Spray pyrolysis processes

For large area film formation at low cost, the spray pyrolysis process is used. A solution of a metal chloride or acetylacetonate with a source such as thiourea in a polar solvent is pyrolysed on a hot (300-500°C) substrate. A typical reaction is... 

Wienke et al. (2003) and Bayon et al. (2004) showed that substantial improvement in conversion efficiency is obtained when a thin indium hydroxysulphide (ln c(OH)j,S0 layer with a bandgap of approximately 2.5 eV is deposited prior to the CuInSz deposition. The observed improvement is attributed to a reduced hole density in the vicinity of the ln ,(OH)j,S2 contact. The CuInSz was prepared in a spray pyrolysis process. Nanu et al. (2003, 2004) employed atomic-layer chemical vapour deposition to obtain ultra-thin CuInSz layers inside the pores of nanostructured TiOz. CuCl, InCh and HzS are used as precursors in this process. A growth rate of 1-3 A s is observed, and conversion efficiencies shghtly above 4% have been obtained. While the process may not be suited for large-area applications, the results can clearly be taken as another confirmation that the ETA cell concept constitutes a feasible route towards efficient solar cells. 

Kang Y C, Lim M A, Park H D, Han M. Ba2+ co-doped Zn2Si04 Mn phosphor particles prepared by spray pyrolysis process. J Electrochem Soc 2003 150 H7-11. 

A variation of the spray drying process, known as spray pyrolysis, uses a higher temperature and a reactive (often an oxidizing) environment in the chamber. This allows the salts to be dried and decomposed directly. Figure 20.4 shows the stages in the spray pyrolysis process. In addition to producing powders this technique has been used to produce thin films and fibers. 

Fig. 3.45 Schematic of the stages in the spray pyrolysis process. Reproduced with permission from [224], Copyright 1993, John Wiley Sons. Reused with permission from [47]. Copyright 2007, Springer...

The spray pyrolysis process is able to produce particles with a variety of morphologies through controlling the experimental conditions. For the fabrication of... 

Mooney JB, Radding SB (1982) Spray pyrolysis processing. Annu Rev Mater Sci 12 81-101... 

Structures and Substructures in Spray Pyrolysis Process Nanodesigning... 

A. Spray Pyrolysis Processes in Periodical Ultrasonic Fields. 515... 

The concept or the basis of spray pyrolysis method assumes that one droplet forms one product particle. To date, submicrometer- to micrometer-sized particles are typically formed in a spray pyrolysis process. A variety of atomization techniques have been used ftn- solution aerosol formation, such as ultrasonic spray pyrolysis, electrospray pyrolysis, low pressure spray pyrolysis using a filter expansion aerosol generator (FEAG), salt-assisted spray pyrolysis, two-fluid pyrolysis method, etc. [15-18]. These atomization methods differ in droplet size, rate of atomization, and... 

The droplet size reduction occurs through different stages of spray pyrolysis process evaporation of the solvent from the surface of the droplet, diffusion of the solvent vapor away from the droplet in the gas phase, diffusion of solute toward the center of the droplet, shrinkage of the droplet, and change in droplet temperature and drying process, preferentially. The characteristic value for estimation of evaporation time needed for solvent evaporation and droplet precipitation is the evaporation rate given by [28,62] ... 

Some review articles pertaining to spray pyrolysis processing and the range of thin films deposited by this technique for various appKcations have appeared in the literature. Viguie and Spitz [74] have classified chemical spray deposition process according to the type of reaction. A most recent survey on thin-film materials prepared by spray pyrolysis and advances in the field, especially different atomization techniques, was presented [12j. The critical operations for the spray pyrolysis technique are (1) preparation of uniform and fine droplets and (2) the controlled thermal decomposition of these droplets in terms of environment, location, and time. 

Figure 2.30 Schematic of the stages in the spray pyrolysis process. (From Ref. 89.)...

A considerable amount of effort has gone into trying to understand the requirements for formation of solid particles, " since this incomplete understanding is one of the major impediments to widespread commercial use of spray pyrolysis processing. Typically, these studies have focused on control of the solvent evaporation... 

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