Telluride Thin Films Research Articles

Identifying Optimal Strain in Bismuth Telluride Thermoelectric Film by Combinatorial Gradient Thermal Annealing and Machine Learning.

The thermoelectric properties of bismuth telluride thin film (BTTF) was tuned by inducing internal strain through a combination of combinatorial gradient thermal annealing (COGTAN) and machine learning. BTTFs were synthesized via magnetron sputter coating and then treated by COGTAN. The crystal structure and thermoelectric properties, namely Seebeck coefficient and thermal conductivity, of the treated samples were analyzed via micropoint X-ray diffraction and scanning thermal probe microimaging, respectively. The obtained combinatorial data reveals the correlation between internal strain and the thermoelectric properties. The Seebeck coefficient of BTTF exhibits largest sensitivity, where the value ranges from 7.9 to -108 μV/K. To further explore the possibility to enhance Seebeck coefficient, the combinatorial data were subjected to machine learning. The trained model predicts that optimal strains of 3-4% and 1-2% along the a- and c-axis, respectively, significantly improve Seebeck coefficient. The technique demonstrated herein can be used to predict and enhance the performance of thermoelectric materials by inducing internal strain.

Direct measurement of the thermoelectric properties of electrochemically deposited Bi2Te3 thin films

The best known thermoelectric material for near room temperature heat-to-electricity conversion is bismuth telluride. Amongst the possible fabrication techniques, electrodeposition has attracted attention due to its simplicity and low cost. However, the measurement of the thermoelectric properties of electrodeposited films is challenging because of the conducting seed layer underneath the film. Here, we develop a method to directly measure the thermoelectric properties of electrodeposited bismuth telluride thin films, grown on indium tin oxide. Using this technique, the temperature dependent thermoelectric properties (Seebeck coefficient and electrical conductivity) of electrodeposited thin films have been measured down to 100 K. A parallel resistor model is employed to discern the signal of the film from the signal of the seed layer and the data are carefully analysed and contextualized with literature. Our analysis demonstrates that the thermoelectric properties of electrodeposited films can be accurately evaluated without inflicting any damage to the films.

Impact of ZnTe, SbZnTe and SnZnTe absorber materials for multi-layered solar cell: Parametric extraction and layer wise internal analysis

In this research paper, Sb and Sn doped Zinc Telluride (ZnTe) thin films are prepared on the glass substrate through low-cost melt-quenching technique. These films are characterized to observe the nature of materials through XRD patterns. Subsequently, these materials are explored as the absorber-layer in the multi-layered solar cell. At 1.5 μm absorber thickness, the current density for SbZnTe and SnZnTe cells is improved by 1.1x and 2.6x respectively, as compared to ZnTe cell. This current density is augmented by 26 % and 31 % when thickness is incremented from 0.5 to 2.5 μm for SbZnTe and SnZnTe layers, respectively. The Fill Factor improves by 5.3 % for SbZnTe and 49 % for SnZnTe than ZnTe cell. Further, these cells are examined through horizontal-cut-line within the absorber layer and vertical-cut-line along the device thickness to explore layer-wise internal processes. Subsequently, potential distribution, Valance/Conduction band energy, charge carrier concentration, hole/electron current density, electric field and recombination rate are analyzed. The holes and electrons concentration are higher by 9.84 % and 8.96 % respectively for SnZnTe than SbZnTe cell. The conversion efficiency of SbZnTe and SnZnTe is achieved as 10.6 % and 17.8 % at 2.5 μm, which is higher by 1.15x and 1.93x in comparison to the ZnTe based solar cell. The SnZnTe cell shows holistic performance owing to its lowest band-gap of 1.39 eV. Moreover, this absorber material leads to highest charge carrier generation, thereby hole and electron current densities are improved by 11.86 % and 35.50 % than the SbZnTe cell.

Ammonia gas sensing response of gamma-irradiated CdTe thin films

In this work, cadmium telluride (CdTe) thin films of thickness 250 nm are deposited on the glass substrate using the thermal vacuum evaporation (TVE) method. The as-deposited CdTe thin films are then exposed to three different doses of gamma rays (50, 100 and 150 kGy) from 60Co source at Inter University Accelerator Centre, New Delhi, India. The structural, morphological, electrical and gas sensing properties of as-prepared and gamma-irradiated thin films are investigated using grazing incidence X-ray diffraction (G-XRD), Field emission scanning electron microscopy (FESEM) and two-probes set up connected with current-voltage (I–V) source meter, respectively. The assessment of adsorption and desorption rate of pristine and gamma-irradiated films is studied using Brunauer –Emmett-Teller (BET) analysis. After irradiation, the XRD pattern indicates the polycrystalline nature of thin films along with the retention of cubic structure with a minor decrease in the crystallite size at the highest gamma dose. From FESEM, relevant changes in the surface morphology of thermally deposited CdTe thin films have been observed after irradiation. Moreover, the films after irradiation were found to be highly conductive up to the dose of 100 kGy as depicted from electrical studies. The gamma irradiated films are further proposed for gas sensing applications. For the highest concentration of ammonia (36.02 ppm), the maximum sensitivity of the as-deposited film is found to be (14.59%) which is higher than the sensitivity at a maximum gamma dose of 150 kGy (10.28%) for the same concentration of gas which shows that process of gamma irradiation deteriorates the sensing performance of CdTe thin films.

Development of a Comprehensive Matlab/Simulink Based Model for High-Efficiency 2nd Generation Photovoltaic (PV) Modules

Background:The accurate energy yield prediction of a PV system under various environmental conditions is important for designing a high-performance PV system.Objective:The robust and cost-effective digital simulation studies on PV systems have the advantage in comparison to studies based on measurements because they provide the opportunity for sensitivity analysis on various design parameters of the PV system.Methods:Herein, we present the development and implementation of a generalized photovoltaic computational model using Matlab/Simulink software package. The model is based on the equivalent diode circuit approach. It is designed to simulate two ubiquitous and high performing 2nd generation photovoltaic (PV) modules constructed with Cadmium Telluride (CdTe) and Copper Indium Gallium di-Selenide (CIGS) photoactive thin films, respectively. The values of key input parameters to the simulator, i.e., parallel resistor (Rp) and series resistor (Rs) have been computed by an efficient Newton-Raphson iteration method.Results:The output current-voltage (I-V) and power-voltage (P-V) characteristic curves of the aforementioned PV modules have been simulated by taking two input variables (ambient irradiance and temperature) into consideration. The electrical performance of both PV modules under various environmental conditions have been mathematically investigated by the solution of classical non-linear equations.Conclusion:The developed PV model has been validated with the experimental results obtained from standard PV module datasheets provided by manufacturers. The relative error between the simulated and experimental values of various photovoltaic parameters for CdTe and CIGS PV modules at Standard Test Conditions (STC) has been observed to be below 3%.

An approach to alternative post-deposition treatment in CdTe thin films for solar cell application

Abstract In this study, preliminary investigation of different post-deposition treatments using materials such as cadmium chloride (CdCl2), magnesium chloride (MgCl2), copper chloride (CuCl2), and silver nitrate (AgNO3) has been reported for close-spaced sublimation (CSS) grown cadmium telluride (CdTe) thin films. The treatment of CdTe thin films was conducted in open air at 390 °C. Treated CdTe thin films were then exposed to different characterization tools to explore the effects of treatment on the structural and optoelectronic properties of CdTe films. Hall effect measurement was executed for electrical properties measurement as well as X-ray diffraction (XRD) analysis was utilized for the detection of structural parameters. The energy band gap was obtained at approximately 1.47 eV for all the treated films. CuCl2 treated CdTe films exhibited a higher carrier concentration of 1015 cm−3 than other treatments. The impact of Cu diffusion during CuCl2 treatment was suggested as an effect of doping during recrystallization. The average grain sizes changed moderately in the range 4–7 μm for different post-deposition treatments. The optimized results can provide an indication for other materials to be used as the alternative post-deposition treatment to conventional CdCl2.

Effects of Erbium on the Properties of Electrochemically-Deposited Zirconium Telluride Thin Films

This work studies the effects of varying erbium dopant percentages on the optical, structural, morphological,elemental, and electrical properties of zirconium telluride thin films deposited via electrochemical deposition technique.The obtained films were characterized using Uv-Visible Spectrophotometer, X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive x-ray spectroscope (EDX), and a four-point probe system. XRD analyses showed cubic polycrystalline films with the most intense peak at (111) plane. SEM micrographs revealed spherical balls while EDX spectra confirmed the deposition of basic elements. Good optical features and decreased band gap energies from 1.80 eV to 1.76 eV were observed upon addition of erbium. The electrical conductivities of the films improved significantly upon doping. The deposited films are potential solar cells, and optical materials.

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.

Electron Microscopy and Interface Plasmons Characterization of Cadmium Telluride Thin Film Grown Incommensurately with Weak Bonding on Sapphire

Electron Microscopy and Interface Plasmons Characterization of Cadmium Telluride Thin Film Grown Incommensurately with Weak Bonding on Sapphire

Influence of nanocellulose concentration on the tunability of energy bandgap of cadmium telluride thin films

Cadmium telluride (CdTe) doped nanocellulose thin films were successfully deposited on glass/fluorine-doped tin oxide substrates from an aqueous electrolyte bath containing hydrated cadmium sulfate (3CdSO4·8H2O) and tellurium dioxide using electrodeposition technique. Six samples of CdTe thin films were grown with nanocellulose concentrations of (0, 1, 3, 5, 7, and 9) ppm. The results obtained from electronic data of the deposited layers using UV–Vis spectrophotometer agree favourably with the theoretical formulation. The bandgap of the films ranges from 1.32 to 1.67 eV. The lowest bandgap of CdTe (1.32 eV) was achieved at a concentration of 9 ppm. This relatively low energy bandgap is remarkable in recent formation of CdTe. Photoelectrochemical cell measurement shows that the electrical conductivity type of undoped CdTe is n-type while the nanocellulose doped CdTe is p-type in electrical conduction. Hence, it is possible to effectively tune the conductive properties of CdTe by careful addition of nanocellulose concentration.

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.

Fabrication of PEDOT: PSS-PVP Nanofiber-Embedded Sb2Te3 Thermoelectric Films by Multi-Step Coating and Their Improved Thermoelectric Properties.

Antimony telluride thin films display intrinsic thermoelectric properties at room temperature, although their Seebeck coefficients and electrical conductivities may be unsatisfactory. To address these issues, we designed composite films containing upper and lower Sb2Te3 layers encasing conductive poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)- polyvinylpyrrolidone(PVP) nanowires. Thermoelectric Sb2Te3/PEDOT:PSS-PVP/Sb2Te3(ED) (STPPST) hybrid composite films were prepared by a multi-step coating process involving sputtering, electrospinning, and electrodeposition stages. The STPPST hybrid composites were characterized by field-emission scanning electron microscopy, X-ray diffraction, ultraviolet photoelectron spectroscopy, and infrared spectroscopy. The thermoelectric performance of the prepared STPPST hybrid composites, evaluated in terms of the power factor, electrical conductivity and Seebeck coefficient, demonstrated enhanced thermoelectric efficiency over a reference Sb2Te3 film. The performance of the composite Sb2Te3/PEDOT:PSS-PVP/Sb2Te3 film was greatly enhanced, with σ = 365 S/cm, S = 124 μV/K, and a power factor 563 μW/mK.

Features of optical properties of high stable CdTe photovoltaic absorber layer

In this paper, the technology of obtaining and effect of annealing on the morphology and optical properties of cadmium telluride thin films has been investigated. The effect of vacuum chamber modes on the growth of thin films has been studied. For obtained cadmium telluride thin films were used a modified thermal evaporation method deposited by Physical Vapor Deposition technique on a glass substrate with different thicknesses. The transmission measurements were carried with UV-ViS-NIR Spectrophotometer in the wavelength range 180-3300 nm, to analyze the optical properties as a function of wavelength. The optical band gap values were 1.49 eV for as-grown films and 1.46 eV after annealing. The refractive indexes of the samples were defined in the range of 2.6 – 2.8 for as-grown films and the indexes have increased after annealing depending on the wavelength region and film thickness. After annealing, the coalescence mode of growth is observed.

Atomic composition changes in bismuth telluride thin films by thermal annealing and estimation of their thermoelectric properties using experimental analyses and first-principles calculations

Abstract We investigated the structural and thermoelectric properties of bismuth telluride films when the atomic composition is changed by evaporation of Te atoms from the films during thermal annealing. The bismuth telluride films were deposited using a magnetron radio frequency sputtering method without a substrate heating. Thereafter, the films were thermally annealed up to 450 °C in an electric furnace with Ar(95%)–H2(5%) gas mixture. The atomic composition of the as-deposited film was approximately that of Bi2Te3. By increasing the annealing temperature, the Te atoms were evaporated from the films and the composition approached that of Bi1Te1, as discovered from electron probe microanalysis. Furthermore, a change in crystalline phase was observed through X-ray diffraction patterns. When the thermoelectric properties of the films were measured at room temperature, the carrier concentration was significantly affected by the change in atomic composition. We confirmed this finding using energy band structures using first-principles calculations. The highest power factor of 16.9 μW/(cm∙K2) was achieved at an annealing temperature of 300 °C because the film achieved a high crystallinity and crystal orientation with relatively low defects owing to less evaporation of Te atoms.

Optimizing the Structural, Electrical and Thermoelectric Properties of Antimony Telluride Thin Films Deposited on Aluminum Nitride-coated Stainless Steel Foil

In this study, we examined the thermoelectric (TE) properties of co-evaporated p-type antimony telluride (Sb2Te3) thin films on aluminum nitride (AlN)-coated stainless steel foil substrates. We investigated the influence of composition and substrate temperature on the thin-film microstructure and transport properties, by varying the tellurium (Te) concentration in the thin films as well as the substrate temperature during deposition (room temperature (RT) and 300 °C). Thin films prepared with an RT substrate were further annealed at 264 °C to obtain crystallized thin films with high phase purity. Columnar thin films with large grains and a standard multi-oriented crystal structure were obtained when thin films were deposited on substrates heated to 300 °C. Thin films deposited at RT and subsequently annealed at 264 °C had a dense, layered microstructure, with a preferential c-axis or (00 l) texture as the compositions approached phase stoichiometry. The temperature dependence of the thermoelectric properties was measured, and variations were interpreted in terms of the deviation from stoichiometry and the obtained microstructure. A maximum power factor (PF) of 0.87 mW/m ∙ K2 was obtained for off-stoichiometric 65.0 at% Te thin film, which was the highest among the samples deposited at high substrate temperatures. A higher PF of 1.0 mW/m ∙ K2 was found for off-stoichiometric thin films with 64.5 at% Te, which was deposited at RT and subsequently annealed. The improvement of thermoelectric power in films containing excess Te could be related to energy dependent carrier scattering at the Sb2Te3/Te interface.

Tunability of conductivity type and energy band gap of CdTe thin film in the electrodeposition technique

In this research, cadmium telluride (CdTe) thin films were fabricated using electrodeposition technique at 1400 mV cathodic potential. CdTe films were deposited on fluorine doped tin oxide (FTO) substrate of dimension 2.3 by 2.4 cm2 at varied time of deposition. X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet visible spectrophotometer (UV-vs), photoelectrochemical cell measurement (PEC), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the structural, morphological, optical, electrical conductivity and elemental composition of electrodeposited films respectively. The particle average crystallite size was estimated as 11.98 nm. The energy band gap of as deposited films decreases as the period of deposition increases for both annealed and unannealed samples. Furthermore, the period of deposition was found to constitute major factor in the dominance of the constituent elements, thereby influencing the electrical conductivity and band gap properties of the films. Consequently, the conductivity of CdTe can be reasonably tuned when heat-treated and the tunability of the energy band gap can be achieved by varying the period of deposition in the electrodeposition technique. Despite the potential of electrodeposited CdTe in solar cells applications, synthesis of p-type CdTe in a stable way place a bottleneck to the utilization of CdTe as a good absorber layer in preventing front surface recombination when CdTe form a heterojunction with any window layer material.

Study on thermoelectric property optimization of mixed-phase bismuth telluride thin films deposited by co-evaporation process

The development of Bi2Te3 thin films has huge potential in the pursuit of efficient thermoelectric micro/nanodevices due to their high Seebeck coefficient, high electrical conductivity and low thermal conductivity. The optimization of experimental parameters of Bi-Te thin films produced by co-evaporation will be investigated in this study. Co-evaporation is a low cost, easy-to-control process which can be used for high throughput and is scalable. We found that an optimal Te/Bi ratio of 1.5 with good thermoelectric properties can be directly synthesized by Bi and Bi2Te3 co-evaporation. Compared to the conventional Bi/Te co-evaporation process, high temperature annealing or substrate heating is not necessary for the process mentioned in this paper, which is a desirable feature when using polymer-based substrates, organic/inorganic hybrid thermoelectric generators, and flexible devices since they have relatively low tolerance to heat. The optimized Bi2Te3 thin films, which are mixed phases of Bi2Te3, Bi3Te4 and Te, possess high carrier concentration (6.65 × 1020 cm−3), low electrical resistivity (3.17 × 10−3 Ωcm), and extremely low thermal conductivity (0.59 W/mK) at room temperature on a smooth surface (roughness <5.5 nm) and are achieved by adjusting the deposition rate of Bi and Bi2Te3. The correlation between the structures of mixed phases, electrical and thermal properties will be discussed in detail.

Transport properties of the bismuth telluride thin films with different stoichiometry in the temperature range 77-300 K

Transport properties of the bismuth telluride thin films with different stoichiometry in the temperature range 77-300 K

Research Status of Recovery of Tellurium from Cadmium Telluride Photovoltaic Modules

Cadmium telluride is a direct band gap semiconductor with high optical absorption coefficient and excellent photoelectric conversion efficiency. Therefore, the proportion of cadmium telluride thin film solar cells in photovoltaic emerging technologies is increasing. The shortage of metal tellurium is the main factor restricting the development of cadmium telluride thin film photovoltaic cell technology. Therefore, it is necessary to recover tellurium from decommissioned cadmium telluride photovoltaic modules. In this paper, the treatment status of cadmium telluride photovoltaic decommissioning components is studied, and the characteristics of various recycling methods are analyzed and compared. Based on recent research progress and important findings, the challenges and future prospects of commercialization are forecasted.

Effect of an Organic Additive, N-Dimethyldithiocarbamic acid Ester Sodium salt, on Properties of Bismuth Telluride thin Films Fabricated by Galvanic Displacement Reaction of Electroplated Cobalt thin Films

Effect of an Organic Additive, N-Dimethyldithiocarbamic acid Ester Sodium salt, on Properties of Bismuth Telluride thin Films Fabricated by Galvanic Displacement Reaction of Electroplated Cobalt thin Films