CIGS absorbing layers prepared by RF magnetron sputtering from a single quaternary target

Cu(In_1−xGa_x)Se₂ (CIGS) thin films were prepared by RF magnetron sputtering from a single quaternary target at multiple processing parameters. The structural, compositional, and electrical properties of the as-deposited films were systematically investigated by XRD, Raman, SEM, and Hall effects analysis. The results demonstrate that by adjusting the processing parameters, the CIGS thin films with a preferential orientation along the (112) direction which exhibited single chalcopyrite phase were obtained. The films deposited at relatively higher substrate temperature, sputtering power, and Ar pressure exhibited favorable stoichiometric ratio (Cu/(In+Ga):0.8–0.9 and Ga/(In+Ga):0.25–0.36) with grain size of about 1–1.5 µm, and desirable electrical properties with p-type carrier concentration of 10¹⁶−10¹⁷ cm⁻³ and carrier mobility of 10–60 cm²/Vs. The CIGS layers are expected to fabricate high efficiency thin film solar cells.     

Selenium Flux Effect on Cu(In,Ga)Se2 Thin Films Grown by a 3-stage Co-evaporation Process

An investigation into the effects of Se flux on absorber thin film growth at each step of a 3-stage co-evaporation process was conducted to further optimize the performance of CIGS solar cells. In ‘step I’ forming an In-Ga-Se precursor thin film during the 3-stage process, Se flux affected the preferred orientation of the CIGS crystal structure, but not the film morphology. In ‘step II’, no correlation was found between Se flux and the crystal structure, although excessively high Se flux employed throughout the 3-stage process degraded the solar cell performance. A CIGS thin film, with a (220/204) crystal orientation, minor physical surface defects and ∼20 nm thick MoSe₂ at CIGS/Mo interface, was obtained by fine control of Se flux conditions (high Se flux at ‘step I’ and low Se flux at ‘step II’) at optimum substrate temperatures. The solar cell fabricated using the aforementioned CIGS thin film showed the highest conversion efficiency of 20.02 %.     

Structural and optical properties of ZnS thin films deposited by RF magnetron sputtering

Zinc sulfide [ZnS] thin films were deposited on glass substrates using radio frequency magnetron sputtering. The substrate temperature was varied in the range of 100°C to 400°C. The structural and optical properties of ZnS thin films were characterized with X-ray diffraction [XRD], field emission scanning electron microscopy [FESEM], energy dispersive analysis of X-rays and UV-visible transmission spectra. The XRD analyses indicate that ZnS films have zinc blende structures with (111) preferential orientation, whereas the diffraction patterns sharpen with the increase in substrate temperatures. The FESEM data also reveal that the films have nano-size grains with a grain size of approximately 69 nm. The films grown at 350°C exhibit a relatively high transmittance of 80% in the visible region, with an energy band gap of 3.79 eV. These results show that ZnS films are suitable for use as the buffer layer of the Cu(In, Ga)Se₂ solar cells.     

Characterization of Cu(In,Ga)Se2 thin films prepared by RF magnetron sputtering using a single target without selenization

Cu(In_1?xGa_x)Se₂ (CIGS) thin films were prepared using a single quaternary target by RF magnetron sputtering. The effects of deposition parameters on the structural, compositional and electrical properties of the films were examined in order to develop the deposition process without post-deposition selenization. From X-ray diffraction analysis, as the substrate temperature and Ar pressure increased and RF power decreased, the crystallinity of the films improved. The scanning electron microscopy revealed that the grains became uniform and circular shape with columnar structure with increasing the substrate temperature and Ar pressure, and decreasing the RF power. The carrier concentration of CIGS films deposited at the substrate temperature of 500 °C was 2.1 × 10¹⁷ cm^?3 and the resistivity was 27 Ω cm. At the substrate temperature above 500 °C, In and Se contents in CIGS films decreased due to the evaporation and it led to the deterioration of crystallinity. It was confirmed that CIGS thin films deposited at optimal condition had similar atomic ratio to the target value even without post-deposition selenization process.     

Influence of deposition parameters on the structure and microstructure of Bi12TiO20 films obtained by pulsed laser deposition

The structure, morphology and surface roughness of Bi₁₂TiO₂₀ (BTO) thin films grown on R-sapphire by pulsed laser deposition (PLD) were studied at different substrate temperatures, target-substrate distances, oxygen pressures and laser-pulse repetition rates. Although the substrate temperature seems to be the most important experimental parameter, the gas pressure and the target–substrate distance played important role on the phase formed and film thickness, with a significant effect of the laser-pulse repetition rate on the films thickness and preferred orientation of the deposited film. Single-phase γ-Bi₁₂TiO₂₀ was obtained on substrates at 650?°C, while several BTO metastable phases were observed in films deposited on substrates at temperatures between 500 and 600?°C. By the first time, thin films of pure and textured δ-Bi₁₂TiO₂₀ were successfully growth on substrates at 450?°C. When annealed, all the films deposited at lower temperatures resulted in the thermodynamically stable γ-Bi₁₂TiO₂₀.     

Surface modifications of CIGS absorbers and their effects on performances of CIGS solar cells

The surface roughness of CIGS absorber and residual Cu–Se phase on the surface are two major factors greatly affecting the performance of CuInGaSe₂ (CIGS) solar cells with the absorbers fabricated by the selenization annealing of Cu–In-Ga precursors. In this work, Br₂–CH₃OH solution is used to etch the surfaces of CIGS films to address these two challenges. The effects of the etching treatment on CIGS films and devices are investigated. It is found that etching significantly reduces the film roughness and removes the Cu–Se phase. Thus, the performance of the device is improved within a certain range. In addition, it is found that CIGS films with suitable surface roughness effectively absorb incident light and possess a higher J_sc. However, excessive etching causes the film to be too thin, and the carrier recombination at the back electrode increases. Based on these characteristics, this work optimizes the Br₂ etching process.     

Nanoscale observation of surface potential and carrier transport in Cu2ZnSn(S,Se)4 thin films grown by sputtering-based two-step process

Stacked precursors of Cu-Zn-Sn-S were grown by radio frequency sputtering and annealed in a furnace with Se metals to form thin-film solar cell materials of Cu₂ZnSn(S,Se)₄ (CZTSSe). The samples have different absorber layer thickness of 1 to 2 μm and show conversion efficiencies up to 8.06%. Conductive atomic force microscopy and Kelvin probe force microscopy were used to explore the local electrical properties of the surface of CZTSSe thin films. The high-efficiency CZTSSe thin film exhibits significantly positive bending of surface potential around the grain boundaries. Dominant current paths along the grain boundaries are also observed. The surface electrical parameters of potential and current lead to potential solar cell applications using CZTSSe thin films, which may be an alternative choice of Cu(In,Ga)Se₂.PACS number: 08.37.-d; 61.72.Mm; 71.35.-y     

A new method for measuring wetness of flowing steam based on surface plasmon resonance

Stacked precursors of Cu-Zn-Sn-S were grown by radio frequency sputtering and annealed in a furnace with Se metals to form thin-film solar cell materials of Cu₂ZnSn(S,Se)₄ (CZTSSe). The samples have different absorber layer thickness of 1 to 2 μm and show conversion efficiencies up to 8.06%. Conductive atomic force microscopy and Kelvin probe force microscopy were used to explore the local electrical properties of the surface of CZTSSe thin films. The high-efficiency CZTSSe thin film exhibits significantly positive bending of surface potential around the grain boundaries. Dominant current paths along the grain boundaries are also observed. The surface electrical parameters of potential and current lead to potential solar cell applications using CZTSSe thin films, which may be an alternative choice of Cu(In,Ga)Se₂. PACS number: 08.37.-d; 61.72.Mm; 71.35.-y     

Annealing Effect on the Properties of Cu(In0.7Ga0.3)Se2 Thin Films Grown by Femtosecond Pulsed Laser Deposition

This work reports the crystallization, microstructure, and surface composition of CuIn_0.7Ga_0.3Se₂ (CIGS) thin films grown by femtosecond pulsed laser deposition at different annealing temperatures. The structural and optical properties of the CIGS films were characterized by X‐ray diffraction, Raman scattering, UV‐visible spectroscopy, and Hall effect measurement. The results indicate that binary crystals of CuSe initially formed on the as‐deposited film, but then completely turned into a quaternary chalcopyrite structure after annealing at 400°C. Phase transformation significantly affects the surface morphology, Hall properties, and band gap. Transmission electron microscopy further revealed that an interface between the Mo substrate and CIGS crystallites contains an amorphous layer even at the high temperature of 500°C. For the application of photovoltaic devices, we also report on the photoresponse of both as‐deposited and annealed films as demonstrated by preliminary tests.     

Electrochemical study of one-step electrodeposition of copper–indium–gallium alloys in acidic conditions as precursor layers for Cu(In,Ga)Se2 thin film solar cells

This paper investigates one step electrodeposition of copper indium gallium metallic precursor layers for preparing CuIn_1−xGa_xSe₂ (CIGS) absorber layers in thin film solar cells (0 ≤ x ≤ 1). Electrodeposition was carried out in acidic aqueous solutions at about pH 2. At first partial single or binary electrodeposition systems Cu, In, Ga, Cu–Ga, Cu–In were investigated by cyclic voltammetry. Then ternary Cu–In–Ga electrodeposition system was studied. The nature of the supporting electrolyte (sodium sulfate vs. sodium chloride) and the influence of sodium citrate were more specifically investigated. The applied potential, the pH and the nature of the electrolyte were optimized to obtain x values around 0.3 needed for high efficiency devices. Depositions were carried out under potentiostatic conditions in a paddle cell configuration. The electrodeposited Cu–In–Ga alloys were annealed under Se atmosphere at temperatures between 400 and 600 °C to produce CIGS absorbers. Films were characterized by XRF, SEM and XRD analysis. Device efficiencies up to 9.3% are achieved for optimal gallium content.     

Preparation and Characterization of Copper Gallium Diselenide Thin Films from the Solgel‐Derived Precursors

A simple process for preparing CuGaSe₂ (CGS) absorber layers was developed in this study. The solgel‐derived Cu‐Ga‐O precursor paste with variable Ga³⁺/Cu²⁺ ratios was coated on glass substrates using a doctor‐blade technique. The precursor films were selenided with a selenium vapor at the temperature ranging from 250 to 550°C. The GIXRD patterns showed that single‐phase CuGaSe₂ through the whole films was obtained at a Ga³⁺/Cu²⁺ molar ratio of 1.5 on selenization at 450°C. The Raman measurements also indicated that the grown CuGaSe₂ thin films exhibited the chalcopyrite structure. The SEM images of the films reveal that with an increase in Ga/Cu ratio in the films, the amount of Cu₂Se particles on the surface of the film was reduced. The resistivity of the films was increased with the increase in Ga content in the films. The formation mechanism of CuGaSe₂ thin films was proposed based on the XRD and Raman measurements of the films. The binary copper selenides are formed first, and then these phases lead to the formation of CuGaSe₂.     

Growth of Zn2GeO4 thin film by thermal evaporation on ITO substrate for thermoelectric power generation applications

In this paper, we have reported the growth of Zn₂GeO₄ thin film and investigated its potential for thermoelectric power generation applications. Zn₂GeO₄ alloy thin film was grown on Indium coated glass substrate by the evaporation of Zn and Ge metals with constant oxygen gas flow rate of 100 sccm in tube furnace. The grown film was cut into pieces and annealed at various temperatures from 500° to 700°C with a step of 100?°C in a programmable furnace for one hour. The structure of as grown and annealed thin films was verified by XRD and Raman spectroscopy measurements. The XRD data evident that Zn₂GeO₄ alloy hexagonal structure along with GeO₂ and ZnO phases were observed at annealing temperatures 600 and 700?°C but below this temperature no alloy phase was detected by XRD and Raman Spectroscopy. To calculate the thermoelectric properties, temperature dependent Seebeck measurements were performed in the temperature range of 25–100?°C. It was observed that the value of Seebeck coefficient was increased from 91 to 847?μV/K as the annealing temperature increases from 500° to 700°C. This behavior was explained as; high temperature causes stress and cracks in the grown films which may induce electric and thermal discontinues at tips of cracks which cause high thermoelectric concentration. Scanning electron microscope images verified the development of cracks in the samples as annealing temperature increases. The behavior of Seebeck coefficient with the measurement temperature was also observed and explained in detail. The high value of Seebeck coefficient suggested that this material can be a potential candidate for thermoelectric power generation applications in near future.     

Cu_3N薄膜制备及其性能研究

Cu3N薄膜的晶面取向、沉积速率、电学特性等性质除与制备方法有关外,还和制备工艺参数有很大关系。溅射法制备Cu3N薄膜工艺参数主要有,混合气体(N2+Ar)中氮气分压比r、基底温度T(℃)、溅射功率P(W)。为了研究Cu3N薄膜的性能与其制备工艺参数之间关系,本文采用反应射频磁控溅射法,在玻璃基底上成功制备了Cu3N薄膜,并研究了工艺参数对其晶面取向、膜厚、电学性能、沉积速率的影响。     

Investigation of CIGS Solar Cells on Polyethylene Terephthalate Substrates

CIGS nanoparticles ink with composition of Cu (Ga_0.3 In_0.7) Se₂ was prepared by using dissolved copper, indium, gallium acetylacetonate, and Se powder in oleylamine using hot injection methods. The structural properties of the CIGS films deposited on the polyethylene terephthalate (PET) substrate were studied using an X-ray diffraction technique. The as-deposited CIGS films were found to be a chalcopyrite-type structure with crystallite grain size of about 43.8 nm. An optical study shows that the band-gap energy of the CIGS film is 1.25 eV. The flexible CIGS solar cell on a PET substrate with the best conversion efficiency of 4.21% is demonstrated.     

Effect of periodic precursor on sulfurization process of Cu2ZnSnS4 thin film

In this study, Cu₂ZnSnS₄ (CZTS) thin films were fabricated by periodically sequential depositions of metallic precursors by magnetron sputtering followed by sulfurization. The element compositions, crystal structures, and surface morphologies of the single-period precursor (Zn/Sn/Cu) and four-period precursor (Zn/Sn/Cu/Zn/Sn/Cu/Zn/Sn/Cu/Zn/Sn/Cu) during the sulfurization process were investigated. The experimental results showed that in the initial stage of sulfurization, the single-period precursor had a more efficient reaction with sulfur vapor below 300?°C because of its thicker metal layers. During the process of sulfurization, the CZTS phase first formed in the four-period film at 400?°C, owing to the wide distribution of the internal layer in the periodic thin film. With a further increase in temperature, the crystallinity of CZTS was enhanced and the secondary phases were reduced. A CZTS phase with Cu-poor and Zn-rich composition was confirmed in both thin films after complete sulfurization. The CZTS thin film with a four-period precursor showed a better degree of crystallization, and a single phase of CZTS was obtained more easily than in the single-period thin film. Therefore, using a periodic structure can promote the sulfurization reaction of Cu-Zn-Sn precursors and enhance the properties of CZTS thin films.     

A study of the oxidation behavior of CrN and CrZrN ceramic thin films prepared in a magnetron sputtering system

CrN and CrZrN ceramic thin films were produced by a planar type reactive sputtering system on glass and stainless steel substrates. We investigated oxidation resistance of CrN and CrZrN ceramic thin films with different Zr contents. The structure of the films at different thermal-annealing temperatures was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The mechanical properties of the films at different thermal-annealing temperatures were measured by nano-indentation. The results of this study showed that the addition of few amount of Zr (0.4 at%), can improve thermal stability of CrZrN ceramic thin film and increase the oxidation temperature of the film from 600 °C to 800 °C. The relatively good oxidation resistance (800 °C) and high hardness of the film with the lowest Zr content, indicates that this film is a good candidate for high temperature applications.     

Investigation of large Seebeck effect by charge mobility engineering in CuAlO2 thin films grown on Si substrate by thermal evaporation

In this research paper, we have reported giant enhancement in Seebeck coefficient of AlCuO₂ thin films by charge mobility engineering. Thin films of AlCuO₂ were grown by the evaporation of Al and Cu powder in tube furnace on Si (100) substrate. The experimental conditions were sets as; tube pressure (0.2?Torr), source to substrate distance (3?cm), evaporation temperature (1000?°C), oxygen flow rate (60?sccm) and evaporation time was (30?min). The charge mobility and diffusion of oxygen atoms were controlled by annealing the grown samples in oxygen environment at various temperatures from 600 to 800?°C with a step of 100?°C for one hour in muffle furnace. The observed giant enhancement in Seebeck coefficient (150–1050?μV/K) can be explained as; The annealing generates oxygen interstitials and causes the charge scattering mechanism shift from lattice to impurity scattering mechanism. In the impurity scattering mechanism, mobility of charge carriers increased with temperature. This increase in mobility results in the giant enhancement of Seebeck coefficient. The argument was verified by Hall data which suggested that concentration of oxygen interstitials increased by annealing temperature. To further strengthened our argument we have performed XRD and FTIR measurements. XRD data has showed that as grown sample consists of one peak at angle 32° related to (006) phase of CuAlO₂. Annealing resulted in the generation of new phases at angles 35°, 42.5° and 48.4° which were related to CuO (111), CuAlO₂ (104) and CuAlO₂ (009) respectively. FTIR spectrum verified the presence of Cu-O and Al-O at wavenumbers 450?cm^?1 and 600?cm^?1 respectively.     

Microstructures and photovoltaic performances of bismuth-ion doped Cu(In,Ga)Se2 films prepared via sputtering process

Bismuth-ion doped Cu(In,Ga)Se₂ (CIGS) solar cells were fabricated via sputtering technique. The influence of bismuth-ion doping on structural and photovoltaic characteristics of the fabricated CIGS films were explored in details. With doping of bismuth ions, the grain sizes of CIGS layers were enhanced appreciably due to liquid-phase sintering with the yielded intermediate compound. The secondary ion mass spectroscopy profile results indicated that the diffusion of bismuth ions into CIGS layers promoted dissemination of gallium species from the back contacts to the surface of CIGS layers. According to Hall measurement analysis, the carrier concentration in CIGS films was enhanced significantly with the doping of bismuth ions in the prepared films. The conversion efficiency of the bismuth-ion doped samples was increased approximately 10% in comparison with undoped samples due to the elevated gallium-ion diffusion and grain growth. Various photovoltaic parameters including saturated current and diode factors of the prepared doped CIGS solar cells were decreased owing to the inhibition of electron-hole recombination. This investigation demonstrated the improved photovoltaic performance and the structural characteristics of fabricated CIGS films after the doping of bismuth ions.     

Thermal oxidation of oxynitride films as a strategy to achieve (Sr2Ta2O7)100-x(La2Ti2O7)x based oxide perovskite films with x = 1.65

• •This study concerns STLTO compounds of the ferroelectric (Sr₂Ta₂O₇)_100-x(La₂Ti₂O₇)_x solid solution. The purpose is to produce the STLTO composition x = 1.65 as thin films by thermal oxidation of the corresponding oxynitride composition. Indeed, the combination of an STLTO oxide target with a dioxygen-rich reactive atmosphere during the sputtering deposition leads to Sr-deficient oxide thin films, shifting composition and structure from the perovskite to the tetragonal tungsten bronze type. An alternative synthesis pathway is to first deposit, under nitrogen-rich atmosphere, stoichiometric oxynitride films and produce, by thermal annealing under air, the stoichiometric oxide. For low oxidation temperatures ([550–600 °C]), samples remain intact and display an oxide character but still contain a significant amount of nitrogen, they could be described as intermediate phases containing nitrogen-nitrogen pairs as demonstrated by Raman. Dielectric characteristics of these original film materials are of interest with a tunability value of 26 % at 30 kV/cm (10 kHz).

     

Effect of Substrate Temperatures on Structural and Morphological Properties of Nano-Crystalline Silver Thin Films Grown on Silicon Substrates

The silver (Ag) thin films were deposited on silicon substrates by DC magnetron sputtering method under different substrate temperatures of 100–500?°C. Then the as-deposited films were subjected to annealing treatment. The XRD results revealed that the Ag thin films have a good nanocrystalline structure and a considerable increase in the crystallinity of Ag (111) peak was observed at substrate temperature of 200?°C. The average crystalline size of Ag films varied between 18 and 44 nm which confirms the presence of nanocrystal’s in the films. The AFM and SEM images demonstrated that the grain size and surface roughness of the films are sensitive to substrate temperature during deposition of the films and annealing treatment. The SEM results is in good agreement with the results of XRD and AFM analysis.