Characterization of Cu(InxGa1−x)2Se3.5 thin films prepared by rf sputtering

Cu(In_xGa_1−x)₂Se_3.5 thin films were fabricated by rf sputtering from CuIn_xGa_1−xSe₂ and Na mixture target by controlling the mixture ratio. X-ray diffraction analyses show that the structure of Cu(In_xGa_1−x)₂Se_3.5, thin films is different from chalcopyrite structure: especially, CuIn₂Se_3.5 thin films have a defect chalcopyrite structure. The lattice parameters for Cu(In_xGa_1−x)₂Se_3.5 thin film are slightly smaller than those for CuIn_xGa_1−xSe₂ thin film and linearly decreased with increasing Ga content. The optical absorption coefficients for Cu(In_xGa_1−x)₂Se_3.5, thin films exceed 2 × 10⁴ cm⁻¹ in energy region above the fundamental band edge. The band gap for Cu(In_xGa_1−x)₂Se_3.5 thin films is larger than that for CuIn.Ga_1−x2Se₂ with the same Ga content and increased with increasing Ga content.     

Stability of Cu(In,Ga)Se2 solar cells and evaluation by C–V characteristics

To confirm the long-term reliability of Cu(In,Ga)Se₂, (CIGS) solar cells, we investigated the I–V and C–V characteristics during tests under irradiation or dark condition. Under irradiation, the test samples showed a little increase in efficiency (η) and open-circuit voltage (V_oc) which showed their electrical durability to light irradiation. But the diode factor (n) and series resistance (R_s) showed large changes in value. Also, the built-in voltage (V_b) and density gradient (dN_A/d_x) in the CIGS layer calculated from the C–V characteristics showed distinct changes during the test. After 4 SUN irradiation, two samples in the same fabrication-lot showed new light absorption in the lower-energy range than sun the energy gap of CIGS. We explain the change of C–V characteristics for the samples under strong irradiation with a new model named “Junction retrograde” which can treat defect generation by irradiation to reduce the acceptor density in graded p-n junction. This model for C–V analysis can be used to investigate the long-term reliability of CIGS solar cells under irradiation.     

Electrical properties of CuInSe2 films prepared by evaporation of Cu2Se and In2Se3 compounds

We prepared CuInSe₂ films by evaporating In₂Se₃ and Cu₂Se compounds instead of elemental sources. The resulting CuInSe₂ film grown at 680°C had a smooth and dense microstructure with the grain size of 2 3 μm. But the CuInSe₂ films were Cu-rich, with a low resistivity of about 0.1 Ω cm. So we conducted H₂ post annealing to control the electrical resistivity and composition of CuInSe₂ films. In a H₂ atmosphere, the resistivity increased to about 100 Ω cm by annealing at 350°C for 1 h. The resistivity decreased again when the annealing temperature was above 350°C. This resistivity change might be related to the contents of Cu, In, Se atoms and the valency states of Cu and In ions in the films. We discussed the reason of resistivity change caused by H₂ post annealing in this paper.     

Importance of the band gap energy and flat band potential for application of modified TiO2 photoanodes in water photolysis

The influence on water photolysis of two important parameters of the electronic structure of photocatalytic semiconductors: the forbidden band gap, E_g, that decides about the absorption spectrum and the flat band potential, V_Fb, that affects the recombination probability, was studied. The photoelectrochemical experiments were performed in a three-electrode cell PEC with a TiO₂ thin film photoanode immersed in liquid electrolyte of variable pH. Titanium dioxide photoanodes doped with chromium (up to 16 at.%) and tin (up to 50 at.%) were prepared by rf reactive sputtering. Different methods of flat band potential determination: Mott–Schottky plots and photocurrent versus voltage characteristics were used. The energy band gap was derived from the spectrophotometric measurements of optical transmittance and reflectance coefficients of thin films. For TiO₂ + 7.6 at.% Cr high and negative flat band potential V_Fb = −0.72 eV (at pH 4) has been found but the recombination time τ = 8 s was the shortest of all TiO₂ modifications. Despite additional absorption feature at about 2.8 eV, i.e., at wavelength corresponding to visible range of the light spectrum, the photoconversion efficiency of TiO₂ + 7.6 at.% Cr was found to be much smaller (η_c = 0.1%) than that of undoped TiO₂ (η_c = 1.8%) and TiO₂ doped with 8 at.% of Sn (η_c = 1.0%).     

Cadmium telluride films prepared by pulsed electrodeposition

Cadmium telluride polycrystalline films were deposited on various transparent semiconductors on glass using periodic pulse electrolysis from an aqueous solution of Cd²⁺ and HTeO₂⁺ ions. Substrates included fluorine doped tin oxide/glass, tin oxide/indium tin oxide/glass and on those substrates with an electrodeposited cadmium sulphide film on the oxide. The properties of the deposited films were determined as a function of variables, viz. initial cathodic voltage V₁, on-time t₁, second cathodic voltage V₂, on-time t₂, solution concentration and type of substrate. Film quality was judged by adherence, continuity, optical quality, composition and morphology. The preferred deposition conditions (versus SCE) were V₁ = −0.76 V, t₁ = 1 s, V₂ = −0.60 V, t₂ = 0.1 s using a stirred 90°C solution with composition 2.5 M Cd²⁺, 160 ppm HTeO₂⁺ and pH of 1.7. Films deposited under those conditions were cubic polycrystals. X-ray diffraction spectra showed reflections from the (111) (220) and (311) planes with the most intense being the (111) reflection. As the concentration of species in the solution decreased, the reflection intensities from the (220) and (311) planes decreased relative to the (111) reflection. After annealing under conditions to type convert the n-CdTe to p-CdTe, the crystallinity improved and if a CdS layer was present, the (220) and (311) planes were further developed relative to the (111) plane. Resistivity through the film was (3.0±0.8)×10⁸) Ω cm but reduced to (1.0±0.3) × 10³ Ω cm after annealing. The band gap was 1.48±0.03 eV for both deposited and annealed films. There was a limited range over which the deposition variables could be altered. The pulse duration for the more cathodic phase needed to be longer than the less cathodic phase for adherent films. Better adherence was achieved when pulse durations were greater than 0.1 s, especially for the more cathodic phase. The magnitude of the pulse duration and potential in each phase of a particular cycle determined whether the deposited film was rich or deficient in cadmium and whether the film adhered.     

Porous TiO2 thin films synthesized by a spray pyrolysis deposition (SPD) technique and their application to dye-sensitized solar cells

Titanium dioxide (TiO₂) thin films were synthesized on glass substrates from titanium(IV)oxy acetylacetonate 2-butanol solution by a spray pyrolysis deposition (SPD) technique. The films consisted of TiO₂ leaflets and showed the oriented growth along the (2 0 0) direction. The surface area of the film was successfully increased by adding a small amount of aluminum(III) acetylacetonate (AA) in the source solution. This is because AA sublimates easily during the film formation to leave many pores within the film. A dye-sensitized solar cell was constructed with the TiO₂ film which was deposited on the fluorine-doped tin(IV) oxide layer by the SPD technique. The conversion efficiency of the cell was effectively enhanced as high as 3.2% at AA content of 0.6 at% in the source solution, attributing to the fact that the amount of a dye anchored on the surface of TiO₂ layer was the highest at this AA content. Although the conversion efficiency is relatively low, this finding leads to the possibility of an industrial production of a dye-sensitized solar cell in the near future.     

Physicochemical properties and photocatalytic hydrogen evolution of TiO2 films prepared by sol–gel processes

Anatase TiO₂ films were obtained on glass substrates using a sol–gel method using titanium isopropoxide as a precursor. The thickness of the film was about 140 nm for one coating, and the thickness is controlled by the number of coating cycles. The spectra of UV-VIS absorption indicated that the absorption edge of the TiO₂ films is ca. 385 nm, corresponding to the band gap energy of 3.20 eV. We obtained TiO₂ films having a high activity for the hydrogen evolution from photocatalytic water cleavage. By loading with 0.3 wt% Pt rate of hydrogen production increases. No influence of film thickness and calcination temperature on the photocatalytic property is observed.     

Synthesis and characterization of rough electrochromic phosphotungstic acid films obtained by spray-gel process

Rough electrochromic phosphotungstic acid (PWA) films were fabricated by spraying a gel of phosphotungstate anions with a molar ratio of P:W=1:12 onto glass substrates. The substrates were coated with transparent and electrically conducting SnO₂:F at 300°C. Analysis by X-ray photoelectron spectroscopy determined that the P:W molar ratio in the films was approximately 1:14. Infrared spectroscopy and X-ray diffraction showed that the film is a form of polycrystalline phosphotungstic acid. SEM micrographs showed that the films have a rough morphology based on fiber-shape bridges. Optoelectrochemical measurements demonstrated pronounced electrochromism in the PWA films upon H⁺ intercalation/deintercalation with a high diffuse reflectance (R_d) and transmittance (T_d). We found for as-deposited films that R_d/total reflectance (R_t) and T_d/total transmittance (T_t) at 550 nm was around 0.83 and 0.68, respectively. This ratio decreases at bleached state to 0.74 and 0.41 for R_d/R_t and T_d/T_t, respectively.     

Cdln2O4膜红外性质分析

利用射频反应溅射Cd-In合金靶沉积的CdIn_2O_4薄膜是n型高兼并半导体,其红外反射率随溅射气体中氧浓度的不同而有异,相同氧浓度下沉积的薄膜经过退火处理后红外反射率也会发生变化。原因是不同氧浓度下沉积薄膜的氧空位不同,其自由载流子浓度也就不同,从而使薄膜有不同的吸收系数。实验结果与理论计算值符合较好。     

Optical and electrochemical characteristics of niobium oxide films prepared by sol-gel process and magnetron sputtering A comparison

Electrochromic niobia (Nb₂0₅) coatings were prepared by the sot-gel spin-coating and d.c. magnetron sputtering techniques. Parameters were investigated for the process fabrication of sol-gel spin coated Nb₂0₅ films exhibiting high coloration efficiency comparable with that d.c. magnetron sputtered niobia films. X-ray diffraction studies (XRD) showed that the sot-gel deposited and magnetron sputtered films heat treated at temperatures below 450°C, were amorphous, whereas those heat treated at higher temperatures were slightly crystalline. X-ray photoelectron spectroscopy (XPS) studies showed that the stoichiometry of the films was Nb₂0₅. The refractive index and electrochromic coloration were found to depend on the preparation technique. Both films showed low absorption and high transparency in the visible range. We found that the n, k values of the sot-gel deposited films to be lower than for the sputtered films. The n and k values were n = 1.82 and k = 3 × 10⁻³, and n = 2.28 and K = 4 × 10⁻³ at 530 urn for sot-gel deposited and sputtered films, respectively. The electrochemical behavior and structural changes were investigated in 1 M LiC10₄/propylene carbonate solution. Using the electrochemical measurements and X-ray photoelectron spectroscopy, the probable electrode reaction with the lithiation and delithiation is Nb₂O₅ + x Li⁺ + x e⁻ ↔ Li_xNb₂0₅. Cyclic voltametric (CV) measurements showed that both Nb₂0₅ films exhibits electrochemical reversibility beyond 1200 cycles without change in performance. “In situ” optical measurement revealed that those films exhibit an electrochromic effect in the spectral range 300 < λ < 2100 nm but remain unchanged in the infrared spectral range. The change in visible transmittance was 40% for 250 nm thick electrodes. Spectroelectrochemical measurements showed that spin coated films were essentially electrochemically equivalent to those prepared by d.c. magnetron sputter deposition.     

The dependence of anti-corrosion behaviors of iron sulfide films on different reactants

As the product of hydrogen sulfide corrosion, iron sulfide compound can be used as hydrogen permeation barrier. In this study, chemical vapor deposition was used to synthesize iron sulfide films on the surface of X80 steel with different sulfur sources, and the effects of different sulfur sources on the products were studied. The film was characterized by its morphology, composition and performance. The results show that the hydrogen resistance of our product and the bonding degree between the substrate and the film are strongly relevant with the compactness of the films. When we used TBDS as sulfur source, the highest impendance and the smallest hydrogen permeation current (0.53 μA/cm²) was obtained, which is due to the better adhesion and dense structure compare to the other two sulfur sourses.     

Preparation of Culn(SxSe1−x)2 thin films by sulfurization and selenization

A CuIn(S_xSe_1−x)₂ alloy thin-film was prepared by selenization of CuInS₂: its composition ratio x can be controlled by the number of selenization cycles implemented. Crystallinity of the films was improved by annealing in vacuum. The resistivity of the film was about 1 Ω cm and increased by one to two orders of magnitude after KCN treatment. An 8.1 % efficiency solar cell was obtained by using this annealed alloy thin-film.     

CuInSe2 thin film preparation through a new selenisation process using chemical bath deposited selenium

Copper indium selenide thin films were prepared through a novel and an eco-friendly selenisation process. In this method, selenium film required for selenisation was prepared using chemical bath deposition technique, at room temperature. Thus, totally avoided usage of highly toxic H₂Se or selenium vapour. Here, the process involved annealing the Stacked layer, Se/In/Cu in which Cu and In were deposited using vacuum evaporation technique. Investigations on the solid-state reaction between the layers were done by analysing structural and optical properties of films formed at different annealing temperatures. Optimum annealing condition for the formation of copper indium selenide thin film was found to be 673 K for 1 h in high vacuum. Compositional dependence of the growth process was also studied using various Cu/In ratios. Optical band gap was decreased with increase in Cu/In ratio. Carrier concentration and hence conductivity were found to be increased with increase in Cu/In ratio. The films obtained were p-type and highly Cu-rich films were degenerate.     

Electrochromic Devices Incorporating Cr Oxide And Ni Oxide Films:: A Comparison

Transparent films of Cr oxide and Ni oxide were made by reactive DC magnetron sputtering in Ar+O₂+H₂. They displayed anodic electrochromism with charge capacities similar to that of W oxide. Cr oxide was stable in acidic environments, while Ni oxide was stable in basic environments. Electrochromic devices were made with pristine Cr oxide or Ni oxide films operating in conjunction with W oxide and a proton conducting electrolyte. Of the two oxides, Cr oxide film allowed device operation at a lower voltage span, while the device with Ni oxide film yielded a higher transmittance in the bleached state, a larger absorptance modulation, and a more neutral color.     

Formation of CuInSe2 and Cu(In,Ga)Se2 films by electrodeposition and vacuum annealing treatment

Polycrystalline thin films of CuInSe₂ and Cu(In,Ga)Se₂ (CIGS) were grown on both polished Mo substrates and Mo-coated glass substrates by one-step electrodeposition. All the as-deposited films have been annealed in vacuum at 450°C for a short time to improve the crystalline properties. The films have been characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The results indicate that the crystallization of the films was greatly improved after annealing. Further more, a CIGS film with 23 at% Ga was obtained.     

Low temperature μc-Si film growth using a CaF2 seed layer

This paper describes low temperature thin film Si growth by remote plasma chemical vapor deposition system for photovoltaic device applications. Using CaF₂/glass substrate, we were able to achieve an improved μc-Si film at a low process temperature of 300°C. The μc-Si film on CaF₂/glass substrate shows that a crystalline volume fraction of 65% and dark conductivity of 1.65×10⁻⁸ S/cm with the growth conditions of 50 W, 300°C, 88 mTorr, and SiH₄/H₂=1.2%. XRD analysis on μc-Si/CaF₂/glass showed crystalline film growth in (1 1 1) and (2 2 0) planes. Grain size was enlarged as large as 700 Å for a μc-Si/CaF₂/glass structure. Activation energy of μc-Si film was given as 0.49 eV. The μc-Si films exhibited dark- and photo-conductivity ratio of 124.     

Thin film of CeO2-SiO2: a new ion storage layer for smart windows

Thin solid films of CeO₂-SiO₂, used as a counter-electrode layer in electrochromic devices, were prepared by the sol–gel dip coating, using an aqueous-based process. The influence of the SiO₂ addition on electrochemistry of the CeO₂ oxide coatings was determined by chronoamperometric measurements. The films exhibit a larger charge storage capacity, which was determined as a function of the coatings thickness. The peak occurrence in the chronoamperometric curve during the deintercalation of lithium ions in the cerium/silicon films is analyzed in terms of trapping energy levels for Li⁺ ions into the film.

In situ UV–Vis spectroelectrochemical measurements of the CeO₂-SiO₂ coatings indicated that the films remained transparent in the visible spectral range during the intercalation process. Powders were characterized by X-ray diffraction after the same thermal treatment of the films, indicating a decrease of crystallinity with the doping. The feasibility for use of these electrodes as ion storage for electrochromic devices was investigated.     

锑基硫属化合物半导体及太阳电池

锑基硫属化合物是一类性质稳定、环境友好、元素含量丰富、带隙连续可调、光电性质优异的半导体材料,包括硒化锑（Sb₂Se₃）、硫化锑（Sb₂S₃）以及硒硫化锑[Sb₂(S,Se)₃]等。其中,Sb₂(S,Se)₃的带隙和太阳光谱的匹配度较高,比较适合作为太阳电池的光吸收层材料。以Sb₂(S,Se)₃为光吸收层的太阳电池取得了10% 的认证能量转换效率,显示了锑基硫属化合物太阳电池的巨大潜力。本文详细阐述了锑基硫属化合物的材料及光电特性、薄膜制备工艺及缺陷特性。结合近年来锑基硫属化合物太阳电池的研究进展,提出进一步提高锑基硫属化合物太阳电池性能的方向和策略。     

The dependence of the chemical potential of WO3 films on hydrogen insertion

Knowledge of the chemical potential of electrochromic films coloured by hydrogen is important for matching the elements of an electrochromic device, for understanding the colouring mechanism and for obtaining information about the microscopic structure of the film. The dependence of the chemical potential on the hydrogen concentration was measured electrochemically for tungsten oxide films of different crystallinity and water content. A new method for determining the chemical potential by catalytic coloration by hydrogen gas is introduced. It revealed that the increase in electromotive force with increasing crystallinity is due only to different binding energies of the protons. We expect the protons to be located in the centres of hexagons, which are created by WO₆ octahedra. According to our model, amorphous sputtered films show a hexagonal structure which is similar to that of evaporated films, but the hexagons are connected, leading to more hexagon centre sites, which increases the electromotive force.     

空气中制备NiOx基钙钛矿太阳能电池和光电探测器

钙钛矿材料可通过溶液法制备,但也易受溶剂氛围影响,导致膜的质量和可重复性降低。开发空气中高质量钙钛矿膜的制备工艺,可以大幅降低成本和提升钙钛矿材料的应用价值。深入研究空气中水汽对中间相和成膜过程的影响,有助于指导空气中的制备工艺参数。有水存在时,PbI₂-DMSO中间相上的DMSO更容易脱去,导致由配位更多DMSO的中间相向配位更少DMSO的中间相转变;同时,有水存在时更容易生成大尺寸的MA₂Pb₃I₈?2DMSO中间相,不利于形成致密的钙钛矿膜。本文主要简述在空气中分别采用“预成核”法和“气-液-固”法制备高质量钙钛矿薄膜,用于钙钛矿太阳能电池和窄带光电探测器。