The Different Solution Processes

Hydrolysis or complexation The following very schematic reactions describe the most common representation of a solution process, starting from a stable stock solution of some metal complexes to which reagents are added. The first step consists in the substitution or addition of molecular groups in the coordination sphere of a cation M. Most common reactions are (9)  

M(H20)mn+ + OH —- M0H(H20)m.1( -1)++ H20 (complexation with a hydroxide ligand replacing water in an aqueous solution) 

Condensation or precipitation The species that are so formed may be unstable and in a second step may condense upon elimination of molecules such as ROH or H20, thus leading to the formation of a hydroxide or oxide network. This step corresponds to an inorganic polymerization such as (9)  

This process leads to the precipitation of the oxides, hydroxides or carboxylates if we replace OH by L in the last reaction. If this polycondensation can be stopped or if it is slow enough, a colloidal solution is obtained that has rheological properties useful for application purposes. 

As a matter of fact, the major difficulty in applying the solution techniques to the superconducting cuprates is the choice of precursors, since the low charges of Cu, Y, Ba and their relatively large ionic radii make it difficult to find versatile soluble precursors. 

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Although all the different solution-processed metal oxide based materials exhibit great potential for performance optimization and commercialization, there are still some limitations regarding optical, electrical, chemical and mechanical properties for each solution-process method and materials. Therefore additional research is required in the field of CTL development to improve the performance of the OSCs and OLEDs further. 

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