical properties suggest that the deposited CdTe films can be used as a suitable absorber layer for the thin film-based solar cells.

Influence of the CdCl2 Solution Concentration on the Properties of CdTe Thin Films

this work presents the influence of the concentration of CdCl 2 -treatment-solution on the microstructural, morphological, and optical properties of CdTe thin films. The CdTe films were deposited on CdS coated borosilicate glass by Close-Spaced Sublimation (CSS) technique using a standard recipe. The CdS films were grown by RF magnetron sputtering. The deposited CdTe films were treated with CdCl 2 solution of 0.20 M, 0.25 M, 0.30 M, 0.35 M, and 0.40 M concentration at 395 °C for 25 minutes. All the films exhibit polycrystalline nature with a predominant (111) Bragg peak of cubic CdTe. The highest crystallite size and smallest micro-strain and dislocation density are found for the treatment solution of 0.35M concentration. The results present that the treatment concentration enhances the S diffusion into the CdTe layer up to a certain limit of molar concentration. The highest S concentration (~2%) among the investigated samples are found for 0.35 M concentration. The SEM micrographs of the as-grown and treated films reveal that the grain size follows an increasing trend with the solution concentration up to 0.35 M. The optical bandgap of all samples are found to be in the range of 1.42 – 1.45 eV estimated from the UV-Vis-NIR transmission data. The lowest bandgap of 1.42 eV is found for the sample treated with 0.35 M solution due to the highest crystallinity among the samples investigated evident from both XRD and SEM results.

The effects of sodium tartrate concentration on the properties of CdTe thin films prepared by electrodeposition

In this paper, we successfully fabricate compact and uniform cadmium telluride (CdTe) films on flexible nickel foils using simple electrodeposition technique and sintering in a nitrogen atmosphere. The effect of the concentration of sodium tartrate on the structures and properties of the deposited CdTe thin films are studied. Various test techniques are used to characterize the results. The results of XRD analysis show that the highest crystallinity film is obtained when the added sodium tartrate concentration is 0.05 M. With the increase of sodium tartrate concentration, the composition of the film gradually changes from Te-rich to Cd-rich, and the thickness of the film becomes thin gradually. We also find that the CdTe thin film prepared under 0.05 M sodium tartrate shows the best optical and optoelectronic properties. Thus, a moderate amount of sodium tartrate is added into an acidic solution as surfactant for CdTe thin film fabrication. Moreover, sodium tartrate is easily volatilized from the film during the annealing process because of its small molecular weight, which can prevent the carbon precipitation.

Influence of deposition time in CdTe thin film properties grown by Close-Spaced Sublimation (CSS) for photovoltaic application

Abstract Cadmium Telluride (CdTe) thin films were grown on borosilicate glass substrates by close-spaced sublimation (CSS) at a pressure of 1.5–2 Torr in Ar ambient. CdTe thin films were sublimed at a source temperature of 625 °C and substrate temperature of 595 °C. In this study, the impact of various deposition times on the structural, morphological, topographical, electrical and optical properties of CdTe thin films has been explored to achieve high quality thin film absorber layer for solar cells applications. The crystalline structure, surface morphology, surface topology, electrical and optical properties of the films were examined by using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), Hall Effect measurement and UV–Vis spectrophotometry, respectively. XRD investigation demonstrated that CdTe film shows polycrystalline nature pronounced with cubic zinc blende structure with a strong preferential (1 1 1) orientation. The FESEM images illustrated that the surface morphology and the average grain size of the films were dependent on the deposition times of CdTe thin films. AFM analysis revealed noteworthy changes in the film’s surface roughness values for different deposition times. Carrier concentration was found in the order of 1013 cm−3. Band gap of CdTe thin film was found in the range 1.45–1.48 eV, which is suitable to be used in CdTe thin film solar cells.

Effect of Substrate Properties on Nanostructure and Optical Properties of CdTe Thin Films

Cadmium telluride (CdTe) nanoparticles were deposited on amorphous glass and crystal quartz as nonconductive films, indium tin oxide and fluorine doped tin oxide as transparent conducting films, and silver as a metal at 100°C under pressure of 2 × 10−5 mbar. CdTe thin films prepared by a thickness about 80 nm. The results of x-ray diffraction analysis show the grain size of preferential orientation was between 5.48 nm and 15.37 nm. Also, the preferential orientation changed from (111) for non-conducting substrates to (220) for conducting substrates. The investigation of texture coefficient (TC) has indicated the deviation of TC from unity for metals substrates is further than the other substrates. The optical properties of CdTe thin films such as the optical band gap, extinction coefficient and refractive index, real and imaginary parts of dielectric constant were investigated by ultraviolet–visible spectroscopy (UV–Vis) as a function of photon energy in the wavelength range of 600–1600 nm. These measurements indicated the increasing of optical band gap by increasing the conductivity of substrates. Scanning electron microscopy analysis used to investigate the morphology of thin films.