Preparation and characteristics of CdS thin films by dip-coating method using its nanocrystal ink

CdS nanocrystals were synthesized by hot injection method using EG as solvent, polyvinylpyrrolidone as dispersant, triethanolamine as stabilizing agent, Cd(NO₃)₂·4H₂O and H₂NCSNH₂ as cadmium and sulfur sources respectively. The synthesized nanocrystals were washed and ultrasonically dispersed with absolute ethanol to prepare nanocrystal ink. CdS thin films were deposited by dip-coating glass substrates with the nanocrystal ink and annealed at 450 °C in Ar atmosphere. Crystalline phase, morphology and element stoichiometry of the CdS nanocrystals derived from different synthesis temperatures were investigated by XRD, TEM and EDS. Surface morphology, crystalline phase and optical absorption spectrum of the CdS films were characterized by SEM, XRD and UV-Vis.     

Preparation and characterization of flash-evaporated CuInSe2 thin films

Thin films of CuInSe₂ have been evaporated onto glass substrates by flash evaporation. The as-deposited films are amorphous and annealing in selenium atmosphere produces polycrystalline films. The films were characterized bytem and x-ray diffraction techniques. The optical absorption of the films shows three energy gaps of 1·03, 1·07 and 1·22 eV. The crystal field and spin-orbit splitting are thus found to be 0·04 eV and 0·16 eV respectively. The percentaged-character of the valence band states is ∼35%. The Arrhenius plot of electrical conductivity of films showed impurity ionization ofE _A = 75 meV.     

Preparation and characterization of pulse-plating electrodeposited CuInSe2 thin films

CuInSe₂ thin films were electrodeposited on an indium-tin-oxide glass substrate by a pulse-plating technique from an aqueous electrolyte solution, containing CuSO₄, InCl₃ and SeO₂ with the pH adjusted to 1.5 at room temperature. The deposited and heat-treated films were characterized structurally using X-ray diffraction (XRD), scanning electron microscopy (SEM) and auger electron spectroscopy (AES) analysis. The optical and the electrical properties of the films were also examined. When the film was submitted to heat-treatment above 300 C in air for 1 h, the sample showed a chalcopyrite structure and n-type conductivity with a carrier concentration of ~ 10¹⁷ cm^–3 and a band-gap (direct allowed transition) energy of 0.99 eV.     

Preparation and electrical properties of ITO thin films by dip-coating process

Indium tin oxide (ITO) thin films were prepared on quartz glass substrates by a dip-coating process. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. The ITO thin films containing 0 20 mol% SnO₂ were successfully prepared by heat-treatment at above 400 °C. Chemical stability of sol were investigated by using a FTIR spectrometer. The electrical resistivity of the thin films decreased with increasing heat-treatment temperature, that is carrier concentration increased, and mobility decreased with increasing SnO₂ content. The ITO thin films containing 12 mol% SnO₂ showed the minimum resistivity of =1.2 × 10^–3 ( cm). It also showed high carrier concentration of N=1.2 × 10²⁰(cm^–3) and mobility _H=7.0(cm² V^–1 s^–1).     

Preparation of CuInSe2 thin films by selenization of co-sputtered Cu-In precursors using rapid thermal processing

CuInSe₂ thin films have been synthesized by selenization of co-sputtered Cu-In precursors using rapid thermal processing (RTP). Heat treatments from 400 to 450 °C for periods between 1 min and 10 min were carried out on (Cu-In)/Se precursors. Phase evolution as function of reaction temperature and holding time was analyzed according to XRD and SEM results. Severe Se loss during RTP was proved in our experiments and has been reported by many other researchers. To solve the problem, a new effective way of reducing Se loss was presented, which is based on low temperature heat treatment at 250 °C before high temperature annealing. Nearly single-phase CuInSe₂ thin films have been achieved by annealing precursors at 250 °C for 5 min then 450 °C for 1 min. Se loss can be significantly reduced via low temperature heat treatment by the fact that under 250 °C, Se is evaporated mildly and largely consumed as Cu-Se and In-Se binary selenides.     

Flash-evaporated thin films of CuInSe2

Flash-evaporated technique has been developed for deposition of CuInSe₂ thin films. A control over the stoichiometry and chemical composition of the films has been obtained by varying the deposition parameters. Single phase chalcopyrite structure films with optical gap ∼ 1·15 eV have been obtained. The electronic properties of the films have been tailored for solar cell applications.     

Preliminary impurity analysis of CuInSe2 thin films using the elastic recoil detection method

Knowledge of impurities in thin films is important for fabrication and characterization of photovoltaic devices. The lightimpurity distribution in electrodeposited CuInSe₂ thin films has been investigated by an elastic recoil detection method using a 30 MeV ³⁵Cl beam and identifying the recoil masses using a time-of-flight technique. It was found that both oxygen and hydrogen were present and distributed uniformly throughout the thickness studied. Upper limits for carbon and nitrogen were also established. The energy spectra for oxygen and hydrogen were deconvolved to obtain the relative concentrations as a function of depth. Using the same technique, the compositional uniformity of Cu, In and Se was also determined, yielding results qualitatively consistent with that obtained by secondary ion mass spectroscopy.     

Growth and characterization of CuInSe2 thin films

Films of CulnSe₂ have been grown using a technique similar to close-spaced vapour transport. The effect of substrate temperature and the distance of the substrate from the source have been optimised to grow well-oriented chalcopyrite phase of CuInSe₂. D.c. conductivity and Hall coefficient studies have been made in the temperature range 77–300 K. The films grown at a substrate temperature of 350 °C have an electron mobility of 3.4×10³ cm²V^–1 s^–1 at 77 K.     

Preparation of transparent conductive indium tin oxide thin films from nanocrystalline indium tin hydroxide by dip-coating method

Indium tin oxide (ITO) thin films with well-controlled layer thickness were produced by dip-coating method. The ITO was synthesized by a sol-gel technique involving the use of aqueous InCl₃, SnCl₄ and NH₃ solutions. To obtain stable sols for thin film preparation, as-prepared Sn-doped indium hydroxide was dialyzed, aged, and dispersed in ethanol. Polyvinylpyrrolidone (PVP) was applied to enhance the stability of the resulting ethanolic sols. The transparent, conductive ITO films on glass substrates were characterized by X-ray diffraction, scanning electron microscopy and UV-Vis spectroscopy. The ITO layer thickness increased linearly during the dipping cycles, which permits excellent controllability of the film thickness in the range ~ 40-1160 nm. After calcination at 550 °C, the initial indium tin hydroxide films were transformed completely to nanocrystalline ITO with cubic and rhombohedral structure. The effects of PVP on the optical, morphological and electrical properties of ITO are discussed.     

Preparation of spinel-type ferrite thin films by the dip-coating process and their magnetic properties

Films of spinel-type ferrite, MFe₂O₄ (M=Ni, Co, Mg, Li_0.5Fe_0.5) have been prepared by a dip-coating method from the sol-gel process. Ferric nitrate, nickel nitrate, cobalt nitrate and lithium nitrate were used as raw materials, and glycerol and formamide were used as solvents. A film was prepared by dipping a silica glass plate. The spinel-type ferrite was obtained by heat-treatment at 700–900°C for 2 h in air. The film thickness was about 0.8 m. The saturation magnetization, _r, of the film and powder with composition 50NiO·50Fe₂O₃ was 196 emu cm^–3 and 29.1 emu g^–1, respectively, and the coercive force,H _c, was 140 and 95 Oe, respectively, after heat-treatment at 800°C for 2 h. In particular, the films were shown to have a much largerH _c than the powder. The grain growth of spinel ferrite may be subject to restriction because it is in progress above an amorphous base-plate. The crystals are therefore aligned with the base-plate and have uniaxial anisotropy.     

Some physical properties of CuInSe2 thin films

Semiconducting thin films of CuInSe₂ have been grown by thermal annealing in air of evaporated layers of Cu, In and Se on glass substrates. The structure of the films has been studied using the X-ray diffraction (XRD). The films were polycrystalline and showed mixture phases (binary and ternary) depending on the annealing temperature. The electrical properties revealed resistivity range of 10¹–10⁴Ωcm, respectively. The resistivity influenced with the annealing temperature and decreased with increasing temperature. The films have been analyzed for optical band gap.     

Structural analysis of CuInSe2 thin films prepared by selenization of Cu-In films

This study involves the characterization of thin films of copper indium diselenide (CuInSe₂) deposited on soda-lime glass substrates using a two-step process. In this technique electron-beam-evaporated Cu-In precursor layers were reacted with an atmosphere containing H₂Se gas. The morphological and structural aspects of the CuInSe₂ layers were studied (by scanning electron microscopy and X-ray diffraction) as a function of the Cu-In film morphology and the selenization temperature profile and exposure time. It was found that the Cu-In precursor morphology has a significant influence on the structural properties of the final CuInSe₂ film. Selenization of the Cu-In alloys (irrespective of the structure considered) directly at high temperature resulted in films with poor structural properties. However, a vast improvement in the adhesion properties and morphology of the CuInSe₂ films were observed when the Cu-In films were exposed to a reactive selenium atmosphere while ramping the temperature between 150 C and 400 C. Selenization of triple-layer structures (Cu/In/Cu and In/Cu/In) resulted in films with good structural properties and excellent compositional uniformity.     

Characterization of titania thin films grown by dip-coating technique

A dip-coating technique was employed to prepare anatase phase of titania thin films. Fluorine doped tin oxide substrates were used to prepare titania thin films. The samples were annealed at 550 °C for 18 h. X-ray diffraction results revealed the amorphous and anatase phases of TiO₂ for as-synthesized and annealed samples, respectively. The crystallite size of anatase TiO₂ thin films was almost 25 nm for annealed samples. UV–visible confirmed the energy band gap 3.86 and 3.64 eV for as-prepared and calcinated titania thin films. The reduction in the energy band gap could be due to the change in crystallization and agglomeration of small grains after calcination. The morphology of the prepared films was investigated by field emission scanning electron microscopy which demonstrated the agglomeration of spherical particles of TiO₂ with average particle size of about 30 nm. The molecular properties (chemical bonding) of the samples were investigated by means of Fourier Transform Infrared (FTIR) spectroscopy. FTIR analysis exhibited the formation of titania, functional group OH, hydroxyl stretching vibrations of the C–OH groups, bending vibration mode of H–O–H, alkyl C–H stretch, stretching band of Ti–OH, CN asymmetric band stretching, and C=O saturated aldehyde.     

Preparation of VO2 films by organometallic chemical vapour deposition and dip-coating

Low-pressure organometallic chemical vapour deposition (OMCVD) and dip-coating of VO₂ films using vanadyl tri(isobutoxide) as the starting material were investigated. In OMCVD, discontinuous VO₂ films, which were composed of fine needle crystals, formed under very limited conditions, around 600° C with a flow rate of oxygen gas of 0.2 to 0.5 cm³ sec^–1. However, very uniform and tightly packed VO₂ films were grown by deposition at 300 to 700° C in the absence of oxygen gas and subsequent annealing in nitrogen at 500° C for 2 h. The films exhibited a sharp semiconductor to metal transition at 60 to 70° C, accompanied by a change in the resistivity by four to five orders of magnitude. In dip-coating with two-step heat-treatments (300° C for 1 h in nitrogen and subsequently 500° C for 2 h in nitrogen), of the gel films formed from VO(O-i-Bu)₃-H₂O-i-PrOH system, uniform (0 1 1) oriented VO₂ films were formed. A transition in the electrical conductivity by two to two and a half orders of the magnitude was found to occur around 60° C. Before and after the transition, no distinct variation in the XRD pattern was observed.     

CuInSe2 thin films by d.c. and pulse-plated electrodeposition

CuInSe₂ thin films were prepared by electrodeposition from aqueous solution, containing CuSO₄, InCl₃ and SeO₂ under d.c. step pulse-voltage on d.c., and pulse-plating conditions. The films were characterized by scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. The influence of deposition technique on film composition, morphology and structure were studied. Heat treatment of pulse-plated films under vacuum resulted in the formation of CuInSe₂ with single-phase chalcopyrite structure.