Solid-phase crystallization of amorphous silicon on ZnO:Al for thin-film solar cells

The suitability of ZnO:Al thin films for polycrystalline silicon (poly-Si) thin-film solar cell fabrication was investigated. The electrical and optical properties of 700 -nm-thick ZnO:Al films on glass were analyzed after typical annealing steps occurring during poly-Si film preparation. If the ZnO:Al layer is covered by a 30 nm thin silicon film, the initial sheet resistance of ZnO:Al drops from 4.2 to 2.2 Ω after 22 h annealing at 600 °C and only slightly increases for a 200 s heat treatment at 900 °C. A thin-film solar cell concept consisting of poly-Si films on ZnO:Al coated glass is introduced. First solar cell results will be presented using absorber layers either prepared by solid-phase crystallization (SPC) or by direct deposition at 600 °C.     

Electrochemical performance of amorphous-silicon thin films for lithium rechargeable batteries

The effect of deposition temperature and film thickness on the electrochemical performance of amorphous-Si thin films deposited on a copper foil is studied. The electrochemical properties show optimum conditions at 200 °C deposition, and thinner films exhibit superior electrochemical performance than thicker ones. A film of 200 nm Si deposited at 200 °C exhibits excellent cycleability with a specific capacity of ∼3000 mAh g⁻¹. This is probably due to optimization between the strong adhesion by Si/Cu interdiffusion and the film stress.     

Deposition of ZrO2 film by liquid phase deposition

In this study, undoped ZrO₂ thin films were deposited on single-crystal silicon substrates using liquid phase deposition. The undoped films were formed by hydrolysis of zirconium sulfate (Zr(SO₄)₂·4H₂O) in the presence of H₂O. A continuous oxide film was obtained by controlling adequate (NH₄)₂S₂O₈ concentration. The deposited films were characterized by SEM, FT-IR, XRD and DTA. Typically, the films showed excellent adhesion to the substrate with uniform particle diameter about 150 nm. The thicknesses of ZrO₂ film were about 200 nm after 10 h deposition at 30 °C. These films shows single tetragonal phase after heat treated at 600 °C. High annealing temperature (e.g. 750 °C) may result in the phase transformation of (t)-ZrO₂ into (m)-ZrO₂.     

Electrical,optical, and structural characterization of arsenic–tin oxidized transparent conducting films

A comprehensive structural, optical, electrical, and optoelectronic study of arsenic-doped SnO₂ was conducted. Several arsenic-doped SnO₂ thin films with different arsenic content have been prepared on glass and silicon substrates by a vacuum thermal evaporation technique. The structural, electrical and optical study show that some of As⁵⁺ ions occupied locations in interstitial positions of SnO₂ lattice. The prepared oxidized pure tin film is found to be consisting of orthorhombic and tetragonal SnO₂ structure. The optical properties show that arsenic-doped SnO₂ films are good transparent oxides. The bandgap of arsenic-doped SnO₂ varies with arsenic content following the Moss–Burstein rule. The electrical behaviors show that the prepared arsenic-doped SnO₂ films are degenerate semiconductors and might transform into insulators with increasing arsenic doping level. The electrical properties (resistivity, mobility, and carrier concentration) vary depending on the arsenic doping level. The SnO₂ film doped with wt. 0.6% arsenic shows utmost dc electrical conductivity parameters: resistivity of 4.6 × 10^?2 Ω cm, mobility of 6.0 cm²/V s, and carrier concentration of 2.25 × 10¹⁹ cm^?3. From transparent-conducting-oxide (TCO) point of view, low arsenic concentration (less that 1%) is effective for SnO₂ donor doping but not emulate doping with other dopant like Sb.     

Nanocrystalline tin oxides and nickel oxide film anodes for Li-ion batteries

Tin oxides and nickel oxide thin film anodes have been fabricated for the first time by vacuum thermal evaporation of metallic tin or nickel, and subsequent thermal oxidation in air or oxygen ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements showed that the prepared films are of nanocrystalline structure with the average particle size <100 nm. The electrochemical properties of these film electrodes were examined by galvanostatic cycling measurements and cyclic voltammetry. The composition and electrochemical properties of SnO_x (1<x<2) films strongly depend on the oxidation temperature. The reversible capacities of SnO and SnO₂ films electrodes reached 825 and 760 mAh g⁻¹, respectively, at the current density of 10 μA cm⁻² between 0.10 and 1.30 V. The SnO_x film fabricated at an oxidation temperature of 600 °C exhibited better electrochemical performance than SnO or SnO₂ film electrode. Nanocrystalline NiO thin film prepared at a temperature of 600 °C can deliver a reversible capacity of 680 mAh g⁻¹ at 10 μA cm⁻² in the voltage range 0.01–3.0 V and good cyclability up to 100 cycles.     

A thin film silicon anode for Li-ion batteries having a very large specific capacity and long cycle life

A thin film of Si was vacuum-deposited onto a 30 μm thick Ni foil from a source of n-type of Si, the film thickness examined being 200–1500 Å. Li insertion/extraction evaluation was performed mainly with cyclic voltammetry (CV) and constant current charge/discharge cycling in propylene carbonate (PC) containing 1 M LiClO₄ at ambient temperature. The cycleability and the Li accommodation capacity were found to depend on the film thickness. Thinner films gave larger accommodation capacity. A 500 Å thick Si film gave a charge capacity over 3500 mAh g⁻¹ being maintained during 200 cycles under 2 C charge/discharge rate, while a 1500 Å film revealed around 2200 mAh g⁻¹ during 200 cycles under 1 C rate. The initial charge loss could not be ignored but it could be reduced by controlling the deposition conditions.     

Screen-printed thin YSZ films used as electrolytes for solid oxide fuel cells

A thin yttria-stabilized zirconia (8 mol% YSZ) film was successfully fabricated on a NiO-YSZ anode substrate by a screen-printing technique. The scanning electron microscope (SEM) results suggested that the YSZ film thickness was about 31 μm after sintering at 1400 °C for 4 h in air. A 60 wt% La_0.7Sr_0.3MnO₃ + 40 wt% YSZ was screen-printed onto the YSZ film surface as cathode. A single cell was tested from 650 to 850 °C using hydrogen as fuel and ambient air as oxidant, which showed an open circuit voltage (OCV) of 1.02 V and a maximum power density of 1.30 W cm⁻² at 850 °C. The OCV was higher than 1.0 V, which suggested that the YSZ film was quite dense and that the fuel gas leakage through the YSZ film was negligible. Screen-printing can be a promising method for manufacturing YSZ films for solid oxide fuel cells (SOFCs).     

Effect of annealing temperature on electrochemical performance of thin-film LiMn2O4 cathode

Spinel LiMn₂O₄ thin-film cathodes were obtained by spin-coating the chitosan-containing precursor solution on a Pt-coated silicon substrate followed by a two-stage heat-treatment procedure. The LiMn₂O₄ film calcined at 700 °C for 1 h showed the highest Li-ion diffusion coefficient, 1.55 × 10⁻¹² cm² s⁻¹ (PSCA measurement) among all calcined films. It is attributed to the larger interstitial space and better crystal perfection of LiMn₂O₄ film calcined at 700 °C for 1 h. Consequently, the 700 °C-calcined LiMn₂O₄ film exhibited the best rate performance in comparison with the ones calcined at other temperatures.     

Electrodeposited tin selenide thin films for photovoltaic applications

Tin selenide thin films of about 300 nm thickness were electrodeposited on SnO₂:F coated transparent conductive oxide glass substrates. The optimum deposition potential was determined from cyclic voltammetry measurements. The films were polycrystalline with orthorhombic structure and the grain size was about 18 nm. SEM images showed a highly porous film structure. The band gap estimated from optical spectra of these films showed absorption due to direct transition occurring at 1.1 eV. Characteristic vibrational modes of the SnSe were observed in the Raman spectrum. The films are p-type, photosensitive, and the conductivity measured in dark was in the range of 10^?5 Ω^?1 cm^?1. A prototype CdS/SnSe photovoltaic device showed an open circuit voltage of 140 mV and short circuit current density 0.7 mA/cm².     

Cyclic voltammetric studies of the effects of time and temperature on the capacitance of electrochemically deposited nickel hydroxide

A cyclic voltammetric (CV) technique was used to study the combined effects of annealing temperature and time on the pseudocapacitance of thermally treated electroprecipitated nickel hydroxide thin films. Through the analysis of the areas of the CVs cycled between 0 and 0.35 V (versus Ag/AgCl) it is shown that the optimal treatment condition for maximum film capacitance occurs at 300°C for 3 h. On the other hand, using the anodic and cathodic peak currents of the CVs cycled between 0 and 0.5 V (versus Ag/AgCl), the maximum film capacitance is also shown to occur at a thermal treatment condition of 300°C and 3.5 h (or 320°C and 3.2 h for linear approximations). The two methods demonstrate simple ways of extracting useful information on the electrochemical performance properties of thin films.     

Lithium cobalt oxide cathode film prepared by rf sputtering

Thin films of LiCoO₂ prepared by radio frequency magnetron sputtering on Pt-coated silicon are investigated under various deposited parameters such as working pressure, gas flow rate of Ar to O₂, and heat-treatment temperature. The as-deposited film was a nanocrystalline structure with (1 0 4) preferred orientation. After annealing at 500–700 °C, single-phase LiCoO₂ is obtained when the film is originally deposited under an oxygen partial pressure (P_O2) from 5 to 10 mTorr. When the sputtering process is performed outside these P_O2 values, a second phase of Co₃O₄ is formed in addition to the HT-LiCoO₂ phase. The degree of crystallization of the LiCoO₂ films is strongly affected by the annealing temperature; a higher temperature enhances the crystallization of the deposited LiCoO₂ film. The grain sizes of LiCoO₂ films annealed at 500, 600 and 700 °C are about 60, 95, and 125 nm, respectively. Cyclic voltammograms display well-defined redox peaks. LiCoO₂ films deposited by rf sputtering are electrochemically active. The first discharge capacity of thin LiCoO₂ films annealed at 500, 600 and 700 °C is about 41.77, 50.62 and 61.16 μAh/(cm² μm), respectively. The corresponding 50th discharge capacities are 58.1, 72.2 and 74.9% of the first discharge capacity.     

Optoelectronic properties of chemically deposited Bi2S3 thin films and the photovoltaic performance of Bi2S3/P3OT solar cells

Thin films of bismuth sulfide (Bi₂S₃), prepared on conductive tin-doped indium oxide (ITO)-glass substrates by chemical deposition showed a variation of optical band gap with thickness: 1.8 eV for a 50 nm film (deposited at 40 °C for 30 min) to 1.5 eV for a 200 nm film deposited for 2 h. The electronegativity for Bi₂S₃ compound is 5.3 eV, as estimated from the ionization energy and electron affinity of elemental Bi and S, and thus the electron affinity of chemically deposited Bi₂S₃ film was deduced to be 4.5 eV. In the energy level analysis of ITO/Bi₂S₃/P3OT/Au structure, Bi₂S₃ was established as an electron acceptor. To produce ITO/Bi₂S₃/P3OT/Au solar cell structures, poly3-octylthiophene (P3OT), prepared in the laboratory was dissolved in toluene and was drop-cast on the Bi₂S₃ film and a gold film was thermally evaporated. Under 100 mW/cm² tungsten-halogen irradiation incident from the ITO-side, the cell using a Bi₂S₃ film with thickness of 50 nm has the highest open circuit voltage (V_oc) of 440 mV and short-circuit current density (J_sc) of 0.022 mA/cm². The addition of a CdS thin film (90 nm) between ITO and B₂S₃ would increase V_oc to 480 mV, and J_sc to 0.035 mA/cm². The role of surface morphology and optoelectronic properties of the Bi₂S₃ film in the photovoltaic performance of the junction is discussed.     

Preparation of Cu2ZnSnS4 thin films by sulfurizing electroplated precursors

Cu₂ZnSnS₄ (CZTS) thin films were prepared by sulfurizing precursors deposited by electroplating. The precursors (Cu/Sn/Zn stacked layers) were deposited by electroplating sequentially onto Mo-coated glass substrates. Aqueous solutions containing copper sulfate for Cu plating, tin sulfate for Sn plating and zinc sulfate for Zn plating were used as the electrolytes. The precursors were sulfurized by annealing with sulfur at temperatures of 300, 400, 500 and 600 °C in an N₂ gas atmosphere. The X-ray diffraction peaks attributable to CZTS were detected in thin films sulfurized at temperatures above 400 °C. A photovoltaic cell using a CZTS thin film produced by sulfurizing an electroplated Sn-rich precursor at 600 °C exhibited an open-circuit voltage of 262 mV, a short-circuit current of 9.85 mA/cm² and an efficiency of 0.98%.     

A novel Al and Y codoped ZnO/n-Si heterojunction solar cells fabricated by pulsed laser deposition

Al and Y codoped ZnO (AZOY) transparent conducting oxide (TCO) thin films were first deposited on n-Si substrates by pulsed laser deposition (PLD) to form AZOY/n-Si heterojunction solar cells. However, the properties of the AZOY emitter layers are critical to the performance of AZOY/n-Si heterojunction solar cells. To estimate the properties of AZOY thin films, films deposited on glass substrates with various substrate temperatures (T_s) were analyzed. Based on the experimental results, optimal electrical properties (resistivity of 2.8 ± 0.14 × 10^?4 Ω cm, carrier mobility of 27.5 ± 0.55 cm²/Vs, and carrier concentration of 8.0 ± 0.24 × 10²⁰ cm^?3) of the AZOY thin films can be achieved at a T_s of 400 °C, and a high optical transmittance of AZOY is estimated to be >80% (with glass substrate) in the visible region under the same T_s. For the AZOY/n-Si heterojunction solar cells, the AZOY thin films acted not only as an emitter layer material, but also as an anti-reflected coating thin film. Thus, a notably high short-circuit current density (J_sc) of 31.51 ± 0.186 mA/cm² was achieved for the AZOY/n-Si heterojunction solar cells. Under an AM1.5 illumination condition, the conversion efficiency of the cells is estimated at only approximately 4% (a very low open-circuit voltage (V_oc) of 0.24 ± 0.001 V and a fill factor (FF) of 0.51 ± 0.011) without any optimization of the device structure.     

Thin film silicon solar cells by AIC on foreign substrates

This paper presents the fabrication of thin film crystalline silicon solar cells on foreign substrates like alumina, glass–ceramic (GC) and metallic foils (ferritic steel—FS) using seed layer approach, which employs aluminium induced crystallisation (AIC) of amorphous silicon. Effect of hydrogen content in a-Si:H precursor films on the AIC process has been studied and the results showed that defects in the AIC grown films increased with increase of hydrogen content. At the optimal thermal annealing conditions, the AIC grown poly-Si films showed an average grain size of 7.6, 26, and 8.1 μm for the films synthesised on alumina, GC, and FS, respectively. The grains were (1 0 0) oriented with a sharp Raman peak around 520 cm^?1. Similarly, n-type seed layers were also fabricated by over-doping of as-grown AIC layers using a highly phosphorus doped glass solution. The resistivity of as-grown films reduced from 8.4×10^?2 Ω cm (p-type) to 4.1×10^?4 Ω cm (n-type) after phosphorus diffusion. These seed layers of n-type/p-type were thickened to form an absorber layer by vapour phase epitaxy or solid phase epitaxy. The passivation step was applied before the heterojunction formation, while it was after in the case of homojunction. Open circuit voltage of the junctions showed a strong dependence on the hydrogenation temperature and microwave (μW) power of electron cyclotron resonance (ECR) plasma of hydrogen. Effective passivation was achieved at a μW power of 650 W and hydrogenation temperature of 400 °C. Higher values of solar conversion efficiencies of 5% and 2.9% were achieved for the n-type and p-type heterojunction cells, respectively fabricated on alumina substrates. The analysis of the results and limiting factors are discussed in detail.     

Pulsed laser deposition of yttria stabilized zirconia for solid oxide fuel cell applications

Yttria stabilized zirconia (YSZ) films were grown by pulsed laser deposition (PLD) from a 8YSZ target using a KrF excimer laser source (248 nm). The films have been deposited under oxygen atmospheres on porous NiO/YSZ substrates heated from room temperature to 600 °C. YSZ films were obtained in the range of 1–2 μm thickness. The films have been investigated with respect to surface morphology, microstructure and film–substrate interface interaction. The film morphology varied from columnar to an irregular crystalline structure depending on the oxygen pressure and the substrate temperature. In all cases the films consisted of YSZ with the cubic fluorite structure. The formation of oxide layers under low oxygen pressures on the NiO/YSZ substrates is due to a film–substrate redox interaction. The NiO grains close to the coating interface are partially reduced and serve as an oxygen source for the oxidation of the film. The measured He leakage rates to analyze the gas tightness of the YSZ films have so far shown no improvements as compared with uncoated substrates.     

Transmittance from visible to mid infra-red in AZO films grown by atomic layer deposition system

We report transmittance and conductivity measurements of aluminum-doped zinc oxide films grown by atomic layer deposition. The results show that the films have 80–90% transmittance in the visible region and good transmittance in the infrared. To our knowledge, this is the first time that the transmittance of aluminum-doped zinc oxide is reported to extend beyond 2500–5000 nm. Following annealing, an optimal sheet resistance of 25 Ω/□ was obtained for a 575 nm thick film with a carrier density of 2.4 × 10²⁰ cm^?3 without compromising the transmittance in the visible regime.     

Electrophoretic deposition of binary energetic composites

This work utilizes electrophoretic deposition (EPD) as a facile and effective method to deposit binary energetic composites. In particular, micron-scale aluminum and nano-scale copper oxide were co-deposited as a thin film onto a conductive substrate without the use of surfactants. For comparative purposes, films of this energetic mixture were also prepared by drop-casting (DC) the premixed suspension directly onto the substrate, then allowing the liquid to dry. The structure and microscopic features of the two types of films were compared using optical and electron microscopies. The films prepared using EPD had an appreciable density of 2.6 g/cm³, or 51% the theoretical maximum density, which was achieved without any further processing. According to the electron microscopy analysis, the EPD films exhibited much more uniformity in composition and film thickness than those produced by DC. Upon ignition, the EPD films resulted in a smoother and faster combustion event compared to the DC films. The dispersion stability was improved by adding water and decreasing the particle concentration, resulting in dispersions stable for >30 min, an ample amount of time for EPD. Patterned electrodes with fine feature sizes (20 × 0.25 mm) were then combined with EPD to deposit thin films of thermite for flame propagation velocity studies. The fastest velocity (1.7 m/s) was observed for an equivalence ratio of 1.6 ± 0.2 (Al fuel rich composition). This peak value was used to investigate the effect of film mass/thickness on propagation velocity. The deposition mass was varied from 20 to 213 μg/mm², corresponding to a calculated range of film thicknesses from 9.8 to 104 μm. At lower masses, a flame did not propagate, indicating a critical mass (20 μg/mm²) or thickness (9.8 μm). Over the range of thicknesses, in which self-propagating combustion was observed, the flame velocity was found to be independent of sample thickness. The lack of a thickness dependence suggests that under these particular conditions heat losses are negligible, and thus the velocity is predominantly governed by the intrinsic reactivity and heat transfer through the material.     

Structural characterization and electrochemical properties of RF-sputtered nanocrystalline Co3O4 thin-film anode

Nanocrystalline Co₃O₄ thin-film anodes were deposited on Pt-coated silicon and 304 stainless steel by radio frequency (RF) magnetron sputtering. The as-deposited and annealed cobalt oxide thin films showed smooth and crack-free morphologies. Both the as-deposited and annealed films exhibited spinel Co₃O₄ phase with nanocrystalline structure. High-temperature annealing enhanced the crystallinity of RF-sputtered cobalt oxide films due to rearrangement of cobalt and oxygen atoms. Electrochemical characterization of RF-sputtered films was carried out by cyclic voltammetry and charge/discharge tests in the voltage range of 0.3–3.0 V. Cyclic voltammetry plots showed that the RF-sputtered Co₃O₄ thin films were electrochemically active. X-ray photoelectron spectrometer (XPS) showed that the fresh cobalt oxide films had two peaks of Co₃O₄. In addition to the binding energy of cobalt oxide, the XPS spectrum of discharged film presented two additional binding energies correspond to Co metal. The first discharge capacities of as-deposited, 300, 500, and 700 °C-annealed films were 722.8, 772.5, 868.4, and 1059.9 μAh cm⁻² μm⁻¹, respectively. High-temperature annealing could enhance the capacity and cycle retention obviously. After 25 cycles discharging, the annealed films showed better cycle retention than as-deposited film. The 700 °C-annealed film exhibited excellent discharge capacity approximated to the theoretical capacity.     

Large grain Cu(In,Ga)Se2 thin film growth using a Se-radical beam source

Cu(In,Ga)Se₂ (CIGS) thin films were grown by the three-stage process using a rf-plasma cracked Se-radical beam source. CuGaSe₂ (CGS) films grown at a maximum substrate temperature of 550 °C and CuInSe₂ (CIS) and CIGS films grown at the lower temperature of 400 °C exhibited highly dense surfaces and large grain size compared with films grown using a conventional Se-evaporative source. This result is attributed to the modification of the growth kinetics due to the presence of active Se-radical species and enhanced surface migration during growth. The effect on CIGS film properties and solar cell performance has been investigated. Enhancements in the cell efficiencies of 400 °C-grown CIS and CIGS solar cells have been demonstrated using a Se-radical source.