Electrical and optical properties of F-doped textured SnO2 films deposited by APCVD

This paper presents the structural, electrical and optical properties of transparent conducting F-doped textured SnO₂ films prepared by atmosphere pressure chemical vapour deposition (APCVD). Polycrystalline SnO₂:F films having a variable preferred orientation have been obtained with resistivity as low as 5 × 10⁻⁴ Ωcm, with carrier concentrations between 3.5 × 10²⁰ and 7 × 10²⁰ cm⁻³, and Hall mobilities from 15.7 to 20.1 cm²/V/s. The average transmittance (including diffusion transmittance) is as high as 94% in the wavelength range of the visible spectrum and the maximum infrared reflectance reaches 92% for a film 655 nm thick. The figure of merit ƒ_TC = T10/_sh, (7.12 × 10⁻² S) of these films is the highest amongst the results reported on doped SnO₂ films.     

Synthesis and characterization of CuInSe2 thin films from Cu, In and Se stacked layers using a closed graphite box

Various techniques have been used to produce CuInSe₂ but the problem of producing films with the desired properties for efficient device fabrication over large areas has always persisted. The Stacked Elemental Layer (SEL) technique has been demonstrated as a method for producing films over a large area, but the films normally annealed in vacuum or in Se ambient, mostly exhibited poor morphology with small grain sizes which result in poor devices. A method of synthesizing CuInSe₂ films by annealing or selenization of the Cu, In and Se elemental layers using a closed graphite box was developed. SEM, EDX, XRD, spectrophotometric and Hall measurements were used to characterize all annealed films. Results have shown single phase chalcopyrite films with improved crystal sizes of about 4 μm The film composition varied from Cu-rich to In-rich with electrical resistivities of 10⁻³ to 10⁴ Ωcm, cattier concentrations of 5 × 10¹⁵ to 10¹⁷ cm⁻³ and mobilities of 0.6 to 7.8 cm² V⁻¹ s⁻¹ An energy band gap of 0.99 eV and 1.02 eV was obtained for a Cu-rich and near stoichiometric In-rich films respectively. Heterojunction devices using the structure ZnO/CdS/CuInSe₂ were fabricated with electrical conversion efficiencies of 6.5%.     

Preparation and properties of transparent conducting zinc oxide and aluminium-doped zinc oxide films prepared by evaporating method

Undoped and aluminium-doped zinc oxide films have been prepared by thermal evaporation of zinc acetate [Zn(CH₃COO)₂ 2H₂O] and aluminium chloride [AlCl₃] onto a heated glass substrate. The structural and optoelectrical properties of the films have been studied. The effects of heat treatment for the as-deposited films in air and vaccum are investigated. Highly transparent films with conductivity as low as 2×10⁻³ Ω cm can be produced by controlling the deposition parameters. The electron carrier densities are in the range 0.2–7×10¹⁹ cm⁻³ with mobilities of 22–58 cm² V⁻¹ s⁻¹.     

Preparation and properties of sprayed CuGa0.5In0.5Se2 thin films

CuGa_0.5In_0.5Se₂ thin films were prepared by spray pyrolysis technique at substrate temperatures (T_s) in the range 100–400°C. The films prepared at T_s = 300–350°C were nearly stoichiometric, polycrystalline with a strong preferred (112) orientation. The resistivity of the films varied in the range, 50–1000 Ω cm and the evaluated optical band gap was 1.35 eV.     

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.     

A simple method for the determination of the optical constants, n and k of cadmium sulfide films from transmittance measurements

The dispersive refractive index n(λ) and extinction coefficient k(λ) of CdS thin films were evaluated from spectrophotometric transmittance characteristic in the visible region. A method is presented to determine n(λ) and k(λ) in the region k² n², using wavelength and transmittance values. This method has been used for the investigation of the effect of the deposition rate on the optical properties of cadmium sulfide films. The refractive indices are found to depend on the deposition rate with values between 2.48 and 2.60. The energy gap of the samples is found to be independent of deposition rate with the value 2.44 eV. The real and imaginary parts of the dielectric constant have also been evaluated.     

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.     

Temperature effect on the electrical and optical properties of indium-selenide thin-films

Indium-Selenide thin-films have been prepared by the thermal-evaporation technique at a pressure of 4.5×10⁻⁶ torr and a temperature of 673–873 K. For both the as-deposited and annealed films, (i) the electrical conductivity increased with increasing temperature and (ii) the variation of activation energy follows the island structure theory. The temperature co-efficient of resistance (T.C.R.) and Hall-effect measurements indicate that the sample is a n-type carrier. The optical spectra for both types of films were obtained in the wavelength range 0.3<λ<2.5 μm, and by comparing the magnitude of transmittance spectra, it is found that the annealed films are more transparent than the as-deposited ones in the UV and visible range. The integrated transmittance and reflectance values were obtained: the high values of T_lum and T_sol for the annealed films suggest that indium selenide may be used in selective-surface devices.     

退火气氛对Al-F共掺杂ZnO薄膜结构和光电性能的影响

用射频磁控溅射法制备了Al-F共掺杂ZnO（ZnO（Al,F））透明导电薄膜,研究了不同退火气氛对ZnO（Al,F）薄膜的结构、电学和光学特性的影响。结果表明:在真空和还原性气氛中退火后的薄膜透光率呈现"蓝移"趋势,在空气中退火处理后的薄膜透光率则表现为"红移";在真空中,400℃×60min的退火处理,使ZnO（Al,F）薄膜的电阻率降低至1.41×10^-3Ω·cm,透光率则上升到93%以上,有效提高了薄膜的光电特性;所有退火气氛下,薄膜均具有（002）单一择优取向的多晶六方纤锌矿结构;薄膜的晶粒尺寸为25～30nm。     

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.     

Briquetting of palm fibre and shell from the processing of palm nuts to palm oil

Malaysia is the major producer of palm oil in the world. It produces 8.5 million tonnes per year (8.5×10⁶ ty⁻¹) of palm oil from 38.6×10⁶ ty⁻¹ of fresh fruit bunches. Palm oil production generates large amounts of process residues such as fibre (5.4×10⁶ ty⁻¹), shell (2.3×10⁶ ty⁻¹), and empty fruit bunches (8.8×10⁶ ty⁻¹). A large fraction of the fibre and much of the shell are used as fuel to generate process steam and electricity in the palm processing mill itself. However, much is wasted by pile burning in the open air with attendant air pollution, dumped in areas adjacent to the mill, or utilized as manure in the palm oil plantation. In this paper, an attempt has been made to convert these residues into solid fuel. The palm shell and fibre is densified into briquettes of diameter 40, 50 and 60 mm under moderate pressure of 5–13.5 MPa in a hydraulic press. Experiments are carried out to determine density, durability, impact and compressive strength of the briquettes. The heating value, burning characteristics, ash and moisture content are other objects of the study. A relationship between press pressure and the briquette density has been established. The produced briquettes have densities between 1100 and 1200 kgm⁻³. The briquettes properties are quite good with good resistance to mechanical disintegration, and will withstand wetting. The gross calorific value is about 16.4 MJkg⁻¹ (maf), and the ash content is about 6% and the equilibrium moisture content is about 12%. Further work is required to acquire complete understanding of the densification process before good quality and durable briquettes could be made free from cracks.     

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.     

RPD技术生长ICO∶H薄膜及其在晶体硅异质结太阳电池中的应用

通过反应等离子体沉积(RPD)技术室温下生长掺铈的氧化铟薄膜,且沉积过程中通入氢气。高迁移率可使透明导电薄膜在较低的电阻率时保持较高的近红外透过率;透明导电薄膜中较低的载流子浓度能够减少自由载流子的吸收。迁移率的大小主要由薄膜内的散射机制决定,并且受薄膜非晶结构制约。ICO∶H薄膜表面平整,在近红外长波段透过率超过80%。在氢气流量为2 sccm时,薄膜获得1.34×10^-3Ω·cm的最低电阻率和94 cm²/Vs的高迁移率。在晶体硅异质结(SHJ)太阳电池应用中,获得了较高的短路电流密度38.44 mA/cm²,相应的转换效率为16.68%。     

Highly transparent and conductive Zn0.85Mg0.15O:Al thin films prepared by pulsed laser deposition

Zn_1−xMg_xO:Al thin films have been prepared on glass substrates by pulsed laser deposition (PLD). The effect of substrate temperature has been investigated from room temperature to 500 °C by analyzing the structural, optical and electrical properties. The best sample deposited at 250 °C shows the lowest room-temperature resistivity of 5.16×10⁻⁴ Ω cm, and optical transmittance higher than 80% in the visible region. It is observed that the optical band gap decreases from 3.92 to 3.68 eV when the substrate temperature increases from 100 to 500 °C. The probable mechanism is discussed.     

Synthesis and characterization of a highly stable amorphous silicon hydride as the product of a catalytic helium–hydrogen plasma reaction

A novel highly stable surface coating SiH(1/p) which comprised high-binding-energy hydride ions was synthesized by a microwave plasma reaction of a mixture of silane, hydrogen, and helium wherein it is proposed that He⁺ served as a catalyst with atomic hydrogen to form the highly stable hydride ions. Novel silicon hydride was identified by time of flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The ToF-SIMS identified the coatings as hydride by the large SiH⁺ peak in the positive spectrum and the dominant H⁻ in the negative spectrum. XPS identified the H content of the SiH coatings as hydride ions, H⁻(1/4), H⁻(1/9), and H⁻(1/11) corresponding to peaks at 11, 43, and 55 eV, respectively. The silicon hydride surface was remarkably stable to air as shown by XPS. The highly stable amorphous silicon hydride coating may advance the production of integrated circuits and microdevices by resisting the oxygen passivation of the surface and possibly altering the dielectric constant and band gap to increase device performance.

The plasma which formed SiH(1/p) showed a number of extraordinary features. Novel emission lines with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 were previously observed by extreme ultraviolet spectroscopy recorded on microwave discharges of helium with 2% hydrogen (Int. J. Hydrogen Energy 27 (3) 301–322). These lines matched H(1/p), fractional Rydberg states of atomic hydrogen where p is an integer, formed by a resonant nonradiative energy transfer to He⁺ acting as a catalyst. The average hydrogen atom temperature of the helium–hydrogen plasma was measured to be 180–210 eV versus ≈3 eV for pure hydrogen. Using water bath calorimetry, excess power was observed from the helium–hydrogen plasma compared to control krypton plasma. For example, for an input of 8.1 W, the total plasma power of the helium–hydrogen plasma measured by water bath calorimetry was 30.0 W corresponding to 21.9 W of excess power in 3 cm³. The excess power density and energy balance were high, 7.3 W/cm³ and −2.9×10⁴ kJ/molH₂, respectively. This catalytic plasma reaction may represent a new hydrogen energy source and a new field of hydrogen chemistry.     

Effect of the Cu underlayer on the optoelectrical properties of ITO/Cu thin films

Sn doped indium oxide (ITO) single layer films and ITO/Copper (Cu) bi-layer films were prepared on polycarbonate substrates by DC and RF magnetron sputtering without intentional substrate heating. In order to consider the influence of the Cu underlayer on the optoelectrical properties and microstructures of the films, the thickness of the Cu bottom layer in the ITO/Cu films was varied from 5 to 20 nm.Conventional ITO films had a constant optical transmittance of 74% and an electrical resistivity of 3.1 × 10⁻³ Ω cm, while ITO/Cu films had different optoelectrical properties that were influenced by the thickness of the Cu bottom layer. The lowest electrical resistivity, 5.7 × 10⁻⁵ Ω cm, was obtained from ITO 80 nm/Cu 20 nm films and the highest optical transmittance of 72%, was obtained from the ITO 95 nm/Cu 5 nm films. From the figure of merit (_TC) which is defined by _TC = T¹⁰/R_s, where T is the optical transmittance at 550 nm and R_s is the sheet resistance, it can be concluded that the most effective Cu thickness in the ITO/Cu films on the optoelectrical properties was 5 nm.     

A simple analytical treatment of edge-illuminated VMJ silicon solar cells

The series connected silicon vertical multi-junctions (VMJs) solar cells have been suggested as means for ensuring high voltage high efficiency solar cells. This study includes a review of some previously published work concerning the edge-illuminated VMJs solar cells. We introduce a simple one-dimensional analysis to study the high voltage series connected silicon VMJs solar cells. The cell, under study, consists of 40 VMJs. Each junction (unit cell) has dimensions of 250 μm × 0.78 cm × 500 μm. We calculate the short circuit current, the open circuit voltage and the efficiency for an ideal cell, having perfect carrier collection at short circuit conditions, and for real cells. An optimization with respect to the base doping, the emitter doping, the surface recombination velocity and the number of junctions is done for the real cell. A conversion efficiency of 20% has been calculated under AM1.5 light spectrum for real cells having a base doping of 10¹⁶ cm⁻³ and an emitter doping of 10¹⁷ cm⁻³.     

Effect of temperature dependence of electrical resistivity on the cooling performance of a single thermoelectric element

The coefficients of performance (COP) φ₀ and φ for a single thermoelectric (TE) element welded with two metal plates were calculated as functions of temperature difference (ΔT) and thermoelectric figure of merit (ZT) from the conventional thermal rate equations and the new thermal rate ones proposed here, respectively. We made an attempt to take the differences in the Seebeck coefficient , electrical resistivity ρ and thermal conductivity κ of TE materials at the hot and cold sides of a TE element into the thermal rate equations on the assumption that their TE properties change linearly with temperature. However, the difference in κ was neglected even in the new thermal rate equations because its temperature dependence was too small when φ was applied to the high-performance Bi–Te alloys. The normalized temperature dependences at 300 K of and ρ were denoted by A and B, respectively. The term of A in the thermal rate equations was canceled out by the Thomson coefficient, but that of B remained. When B > 0 K⁻¹, φ/φ₀ is enhanced more significantly with an increase of B at larger ΔT and lower ZT, and it reached about 1.20 at ΔT = 80 K for Bi–Te alloys with B ≈ 5 × 10⁻³ K⁻¹. It was thus found that the COP of a cooling module is also affected strongly by B as well as ZT.     

Large area CIGS2 thin film solar cells on foils: nucleus of a pilot plant

In earlier research, conversion efficiency of 10.4% (AM1.5) and 9.9% (AM0) has been achieved on small area CuIn_xGa_1−xS₂ (CIGS2) solar cell on 127 μm thick stainless steel substrate. The area of research is mainly focused on studying CIGS2 thin films as solar cell absorber material and growing high efficiency cells on ultralightweight and flexible metallic foils such as 127 μm thick stainless steel and SiO₂ coated 25 μm thick Ti foils. This paper presents the scaling up process of CIGS2 thin film substrate from 2.5 × 2.5 cm² to 10 × 10 cm². Initial scaling up efforts focused on achieving uniform thickness and stress-free films. Process of scaling up consisted of refurbishment of selenization/sulfurization furnace, design and fabrication of scrubber and enlargement of new CdS deposition setup. The scaling up from 2.5 × 2.5 cm² to 10 × 10 cm² substrate size has laid the foundation for PV Materials Lab of Florida Solar Energy Center becoming the nucleus of a pilot plant.     

Synthesis of CuInS2 films by sulphurization of Cu/In stacked elemental layers

CuInS₂ films were synthesized by sulphurization of In/Cu stacked elemental layers (SEL) deposited onto glass and Mo-coated glass substrates by graphite box annealing at temperatures of 620–880 K. The films thus synthesized were characterized by measuring electrical, optical, microstructural and photoluminescence properties. The microstructure and hence the physical properties of the films depended critically on the amount of sulphur incorporation. Nature of charge carriers depended on both Cu/In and S/(Cu+In) ratio and the carrier concentration varied between 10¹⁴ and 10¹⁸ cm⁻³. Grain boundary scattering effects were critically studied by measuring the electrical conductivity and Hall mobility simultaneously on the same sample. The shape of the grains depended critically on the sulphur content. The PL spectra were dominated by the excitonic peak 788 nm followed by another peak at 892 nm which may be ascribed to the DA transition.