Substrates Chalcopyrite

A procedure involving (a) the deposition of nearly stoichiometric films of copper and indium on suitable substrates using vacuum evaporation or electrodeposition and (b) the heat treatment of Cu-In films in a hydrogen-selenium atmosphere at temperatures above 630 °C was reported to yield large grain (several mm in size), stoichiometric thin films of chalcopyrite CIS with a preferred 112 orientation [167]. 

By electrodeposition of CuInSe2 thin films on glassy carbon disk substrates in acidic (pH 2) baths of cupric ions and sodium citrate, under potentiostatic conditions [176], it was established that the formation of tetragonal chalcopyrite CIS is entirely prevalent in the deposition potential interval -0.7 to -0.9 V vs. SCE. Through analysis of potentiostatic current transients, it was concluded that electrocrystallization of the compound proceeds according to a 3D progressive nucleation-growth model with diffusion control. 

If this early work on CD of Cu-S was driven by the attractive colors they imparted to metallic substrates, more recent studies were driven initially by their potential use in CuiS/CdS photovoltaic cells (these cells are no longer studied to any extent due to their perceived instability, although, with what has been learned about Cu-containing chalcopyrite, such as CuInSei, thin-fihn cells over the past couple of decades, it would not be surprising if such studies were again pursued) and later in solar control coatings (see Sec. 2.13). 

Fig. 9.2. Scanning electron micrograph of the cross-section of a typical chalcopyrite solar cell with Cu(In,Ga)Se2 (CIGSe) absorber (substrate now shown). Reprinted with permission from [1]...

Since in the chalcopyrite module the ZnO films are the last to be deposited, the processing must be compatible with the remainder of the cell structure. This implies in particular that substrate temperatures must be limited to 200-250°C [10] even though better ZnO properties could be achieved at higher deposition temperatures. Interdiffusion at the absorber/buffer interface has been made responsible for the instability [27] but it is believed that a detailed study using current state of the art material would be required to clarify this point. 

The efficiency of wide gap chalcopyrite cells, even on standard nontransparent substrate is too low for the realization of tandem cell. Using a TCO back contact reduces the efficiency even further. Establishing a high transparency is also not straightforward. Nevertheless, the potential of tandem... 

The investigations of Landesman et al. (1966a, b) clarify the effects of the various conditions controlling the optimum oxidation rates of ferrous iron, sulfur and reduced sulfur compounds by T. ferrooxidans. Experiments on soluble iron, sulfur and iron-containing sulfide minerals (chalcopyrite, CuFeS2, bornite, CUsFeS4, and pyrite) established that iron and sulfur can be oxidized simultaneously. With a mixed iron-sulfur substrate a rate of oxidation, equal to that of the sum of the maximum rates of oxidation of the two substrates individually was observed with both S-adapted and Fe-adapted cells. Subsequently, Duncan et al. (1967) established the differential susceptibility of the bacterial oxidation of ferrous iron and sulfur to N-ethyl maleimide and sodium azide, and determined the effect of these inhibitors on pyrite and chalcopyrite oxidation. Decreased rates... 

When the compound formation step is performed in the gas phase, as in ILGAR, the end product is less mobile and therefore more homogeneously distributed over the surface. Very thin continuous layers can therefore be prepared in this way, as shown by Muffler et al. (2002). In their work one or more metallic components are deposited from solution on the substrate and then converted to the semiconductor compound by exposure to a reactant gas. The method is able to produce extremely thin coatings of chalcopyrite, chalcogenide and oxide semiconductors on nearly arbitrarily shaped substrates, including very deep nanoporous structures. A number of binary and ternary compounds, such as CdS, ZnS, CulnSa, In2Sc3, ZnO, ZrOa, 263 and others, have been prepared. 

The same sensitivity can be achieved in the in situ ATR spectra of the Vfl CH2 bands of surfactants with the chains 12-16 carbon lengths adsorbed on colloid oxide films [174, 178], For coarser particles of a higher refractive index, the sensitivity decreased. For example, for xanthate adsorbed on chalcopyrite (CuFeS2) particles <30 p,m size (Fig. 7.26), surface sensitivity is about 0.3 ML [179]. For such substrates, the SNR is comparable to that from the in situ ATR spectra... 

Spray pyrolysis technique has been used to deposit polycrystalline thin films comprising of CuInSa nanocrystals onto glass substrates. p-XRD studies demonstrate that the films have a chalcopyrite structure with preferred orientation along (112) lattice plane. Average diameter of the nanocrystals, as determined by SEM and TEM images, was found to be about 40-60 nm while band gap calculated through optical absorption studies was found to be 1.55 eV. A solar device fabricated by using these films demonstrated a power conversion efficiency of 7.60%. 

X-ray diffraction spectra of the films deposited onto substrates in the temperature range 175 - 210 C showed that the films consisted of CuInSe2 of the chalcopyrite structure and of another material, which has been identified as In20T. As the substrate temperature was increased over the range 220 - 250°C, the intensity of the chalcopyrite peaks decreased and for temperatures in excess of 250°C, only the sphalerite structure was observed. The dif-... 

Figure 5.8 Chalcopyrite grains imbedded in a prepolished conductive epoxy substrate as imaged by (a) SEM, (b) EDX (the Ni distribution shown), and (c) SIMS operated in the microscope mode (the CsNF secondary ions are displayed). The SIMS image resolution is defined via line scan analysis (see white line in SIMS image) as illustrated in (d) and in (e). Raw MCs signals, where M is an isotope of Nickel, are shown.

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