Precursor films electrodeposited

Nonvacuum electrodeposition and electroless deposition techniques have the potential to prepare large-area uniform precursor films using low-cost source materials and low-cost capital equipment. Therefore, these techniques are very attractive for growing CIGS layers for photovoltaic applications. 

Figure 7.6. SEM of the electrodeposited CIGS precursor film (a) surface morphology and (b) cross section. 

The electrodeposited precursor films prepared in our laboratory that produced high-efficiency devices were Cu-rich films. These precursor films required additional In, Ga, and Se, deposited by PVD, to adjust their final composition to Culni xGaxSe2. During this second step, the substrate temperature was maintained at 560 °C 10 °C. Figure 7.7 presents the Auger analysis of the final absorber and shows nonuniform distribution of Ga in the absorber and more Ga near the surface. This result is primarily from the second-stage PVD addition. The Ga hump is not helpful for hole collection. The device efficiencies are expected to increase by optimizing the Ga distribution in the absorber layers. The optimized layers should have less Ga in the front and more Ga on the back, which facilitates hole collection. 

The electrodeposited precursor films, annealed in air at 870 °C in the presence of a TBSBCCO pellet, produce a biaxial textured Tl-1223 phase, as confirmed by an XRD pole-figure measurement. The omega and phi scans indicate full-width at half-maximum (FWHM) values of only 0.92° and 0.6°, respectively, which indicates a very high-quality film. The superconductive transition temperature of the Tl-1223 film, determined resistively, was about 110 K. Figure 7.11... 

The electrodeposited Bi2Sr2CaiCu2Ox (BSCCO) precursor films were obtained by co-electrodeposition of the constituent metals using nitrate salts dissolved in DMSO solvent. The electrodeposition was performed in a closed-cell configuration at room temperature ( 24°C). The cation ratios of the electrodeposition bath were adjusted systematically to obtain BSCCO precursor compositions. A typical electrolyte-bath composition for the BSCCO films consisted of 2.0-g Bi(N03)3-5H20,1.0-g Sr(N03)2, 0.6-g Ca(N03)2-4H20, and 0.9-g Cu(N03)2-6H20 dissolved in 400 mL of DMSO solvent. The substrates were single-crystal LAO coated with 300 A of Ag. 

The effect of chemical bath composition, electrodeposition potential, etc., on film composition was determined [317]. The precursor films were loaded in a physical evaporation chamber and additional In or Cu and Se were added to the films to adjust the final composition of CIS. The device fabricated using electrodeposited Cu-In-Se precursor layers had a solar cell efficiency of 9.4%. CIS thin films have also been obtained from different precursors prepared by direct or sequential electrodeposition processes [303]. The results showed that thin crystalline chalcopyrite CIS films with the desired composition can be obtained after annealing, whether directly or sequentially electrodeposited precursors at 400 °C. An improvement in film quality was obtained by using an electrodeposited Cu layer as the growth surface for CIS formation. If elemental Se was also added during the heat treatment, then a higher recrystalHzation of the films was observed. A new approach for CIS formation by sequential electrodeposition of Cu and In-Se layers and subsequent heat treatment with elemental selenium in Ar + H2 flows has been presented [304]. An increase in the film crystallinity was achieved... 

A) and the same electrode covered with thiol-functionalized silica films electrodeposited from precursor solutions with different content of MPTMS (molar ratio to total silane) 5%... 

Electrodeposited sol-gel-based composite films also showed optical applications. Gu and coworkers [85,86] co-electrodeposited Te0 > -Si02 hybrid films from the TEOS-Te(i-PrO)4 niixed precursor for nonlinear optics. Te(IV) was partially reduced during electrodeposition, as characterized by EDX of the obtained films. The as-prepared films had third-order nonlinear susceptibility ix ) of 5.9 X10 to 4.29 X 10 esu, and the films had of 1.551 X 10 esu after posttreatment annealing. Mandler and coworkers co-electrodeposited TMOS with multiwalled carbon nanotubes (MWCNTs) on ITO and silver. The optimized films electrodeposited on ITO showed transparency of about 50% with nonlinear optical properties, and the optimized films electrodeposited on silver had specular reflectance lower than 0.5% in the wavelength range of 400-15 000 nm, which can be used as antireflection coatings. 

If the electrolysis parameters (precursor concentrations, pH, temperature, cur-rent/potential, substrate) be defined in a precise manner, a self-regulated growth of the compound can be established, and highly (111 )-oriented zinc blende (ZB) deposits up to several p,m thickness are obtained at potentials lying at the anodic limit of the diffusion range (Fig. 3.3) [60]. Currently, the typical method of cathodic electrodeposition has been developed to yield quite compact and coherent, polycrystalline, ZB n-CdSe films of well-defined stoichiometry. The intensity of the preferred ZB(f 11) orientation obtained with as-deposited CdSe/Ni samples has been quite high [61]. 

Electrodeposition of copper indium disulfide (CulnS2) has been reported [180-182], In a typical instance, single-phase polycrystalline CuInS2 thin films composed of 1-3 fim sized crystallites were grown on Ti by sulfurization of Cu-ln precursors prepared by sequentially electrodeposited Cu and In layers [183]. In this work, solar cells were fabricated by electrodepositing ZnSe on CuInS2. Cyclic... 

The quality of an elemental deposit is a function of the deposition rate, surface diffusion, the exchange current and the substrate structure. Electrodeposition of a compound thin-film not only requires all these things, but stoichiometry as well. Under ideal conditions, the mass transfer rates and discharge rates of two elemental precursors can be tuned to produce a deposit with the correct overall stoichiometry for a compound. Whether the two elements will form the right compound, or a compound at all, is another question. 

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