Chalcopyrite materials

Siebentritt, S. 2002. Wide gap chalcopyrites material properties and solar cells. Thin Solid Films 403-404 1-8. 

Banger, K. K. Harris, J. D. Cowen, J. E. Hepp, A. F. 2002. Facile modulation of single source precursors The synthesis and characterization of single source precursors for deposition of ternary chalcopyrite materials. Thin Solid Films 403-404 390-395. 

The most prevalent ternary chalcopyrite materials are p-type Cu(In Ga)(S Se)2 (CIGS), which crystallize in the tetragonal chalcopyrite stmcture and are used in the photovoltaic modules. The complexity of the phase diagrams for Cu-III-VI materials results in a large number of intrinsic... 

The lattice constants of the chalcopyrite material were determined from the x-ray diffraction patterns. Lattice constants were calculated to at least three significant figures. They were used to construct actual iso-lattice constant maps like those shown in Fig. 10 where it is evident that these lines depart from the strictly linear behavior predicted by Vegard s law. The experimentally deduced curves are then subjected to a least squares fit to calculate values for the a coefficients of Eq. (14). 

Segregated phases, other than the target material, usually found on the surface of deposited polycrystalline chalcopyrite semiconductor films, such as CuInSc2 and CuInS2, constitute a shortcoming in material quality for solar cell and other applications. In fact, these films are usually prepared purposefully with an excess of... 

Spray CVD of Single-Source Precursors for Chalcopyrite I—III—Vl2 Thin-Film Materials... 

The reduced tailings were found to be comprised of 20-30 % sulfides, and 70-80% gangue minerals and very finegrained unidentifiable material. Sulfides were 50 -75 % pyrite, 30-40 % pyrrhotite, <5 % chalcopyrite, and <5 % sphalerite. 

Yelloji Rao M. K. and Natarajan, K. A., 1988. Influence of galvanic interaction between chalcopyrite and some metallic materials on flotation. Minerals Engineering, 1(4) 281 - 294 Yelloji Rao M. K. and Natarajan, K. A., 1989a. Effect of electrochemical interactions among sulphide minerals and grinding medium on chalcopyrite flotation. Minerals Metallurgical Processing, 6(3) 146- 151... 

Ternary semiconductors of the I-III-VI groups (I = Cu, Ag III = Al, Ga, In VI = S, Se, Te) with a chalcopyrite structure have attracted attention as new functional materials for solar hydrogen production [164-167]. With the aim of capturing a larger fraction of solar light, solid solutions of two or more sulfides were prepared. A... 

Nickel usually is recovered from its sulfide ore, pentlandite (Ni,Fe)9Sie. Although laterite type oxide ores sometimes are used as starting materials, pentlandite is used in many commercial operations. Pentlandite often is found in nature associated with other sulfide minerals, such as pyrrhotite, Fe7Ss,and chalcopyrite, CuFeS2. 

CuInSi (and, even more, CuInSei) are strong candidates for thin-film photovoltaic cells. For this purpose, the chalcopyrite structure (which is an ordered lattice) is preferred over the disordered, zincblende form. Due to the large absorption coefficients of these materials, a 1-iJim-thick film is more than enough to absorb almost all the suprabandgap radiation. Somewhat thicker films are generally used, due to problems of pinholes, which commonly occur in thinner films. A number of methods have been used to deposit these films. Surprisingly, very few (published) attempts have been made to deposit them by CD. 

A note of caution is necessary when deahng with these materials. It is not trivial to distinguish between CuInS(Se)2 and some phases of Cu—S(Se). Diffraction and optical properties may be similar. Elemental analysis is particularly important to verify inclusion of indium in the films and in the correct ratio. A fingerprint of the chalcopyrite XRD is the presence of a weak peak at 26 = 17-18°, corresponding to the (101) chalcopyrite reflection. This is often not seen, although this could be either because the deposit is not chalcopyrite or because weak peaks are usually not seen in nanocrystaUine materials with particularly small crystal size. 

The Se-capped Cu(In,Ga)Se2 films used for the present studies were prepared at the Zentrum fur Sonnenenergie und Wasserstoffforschung in Stuttgart, Germany with 30% of the In substituted by Ga. The films are also used for solar cell preparation and yield an energy conversion efficiency of-14% [36,123]. Good conversion efficiencies are obtained from films, which are prepared with a slight Cu deficiency (—22% Cu instead of the nominal 25 % of Cu in stoichiometric chalcopyrites) [124]. Surfaces of such materials are, however, considerably depleted of Cu and show a surface composition that corresponds to the Cu(In,Ga Ses vacancy compound with a typical Cu concentration of 11 — 13% [36,123,125]. The importance of this compound for the Cu(In,Ca)Se2 surfaces and interfaces has been pointed out first by Schmid et al. [126,127]. 

Fig. 9.1. Schematic cross-section of a chalcopyrite-based thin-film solar cell. Typical materials for the individual parts of the cell are given in square brackets...

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 standard device comprises a thin CdS buffer layer as described above. It is believed that market acceptance of chalcopyrite-based photovoltaics could be improved by introducing a Cd-free buffer layer. There may also be cost benefits in view of the cost associated with (occupational) safety, handling of toxic waste in production, and recycling of modules at their end of life. Research has identified Cd-free materials well suited for alternative buffer layers. They can be deposited by CBD in analogy to the standard CdS buffer layers or by other processes. In particular, dry processes are attractive because they offer a better compatibility with the other process steps used for the remainder of the module. Ultimately, the best solution would be to omit the buffer layer altogether in favor of a direct chalcopyrite-sputiered/MOCVI) ZnO junction. Here we will limit the discussion to the state of these latter direct junctions and to ZnO-based buffer layers (Table 9.1). Results achieved with other materials can be found in the literature [67,68]. 

This book is devoted to the properties, preparation and applications of zinc oxide (ZnO) as an transparent electrode material. It focuses on ZnO for thin film solar cell applications and hopefully inspires also readers from related fields. The book is structured into three parts to serve both as an overview as well as a data collection for students, engineers and scientists. The first part, Chaps. 1-4, provide an overview of the application and fundamental material properties of ZnO films and their surface and interfaces properties. Chaps. 5-7 review thin film deposition techniques applied for ZnO preparation on lab scale but also for large area production. Finally, Chaps. 8 and 9 are devoted to applications of ZnO in silicon- and chalcopyrite-based thin film solar cells, respectively. One should note that the application of CVD grown ZnO in silicon thin film cells is discussed earlier in Chap. 6. 

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