The most widely used transparent conducting oxide (TCO) for various optoelectronic applications is tin-doped indium oxide (ITO). However, indium is toxic and scarce and this makes its use in various applications difficult. The development of improved or alternative TCOs for optoelectronic devices that currently use ITO is a challenging materials problem. Also, only a few works had been done on the development of p-type TCOs. Without p type transparent film, the fabrication of transparent p-n junctions exclusively from TCO is impossible. C-MET has developed TCOs which can be used as more economical and resource abundant than indium based TCOs.
In addition, a major challenge is the need for low cost processes. Current methods for the production of devices are based on vacuum deposition techniques such as physical or chemical vapour depositions, which contribute to high manufacturing costs. Hence C-MET developed cost effective solution-based techniques for depositing transparent films.
Aluminium doped zinc oxide transparent films
Aluminium doped zinc oxide thin films are widely used as front electrodes in cadmium telluride (CdTe) and copper indium selenide (CIS) thin film solar cells and dye-sensitized solar cells. C-MET has developed AZO transparent thin films by solution deposition techniques.
Zinc Tin Oxide transparent films
Zinc tin oxide thin films can be used as buffer layer in thin film solar cells because these films are chemically stable and they exhibit higher resistivity matched to that of the cadmium sulphide window layer. Zinc tin oxide combines the properties of both zinc oxide and tin oxide. These films were fabricated by spin coating technique.
Specification of the n type TCOs
Resistivity : 8x10-3W cm
Carrier concentration: ~1019 cm-3
Optical bandgap: 3.4 eV
Film thickness : 200-800 nm
p type transparent conducting oxide films
Only a few oxides are known to have p-type conductivity. Copper aluminium oxide, CuAlO2, is a p type material, which is transparent in the visible range. C-MET has developed this p type transparent film by dip coating technique.
Specification of the p type TCO
Resistivity: ~10W cm
Carrier concentration : 1018 cm-3
Optical bandgap: 3.7 eV
Film thickness: 300nm