A COMPARISON OF COMPOSITE TRANSPARENT CONDUCTING OXIDES BASED ON THE BINARY COMPOUNDS CdO AND SnO_2

摘要

Transparent conducting oxides (TCOs) are used extensively for a variety of applications including architectural windows, flat-panel displays, thin-film photovoltaics, smart windows, and polymer-based electronics. Some of these applications constitute a very large market, indicating that TCOs are of great commercial importance. The work on TCO semiconductors such as tin oxide (SnO_2), cadmium oxide (CdO), and cadmium stannate (Cd_2SnO_4) has been of great technological interest due to their high-quality of electrical and optical properties. Owing to their durability, conductive SnO_2 films on glass substrates are used extensively for low-E glass windows for energy conservation and thin-film photovoltaic solar cells. The quantity of energy-efficient architectural glass produced annually reaches tens of square kilometers, and the market continues to grow. CdO thin film (polycrystalline) is not a popular TCO material due to its narrow optical bandgap. However, it has demonstrated unusually high electron mobility that is 5-10 times higher than commercially available TCOs. Both SnO_2 and CdO thin films are naturally n-type semiconductors with tetragonal and cubic structures. Thin films of Cd_2SnO_4 combine the characteristics of SnO_2 and CdO are known to have high electron mobility, high electrical conductivity, and low visible absorption, which makes them suitable for a wide range of applications. Recently, a world-record CdS/CdTe thin-film solar cell was made with Cd_2SnO_4 as the front contact. Cd_2SnO_4 is an n-type semiconductor with either orthorhombic or spinel crystal structures.