Perspective on the band structure engineering and doping control of transparent conducting materials

Transparent conducting materials (TCMs), which combine high electrical conductivity and high optical transmission in the visible spectral range, are needed in many modern optoelectronic devices such as solar cells, flat-panel displays, touch-screen sensors, light emitting diodes, and transparent thin film transistors. However, many physical properties of the TCMs are still not very well understood. Understanding the band structure and physical origin of the unique properties of the TCMs is, therefore, crucial for the future design of these fascinating materials. In this Perspective, we will first present a brief review of the unique band structure and doping control of TCMs. In particular, we will discuss (i) the fundamental band structures and defect properties for the TCMs and why most of them are oxides (transparent conducting oxides, TCOs); (ii) how to achieve simultaneously high transparency and conductivity in n-type TCMs; (iii) why p-type TCOs are difficult to achieve; (iv) how to modify the band structure or design new materials to achieve p-type TCMs or even bipolarly dopable TCMs. Finally, we will discuss some of the remaining challenges and opportunities for the development of TCMs in the near future.