Singly and co-doping of ZnO thin films by spray pyrolysis

Indium-based transparent conducting oxides (TCOs) are widely used in optoelectronic devices. An important goal of this project is to search for TCOs that have reduced In content or indeed no In. The cheap zinc-based TCOs are good candidates to replace expensive indium-based TCOs in applications. A co-doping protocol has been established using both Si and In to obtain films with both good optical and electrical properties. This co-doping strategy can dramatically reduce the cost of the expensive element In while maintaining better optoelectronic performances compared to singly doped ZnO thin films. The spray pyrolysis technique is used to deposit TCO thin films, which is famous for its lower cost compared with physical deposition methods such as sputtering. I have studied the detailed properties of singly doped (Si or In) ZnO together with co-doped (Si and In together) ZnO thin films. I have also related their optoelectronic performances with structures, elemental compositions, and chemical environment to understand their properties in depth. It is the first time co-doped ZnO thin films based on Si and In have been successfully synthesised with high optoelectronic performances. Therefore, it is a basis for further development in co-doping and material design. The total chemical composition of elements in the bulk of a TCO material has not been measured previously. Nevertheless, I have studied these to see the limitations or restrictions in doping, thus understanding how doping affects optoelectronic properties including metal-insulator transition. Our ultimate goal is to develop an applicable deposition method and find suitable TCO materials to meet application requirements on both the optoelectronic performance and cost.